Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 1/124 Version 2.0 Communication, Navigation & Surveillance Manual Volume V Lightning, Surge Protection and Earthing System for CNS Installations Version 2.0, April 2014 भारतीय विमानपत्तन प्राधिकरण Airports Authority of India संचार, दिक्चालन एव्म ननगरानी – प्रचालन एिं अनरु क्षण ननिेशालय Directorate of CNS-OM Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 2/124 Version 2.0 PREFACE This is the Version 2.0 of CNS Manual Vol. V in the series of eight volumes of CNS Manuals prepared and maintained by Directorate of CNS-OM, CHQ on behalf of Airports Authority of India for the use and guidance of its executives and maintenance personnel. The topics covered under these volumes are as under:- Volume I – Maintenance of CNS Facilities Volume II – Communication Procedures Volume III – Siting Criteria of CNS Facilities Volume IV – Flight Inspection of CNS Facilities Volume V – Lightning & Surge Protection and Earthing System of CNS Installations Volume VI – Technical Specifications Volume VII– Maintenance Schedules of CNS facilities Volume VIII- Document Management Manual This volume contains the guidelines, recommended processes, procedures and practices for protection of CNS installations from Lightning strikes, surge and transient pulses which not only obliterate the expensive CNS/ATM systems but also disrupt Air Navigations Services. The guidelines contained in this manual were framed by a duly constituted committee by the competent authority for defining the standards and recommended practices. The guidelines, procedures and practices described in this volume, meticulously followed by CNS maintenance personnel at Aeronautical Communication Stations will go in a long way in protecting the vital CNS installations against damage and operational disruptions occurring due to lightning and surges. Views, comments and suggestions for improvement of this volume may be sent to ED CNS-OM so as to incorporate them in the next Amendment/Version. --------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 3/124 Version 2.0 Record of Amendments No. Amendment Date Description of Change Incorporated by 1 29.06.2016 (i) Para 3.14.8 included in Chapter 3 for" DSCN system Lightning protection guidance material" (ii Para 5.16 included in Chapter 5 for "Surge protection for typical DSCN System" (iii Para 5.17 included in Chapter 5 for "Coaxial Connector Seal" (iv Para 8.8 included in Chapter 8 for " Preventive Maintenance Schedules" CNS-OM Dte. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 4/124 Version 2.0 Table of Contents Chapter 1 General 05 Chapter 2 General Requirements 08 Chapter 3 Lightning Protection System 10 Chapter 4 Earthing System 47 Chapter 5 Surge and Transient Protection System 66 Chapter 6 Earth Resistance Measurement 98 Chapter 7 SITC of Lightning, Surge Protection and Earthing 100 System as part of turn key projects Chapter 8 Maintenance Procedures of Lightning, Surge Protection 102 And Earthing System Chapter 9 Definitions and Acronyms 107 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 5/124 Version 2.0 Chapter – 1 General 1.1Title of the Document: This document is identified as Communication, Navigation & Surveillance Manual – Vol. V (CNSM- Vol .V) Version 2.0 “Lightning, Surge Protection and Earthing System for CNS Installations.” 1.2 Scope of this Document: This document mandates standard lightning protection, transient protection, surge protection, grounding, bonding and shielding configurations to be provided for CNS/ATM Automation facilities which are in operation at various airports. 1.3 Purpose of this Document: Purpose of this document is to provide information and guidelines for provisioning of Lightning, Surge Protection and Earthing System of CNS facilities, which are essential for the provision of safe and efficient Air Navigation Services by Airports Authority of India. It is published for the use and guidance of its CNS Maintenance personnel. 1.4 Responsibility for documentation, review, amendments and publication: 1.4.1 The General Manager (Automation & Surveillance), AAI, CHQ is responsible for development, review and amendments of CNS – Manuals Vol. V. He will ensure that the information and guidelines pertaining to provisioning of Lightning, Surge Protection and Earthing System of CNS facilities as detailed in this manual are in conformity and current with respect to various National/International guidelines issued on the subject. 1.4.2 The Executive Director (CNS-OM) is responsible for the approval of documentation, subsequent amendments and publication of CNS-Manual. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 6/124 Version 2.0 1.5 Effective Date: 1.5.1 Effective date of the Manual is indicated at the bottom of the page. 1.5.2 New version, if any, will be indicated by the same date at the bottom of the page. 1.6 Change History: 1.6.1 This is Version 2.0 of CNS Manual Vol. V. Changes, if any, are indicated on ‘Record of Amendments and corrigenda page’. This Version 2.0 of the manual supersedes Version 1.0 of this manual which was published in 2006. 1.5.2 Amendments – Documentation being inserted in the Manual must contain headers and footers that are consistent with those given in this document. 1.7 Control of the Manual:- Directorate of CNS-OM will control this Manual electronically through AAI, ANS website “aaians.aero” and AAI Intranet “Infosaarthee”. 1.8 Distribution of the Manual:- Directorate of CNS-OM may produce hard copies and control the distribution of these Copies, as deemed appropriate. 1.9 Master Copy:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 7/124 Version 2.0 An electronic and a hard master copy of each Chapter contained in the Manual will be held and maintained by the CNS-OM Directorate. 1.10 Checking Currency of Manual:- A current copy of the Manual will be published on AAI ANS website “aaians.aero” and AAI Intranet “Infosaarthee”. 1.11 Enquiries:- Any suggestions, Comments and Enquiries/Clarifications regarding this document should be addressed to: Executive Director (CNS - OM), Airports Authority of India, Rajiv Gandhi Bhavan, Safdarjung Airport, New Delhi – 110003. Email: smmisns@aai.aero or edcom@aai.aero Telephone: 011- 24652075 FAX : 011- 24654142 --------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 8/124 Version 2.0 Chapter - 2 General Requirements 2.1 Scope:- This document covers Lightning, Surge Protection, Earthing & bonding systems to be adopted for CNS/ATM equipment’s with solid state components which are more susceptible to damage due to surges, transients and over voltages being encountered in the system due to lightning, sub-station switching etc. The recommendations specifically cover the following:- (a) Protection of sensitive electronic CNS/ATM Automation systems from lightning resulting from a lightning strike to the building or its associated services installations. (b) Protection of buildings or structures housing CNS facilities against lightning strike. (c) Protection of sensitive electronic CNS/ATM Automation systems from lightning/induction surges and spikes resulting from a lightning strike, power switching etc. (d) Earthing and bonding system to be adopted for CNS/ATM Automation systems. (e) Maintenance procedures/practices to be followed for maintenance of Lightning 2.2References:- 2.2.1The basic framework of guidelines in this Manual is provided by following references:- IS-2309 Code of protection for Lightning Protection IS -3043 Code of practice for Earthing IS -5216 Safety procedures & practice in electrical work IEC -62305 Protection against Lightning Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 9/124 Version 2.0 IEC -61643 Low Voltage Surge Protective Devices ANSI/UL 467 Grounding & Bonding Equipment IEEE- 80 IEEE guide for Safety in AC sub-station grounding IEEE - 837 Standard for qualifying permanent connections used in sub-station grounding 2.2.2In addition, many inputs have been taken from BS: 7430, IEC-60364 and NFPA 780 etc. 2.2.3 For the details, wherever required, respective Code, Standard or Guidelines as mentioned above may please be referred to. -------------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 10/124 Version 2.0 Chapter - 3 Lightning Protection 3.1 Introduction:- 3.1.1 The effects of lightning discharge can be catastrophic on any installation on ground if it is not adequately protected. In today’s world, almost everything and anything is being controlled and operated through technologies involving the use of VLSI and other electronic circuits which are highly static sensitive. Therefore, protecting this equipment’s from lightning discharges and induction surges is of paramount importance to ensure high level of serviceability and operational availability. 3.1.2 The protection of the structure from direct lightning is only half of the work needed to be done. It is also required to protect the systems and equipment installed within the structure from induction surges arising out of lightning activity, which at times could be costlier than the structure. This demands a holistic view to be taken to cover all the aspects of lightning and surge protection. The installation must be correct using correct material, the air terminal should give the total coverage, the earth terminal must be right, and the right type of down conductor should be correctly installed. The surge protectors must be put at every vulnerable point of entry, planned for restricting the rise of ground potential in case of lightning discharge must be taken to safe guard the facility. It is required to ensure that the outer metallic shield of all the power and data cables entering ATS complex needs to be grounded at entry point. An illustration which protects the building surges in power, RF/Data cable etc in a typical CNS installation is depicted in Figure-3.1. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 11/124 Version 2.0 Figure-3.1 3.1.3The basic framework of this standardization is provided by Indian Standard document IS-2309(Lightning Protection). In addition, many inputs have been taken from IEC-62305, IS 3043 (for Earthing), IS 5216 (Safety procedures & practices in electrical work), BS: 7430, IEEE 80, IEC-60364, NFPA 780 etc. 3.1.4Some details of the lightning phenomenon, characteristics of devices used in the lightning and surge protection, methods to be used for CNS facilities Viz. LLZ, GP, DVOR, Radar installations, Antenna, DSCN System etc. have also been included in the document. 3.2 Lightning Protection system :- Lightning Protection comprises basically two types of protection:- 3.2.1 Direct Protection:-Protection of the structures, antenna and buildings against the direct impact of lightning. The direct impact of lightning can cause serious damages to the buildings, structures including fire accidents. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 12/124 Version 2.0 3.2.2 Indirect Protection: The indirect effects of lightning like surges and spikes will cause malfunction and failure of sensitive electrical and electronic equipment through induction. Appropriate surge and spike suppression mitigation techniques are to be implemented accordingly. 3.3.3For protection against both Direct and Indirect protection systems to work efficiently, an effective Earthing system offering a consistent low earth resistance is essential. Hence protection system consists of three parts: - - External Lightning protection - Earthing system - Surge Protection 3.3 Lightning phenomenon The phenomenon of discharge of static electricity generated in storm clouds to the earth is lightning. It comes into existence when warm air masses containing sufficient moisture are transported to greater altitudes. This transport can occur in number of ways. Due to immense landmasses continent receives greater isolation and air near the ground rise up. This creates up draught channels with vertical speed of more than 100 kmph. This warm air when gets mixed with colder air creates surges because of the opposite charged nature of warm and cold air front. It occurs with generation of tremendous light, heat, sound and pressure in the form of thunder. 3.3.1 Charge formation in clouds:- Numerous theories have been advanced regarding the formation of charge centers, charge separation within a cloud, and the ultimate development of lightning strokes. One theory attributes charge separation to the existence of both positive and negative ions in the air and the existence of a normal electric field directed toward the earth. Large drops of water in the electric field are polarized, the upper sides acquiring a negative charge Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 13/124 Version 2.0 and the lower sides a positive charge. As the polarized drops of water fall due to gravity, the undersides (positive sides) attract negative ions, while no such action occurs at the upper surfaces. As a result of this action, the drops accumulate negative charge. Thus, the original charges, which were distributed at random and produced an essentially neutral space charge, become separated. The large drops of water carry the negative charges to the lower portion of the cloud, causing the lower portion to be negatively charged and the upper portion to be positively charged. Another theory is that the interaction of ascending wind currents in the leading head of a cloud breaks up the water droplets causing the resulting droplets to be positively charged and the air to be negatively charged. The positively charged water droplets are unable to fall through the ascending wind currents at the head of the cloud, which causes this portion of the cloud to be positively charged while the remaining larger portion becomes negatively charged. Yet another theory suggests that there are regions of subzero temperature within a cloud and the subsequent formation of ice crystals is an essential factor in the explanation of the charge centers within clouds. It has even been suggested that perhaps all of the physical phenomena postulated in the various theories can occur. At best, the processes occurring within a cloud formation that cause charge separation are complicated. The important fact to the designing engineer is that a charge separation does occur in thunderstorm clouds. Scientists have conducted various experiments using balloons equipped with electric gradient measuring equipment to investigate typical charge distribution in thunderclouds, and these experiments have shown that, in general, the main body of a thundercloud is negatively charged and the upper part positively charged. A concentration of positive charge also frequently exists in the base of the cloud. Such charge distribution in a cloud causes an accumulation of charge of the opposite polarity on the earth’s surface and on objects (e.g., trees, buildings, electric power lines, structures, etc.) beneath the cloud. A typical charged cloud and the resulting electric fields are shown in Figure 3.2(a) & (b). The electric fields shown in this figure have been verified by data obtained by scientists from ground gradient measuring equipment during the passage of storm Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 14/124 Version 2.0 clouds.The phenomenon of discharge of static electricity generated in storm clouds to the earth is lightning. Figure 3.2 (a) Figure 3.2(b) 3.3.2 Lightning Mechanism:- 3.3.2.1 The charged cloud potential can assume any value in the range of hundreds of mega Volts. The lightning stroke starts by the step by step descent from the cloud of a leader stroke stepping some tens of meters at a time. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 15/124 Version 2.0 3.3.2.2 When the last step brings the tip of the leader sufficiently close to earth, an upward streamer leaves the earth to join the tip of downward leader. 3.3.2.3 The initiation of this upward streamer depends on a critical field being exceeded at the earth emission point and is also a function of the charge deposited by the down-coming leader and any enhancement of the field caused by the geometry of the earth. 3.3.2.4 The length of the upward streamer will be greater for greater charges and hence high current flashes will start preferentially from high structures for which the field enhancement is high. 3.3.2.5 This phenomenon is depicted in Figure 3.3 below:- Figure 3.3(a) Figure 3.3(b) Figure 3.3(c) Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 16/124 Version 2.0 3.4 Electrical characteristics of Lightning:- 3.4.2 Current in a Lightning Stroke : Current flow in an ‘average’ lightning flash can be accessed from the diagram below:- Figure-3.4(a) Fig 3.4(b) Figure 3.4 (c) Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 17/124 Version 2.0 Further, from the above figures, following four important parameters for lightning protection technology can be obtained from the lightning current profiles:-  The peak value of lightning current I;  The charge of the lightning current Qflash, comprising the charge of the short strike Qshort and the charge of the long strike Qlong;  The specific energy W/R of the lightning current; and  The steepness di/dt of the lightning current. Lightning current does not depend on load, in other words lightning current can be considered as ideal current source if a load-independent active electric current flows through conductive components, the amplitude of the current, and the impedance of the conductive component the current flows through, help to regulate the potential drop across the component flown through by the current. If a current is formed at a single point on a homogeneously conducting surface, the well-known potential gradient area arises. This effect also occurs when lightning strikes homogeneous ground. Figure 3.5(a): Potential distribution of a lightning strike into homogeneous soil. Higher the conductivity of the ground, flatter will be the shape of the potential gradient area. If lightning strikes a building which is already equipped with a lightning protection system, the lightning current flowing away via the earth-termination system of the building gives rise to a potential drop across the earthing resistance RE of the earthtermination system of the building (as shown in Figure 3.5(b)). In addition to this threat any electrical installation near this building also has a potential threat due to the differential earth resistance of the two sites. This difference in the presence of lightning Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 18/124 Version 2.0 can induce a voltage of the order of 1000kV, which can harm the electrical insulations nearby and can gravely endanger the network. Figure 3.5 (b) 3.4.3 Typical lightning re-strike pattern Usually lightning is continuous phenomenon of short duration i.e. there may be multiple strike with random temporal variation with varying steepness of lightning current (di/dt). Nature of this di/dt variation determines the height of electromagnetically induced voltage as given in Figure 3.6. Figure-3.6 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 19/124 Version 2.0 3.4.4 Typical lightning current multiplier e-strike pattern Figure-3.7 3.4.5 Lightning Strike Electromagnetic Environmental Effects:- Figure-3.8 3.4.6 The characteristics wave form of a lightning surge is as follows:- Figure-3.9 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 20/124 Version 2.0 3.5 The ‘Return stroke’: It is the most important part of a lightning flash considering the resulting damages. This is that part of the flash in which a charged cell in a thunder-cloud is discharged to earth. The current in this return stroke ranges from about 2, 000A to about 2, 00, 000A and its distribution of values is of the form which occurs frequently in nature, the so called ‘log/normal’ distribution. Out of all the lightning strokes, approximately 1% strokes exceed 200, 000A; 10% exceed 80, 000A; 50% exceed 28, 000A; 90% exceed 8, 000A and 99% exceed 3000A, hence, it is expected that only 1% of lightning strikes are less than 3000A. 3.5.1 The current in most ground flashes is from the negatively charged cells in the thunder cloud, and the flash current is, therefore, a negative flow from cloud to ground; less frequently, strokes from a positive part of the cloud also occur. 3.5.2 For either polarity, however, the current flow is uni-directional with a rise time of less than 10μs for the negative flash (but considerably longer for the positive flash) and then decays to a low value, for a simple single stroke, in about 100μs or less. Some flashes comprise two or more strokes which individually conform to the description for a single stroke but which may be spaced in time 50ms to 100ms apart. There are multi-stroke flash having more than 10strokes may, therefore, last for upto1second. 3.6 Voltage in a lightning strike: Before the flash takes place, the potential of the charge cell may be estimated very roughly to be around 10 9V. It is reasonable, therefore, to assume that the cloud potential is more than 100MV. This potential is high enough to ensure that the potentials sustained by whatever is struck will be controlled by the product of current and impedance, because this product will never be high enough in comparison with the cloud potential to modify the current magnitude. 3.7 Effects of lightning Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 21/124 Version 2.0 3.7.1 Electrical effect: As the current is discharged through the resistance of the earth electrode of the Lightning Protection System, it produces are resistive voltage drop which may momentarily raise the potential of the protective system to a high value relative to true earth. It may also produce around the earth electrodes a high potential gradient which is catastrophic to persons and animals. In the same general manner, the inductance of the protective system must also be considered because of the steep leading edge of the lightning pulse. The resulting voltage drop in the protective system is, therefore, the combination of the resistive and inductive voltage components. 3.7.2 Side Flash: The point of strike on the protective system may be raised to a high potential with respect to adjacent metal. There is, therefore, a risk of flashover from the protective system to any other metal on or in the structure. If such flashover occurs, part of the lightning current is discharged through internal installations, such as pipes and wiring, and so this flashover constitutes a risk to the occupants and fabric of the structure. 3.7.3 Thermal effects: Asfar asit affectslightning protection, the effect of a lightning discharge is confined to the temperature rise of the conductor through which the current passes. Although the current is high, its duration is short, and the thermal effect on the protective system is usually negligible. (This ignores the fusing or welding effects on damaged conductors or those which were not adequate in the initial installation). In general, the cross- sectional area of a lightning conductor is chosen primarily to satisfy the requirements of mechanical strength, which means that it is large enough to keep the rise in temperature to 1°C. For example, with a 50mm 2 copper conductor, a severe stroke of 100kA with duration of 100μs dissipates less than 400J per meter of conductor resulting in a temperature rise of about 1°C. The substitution of steel for copper results in a rise of less than 10°C. 3.7.4 Mechanical e f f ec t s: Where a high current is discharged along parallel conductors at close proximity, or along a single conductor with sharp bends, considerable amount of mechanical force is produced. Secure mechanical fittings are, Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 22/124 Version 2.0 therefore, essential. A different mechanical effect exerted by a lightning flash is due to the sudden rise in air temperature to 30, 000 K and the resulting explosive expansion of the adjacent air in the channel along which the charge is propagated. This is because, when the conductivity of the metal is replaced by that of an eructated path, the energy increases about one hundredfold, A peak power ofabout100 MW/m can be attained in the return stroke and the shockwave close to this stroke readily dislodges tiles from a roof. Similarly, with a secondary flash inside the building, the shockwave can result in damage to the building fabric. 3.8 Lightning damages to the installations:- 3.8.1 Lightning effects can be direct and/ or indirect. Direct effects are from resistive (ohmic) heating, arcing and burning. Indirect effects are more probable. They include capacitive, inductive and magnetic behaviour. Lightning "prevention" or "protection" (in an absolute sense) is impossible (IS 2309). A diminution of its consequences, together with incremental safety improvements, can be obtained by the use of a holistic or systematic hazard mitigation approach, described later. 3.8.2 A direct lightning attachment to an unprotected structure usually causes fire and electrical damage. Occasionally explosive damage will occur if lightning strikes a chimney or other porous structural component. Typically lightning strike to a roof or protrusion causes arcing within the structure resulting ignition of structural materials. Since lightning prefers the path of least impedance, it will tend to flow to the electrical system and then to earth, causing severe damage to the wiring. 3.8.3 There are many indirect electrical effects due to lightning strike. Flashover occurs when lightning attaches to something which has a relatively high impedance path to ground. The high impedance can develop a significant voltage on the object. If this voltage exceeds the air breakdown value (approx1MV/m), the lightning may jump from that object to a nearby grounded object. Common example is that of a man injured through a nearby residential telephone line when it is energized by a distant lightning Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 23/124 Version 2.0 strike. 3.8.4 Most lightning damages are noted for electronic equipment. A lightning current pulse in a wire results induced voltage on the termination of other nearby conductors. So called Surges are generated in secondary loops and metallic structures mainly because of inductive coupling close to lightning current carrying conductors. Surge current are generated with typical wave shape of T1/T2 = 8/20µs (i.e. rise time 8 µs and fall times 20 µs) with peak value of some kA up to some 10kA. The high voltage surge of a very small duration is potentially capable of damaging the electronic circuitry. 3.9 Protecting the installations from lightning damages:- 3.9.1 It is impossible to stop or prevent the natural phenomenon of lightning strikes [IS2309]. What can be done is to take measures so that the lightning energy is given a safe passage to earth without harming the structure of interest. Universally, the lightning rods are installed at topmost points of the structure and it is electrically connected to a good earth using a good conductor to protect it from lightning damages. 3.9.2 To protect the electronic equipment from lightning surges and transients, it is required to shunt the current, block energy from travelling down the wire, filter certain frequencies, clamp voltage levels or perform a combination of these tasks. 3.9.3 Voltage clamping devices capable of handling extremely high amperage of the surge, as well as reducing the extremely fast rising edge (dv/dt& di/dt) of the transients are desired. 3.9.4 Adopting a fortress defence against surges and spikes is prudent, i.e., protect the AC mains panel, all relevant secondary distribution panels, incoming and outgoing data and signal lines and also the incoming and outgoing RF cables. 3.10 Methodology for Direct Lightning Protection:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 24/124 Version 2.0 3.10.1 Protection from direct lightning : The probability of direct lightning for a normal structure is extremely low. However, depending on the functional importance of a structure and its usage and its surrounding structures, all relatively taller structures are required to be equipped with a lightning protection system. This is to save the installation from damage and to save lives in case of lightning strike. 3.10.2 Importance for protection: Protection is very much essential because a lightning strike can damage the fabric of the structure, start a fire and also can cause loss of lives besides damaging the equipment. 3.11 Use of Air terminations:- 3.11.1 Air termination networks may consist of vertical or horizontal conductors or combination of both types of conductors. Since the range of attraction is little affected by the configuration of the conductor, vertical and horizontal arrangements are equivalent. 3.11.2 Minimum dimension for air terminations are as follows:- Components Dimension (in mm) Area (mm2) Air Termination Aluminum, Copper & Galvanized steel 20x3 60 Aluminum & its alloy, Phosphor Bronze & Galvanized steel rods 10.0dia 78.54 Suspended Conductors Stranded Aluminum 19/2.14 70.0 Stranded copper 19/2.14 70.0 Steel reinforced stranded Aluminum or stranded galvanized steel 6/4.72 100.0 3.11.3 Simple Vertical conductor(s): Use of pointed air terminals on conical top of a structure is simple and considered to be sufficient since its coverage is generally adequate. Also putting horizontal air terminals on top of such structures presents lot of challenges. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 25/124 Version 2.0 3.11.4 Horizontal conductor(s) for flat roofs: Putting horizontal air terminals on flat roofs is simpler than putting vertical air terminals. Using vertical air terminals for such structure will give inadequate coverage unless they are installed in huge number. 3.12 Coverage of Air Terminations:- 3.12.1 Following diagram shows a simple vertical conductor and the zone of protection in plan and elevation. The protective angle of any single component part of an air termination network is 45Deg. as shown in Figure 3.10:- Figure-3.10 3.12.2 Between three or more vertical conductors, space data distance not exceeding twice their height, the equivalent protective angle may be taken as 60Deg. to the vertical. As shown in Figure 3.11 below:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 26/124 Version 2.0 Figure-3.11 Figure 3.11 shows four vertical conductors with the increased angle of protection. However, it must be realized that although in suitable cases advantage may be taken of the increased protective zone; this is only a statistical concept. 3.12.3 The zone of protection also extends to 45 Deg. of the Horizontal conductor at each point of the conductor. Figure-3.12 (a) Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 27/124 Version 2.0 Figure-3.12 (b) Figure-3.12© 3.12.4 The Zone of Protection offered by an air termination network is considered to be 45 Degree for heights up to 20 meter. Above this height the zone of protection is determined by the “Rolling Sphere Method”. This involves rolling an imaginary sphere of 60 meter radius over a structure. The areas touched by the sphere are deemed to require protection. On tall structures, this can obviously include the sides of the building. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 28/124 Version 2.0 Figure-3.13 Rolling sphere method to check coverage of air terminals 3.12.5 The maximum allowed spacing between horizontal conductors is 18 meter for structures without special inherent risk. 3.13 Air Terminal Support:- 3.13.1 The materials used for installation should be non-corrosive and long lasting. 3.13.2The installation of air terminal on the tower should be such that the tip of the air terminal is at the height of minimum 26 cm (10”) from the top level of the surface / structure. Figure-3.14 3.13.3 The support shall be securely bolted to other mast materials which are necessary Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 29/124 Version 2.0 to enable the air termination and mast system to withstand maximum locally recorded wind velocities. Figure 3.15 3.13.4 Stainless steel Fasteners shall be used in the mounting structure at all the places. 3.14 Typical Air Terminals for CNS Facilities:- Typical air Terminals for lightning protection of CNS facilities are given below. It must be understood that depending on the site conditions and other criteria like maximum permissible height at the location, site specific requirement may vary. 3.14.1 DVOR/VOR installation:- 3.14.1.1 It is recommended to use vertical air terminals whose height and number should be so adjusted that the antenna array is protected. 3.14.1.2 The Vertical air terminal on the collocated DME antenna should also be taken into consideration while deciding required extent of coverage by the air terminals for the VOR/ DVOR antenna array. 3.14.1.3 The height of the conductors must give a clearance of at least 26 cm from Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 30/124 Version 2.0 the nearest antenna to be protected by taking care that the antenna lays completely within the zone of protection. 3.14.1.4 The monitor antenna should also be protected using a vertical air terminal. The vertical conductors may be mechanically and electrically connected to the counterpoise of the DVOR while ensuring that the electrical connection to the earth is secured under all conditions. 3.14.1.5 All the sections of the counterpoise mesh must be bonded to each other through long lasting bonding, taking care so that galvanic corrosion is controlled. 3.14.1.6 Hot dip galvanized iron-steel strip may be used for Earthing of counterpoise members to avoid chemical corrosion between copper strip and iron-steel. 3.14.1.7 Schematic Layout plan for DVOR LPS is shown in Fig. 3.16(a) & (b) below:- Figure-3.16(a) Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 31/124 Version 2.0 Figure-3.16(b) 3.14.2 Glide Path installation:- 3.14.2.1 It is recommended to use a vertical air terminal on top of the GP antenna mast. 3.14.2.2 In fact, since the mast is metallic in nature, the vertical conductor may be joined to the mast at itstop. Proper metallic joints may be ensured between allsections of the mast. 3.14.2.3 The GP equipment shelter will need a vertical air terminal if the shelter is outside the protection zone of the mast air terminal. The height and position of the shelter air terminal should be adjusted to protect the non-protected portion of the shelter. 3.14.2.4 Schematic Layout plan for GP LPS is shown in figure 3.17 below:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 32/124 Version 2.0 Figure-3.17 3.14.2.5 The NF monitor antenna also needs to be protected by a vertical air terminal on top of the monitor mast. 3.14.2.6 The collocated DME antenna needs to be provided with air terminal if it is outside the protection zone of the GP antenna mast. 3.14.3 Localizer installation:- 3.14.3.1 It is recommended that a horizontal air terminal be used for the antenna array. The horizontal conductor is to be supported using poles fixed on the two ends of the antenna structure at least 26 cm away from the nearest antenna structure. 3.14.3.2 The horizontal conductor should have a clearance of at least 26 cm from the nearest antenna under all conditions of sag etc. The total antenna array must be within the zone of protection. 3.14.3.3 The LLZ equipment shelter is required to be protected using vertical air terminal of proper height and the positions should be so adjusted that the total structure comes under its zone of protection. 3.14.3.4 The Far Field Monitor antenna also needs to be protected by a vertical air Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 33/124 Version 2.0 terminal on top of the monitor mast. Height of air termination may be kept keeping in view maximum permissible height at these locations. 3.14.3.5 The NF monitor may not require separate air termination for protection, however RF cable must be provided with a coaxial surge protector. 3.14.3.6 Schematic Layout plan for LLZ LPS is shown in Figure 3.17 below:- Figure-3.17 3.14.4 Marker Installation:- 3.14.4.1Marker antenna installations are generally very near to ground, around 12 ft AGL. This may not necessitate putting lightning protection for this antenna. For Lightning prone areas, however:-  The LPS of the equipment building may be positioned to give the protection coverage.  The LPS of any nearby mast (viz. collocated Locator Antenna) may be positioned to give the protection coverage.  If required an Air Terminal can also be positioned on the Marker mast. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 34/124 Version 2.0 3.14.4.2 In any case, however, the Antenna RF cable must be provided with a Coaxial Surge protector and standard protection may be ensured at the point of entry into the equipment building (shelter). 3.14.5 NDB/Locator Installation 3.14.5.1 The NDB/LOC antennas which are not using self-radiating mast can be protected from lightning by suitably installing Air Terminations on the masts. However, the requirement of height for the lightning rods will be impracticably high. A horizontal LA may also be impracticable. 3.14.5.2 The NDB/LOC antennas which are using self-radiating mast can be protected from lightning by installing Lightning Rods on a suitable mast placed nearby; however the requirement of height for the lightning rods will again be impracticably high. A very near proximity of the Lightning rod mast may affect the antenna performance. 3.14.5.3 Accordingly, it is suggested that no direct Lightning protection be provided to these antennas and only coaxial surge protection to the RF Feeder cables will suffice and suitable entry point protection at the entry of the building be ensured. 3.14.6 DME Installation: - Normally DME Antenna is protected by the LPS of the facility along with it is collocated (i.e. DVOR/GP). However, if required, separate air terminal is to be provided for protecting DME if it is installed separately or is not within the lightning protection zone of the collocated facility. 3.14.7 Surveillance facility (ASR/MSSR/SMR) installation:- 3.14.7.1 The antenna should be protected using horizontal air terminations. The Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 35/124 Version 2.0 horizontal conductors are to be supported using poles installed by the side of the antenna at least 26 cm away from the top of the nearest antenna structure. 3.14.7.2 The horizontal conductor should have a clearance of at least 26cm from the nearest antenna structure under all conditions of sag etc. The total antenna must be protected. 3.14.7.3 The Radar building roof should be protected using a combination of horizontal and vertical air terminations. The horizontal conductors on roofs should form a 10mX20m network and they should not be separated any further. 3.14.7.4 Schematic Layout plan for RADAR LPS (Lightning Protection System) is shown in Figure 3.18 below:- Figure 3.18 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 36/124 Version 2.0 3.14.8 DSCN System 3.14.8.1 To ensure continuous availability of DSCN system in the event of a lightning strike, it is necessary to have the surge protection on both ends of RF cable and UPS power supply. 3.14.8.2 The protection of DSCN system from lightning is provided by efficient functioning of the following components:- 1. The Air terminal rod/lightning arrestor mounted at proper place. 2. Proper earthing to the systems to discharge the lightning energy rapidly to the ground. 3. Surge Protector to protect the systems from induced lightning surges. 3.14.8.3 Items to be installed for Lightning Protection System Following items are required to be installed for providing comprehensive lightning protection system to the DSCN: 1. Pole for Air Terminal 2. Lightning Arrestor/Air Terminal 3. Down conductor 4. Earth pit (Chemical earthing may be deployed only under extreme soil condition where conventional earthing is unable to provide required ohmic value) 5. Surge protectors 3.14.8.4 RF Cables RF cables (Tx and Rx) with proper connectors are also required to be installed with surge protectors. 3.14.8.5 Installation of Poles The pole for the installation of Air Terminal has to be installed as shown in the Figure 3.18.1 below at an optimum distance of 1.0 meter away from the DSCN antenna. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 37/124 Version 2.0 Air Terminal Figure: 3.18.1 Distance between pole and corner of antenna is 1.0 meter. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 38/124 Version 2.0 Figure: 3.18.2 3.14.8.5 Air terminal:- Air Terminal assembly contains the following accessories which are to be used for fixing the air terminal on the pipe. 1. Air Terminal 2. Inline point base 3. Pipe Mount Point Base and Cable Clamp Support Air Terminal shall be made of copper having minimum length 18 inches and diameter 3/8 inch. Ensure procurement of proper fixture for the fixing of Air terminal on the pole Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 39/124 Version 2.0 Figure: 3.18.3 Sample picture of Air terminal rods 3.14.8.6 Installation Instructions of Pole: 1. Pole can be of any suitable diameter of suitable height made of GI or any other metal to withstand heavy wind pressure. 2. The base of pole can be made of cemented/concrete or tripod legs of metal and joint with ground so that it can withstand heavy wind pressure. 3. The pole along with lightning down conductor cable must be separated from the antenna by at least 1.0 meter. 3.14.8.7 Precautions and Instructions: 1. Air terminal height should not be less than 10 inches. 2. Copper Air terminal rod should be used. 3. Copper will stain and cause corrosion to Aluminum and Galvanized steel. Therefore, DO NOT join Aluminum to Copper. Table given in 3.17.4 may be followed to join dissimilar materials in the lightning discharge path. 4. The items like rod to down conductor jointer, clamp, rod holder, rod isolator etc. are also required. 5. Air terminal base shall be of cast bronze or aluminum with bolt pressure or crimp cable connections and shall be securely mounted with stainless steel screws, or nuts / bolts. 6. Cable fasteners shall be made from 20-gauge copper. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 40/124 Version 2.0 3.14.9 Lightning Protection for Antenna Masts/Towers etc. 3.14.9.1 Roof Mounted Antenna Masts Unless it is a radiating or receiving part of the antenna, a metallic mast of a roofmounted antenna shall be bonded to a down conductor. 3.14.9.2 Pole Type Antenna Towers Pole Type Towers shall be protected by at least one air terminal and have at least one down conductor. This is to provide a lightning zone for all antennas located on the tower. 3.14.9.3 Towers without Radomes [Control Tower/Radar Tower] Protection shall be provided for large radar antennas by extending structural members above the antenna and mounting the air terminal on top. The air terminal shall be supported on the structural member. The down conductor from the air terminal shall be connected to a perimeter conductor that forms a loop around the perimeter of the tower platform. Down conductors shall be run from the perimeter conductors to the Earthing System. All tower legs shall be bonded to the Earthing System with a standard size copper conductor. The roof of the control tower is to be protected from lightning as per Para 3.12.3. 3.14.9.4Tower/Antenna Guying All metallic guy wire systems without insulators shall be connected to the Earthing System with a standard copper conductor to the Lightning Protection system of the antenna if they are out of coverage of the Antenna lighting rod. 3.14.9.5Waveguide, Coaxial Cables and Conduit Grounding Waveguide, coaxial cable and conduit located on the tower and feeding into the facility shall be separately bonded to a ground plate mounted on the tower or directly to the earthing system. This bond shall be above and no greater than 2 feet (0.6 m) from the transition bend (90 degree bend) near the tower’s base. Bond the ground plate with a standard copper conductor. A separate bond shall be made from the point Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 41/124 Version 2.0 of origin within tower structure of each coaxial cable or metallic conduit to the metallic tower structure. 3.14.9.6Staircase/Ladder Protection The metallic access to the tower, i.e., staircase, ladder, etc., shall be bonded near its base to the Earthing System with a standard copper conductor installed in a location that avoids accidental tripping or striking that result in personnel jury. Where staircase sections, platforms etc. are not welded together, bonding jumpers shall be installed between them. 3.15 Down conductors, materials, size, etc:- 3.15.1 The down conductors play very important role in the LPS. The minimum dimension for down conductors is as follows:- Component Dimension mm Area mm2 Aluminum, copper or galvanized steel strip 20x3 60.0 Aluminum and its alloy or galvanized steel rods 10.0dia 78.54 3.15.2 A good quality ISI mark copper strip 20 x 3 mm conductor should be provided with suitable clamping/saddling to convey the captured energy by the air terminal to the bonding system to a low impedance earth pit. 3.15.3 The metallic structure like that of a mast may be used as a down conductor by ensuring electrical connectivity of the total structure to the earth. 3.15.4 The shaft of lift should not be used as a down conductor. 3.15.5 Wherever, it is practically impossible to inspect the connectivity of the air terminations on a regular basis, it is recommended to install two down conductors Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 42/124 Version 2.0 separately to the air terminal. This will help in assessing the connectivity of the air terminal to the earth by measuring the loop resistance between the two down conductors. 3.15.6 The down conductor system must, wherever practicable, be directly routed from the air termination to the earth termination network, and be symmetrically placed around the outside walls of relevant structures, starting from the corners. 3.15.7 The number of down conductors should be one for each 30 Meter of the perimeter of the protected structure. 3.15.8 On structures exceeding 20 Meter in height, down conductors should be spaced at not more than 10 Meters apart. 3.15.9 It is important that each down conductor has its own independent earth. 3.15.10 The down conductor must be carefully routed to avoid side flashing. To avoid side flashing, all metallic structures such as pipes, railings, metallic windows etc., which are in contact with general mass of earth should be either isolated or bonded to the down conductor, if this parathion is less than 2 Meter. Minor items like door hinges, metal gutter brackets, isolated reinforced beams may be disregarded. 3.15.11 There should be no discontinuity in the down conductors, joints if any should be preferably brazed. The test joints in the down conductor must conform to the standards for corrosion free good contact. 3.15.12 Every precaution is to be taken to eliminate corrosion of the down conductor, specifically at the joints and bonds. 3.15.13 Two down conductors must be used if the height of the installation is more than 28 meters or the horizontal run of the down conductor is more than the vertical height. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 43/124 Version 2.0 3.15.14 During maintenance check, perfect continuity of the air terminals to the earth must be checked. Wherever there are practical difficulties to reach the air terminal for such check, it is recommended to use two down conductors so that the loop connectivity can be assessed. 3.15.15 Each down conductor should be provided with a test clamp for use during testing. 3.15.16 Down Conductors should be provided for each Air Termination as per the given standard (IS 2309) and should be connected to the common earth bus. 3.15.17 In the final 3 meters to the ground and where it is exposed to human intervention, the down conductor shall be placed in a protective GI pipe, so as to avoid mechanical damage and to increase human safely. 3.15.18 The down conductor shall be installed in accordance with the standard procedure (may follow manufacturer’s instruction) and should not be subjected to bends of less than 0.5 meters radius. 3.15.19 The down conductor shall be secured to the structure/building by metallic fasteners to at least every Meter. 3.16 Routing of down conductor and prevention of side flashing:- 3.16.1 Re-entrant loops in the down conductor can produce high inductive voltage drops which may help lighting discharge to jump across the open side of the loop. 3.16.2 As a rough guide, the loop length must not be more than 8 times the width of the open side of the loop. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 44/124 Version 2.0 Figure-3.19 Figure-3.20 3.16.3 The above requirement should been sure even for a larger e-entrant loop. 3.17 Bonding- importance and application:- 3.17.1 Bonds have to join a variety of metallic parts of different shapes and composition. Due to their varied use, there is the constant problem of corrosion due to the metals involved. 3.17.2 The cross sectional area of the bond should not be less than the employed main conductor. 3.17.3 A bond must be effective both mechanically and electrically and must be Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 45/124 Version 2.0 protected from corrosion and erosion from the operating environment. 3.17.4 Following table gives metallic combinations for which galvanic potentials are acceptable and the resultant corrosion is negligible:- Aluminum alloys Copper Stainless steel Galvanized steel Tin Aluminum alloys OK X 350mV OK 250mV OK 250mV OK 100mV Copper X OK OK X OK Stainless steel OK OK 100mV OK OK OK Galvanized steel OK X OK OK OK Tin OK OK 250mV OK 150mV OK OK 3.17.5 In order to minimize contact corrosion of metal components in outdoor applications, the electrochemical potential difference of unprotected connections should not exceed 300 mV, and for well protected connection, it should not exceed 600 mV. Following Figure 3.21 shows the way to avoid galvanic corrosion:- Figure-3.21 3.18 Precautions to be taken in bonding:- Following points may be noted in this context:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 46/124 Version 2.0 3.18.1 Aluminium is not allowed to be bonded to copper unless properly isolated, for example using bimetal media. 3.18.2 Aluminium and copper should not be allowed in direct contact with soil. 3.18.3 Copper can only be bonded to stainless steel and not to any other iron/non-iron steel. 3.18.4 Tapes and gels etc. may be used to reduce ingress of moisture into the bonds/ joint, which is effective in reducing corrosion. 3.18.5 Metal entering or leaving a structure in the form ofsheathing, armouring or piping for gas, electric, water or any other service should be bonded as directly as possible to the earth termination. This should be done near to the point at which the service enters or leaves the structure. 3.18.6 Any joint other than welded one represents a discontinuity in the current conducting system and is susceptible to failure. 3.18.7 A Lightning Protection System should have minimum number of joints. 3.18.8 Joints should be welded, brazed, riveted, crimped, bolted, screwed or clamped in the order of preference. 3.18.9 Overlapping joints should not be less than 20 mm for all type of conductors. Contact surface to be cleaned and inhibited from oxidation with suitable non corrosive compound. 3.18.10 Different type of joints are shown in Figure 3.22 given below:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 47/124 Version 2.0 Figure-3.22 3.18.11 Dissimilar metal contact must be overlapped for at least 40 mm with the use of corrosion inhibitors as given in Figure -3.23below:- Figure-3.23 3.18.12 Each down conductor should be provided with a test joint, which will be useful in isolating it from the earth during testing. It should preferably be a bolted joint Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 48/124 Version 2.0 and easily accessible however, at the same time unauthorized accessibility should be prevented. 3.19 Transient Event Counter:- 3.19.1 This optional device may be connected to the LPS for having an idea of lightning strike to the system in highly lightning prone areas. 3.19.2 It shall be sensitive enabling to detection of a minimum current of 250A (8/20 microsec) and a max current of 100kA (10/350 microsec). 3.19.3 It shall have a range of 0 to 99, suitable for cable cross section area up to 100 Sq mm capable to withstand a temperature range of -40 degree C to +60 deg. C. 3.19.4 The transient event counter shall be installed at less than 2.0M height from ground. 3.20 EQUIPOTENTIAL PROTECTOR:- 3.20.1 In some rare circumstances, separate earthing systems are required to be provided due to regulatory or special requirements. In such cases, the signal, power and protective earth are separated thus becoming a potential cause of equipment malfunction and damage due to significant difference in earth potential during a lightning strike. 3.20.2 The Equipotential protector shall be used between the different Earth systems which shall consist of a high capacity gas arrester which has a resistance of more than 1Giga ohm under normal condition and thus exhibiting an open circuit with low capacitance. 3.20.3 The protector shall be a very high performance gas filled arrester which will Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 49/124 Version 2.0 momentarily conduct and in connecting the separate earths together there should be a difference in earth potential. After the lapse of the transient impulses, it shall reset automatically and return to its open circuit state. 3.20.4 It shall be totally maintenance free and capable to withstand more than 10000 operations thus guarantee a long working life. 3.20.5 The protector shall be housed in a robust and waterproof enclosure and suitable to be used in any harsh environment. 3.20.6 It shall have following Features :  Long life, maintenance free, robust and waterproof.  Simple installation 3.20.7The technical specifications of Equipotential Protector shall be as described below:- Clamping voltage <380v Voltage tolerance +/- 20% Max. surge rating 20- 150KA (8/20µs) Impulse spark over Voltage <600v (1KV/ µs) Capacitance <10pf Insulation resistance > 1G Ω Humidity 0-95% (R.H) Operating temperature -40 to +80 deg C. 3.20.8For more details regarding equipotential protector, Ref Annexure-2 – IEC 62305- 3 Standard. 3.21 Lightning Protection System(LPS) –Earth termination network, types and specifications:- 3.21.1 An earth electrode should be connected to each down conductor of LPS. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 50/124 Version 2.0 3.21.2 Each of these earths should have a resistance not exceeding the product given by 10Ω multiplied by the number of earth electrodes to be provided. For example, for a system with 15 down conductors, the individual earth reading should not be more than 10x15=150Ω. The whole lightning protective system, including any ring earth, should have a combined resistance to earth not exceeding 10Ω without taking account of any bonding. 3.21.3 A reduction of the resistance to earth to a value below 10Ω hasthe advantage of further reducing the potential gradient around the earth electrode when discharging lightning current. It also further reduces the risk of side flashing to metal in or on a structure. Hence every effort shall be made to ensure as much low ground resistance as possible. 3.21.4 The Earthing shall be provided/ made as per specifications given for Earthing System in the manual. ---------------------------------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 51/124 Version 2.0 Chapter - 4 Earthing Systems 4.1 Earthing:- Lightning, Surges or Unintentional contact between an energized electric conductor and the metal frame or structure that encloses it or an insulation failure in electrical equipment’s etc., can cause dangerously high voltages in the electrical distribution system. Under such circumstances, grounding provides an alternative low impedance path and thereby minimizes damages. A good and an efficient earth ensure that all parts of apparatus other than live parts shall be at earth potential that is zero at all the time. The scope of this section shall cover the following:- a) Earthing electrode/station b) Earthing conductors c) Earthing of equipment and installation The earthing resistance depends on:- a) Resistance of electrode b) Contact resistance between electrode and soil c) Resistance of soil between electrode surface and infinite earth. Resistance of electrode and contact resistance between electrode and soil are very small fraction of an ohm. Approximately 90 % of an earth resistance lies within 2 m between electrode and earth. Moreover, Earth conductivity is essentially electrolytic in nature and is affected by moisture content of soil, its chemical composition and concentration of salt dissolved in the contained water. It is also dependent on grain size and closeness in packing. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 52/124 Version 2.0 4.2 Selection of Earth Pit Site:- Following is the order of preference for selecting an earth pit position.  Wet marshy ground  Clay/loamy soil with little sand  Clay/loamy soil with sand, gravel and stones  Damp and wet sand 4.3 Scope: This specification of earthing system describes in detail, the components to be used and the procedure for constructing the earth system. The main purpose of this is to maintain consistent low earth resistance value over the years without contaminating the Ground water. 4.4 Components: The Earthing system shall consist of Earth Rods / plates and conductive and eco-friendly backfill compound, Earth termination clamps and Earth Bus Bar to facilitate connections to the equipment. The type earth electrode shall be any of the following, as specified:- (a) Pipe / rod earth electrode ; (as per IS 3043) (b) Plate earth electrode; (as per IS 3043) 4.5 Methods of Implementations:- The earthing can be implemented in four ways depending on the requirements, site and ground conditions:- 4.5.1 Conventional earthing using copper plates as per IS 3043:- 4.5.1.1 Earth Pit of the Size of 1 meter diameter and 3 meter depth shall be excavated, after depth of 3 meter the size of excavation shall be 900X300X900mm depth. 4.5.1.2 Plate Electrodes shall be in vertical position. 4.5.1.3PVC pipe for Watering shall be used of 40mm Diameter, length of 3m ( contain hole of 12mm Diameter in Zigzag manner starting from 15cm away from bottom to 2 meter height ). 4.5.1.4 At bottom 150mm layer of salt and charcoal power shall be installed, then Plate shall be installed. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 53/124 Version 2.0 4.5.1.5 Min 120 Kg each of charcoal powder and salt shall be used for each earthing pit. 4.5.1.6 The plate/pipe electrode, as far as practicable, shall be buried below permanent moisture level but in no case less than 2.5 meter below finished ground level. 4.5.1.7 600 mm × 600 mm × 3.15 mm copper plate buried at a depth of 8 ft in vertical position with the pit filled with alternate layers of charcoal and salt up to 4 ft from bottom. 4.5.1.8 The copper plates shall be connected to earth strip by riveting and brazing at no less than two points and the joints shall be protected by heavy coat of bitumen. 4.5.1.9 Schematic diagram for copper plate earthing is shown in Figure 4.1. Figure- 4.1 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 54/124 Version 2.0 4.5.2 Earthing rods directly driven into the earth :- 4.5.2.1 The length of the electrode shall be either 1.22meter or 2meter or 3meter based on the application. 4.5.2.2 Electrodes used for neutral earthing and lightning protection earthing shall be at least 3 meter long and for other applications, electrodes of at least 1.22meter or 2meter length may be used. 4.5.2.3 Earthing System is depicted in Fig 4.2(a) and 4.2(b) below:- Figure-4.2(a) Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 55/124 Version 2.0 Figure-4.2(b) 4.5.2.4The combined earth rod length of a system should be not less than 9 meter whilst each individual earth rod should be not less than 1.5 meter in length. Figure-4.3 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 56/124 Version 2.0 4.5.3 Chemical earthing:- 4.5.3.1 A copper plate or copper coated rod, conventional earthing system should be used as a rule. In general salt and charcoal is used as backfill material for conventional earthing pits and these are eco-friendly. 4.5.3.2 In extreme conditions of rocky or sandy or dry condition where it is difficult to achieve the desired performance of earthing terminals by conventional system, chemical earthing may be employed. 4.5.3.3 The backfill material used in chemical earthing systems for soil treatment shall be highly conductive and should be certified as non-polluting and safe for use near potable ground water systems. 4.5.3.4 The ground conductivity enhancing backfill Material shall be a compound having a low resistance in the range of 0.12 ohm/Meter as specified in IEEE 80 (5 % of the Resistivity of Bentonite), non-corrosive highly conductive powdered material that improves grounding effectiveness, especially in areas of high soil resistivity such as rocky and sandy areas. 4.5.3.5 This material shall be suitable to be installed in either slurry or dry form. The backfill material shall confirm to the following specifications:  Shall be highly electrically conductive and non-soluble.  Shall not leach into ground.  Shall be electronically conductive (like in metals) and shall not depend on moisture / salt for conduction  Shall have a resistivity of less than 0.12 ohm/meter  Shall be compatible with all copper grounding systems  Shall contain a corrosion inhibitor to mitigate corrosion of copper  Shall not contain hazardous chemicals Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 57/124 Version 2.0  Shall be certified to ANSI / NSF standard 60 as safe for use near potable ground water resources  Shall not be affected by drought and shall be stable between -10˚ to +50˚C temperature.  Shall be suitable for any kind of soil  Where, the water table is high or runoff water is foreseen, the backfill compound shall solidify as specified in BS: 7430.The compound shall set like concrete to prevent erosion over a period of time. However under such condition only conventional earthing system should be used. NOTE:-Ref - BS7430 & IEEE80 where use of Carbon backfill compound for obtaining low resistance and maintenance free earthing is clearly recommended under specific conditions. 4.5.4 Horizontal / Lateral Earthing:- Whenever it is not possible to excavate to a depth where the vertical earth electrodes can be installed, the Lateral / Horizontal earthing method shall be adopted as follows:- 4.5.4.1 Three pits of 350 x 150 mm shall be dug to a depth of 3 feet and at a distance of at least 2meter from each other. 4.5.4.2 They can be laid either in a straight line formation or a triangular formation depending on the space availability at site. 4.5.4.3 One copper bonded steel plate of 300 mm× 300 mm× 3 mm shall be placed in each of the earth pits. 4.5.4.4 The earth pits shall be filled with the highly conductive and ecofriendly backfill material up to 6 inches above the top of the plate. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 58/124 Version 2.0 4.5.4.5 These plates shall be interconnected using copper flat / strip of at least 50 sq. mm cross sectional area. Such flat / strip shall be installed in a trench of 100 mm width at a depth of 600 mm (0.6m) from the ground level. 4.5.4.6 The entire trench shall be filled with the highly conductive and eco-friendly backfill material in such a way that there is a minimum of 2 inches of compound on the top and bottom of the interconnecting strip. 4.5 Earth Electrode Specifications:- 4.5.1 The electrodes shall be preferably in one piece of the desired length. 4.5.2 The electrode shall be a solid steel rod made of high tensile low carbon steel and coated with molecularly bonded electrolytic copper on the outside (as per UL 467 or equivalent) . The Earth electrode shall conform to the following specifications :  Steel core: 600 MPa  The thickness of the copper coating shall be at least 250 microns.  Copper jacket should not crack on bending of earth rod  Copper: 99.9% pure electrolytic copper  Copper Structure: Very fine grain structure and highly ductile  Copper Bonding: Fully bonded with steel core  Nominal Diameter over Copper: 14.5mm  Threads: Rolled into copper M16x2  The electrode diameter shall be 14.2 mmdia .  Ends: Chamfer and Pointed (2mm and 6mm x 45deg)  The electrode should be able to carry a minimum short time current of 15 kA for one second.  Couplers should be made of brass  Clamps should be made of brass or stainless steel  Driving head or striker head should be of High tensile steel Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 59/124 Version 2.0  Driving tip should be of mild steel  The earth electrode shall carry standards marking and manufacturer’s name.  Clamps and fixtures should be used in the earthing system to ensure perfect and reliable contact. 4.5.3 Earth rod and accessories are depicted in Figure 4.4 below:- Figure-4.4 NOTE: - Ref – IS-3043 & IEC-60364 where use of such electrodes are permitted & the disadvantage of using plate electrodes are highlighted Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 60/124 Version 2.0 4.6 Soil Treatment:- Approximately 90 % of resistance between electrode and earth lies within a radius of 2m from the electrode. So, for soil treatment, to reduce the earth resistance, a shallow basin, 0.5m around the top of the electrode, half a metre in radius is excavated. This basin is then applied with artificial agents like NaCl, CaCl2, Na2CO3, CuSO4, salt, soft coke, charcoal in suitable proportion. Then the basin is filled several times with water for allowing it to percolate into the ground. 4.7 Earthing System Inspection Chamber:- 4.7.1 A 300X300X300 mm (inside dimension) concrete box with smooth cement plaster finish shall be provided on the top of the pit. A concrete lid, painted black, approx. 50 mm. thick with pulling hooks, shall be provided to cover the earth pit. 4.7.2 Care shall be taken regarding level of the floor surrounding the earth so that the connector is not too deep in the masonry or projecting out of it. 4.7.3 On backside of the cover, date of the testing and average resistance value shall be written with yellow paint on black background. 4.7.4 Alternatively prefabricated earthing inspection chambers may also be used. These have precise dimension and better service life. They are convenient to install and require low maintenance. A Polymer or CI cover shall be provided on the top of the earth system. The prefabricated Earthing inspection chamber should be light weight and suitable for extreme weather conditions. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 61/124 Version 2.0 4.7.5Care shall be taken regarding Care shall be taken regarding level of the floor surrounding the earth so that the connector is not too deep in the masonry or projecting out of it. 4.7.6 Grounding test terminal box shall be installed at an appropriate location suitable for testing the earth resistance. 4.7.7 Typical Inspection Chamber is shown in Figure 4.5 below:- Figure 4.5- Inspection Chamber 4.8 Earthing Conductor: - 4.8.1The earth conductors shall be fixed to the wall/columns etc., at every 500mm with 10mm spacers. The total earthing system shall be mechanically and electrically connected to provide independent path to earth. 4.8.2If the conductor is protected from corrosion, the area of cross section for copper conductor shall be more than 16 mm2 . Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 62/124 Version 2.0 4.8.3If the conductor is not protected from corrosion, the area of cross section for copper conductor shall be more than 25 mm2 . 4.9 Earth Resistance: The earth resistance of combined earth system (to be measured at EEB) shall be less than or equal to 1 ohm, as per the requirement. It shall be measured by an approved earth testing apparatus for individual earth pits. The procedure for measuring earth resistance is given in Chapter- 6. 4.10 Equipotential Earth Bus bar and its connection to equipment’s & Surge protection devices in the Equipment room: - 4.10.1 Equipotential earth bus bars 4.10.1.1There shall be one Equipotential earth bus bar for each of the equipment room. The Equipotential earth bus bars located in individual equipment rooms shall be termed as Sub Equipotential bus bars (SEEB). The Equipotential earth bus bar connected to Class ‘B’ SPDs and the main earth pit shall be termed as Main Equipotential earth bus bar (MEEB). 4.10.1.2The EEBs shall have pre-drilled holes of suitable size for termination of bonding conductors. The EEBs shall be insulated from the building walls. Each EEB shall be installed on the wall with low voltage insulator spacers of height 60mm. The insulators used shall have suitable insulating and fire resistant properties for this application. The EEBs shall be installed at the height of 0.5m from the room floor surface for ease of installation & maintenance. All terminations on the EEBs shall be by using copper lugs with spring washers. 4.10.2 Bonding Connections:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 63/124 Version 2.0 4.10.2.1 To minimize the effect of circulating earth loops and to provide equi-potential bonding, “star type” bonding connection is required. As such, each of the SEEBs installed in the rooms shall be directly connected to MEEB using bonding conductors. Also, equipment/racks in the room shall be directly connected to its SEEB. The bonding conductors shall be bonded to their respective lugs by welding. 4.10.2.2All connections i.e. routing of bonding conductors from equipment’s to SEEB & from SEEBs to MEEB shall be as short and as direct as possible with min. bends and separated from other wiring. However, connection from SPD to MEEB shall be as short as possible and preferably without any bend. 4.10.2.3Materials and dimensions of bonding components for connection of individual equipment’s with Equipotential bus bar and earth electrode shall be as given below:- Component /Bonding Material Size Main Equipotential earth busbar (MEEB) Copper 300X25X6 mm (min.) Sub Equipotential earth busbar (SEEB) Copper 150X25X6 mm (min.) Individual equipment’s to SEEB using copper lugs with stainless steel nut and bolts. Multi-strand single core PVC insulated copper cable as per IS:694 10 sq.mm SEEB to MEEB using copper lugs with stainless steel nut and bolts. Multi-strand single core PVC insulated copper cable as per IS:694 16 sq.mm Surge protection devices (SPD) to MEEB using copper lugs with stainless steel nut and bolts. Multi-strand single core PVC insulated copper cable as per IS:694 16sq.mm Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 64/124 Version 2.0 MEEB to main earth electrode. Multi-strand single core PVC insulated copper cable as per IS:694 (Duplicated) 35sq.mm Main earth pit to other earth pit in case of loop earth Copper tape 25X2 mm 4.11 Markings for Earthing systems:- 4.11.1 Earth bars and terminals at all switch boards shall be marked permanently as “E”. 4.11.2 Main earth terminal shall be marked safety earth – “DO NOT DISCONNECT”. 4.11.3 All earth pits shall be identified properly i.e. by suitable nomenclature identifying earth pit with the facility, Earth pit no etc. 4.12 Earthing System Requirement for CNS facilities:- 4.12.1 The electronic ground conductor shall be PVC insulated standard copper wire of 22 mm² or larger. One such conductor shall run from each equipment area or grouping of related electronic equipment and be terminated at the grounding test terminal box. Electronic ground conductors shall not be interconnected except at the common point. 4.12.2 Each cabinet and isolated item of electronic equipment shall be individually connected to the electronic ground conductor by the shortest possible route. The connecting jumper wire shall be 8 mm² or the size of the power feeder to the electronic equipment cabinet, whichever is larger. In addition, cabinets which are installed sideby-side shall be bonded together by copper wire jumpers, of 8 mm² or larger. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 65/124 Version 2.0 4.12.3 Care shall be taken to assure that ground loops are not created inadvertently. 4.13 COMMUNICATIONS CABLE TRAY SYSTEMS:- 4.13.1 Bond the metallic structures of one cable tray in each tray run following the same path to provide 100 percent electrical continuity throughout this cable tray systems as follows:- 4.13.1.1 Splice plates provided by the cable tray manufacturer can be used for providing a ground bonding connection between cable tray sections when the resistance across a bolted connection is 10 milliohms or less. 4.13.1.2 Install a standard (16 mm²) bonding jumper across each cable tray splice or junction where splice plates cannot be used. 4.13.1.3 When cable tray terminations to cable rack, install standard 16 mm² (bonding jumper between cable tray and cable rank pan. 4.14 Important points regarding Earthing System 4.14.1 Minimum dimensions for earth terminations are as follows:- Component Dia in mm Area mm 2 Copper clad or galvanized steel rods. For Copper clad steel rods, the core should be of low carbon steel of tensile strength700N/mm 2 , (as per Underwriters laboratories UL-467-2007)99.9% electrolytic copper should be molecularly bonded to the steel core and radial width of copper should not be less than 0.25mm. 17.2(with minimum length of 3 meter) 25 32 232 491 804 4.14.2 Earth network/ring: A common earth termination network is recommended for the lightning protective system and all other services. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 66/124 Version 2.0 4.14.3 The resistance to earth should, in this case, be the lowest value required for any of the individual services. In other words, all the earth terminals that of equipment, electrical power, lightning protective system, antenna, etc., are to be connected together to form a common earth network. 4.14.4 One lightning protection system should consist of at least one plate earth terminal and other earth electrodes made by driving copper rods of suitable type into the ground. 4.14.5 No appreciable advantage in resistance reduction is gained by increasing the diameter or surface of the driven electrode. Larger sizes become more difficult to drive and are more expensive in materials. 4.14.6 Where deep driving of earth rods is not possible, a matrix arrangement of rods coupled to one another by conductors can be used. If possible the earth rods must be spaced at a distance at least twice their driven depth. 4.15 Importance of earth ring in reducing potential gradient:- 4.15.1 As the lightning current is discharged through the earth electrode, the surrounding soil is raised for the duration of the discharge to a potential with respect to the body of the earth. The resulting potential gradient is illustrated in Figure 4.6 and it is shown how its voltage gradient can be reduced by adding ring earth electrodes to lower the effective earth resistance. 4.15.2 Such potential difference may be lethal to a person if it exceeds a few thousand volts and to an animal if it exceeds a few hundred volts. 4.15.3 As this potential difference is a function of the product of the lightning current and the resistance of the earth electrode, the importance of keeping the latter as low as possible is evident. For practical purposes, a maximum value of 10Ω is recommended. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 67/124 Version 2.0 4.15.4 The danger to persons within a structure is effectively reduced by the presence of any floor other than that of earth or rock. 4.15.5 To reduce the voltage gradient in case of lightning, a long ground surface near to masts, towers and columns, the earth terminations of each lightning protective system should be interconnected by a ring conductor. 4.15.6 This ring conductor should preferably be buried to a depth of at least 0.5m unless other considerations, such as the need for bonding other objects to it or testing, make it desirable to leave it exposed. 4.15.7 The ring conductor should be connected to the ring conductors of the neighbouring structures. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 68/124 Version 2.0 Figure-4.6 4.16 Anti-corrosive measures (Importance thereof):- Corrosion due to atmospheric, chemical, electrolytic or other causes is likely to impair any part of the lightning protective system; therefore, suitable precautions as mentioned below should be taken to prevent its occurrence:- 4.16.1 Due to the harmful corrosion which is likely to result, coke breeze should not be allowed to come in contact with copper electrodes and salting of the ground in the vicinity of any earth electrode should not be practiced. 4.16.2 In some cases if it is not possible to achieve earth’s resistance less than 1 ohm then all copper to copper joints shall be made by welding or brazing only Bolting of joints shall not be accepted. The minimum distance by which these electrodes should be separated is 3mtrs and maximally it can go up to twice of it i.e. 6mtrs. 4.16.3 Electrolytic corrosion between dissimilar metals: The contacts of dissimilar metals unless the contact surfaces are kept completely dry and protected against the ingress of moisture, are likely to initiate and accelerate corrosion. 4.16.4 The metal of lightning protection system must be compatible to the metals of the structure over which it passes or makes contact with corrosion inhibitors may be used if required. 4.16.5 Aluminium is prone to corrosion when in contact with cement and mortar mixes. 4.16.6 Backfill compound if used for soil treatment shall provide anti corrosion protection to the electrodes. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 69/124 Version 2.0 4.16.7 Fittingsshould be resistant to the corrosive agencies or be otherwise suitably protected. 4.16.8 Joints and bonds may be protected with bitumen or embedded in plastic compound according to the local conditions as shown in figure 4.7 below:- Figure-4.8 ------------------------------------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 70/124 Version 2.0 Chapter-5 Surge and Transient Protection Systems 5.1 Surge & Transient:- Surge is an overvoltage or overcurrent of a short duration occurring on a power line while transient is an overvoltage or overcurrent pulse occurring on a power, signal, control or data line. The term “surge” is used to describe a transient overvoltage on a power line that has duration of a few microseconds. A transient overvoltage can exceed the insulation rating of electrical equipment causing degradation of insulation and immediate damage to the equipment. Relatively low-amplitude transient overvoltages applied repetitively on the equipment will reduce its mean time before failure. The result will be that equipment will have to be repaired more often, increasing operating costs. 5.2 Why Surge Protection is needed:- 5.2.1Power surges can cause failure, permanent degradation, or temporary malfunction of electronic devices and systems. The development of an effective Surge Protection Device (SPD) is of paramount importance to manufacturers and users of industrial electronic equipment. 5.2.2Almost all manufacturers of industrial-type SPDs use metal–oxide varistors (MOVs) in their design. MOVs are composed of a thin disk wafer of material (metal– oxide) that has a known voltage breakdown characteristic. At low voltages, the MOV conducts very little current (microamperes). As the voltage approaches breakdown, the MOV then begins to conduct current. At voltages slightly above the break down, large currents flow, effectively clamping the output voltage. This clamping feature allows the higher voltage levels to be shunted to ground, preventing overvoltages on equipment. 5.2.3 Figure 5.1 and 5.2below show the voltage waveform before and after an ideal Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 71/124 Version 2.0 SPD:- Figure 5.1 Voltagewaveform before SPD. Figure 5.2 Voltage waveform after an ideal SPD 5.2.4 Causes of Power Line Surges:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 72/124 Version 2.0 The sporadic damped phenomena that occur in electrical systems are generally described as transients and surges or in other words Power surges and transient overvoltages are due to the sudden change in the electrical conditions of a circuit and the release of large amounts of energy stored in the inductance and capacitance elements of the system. Sources of power surges can be external or internal to the facility. 5.2.4.1External sources of transient overvoltages can be the following:-  Lightning.  Switching (on/off) of capacitor banks, for power coefficient Correction.  Power-line disconnection and reconnection.  Transformer switching on/off.  Electrostatic discharges.  Power utility load switching.  Poor quality of power transmission and distribution grids. 5.2.4.2 Internal surges are caused by the operation of the following devices:-  circuit breakers or fuses;  electric motors, i.e., elevators;  air conditioners;  VSDs generators. 5.3 It is very important to note that the IS 3043 has specifically recommended the use of surge protection systems to protect the sensitive equipment’s against over voltages induced by lightning and switching surges. 5.4 Transient over voltages are generated due to:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 73/124 Version 2.0 a) Whenever a lightning strikes directly / in the near vicinity; b) As a consequence of different faults in the power system; and c) Switching on and off of different loads etc. d) Hence, it is very important to protect the sensitive electrical and electronic equipment’s against these transient voltage surges. 5.5 The transient voltage surges are broadly classified into two types :-  Lightning Surges ( Handled by Class B or Type I SPDs); and  Switching surges ( Handled by Class C or Type II SPDs) 5.5.1 The lightning surges bring very high amount of destructive energy into the system and hence, are potentially very dangerous. The Class B SPDs are designed to handle the lightning current surges. 5.5.2 The switching surges are relatively frequent than the lightning surges. Although they bring in relatively less energy into the system, however, they still are strong enough to damage the sensitive electronics. The switching surges are handled by the Class C SPDs. 5.5.3 Latest IEEE Guidelines express that lightning activity at a place can induce surges due to Galvanic Coupling for about 1.7 km radius from the point of impact. Hence, it is important to note, both the lightning and the switching surges can come from outside of our power system and hence these surges need to be isolated at the mains input point itself so it is important to put appropriate surge protection devices to all the cables i.e. Power, Data, Remote Control, RF Cables or any other devices which is likely to carry surge and which enters into a equipment room where sensitive CNS/ATM systems are installed. 5.6 Methodology for surge protection:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 74/124 Version 2.0 Surge mitigation technique suggests use of surge suppression devices for power and data lines. The sole function of a good quality surge suppressor is to protect sensitive electronic equipment from transient over voltages. It must limit transient over voltages to a value that do not surpass the AC sine wave peaks by more than 30%. 5.6.1 A surge protector (or surge suppressor) is an appliance designed to protect electrical devices from voltage spikes. A surge protector attempts to limit the voltage supplied to an electric device by either blocking or shorting to ground any unwanted voltages above a safe threshold. 5.6.2 The terms surge protection device (SPD), or the obsolescent term transient voltage surge suppressor (TVSS), are used to describe electrical devices typically installed in power distribution panels, process control systems, communications systems, and other heavy-duty industrial systems, for the purpose of protecting against electrical surges and spikes, including those caused by lightning. 5.7 Main performance parameters of a surge protector are as follows:- 5.7.1 Clamping voltage also known as the let-through voltage. This specifies what spike voltage will cause the protective components inside a surge protector to divert unwanted energy from the protected line. A lower clamping voltage indicates better protection, but can sometimes result in a shorter life expectancy for the overall protective system. 5.7.2 Joules rating: This number defines how much energy the surge protector can theoretically absorb in a single event, without failure. Counter-intuitively, a lower number may indicate longer life expectancy if the device can divert more energy elsewhere and thus will need to absorb less energy. In other words, a protective device offering a lower clamping voltage while diverting the same surge current will cause more of the surge energy to be dissipated elsewhere in the system. Better protectors Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 75/124 Version 2.0 exceed peak ratings of 1000 Joules and 40, 000 Amperes. It is often claimed that a lower Joule rating is undersized protection, since the total energy in harmful spikes can be significantly larger than this. However, if properly installed, for every joule absorbed by a protector, another 4 to 30 joules may be dissipated harmlessly into ground. A MOVbased protector (described below in Para 4.8.1) with a higher let-through voltage can receive a higher joule rating, even though it lets more surge energy through to the device to be protected. 5.7.3 Response time: Surge protectors do not operate instantaneously; a slight delay exists. The longer the response time, the longer the connected equipment will be exposed to the surge. However, surges usually take around a few microseconds to reach their peak voltage, and a surge protector with a nanosecond response time would kick in fast enough to suppress the most damaging portion of the spike. All MOVs have response times measured in nanoseconds, while test waveforms usually used to design and calibrate surge protectors are all based on modelled waveforms of surges measured in microseconds. As a result, MOV-based protectors have no trouble producing impressive response-time specifications. Slower-responding technologies (notably, GDTs) may have difficulty protecting against fast spikes. 5.7.4 Transient surges: These are characterised by different waveforms. The most frequently referenced IEEE waveform used to simulate lightning induced transient activity is the combination wave. This wave is characterised by short duration, high frequency 8/20 µs current and 1.2/50 µs voltage waveform. 5.8 Types of surge protectors:- Systems used to reduce or limit high voltage surges can include one or more of the following types of electronic components. Some surge suppression systems use multiple technologies, since each method has its strong and weak points. Some of these operate primarily by diverting unwanted surge energy away from the protected load, through a protective component connected in a parallel (or shunted) topology. Some others block Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 76/124 Version 2.0 unwanted energy by using a protective component connected in series with the power fed to the protected load, and additionally may shunt the unwanted energy like the earlier systems. 5.8.1 Metal oxide Varistors (MOV) : A metal oxide varistors consists of a bulk semiconductor material (typically sintered granular zinc oxide) that can conduct large currents (effectively short-circuits) when presented with a voltage above its rated voltage. MOVs typically limit voltages to about 3 to 4 times the normal circuit voltage by diverting surge current elsewhere than the protected load. 5.8.1.1 MOVs may be connected in parallel to increase current capability and life expectancy; provided they are matched sets (unmatched MOVs have a tolerance of approximately ±20% on voltage ratings, which is not sufficient). 5.8.1.2 MOVs have finite life expectancy and "degrade" when exposed to a few large transients, or multiple smaller transients. As a MOV degrades, its triggering voltage falls lower and lower. If the MOV is being used to protect a low-power signal line, the ultimate failure mode typically is a partial or complete short circuit of the line, terminating normal circuit operation. 5.8.1.3 If used in a power filtering application, eventually the MOV behaves as a part-time effective short circuit on an AC (or DC) power line, which will cause it to heat up, starting a process called thermal runaway. 5.8.1.4 As the MOV heats up, it may degrade further, causing a catastrophic failure that can result in a small explosion or fire, if the line current is not otherwise limited. 5.8.1.5 When used in power applications, MOVs usually are thermal fused or otherwise protected to avoid persistent short circuits and other fire hazards. In a typical power strip, the visible circuit breaker may be distinct from the internal thermal fuse, which is not normally visible to the end user. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 77/124 Version 2.0 5.8.1.6 If a surge current is so excessively large as to exceed the MOV parameters and blow the thermal fuse, then a light found on some protectors would indicate unacceptable failure. 5.8.1.7 Even adequately-sized MOV protectors will eventually degrade beyond acceptable limits, with or without a failure light indication. 5.8.1.8 Therefore, all MOV-based protectors intended for long-term use should have an indicator that the protective components have failed, and this indication must be checked on a regular basis to insure that protection is still functioning. 5.8.1.9 Because of their good price/performance ratio, MOVs are the most common protector component in low-cost basic AC power protectors. 5.8.2 Transient voltage suppression (TVS) diode: ATVS diode is a type of Zener diode, also called an avalanche diode or silicon avalanche diode (SAD), which can limit voltage spikes. 5.8.2.1 These components provide the fastest limiting action of protective components (theoretically in picoseconds), but have a relatively low energy absorbing capability. 5.8.2.2 Voltages can be clamped to less than twice the normal operation voltage. 5.8.2.3 If current impulses remain within the device ratings, life expectancy is exceptionally long. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 78/124 Version 2.0 5.8.2.4 If component ratings are exceeded, the diode may fail as a permanent short circuit; in such cases, protection may remain but normal circuit operation is terminated in the case of low-power signal lines. 5.8.2.5 Due to their relatively-limited current capacity, TVS diodes are often restricted to circuits with smaller current spikes. 5.8.2.6 TVS diodes are also used where spikes occur significantly more often than once a year, since this component will not degrade when used within its ratings. 5.8.2.7 A unique type of TVS diode (trade names Transzorb or Transil) contains reversed paired series avalanche diodes for bi-polar operation. 5.8.2.8 TVS diodes are often used in high-speed but low power circuits, such as in data communications. These devices can be paired in series with another diode to provide low capacitance as required in communication circuits. 5.8.3 Thyristor Surge Protection device (TSPD), a specialized solid-state electronic device used in crowbar circuits to protect against overvoltage conditions. 5.8.3.1 These Thyristor-family devices can be viewed as having characteristics much like a spark gap or a GDT, but can operate much faster. 5.8.3.2 They are related to TVS diodes, but can "break over" to a low clamping voltage analogous to an ionized and conducting spark gap. After triggering, the low clamping voltage allows large current surges to flow while limiting heat dissipation in the device. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 79/124 Version 2.0 5.8.4 Gas Discharge Tube (GDT): A gas discharge tube (GDT) is a sealed glassenclosed device containing a special gas mixture trapped between two electrodes, which conduct electric current after becoming ionized by a high voltage spike. 5.8.4.1 GDTs can conduct more current for their size than other components. 5.8.4.2 Like MOVs, GDTs have a finite life expectancy, and can handle a few very large transients or a greater number of smaller transients. 5.8.4.3 The typical failure mode occurs when the triggering voltage rises so high that the device becomes ineffective, although lightning surges can occasionally cause a dead short. 5.8.4.4 GDTs take a relatively long time to trigger, permitting a higher voltage spike to pass through before the GDT conducts significant current. It is not uncommon for a GDT to let through pulses of 500 V or more in duration of100 ns. 5.8.4.5 In some cases, additional protective components are necessary to prevent damage to a protected load, caused by high-speed let-through voltage which occurs before the GDT begins to operate. 5.8.4.6 GDTs create an effective short circuit when triggered, so that if any electrical energy (spike, signal, or power) is present, the GDT will short this. 5.8.4.7 Once triggered, a GDT will continue conducting (called follow-on current), until all electric current sufficiently diminishes, and the gas discharge quenches. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 80/124 Version 2.0 5.8.4.8 Unlike other shunt protector devices, a GDT once triggered will continue to conduct at a voltage less than the high voltage that initially ionized the gas; this behaviour is called negative resistance. 5.8.4.9 Additional auxiliary circuitry may be needed in DC (and some AC) applications to suppress follow-on current, to prevent it from destroying the GDT after the initiating spike has dissipated. 5.8.4.10 Some GDTs are designed to deliberately short out to a grounded terminal when overheated, thereby triggering an external fuse or circuit breaker. 5.8.4.11 Many GDTs are light-sensitive, in that exposure to light lowers their triggering voltage. Therefore, GDTs should be shielded from light exposure, or opaque versions that are insensitive to light should be used. 5.8.4.12 Due to their exceptionally low capacitance, GDTs are commonly used on high frequency lines, such as those used in telecommunications equipment. 5.8.4.13 Because of their high current handling capability, GDTs can also be used to protect power lines, but the follow-on current problem must be controlled. 5.8.5 Selenium Voltage Suppressor: An "overvoltage clamping" bulk semiconductor similar to a MOV, though it does not clamp as well. 5.8.5.1 It usually has a longer life than a MOV. It is used mostly in high-energy DC circuits, like the exciter field of an alternator. 5.8.5.2 It can dissipate power continuously, and it retains its clamping characteristics throughout the surge event, if properly sized. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 81/124 Version 2.0 5.8.6 Carbon Block Spark Gap Overvoltage Suppressor: A spark gap is one of the oldest protective electrical technologies still found in telephone circuits, having been developed in the nineteenth century. In this type of suppressor, a carbon rod electrode is held with an insulator at a specific distance from a second electrode. The gap dimension determines the voltage at which a spark will jump between the two parts and short to ground. The typical spacing for telephone applications is 0.076 mm (0.003"). 5.8.6.1 Carbon block suppressors are similar to gas arrestors (GDTs) but with the two electrodes exposed to the air, their behaviour is affected by the surrounding atmosphere, especially the humidity. 5.8.6.2 Since their operation produces an open spark, these devices should never be installed where an explosive atmosphere may develop. 5.8.7 Quarter-wave coaxial surge arrestor :Used in RF signal transmission paths, this technology features a tuned quarter-wavelength short-circuit stub that allows it to pass a bandwidth of frequencies, but presents a short to any other signals, especially down towards DC. The pass bands can be narrowband (about ±5% to ±10% bandwidth) or wideband (above ±25% to ±50% bandwidth). Quarter-wave coax surge arrestors have coaxial terminals, compatible with common coax cable connectors (especially N or 7- 16 types).They provide the most rugged available protection for RF signals above 400 MHz; at these frequencies they can perform much better than the gas discharge cells typically used in the universal / broad band coax surge arrestors. Quarter-wave arrestors are useful for telecommunications applications, such as Wi-Fi at 2.4 or 5 GHz but less useful for TV/CATV frequencies. Since a quarter-wave arrestor shorts out the line for low frequencies, it is not compatible with systems which send DC power for a LNB up the coaxial downlink. A typical Quarter-wave coaxial surge arrestor is shown in figure 5.3 below:- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 82/124 Version 2.0 Figure- 5.3 5.8.8 Series Mode (SM) Surge Suppressors: These devices are not rated in Joules because they operate differently from the earlier suppressors, and they do not depend on materials that inherently wear out during repeated surges. 5.8.8.1 SM suppressors are primarily used to control transient voltage spikes on electrical power feeds to protected devices. 5.8.8.2 They are essentially heavy-duty low-pass filters connected so that they allow 50/60 Hz line voltages through the load, while blocking and diverting higher frequencies. 5.8.8.3 This type of suppressor differs from others by using banks of inductors, capacitors and resistors that shunt voltage spikes to the neutral wire, whereas other designs shunt to the ground wire. Where ground is bonded to neutral at the electrical service entrance, the resulting surge ultimately flows into ground at that connection, but by first dumping into neutral, nearby ground contamination is avoided. 5.8.8.4 Since the inductor in series with the circuit path slows the current spike, the peak surge energy is spread out in the time domain and harmlessly diverted into the capacitor bank. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 83/124 Version 2.0 5.8.8.5 Experimental results show that most surge energies occur at under 100 Joules, so exceeding the SM design parameters is unlikely, but it provides no contingency should rare events induce energies that exceed it. 5.8.8.6 SM suppressors do present a theoretical fire risk, should the absorbed energy exceed design limits of the dielectric material of the components. 5.8.8.7 In practice, surge energy is also limited via arc-over to ground during lightning strikes, leaving a surge remnant that often does not exceed a theoretical maximum (such as 6000 V at 3000 A with a modelled shape of 8 x 20 µs waveform specified by IEEE/ANSI C62.41). 5.8.8.8 SM suppression focuses its protective philosophy on a power supply input, but offers nothing to protect against surges appearing between the input of an SM device and data lines, such as antenna, telephone or LAN connections, or multiple such devices cascaded and linked to the primary devices. 5.8.8.9 In this design philosophy, such events are already protected against the SM device before the power supply. 5.8.8.10 SM low-pass filters are generally not suitable for data communications circuits, because they would also block high-speed data signals from getting through. 5.8.8.11 In comparison to devices relying on components that operate only briefly and do not normally conduct electricity (such as MOVs or GDTs), SM devices tend to be bulkier and heavier than those simpler spike shunting components. 5.8.8.12 The initial costs of SM filters are higher, but a long service life can be expected if they are used properly. In-field installation costs can be higher, since SM Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 84/124 Version 2.0 devices are installed in series with the power feed, requiring the feed to be cut and reconnected. 5.9 Important points regarding installation of Surge Protection at mains input level and at power distribution boxes:- 5.9.1 A comprehensive surge protection system comprising of an INTEGRATED CLASS B +CLASS C TYPE SURGE PROTECTION SYSTEM is ideally suited for installation at the mains input and substation switch boards. 5.9.2 The SPD used shall comply with the performance requirements of the IEC 61643 or equivalent. 5.9.3 The Main Surge Protection System is to be installed in the mains input panel on the LT side. An indicative system is shown in Figure -5.4 below:- Figure- 5.4 5.9.4 The system shall offer comprehensive protection against all types of transient Over Voltages and shall use high capacity MOVs only. It shall be of combined class B+C type. i.e. it shall be capable of handling Lightning as well as Switching Surges. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 85/124 Version 2.0 5.9.5 Class B surge protection device (N-G) may consist of encapsulated air gap device (GDT) and may be used as galvanic separation between N-PE conductors with following characteristics:- i) Protection mode : N-PE ii) Single pole surge protection device iii) Impulse current capacity : 100 kA iv) Max current 160 kA v) Status indicator available 5.9.6 The surge protection system shall be configured such that the system offers all mode (Differential) protection. The protection shall be between each phase to neutral, each phase to earth and between neutral to earth. A typical system is indicated below:- Figure-5.5 5.9.7 The surge protection system shall comprise of multiple MOV based surge arrestors housed in an IP 65 enclosure. 5.9.8 Each Surge arrestor shall consist of at least three elements for backup protection. Each element of the surge arrestors shall comply with the performance requirements of the IEC 61643 or equivalent. 5.9.9 The Surge protection system design shall be modular in nature so that the Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 86/124 Version 2.0 individual surge arrestors can be replaced after its elements have reached the end of their life. 5.9.10 The surge arrestors shall be mounted on a DIN RAIL and housed in an IP 65 or equivalent grade enclosure for reliability and ease of replacement / maintenance. 5.9.11 The design shall be such that when a given element fuses, the balance elements in the surge arrestor continue to offer protection to the installation till it is replaced with a new one in a short period of time. 5.9.12 When any element fuses, the respective status indicator flag shall turn red indicating that the element is out of service. 5.9.13 Each individual element in the surge arrestor shall be rated as follows : - Max. Continuous operating voltage (Uc) 440 V Min. Lightning impulse current (Iimp) 15 KA ( 10/350 µs) per phase Nominal discharge current 80 KA(8/20 µs) Maximum discharge current 150 KA(8/20 µs) Peak value current 40 KA(10/350 µs) Specific energy 400 KJ/Ω Charge 20 As Protection level 1.9 KV(8/20µs);1.7 KV(10/350µs) Response time < 25 ns Residual current < 2.5 mA Follow current 0 Thermo coupler Present Fuse Present Short circuit withstand 25 KA for 50 Hz supply Switching surge current (Imax) 100 KA (8/20 µs) per phase Switching surge current (Inom) 30 KA (8/20 µs) per phase Clamping voltage 1800 V between L-E, L-N, N-E Minimum Inom exposures before fusing 20 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 87/124 Version 2.0 5.9.14 The surge arrestor elements shall be designed to withstand the specified Switching Surge Current (Inom) current for a minimum of 20 times without fusing. 5.9.15 The surge protection system shall be connected in parallel with the circuit and shall not draw the line current. The system shall be connected to the circuit with 10 / 16 Sq mm single core PVC insulated flexible copper conductor cables. The terminal connectors of the system shall be so designed to avoid any loose connections. 5.9.16 In addition to the Main surge protection Device, which provides combined Class B & C protection at the main incoming, a series surge filter may be considered to be installed at all the UPS incoming and outgoing supply which will have the following features:- I) It shall offer All Mode Protection; II) It shall offer redundant protection and staged ; III) LED status indication; and IV) Option for remote monitoring may be considered. 5.9.17 The surge filter shall filter the surges and transients occurring up to the branch panels. It shall offer all mode protection for (L-N, L-E and N-E). 5.9.18 It shall conform to ULI 1449 Edition 2 or equivalent for the metallic enclosure. 5.9.19 The MCB shall be included to ensure safety isolation under power frequency overload condition. 5.9.20 It shall be suitable for a line current of 32A or 63A, 3 phase and up to 320 V 50 Hz power supply. 5.9.21 It shall be connected in series. The surge rating shall be 40 kA, 8/20µs. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 88/124 Version 2.0 5.9.22 Each phase surge arrestor employed shall have two redundant and independent fused and thermal over load protection elements to provide back-up protection for continued equipment survival. 5.9.23 The technical features shall be as described below: Normal Voltage 320Vrms(1p), 380V(3p) Operating Voltage 180-280Vrms(1 ph); 300-480Vrms (3 ph) Operating Frequency 50 Hz Connection type Series Max. surge rating per line 50 kA to 140kA (8/20µs) Let through voltage <380V for 3 KA Cat B Protection mode L-N, L-E, N-E Earth leakage current < 1 µA Efficiency 99% Frequency response 3 dB (at 800 Hz) Response time < 5 ns Standards compliance BS6651-1999 cat.A.B.C AS1768-2003 cat.A.B.C IEEE C62.41 cat.A.B.C CP33-1999 cat.A.B.C IEC 1000-4 5 1995 UL 1449 second edition EMC Compliance BS EN 60950 : 1992; BS EN 61000 : 1999 Alarm isolation 4 Kv Status indicator LED Optional remote alarms Siren sound OK and FAIL LED Alarm(volt free contact) N/O, N/C(2A@250Vac) Alarm conductor size 2.5mm² Conductor size 35 mm² Mounting Back panel screw mount Enclosure material Galvanized steel alloy Enclosure IP rating IP 55 Operating temperature - 40 -85ºc Humidity 0-95% (R.H) Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 89/124 Version 2.0 5.10 COMPUTER NETWORK PROTECTOR: - The Cat5, Cat 5e, Cat 6 and POE (Power over Ethernet) cables shall be provided with a suitable surge protector. It shall be suitable for RJ 45 connectors 5.10.1 It shall be designed to protect all widely used computer network system using Ethernet twisted pairs technology like 10/100/1000 BaseT, CDDI, ATM155 and also the Power-over-Ethernet. 5.10.2 It shall offer protection against transient over voltages due to lightning induced surges, AC power interference and ground loop energies appearing between any signal pair and / or its ground which can damage the sensitive network equipment. 5.10.3 The series protector shall be designed to protect both common and differential mode in all the 8 pins of the RJ 45 port and its ground lead. 5.10.4 It shall have the latest circuitry using Silicon Avalanche diode to ensure very fast response time and exceptional low let-through voltage which results in maximum system reliability and up-time. 5.10.5 The shunt capacitance shall be 5pf and negligible in-line resistance so that even the most demanding high speed gigabit multimedia signal can be passed without much signal degradation. 5.10.6 It shall be compact, in-line and simple plug-in design to enable it to be easily located near the protected equipment. 5.10.7 The technical features shall be as described below:- Max. working Voltage 5V Max. operating current 300mA Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 90/124 Version 2.0 Protection modes Common and transverse Lines protected All pairs Response time < 5 ns Max. surge rating 100A (8/20µs) Max. Data rate 100Mb/s (C5, PoE models), 1000Mb/s(C6 models) Let through voltage 23V (A1 5 KV 10/700µs) Shunt capacitance 5pF (single port models), 25pF(rack-mount models) In line resistance -0 Ω Standards compliance 100 Base T, 1000Base T, CAT5, CAT5e, CAT6 Connector type RJ 45 Earth connection Flying lead(single port models) Earth stud(rack-mount models) Enclosure material Anodized aluminum (single port) Galvanized steel alloy(multi-port) Operating temperature - 40 ºc to 85 ºc Humidity 0-95% (R.H) Altitude 0-3650m 5.11 Telecom line protector: All the telecommunication lines shall be protected with a suitable Surge Protector to protect the modems and other sensitive equipment’s. It shall be designed to protect all widely used telecommunication lines like PSTN, ISDN, DDN and DSL using twisted pairs. Different connectors like RJ45, RJ11 and plug/socket models shall be used to obtain optimum protection. Following are the main characteristics of Telecom line protector:- 5.11.1 The hazard of lightning induction in telephone lines can be managed by using transient protection units in parallel with each line. These multi line protection can have multi stage protection i.e. Hybrid GDT for over voltage protection and PTC for over current protection. 5.11.2 It shall offer Protection against Transient over voltages due to lightning induced surges, AC power interference and ground loop energies appearing between Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 91/124 Version 2.0 any signal pair and/or its ground that can damage the sensitive telecommunication equipment. 5.11.3 The protector shall be designed to protect both common and differential mode in all the connected pins of the RJ 45 or RJ 11 port and its ground lead. 5.11.4 They shall be multi-stage design which employ a combination of high energy gas discharge tube, ultra fast diodes and SAD which results in maximum system reliability and up-time. 5.11.5 It shall have 20KA surge handling capability and 20MHz high bandwidth, so that it can provide the safest protection in lightning intense environment to ensures a smooth data traffic. 5.11.6 It shall be compact, in-line and simple plug-in design enabling it to be easily located near to the protected equipment. 5.11.7 The important technical features of Telecom Line Protector are described as below:- Max. working Voltage (Line to line) 190v (PSTN) , 60 V (ISDN) , 68 V (DDN) 50 V (XDSL) Max. operating current 150mA Protection modes Common and transverse Lines protected 2 wires (RJ11-pin3& 4, RJ45-pin4& 5) 4 wires(RJ11-pin 3& 4, 2& 5, RJ 45-pin 4& 5, 3& 6) Response time < 5 ns Max. surge rating 20A (8/20µs) Max. Data rate 20Mb/s Let through voltage (at 5KV 10/700µs) 220V (PSTN) , 80 V (ISDN) 78V (DDN) , 60V (xDSL) Shunt capacitance < 150pF Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 92/124 Version 2.0 In line resistance 3.9 Ω Standards compliance BS6651-1999, AS1768-2003 IEC61643-21 , ITU(CCITT)1X K17 Connector type RJ 45 or RJ 11 Earth connection Flying lead (single port models) Earth stud (rack-mount models) Enclosure material Anodized aluminum(single port) Galvanized steel alloy (multi-port) Operating temperature - 40 ºc to 85 ºc Humidity 0-95% (R.H) Altitude 0-3650m 5.12 DATA PORT PROTECTOR:- The SPD for Data Line shall be based on transistor and diode circuitry which ensures a lower let through voltage to protect from the surge and transient overvoltage. Following are the main characteristics of Data Port Protector:- 5.12.1 In case of the Surge current above the Rated capacity it shall fuse and isolate the sensitive equipment. 5.12.2 It shall offer common mode & Transverse mode protection against the Transients appearing between any signal pairs. 5.12.3 The DPP RS232 port protectors shall be compact and in-line design which can be easily connected to the data of the equipments. 5.12.4 The V.35 and the RJ21X data port protectors shall be easily secured onto a standard 35mm Top Hat DIN rail. 5.12.5 It shall have fast response circuit not only to protect the equipments from repeated surges but also to allow the DPP protectors to transparently transmit the data at a speed of up to 20 Mbps. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 93/124 Version 2.0 5.12.6 DPP protector shall offer nearly zero in line resistance and a 40pF capacitance which allows the data to transmit smoothly on the lines. 5.12.7 The important technical features of Data Port Protector are described as below:- Max. operating current 300mA Protection modes Common and transverse Response time 1 ns Max. surge rating 200A (8/20µs) Max. Data rate 20Mb/s Insertion loss <1dB at 20 MHz Capacitance 40pf Standards compliance BS6651-1999 Cat.A.B.C AS1768-2003 Cat A.B.C IEC61643-21, ITU(CCITT)1X K17 CP33-1996 Cat A.B.C, UL497B Connector type DB9 female to male (DPP9) DB25 female to male(DPP25) M/34 female to male(DPP35) RJ21X female to male (DPP50) Earth connection DIN clip (DPP35, DPP50) Flying lead(DPP9), shell(DPP25) Enclosure material Anodized aluminum (DPP35, DPP50) Plastic (DPP9, DPP25) Operating temperature - 40 ºc to 85 ºc Humidity 0 to 95% (R.H) Altitude 0-3650m 5.13 RF COAXIAL PROTECTOR:- RF Coaxial protectors are intended to pass through a desired RF signal with minimum loss or disturbance. To minimize the impact of inserting lightning protectors within the RF circuit, seek out products with the lowest Insertion Loss and lowest VSWR at the frequencies that is intended to operate. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 94/124 Version 2.0 5.13.1Other important main characteristics of RF Coaxial Protector (Fig 5.6) are:- i) Reliable RF performance capability from DC – 3GHz ii) Multi – strike capability iii) Easily replaceable gas discharge tube iv) Bi-directional protection v) AC/DC pass vi) High quality construction vii) Full range of connector type Figure-5.6 5.13.2The coaxial RF protectors shall be a high performance gas discharge tube suppressor capable of wide-band operation from DC up to 3 GHz (N, SMA and D type connector). 5.13.3 The let-through voltage shall be as low as possible and it is capable of handling multi-strike in any lightning intensive environment. 5.13.4 CGR protectors feature easily replaceable gas tube arrester elements, which makes it simple, fast and cost effective in case replacement of the gas tube is required. 5.13.5 Both connector ports of this protector shall be equally protected. This provides protection no matter which way it is installed. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 95/124 Version 2.0 5.13.6 The important technical features of RF Coaxial Protector are described as below:- Frequency range 0-3GHz VSWR < 1.1:1 Return loss > 26dB Insertion loss < 0.2dB Impedance 50 Ω for all models Response time <5ns Peak surge rating 20 kA (8/20µs) DC sparkover voltage 90V+/- 20% (230, 350, 600, 1000V) Max. power 0 – 2000 W Standards compliance ITU(CCITT)1x K17 BS6651-1999 Cat.A.B.C AS1768-2003 Cat A.B.C CP33-1996 Cat A.B.C IEC61643-21/UL497B Body material Brass(Nickel plated) Contact pin Brass(silver/gold plated) Contact socket Beryllium or tin brass(silver/gold plated) Elastic contact Beryllium or tin brass(silver/gold plated) Insulator PTFE O-ring material Silastic Earth connection Via suitable screw ground lug Mounting L shape bracket Operating temperature -4-85ºc Humidity 0-95% (R.H) Altitude 0-3650m IP rating IP 65 Moisture resistance MIL-STD-202 Method 106D Salt fog MIL-STD-202 101D/B Temperature shock MIL-STD-202 107D/A-1 Vibration MIL-STD-202 Method204D/B Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 96/124 Version 2.0 5.14 Telephone Line Protector (Krone Type) The main characteristics of Telephone Line Protector which provides surge protection for telecom and other signalling equipment’s terminated on KRONE connectors are:- 5.14.1 The protector shall be available in various assorted configuration like 1 pair, 10 pair, 50 pair etc in a compact module having multi stage protection. 5.14.2 Full range of voltage to suit any particular applications and the let-through voltage shall be as low as possible. 5.14.3 The series protectors shall be easily pluggable type into the KRONE LSAPLUS disconnection blocks and shall be earthed suitably. 5.14.4 It shall offer both line to line (transverse mode) and line to earth (common mode) protection. 5.14.5 It shall have 20 KA high surge rating and 20 MHz wide bandwidth to provide the best protection and to ensure a smooth data flow in high speed data and signal lines. 5.14.6 It shall be designed in such a way that the surge exceeding the capacity of the primary gas arrester, service should be interrupted by blowing the track fuse and thereby giving a fault condition. 5.14.7 The important technical features of Telephone Line Protector are described as below:- Max. working voltage 7-280V Max. operating current 250Ma Protection modes Common and transverse Protection stages 3 stages Earth leakage current < 5 µA Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 97/124 Version 2.0 Response time <5ns Max. surge rating 20 kA (8/20µs)- KDP 10 5 KA (8/20µs) – KDP 1 Max. data rate 20 Mb/s Insertion loss < 1dB at 20 MHz Let through voltage: (At 5KV 10/700 µs) 10-320 V Capacitance 50 pf In line resistance 3.9Ω Standards compliance ITU(CCITT)1x K17 BS6651-1999 Cat.A.B.C AS1768-2003 Cat A.B.C CP33-1996 Cat A.B.C IEC61643-21 UL497B Earth connection Via earth clips on two ends – KDP 10 Via earth bar – KDP 1 Enclosure material ABS plastic Operating temperature - 40 ºc to 85 ºc Humidity 0-95% (R.H) Altitude 0-3650m 5.15 Installation notes and Important points in context of installation of Lightning, Surge Protection and Earthing Systems:- 5.15.1 A Connection made up by materials which do not comply with the chemical chain of materials choice like Copper and steel irrespective of their grade is not allowed to be connected with unless separated by appropriate means as stipulated within IEC62305-3. 5.15.2 IEC stipulates that the spark gaps used for single or multiple load be 100 kA at 8/20 µs single rated. Anything above 60 V is deadly for human life. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 98/124 Version 2.0 5.15.3 IEC 62305 regulatory norm permits only one common grounding network. This common grounding network must interconnect or cross mesh all the sub components of the LLZ system like its building, LLZ antenna array, and NF Monitor. Even the grounds of lightning protection system needs to be connected to the common grounding network. All external metal structures must be connected to the ground network. If there is any other equipment installed at the LLZ site, the same must necessarily be given relevant lightning protection not only for the sake of the equipment itself but for the sake of the whole LLZ installation. As an example wiring diagram of a standard electrical shelter installation (typical) of THALES ILS LLZ is shown below: Fig. Wiring Diagram of Electrical Installation (Typical) Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 99/124 Version 2.0 5.15.4 Implement lightning protection system compliant to IEC 62305 of Cat I. This does not permit the use of such ionizing devices like the prevectron which promise prevention of lightning and wider coverage. 5.15.5 Lightning protection by systems like “Early Streamer emission”, “Dissipation Array Systems” or “Charge Transfer Systems” are not allowed under standards of US National Fire Protection Association (NFPA), IEC, IEEE, Underwriters Laboratories (UL), US Military etc. 5.15.6 The power cable shielding must be connected to a common ground point. 5.15.7 The mains in-leading and out-leading armoured power cable must have its shield grounded with its PEN conductor to one common ground bus bar. The grounding must be done within 20 cm of the cable entry/exit point to/from the building. 5.15.8 The mechanical shield of each RF cable entering or leaving the building must be bonded to the ground at the point where it enters/leaves the building, but not more than 20 cm inside the building. Preferably it should be done outside the building. 5.15.9 The COM cable used for data communication should have its mechanical armouring and inner static shield connected to ground only at one end, say the TWR side and not at both ends. Connecting to ground at both ends is likely to induce strong equalizing ground current between different potentials of such far away buildings, which may reach values above 100 A under worst condition. The other end, both the armour as well as the shield should be grounded through a spark gap to the nearest common ground. The spark gap should be IEC 62305 compliant with low spark over voltage level (< 70 V AC) and high current rating values of 75 kA at 8/320 µs or more. 5.15.10 The IEC 62305 stipulates that there is only one common ground connecting all potentials to one, as well as the PEN, the power cable shield, the COM cable shield, any internal PE and grounds of SPDs, any RF cable shields and others like external Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 100/124 Version 2.0 groundings and lightning protection inclusive of the subsystems e.g. LLZ antenna, NFM etc. 5.15.11 RF cables entering the shelter must have in line surge arrestors. 5.15.12 The PE wire/conductor of a power cable is not a ground connection. The ground connection for static issues must use a connecting wire of cross sectional area 16 mm2 or more and use the shortest path to the near most ground. 5.15.13 All multi strand wire must use cable end sleeves and cable end lugs to enable proper installation and also to reduce chemical chain involved in corrosion. Any flat tape or round wire / cable connections must utilise termination clamps or brackets. 5.15.14 The cable routing of various voltage circuit must be separated, for e.g. the RF, the AC, the DC and the GND and static shields of all the cables must be grounded at point of entry into the building. 5.15.15 All shielded cable like RF, COM, armoured PWR line etc. should be connected to common potential ground at every 20 m along its external path. Same is to be done at every 2.5 m when internally laid. 5.15.16 Common ground network for a DVOR must be connected, DVOR building, Counterpoise steel structure, Counterpoise mesh, power cable shielding, power cable PEN wire, COM cable shield via spark gap, ground connection to SPD related to PWR, COM or RF cabling, Lightning protector rods, DVOR monitor mast/antenna, and other metallic objects of the system. 5.15.17 Copper can be bonded to galvanized steel via special bimetal media or stainless steel media of V4A grade. 5.15.18 PE: Protective earth; PEN: Combined protective earth and neutral; N: Neutral must all be connected to a common bus bar. Electrical conductors entering a Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 101/124 Version 2.0 structure should be metal cased. This metal casing should be electrically continuous within the structure; it should be earthed at the point of entry inside the structure on the user’s side of the service and bonded directly to the lightning protective system. 5.15.19 Where the electrical conductors are connected to an overhead electricity supply line, a 15m length of buried armoured cable should be inserted between the overhead line and the point of entry to the structure. 5.15.20 The overhead supply lines are liable to have large surges induced in them from lightning discharges. Hence is, therefore, needed where they join the buried cable. This will allow a large part of the lightning current to be discharged to earth at a safe distance, which is determined by the rolling sphere’s radius, from the structure. 5.15.21 Surge suppressors should be installed with minimum lead lengths to their respective panels. Under fast rise time conditions, cable inductance becomes important and high transient voltages can be developed across long leads. 5.15.22 In all instances, use high quality, high speed self diagnosing protective components. 5.15.23 Proper ground must be ensured. Earth resistance to be strived to achieved to be as low as possible preferably less than 5 Ω. 5.15.24 Do not install suppressor, if neutral to ground bond is not present. 5.15.25 If neutral to ground voltage is greater than 2 V AC, the electrical system is faulty and needs to be rectified. 5.16 Surge protection for typical DSCN System 5.16.1 A surge protector (or surge suppressor) device is used to protect linkway modem and RF components of DSCN system from lightning spikes and surges. A surge protector removes the lightning spikes induced in the RF cable through earth conduction. Moreover, Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 102/124 Version 2.0 power supply strips installed at DSCN system and RF component ends shall have built in surge protectors. A surge protection device shall also be mounted on a circuit breaker panel of UPS output. Figure below shows power strip with built in surge protector. 5.16.2 RF Connector Type of Surge Protector to be installed in DSCN System: 1. The surge protector of impedance 75Ω shall have F type female and F type male ends for connecting F type male to linkway2100 modem’s RX port and F type female to RF cable. 2. The surge protector of impedance 50Ω shall have N type female and N type male ends for connecting N type male to Linkway 2100 modem’s TX port and N type female to RF cable. 3. The surge protector shall have F type female and F type male ends for connecting F type male to linkway S2 modem’s TX and RX ports and F type female to RF cable. The impedance of surge protector shall be 75Ω for RX path and 50 Ω for TX path. 4. The surge protector of impedance 50Ω shall have N type female and N type male ends for connecting N type male to BUC’s TX port and N type female to RF cable. 5. The surge protector of impedance 75Ω shall have N type female and N type male ends for connecting N type male to LNB RX’s port and N type female to RF cable. Note: Most of LNB consist of N type port but a few LNBs are of F type. Stations may check before procurement. 5.16.3 Connection Diagram of Surge Protector (SPD) for DSCN System: Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 103/124 Version 2.0 5.16.4 Specification of typical Coaxial Cable Surge Protector used in DSCN system Proposed model is 90V DC. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 104/124 Version 2.0 Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 105/124 Version 2.0 NOTE: * Surge protector shall have rating of ‘DC Breakdown voltage’ of 90 Volt. # If 75 Ohm Surge protector is not available than 50 Ohm may be used with same voltage rating as above and LMR 400- 50 Ohm coaxial cable should be used instead of LMR 400-75 Ohm for Rx path. 5.16.5 Connection of Surge Protector Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 106/124 Version 2.0 5.17 Coaxial Connector Seal 5.17.1 Sealing Concepts for Coaxial Connectors: The electrical connecting points in coaxial connectors must be protected against ambient influences. Dust, water and moisture are a constant hazard especially in outdoor applications. Moisture particularly, which penetrates a coaxial system, changes the RF transmission enormously and leads to impedances or poor return loss values. Seals must be fitted at all connecting points to protect the sensitive and expensive electronics. Fig: Sealing Tape 5.17.2 Coax Seal Moisture Proof Sealing Tape 1/2" x 60". Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 107/124 Version 2.0 Coax-Seal is a special material that will quickly and effectively seal all types of coaxial fittings of any shape from moisture, water and corrosion. Coax-Seal stays flexible for years thus insuring moisture proof connections. It ensures good SWR and long coax life. CoaxSeal also allows you to disconnect and reconnect fittings with the same material by simply re-forming the plastic. Coax-Seal is the only material that will adhere to vinyl and poly vinyl connector’s outer covers. Coax-Seal is non-toxic, non-corrosive, non-conducting and stays flexible at any temperature. 5.17.3 Specifications of Self-Fusing Silicon tape/Silicon Rubber Tape: 1. Self-Bonding Silicone 2. Color: Black/oxide-red/Gray 3. Thickness: 30 mil 4. Width: 1.5 inches 5. Length: 15 feet 6. Operating Temperature Range: -30C to +70C 7. Tensile Strength: 700 PSI Minimum 8. Ultimate Elongation: 300% Minimum 9. Tear Resistance: 85 psi 10. Configuration: Rectangular shape Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 108/124 Version 2.0 Fig: Self-fusing Silicone tape ---------------------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 109/124 Version 2.0 Chapter - 6 Measurement of Earth Resistance 6.1 Measurement of Earth Resistivity:- 6.1.1 Need for the measurement of Resistivity:- The resistivity of the soil varies within extremely wide limits, between 1 and 10, 000 Ω-meters. The resistivity of the soil is found to be non-uniform at many station sites. To design the most economical and technically sound grounding system for large installations, it is necessary to obtain accurate data on soil resistivity and on its variation. Resistivity measurements at the site help in designing a good earthing system. The resistivity of the earth varies over a wide range depending on its moisture content. It is therefore, advisable to conduct earth resistivity tests during the dry season in order to get conservative results. 6.1.2 Test Locations:- In the evaluation of the earth resistivity of, at least eight test directions should be chosen from the centre to cover the whole site. This number shall be increased for very large station sites and for sites where, the test results obtained at various locations show a significant difference, indicating variations in soil formation. In case of transmission lines, the measurements shall be taken along the direction of the line throughout the length approximately once in every 4 kilometers. 6.2 Principle of Tests:- 6.2.1 Wenner’s four electrode method is recommended for these types of field investigations. In this method, four electrodes are driven into the earth along a straight line at equal intervals. A current I is passed through the two outer electrodes and the earth as shown in figure below and the voltage difference V observed between the two inner electrodes. The current I flowing into the earth produces an electric field proportional to its density and to the resistivity of the soil. The voltage V measured Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 110/124 Version 2.0 between the inner electrodes is, therefore, proportional to the field. Consequently, the resistivity will be proportional to the ratio of the voltage to current. If the depth of burial of the electrodes in the ground is negligible compared to the spacing between the electrodes, then:- ρ = 2π SV / I Earth testers normally used for these tests comprise the current source and meter in a single instrument and directly read the resistance. The most frequently used earth tester is the four –terminal Megger shown in Fig 1. When using such a Megger, the resistivity may be evaluated from the modified equation as given below. ρ = 2π x SR Where ρ = resistivity in ohm – meters S = distance between successive electrode in meters R = Megger reading in ohms. C1, C2 Current Electrodes P1, P2 Potential Electrodes Fig. 6.1 Measurement of Earth Resistivity ---------------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 111/124 Version 2.0 Chapter -7 Supply, Installation, Testing and Commissioning [SITC] of Lightning, Surge Protection and Earthing System of CNS Facilities as part of Turnkey Project. 7.1When Lightning, Surge Protection and Earthing System of CNS Facilities are being procured under SITC as a part of turnkey project, General Technical specifications of the Tender Document in such cases should clearly specify following:-  The vendor/supplier/system integrator shall be responsible for complete Supply, Installation, Testing and Commissioning of the Lightning, Surge Protection and Earthing System of the facility.  The vendor/supplier/system integrator shall design and provide a comprehensive Lightning, Surge Protection and Earthing System which shall meet the following National and International Standards:- IS-2309 Code of protection for Lightning Protection IS -3043 Code of practice for earthing IS -5216 Safety procedures & practice in electrical work IEC -62305 Protection against Lightning IEC -61643 Low Voltage Surge Protective Devices IEC -60364 Low Voltage electric Installation: ANSI/UL 467 Grounding & Bonding Equipment 7.2 The lightning & Surge Protection System provided shall be a comprehensive system i.e. it should include:- 7.2.1Power Supply Surge Protection System at the input of Equipment room where the facility is proposed to be installed and each distribution board which will supply power to the equipment and its accessories. 7.2.2Surge Protection system should be provided to all incoming and outgoing cables connected to system such as Data lines [Telephone, OFC, RC cables etc] and RF Cables etc. Standard bonding of cable shields/trays to ground at building entry/exit points must be ensured. 7.2.3Air Terminals/Lightning Rods should be positioned to give full coverage of structure [Building, Antenna, Mast etc.] against the lightning. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 112/124 Version 2.0 7.2.4 Earthing system shall meet the following requirements: 7.2.4.1 Provide safety to equipment from power line faults, lightning and surges. 7.2.4.2 Provide a common reference ground plane for electronic equipment which will minimize electronic system noise and electromagnetic interference (EMI). 7.2.4.3 The grounding system design shall be based on single grounding network with multiple earths. 7.2.5 Appropriate references should be made to the guidelines provided in the manual in this regard. 7.2.6 If only a part of Lightning, Surge Protection and Earthing System e.g. only surge protection system is to be supplied by vendor then also appropriate references should be made to standards in this regard in the tender document. 7.3 Any other specific requirement for Lightning, Surge protection and earthing system specific to the equipment being procured should also be clearly specified in the Tender Document. 7.4 Lightning, Surge Protection and Earthing System of CNS facility shall form a part of Factory Acceptance Test (FAT) and Site Acceptance Test (SAT). 7.5 The complete layout of the Lightning, Surge Protection and Earthing System of CNS facility shall be submitted by the vendor/supplier/system integrator before commissioning. ---------------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 113/124 Version 2.0 Chapter -8 Maintenance Procedures of Lightning, Surge Protection and Earthing Systems 8.1Responsibility of Maintenance Maintenance of Earthing, Lightning and Surge Protection System for the CNS installations installed in Terminal Building and/or Technical Block and located inside operational area and around airport (Radar, LLZ, GP, DVOR, OM/MM and NDB etc. ) shall be looked after by the CNS personnel. 8.2 Testing:- 8.2.1 On the completion of the installation, or any modification to it, the following measurements should be made and the results recorded in a lightning protective system logbook: i) The resistance to earth of the whole installation and of each earth termination. ii)The electrical continuity of all conductors, bonds and joints. 8.2.2 If the resistance to earth of a lightning protective system exceeds 5Ω, the value should be reduced. If the resistance is less than 5Ω, but significantly higher than the previous reading, the cause should be investigated and any necessary remedial action should be taken. 8.2.3 Tests should be repeated at fixed intervals, preferably not exceeding 06 months. 8.2.4 It is emphasized that before isolating a lighting protection earth, it should be tested to ensure that it is not “live”, using a sensitive voltage device. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 114/124 Version 2.0 8.3 System Inspection:- 8.3.1 All lightning protective systems should be visually inspected by a competent person during installation, after completion and after alteration or extension, in order to verify that they are in accordance with the recommendations in this code. 8.3.2 Visual inspections should be repeated at fixed intervals, preferably not exceeding 03 months. 8.3.3 In addition, the mechanical condition of all conductors, bonds, joints, and earth electrodes (including reference electrodes) should be checked and the observations noted. 8.3.4 If, for any reason, such as other site works, it is temporarily not possible to inspect certain parts of the installation, this also should be noted. 8.4 Total System Maintenance 8.4.1 Of particular importance is the regular detailed examination of the complete LPS for any evidence of corrosion. If this check is not carried out then vital components within the LPS, which may have suffered from corrosion and which could exhibit a high resistance could be missed. This will have a detrimental effect on the whole system making it an unattractive high impedance path for the lightning current to follow. 8.4.2 The earth resistance for all the electrodes must be measured periodically to ensure their usability. 8.4.3 The resistance of the air terminals to the earth electrode should also be measured periodically. 8.4.4 Maintenance Checks For Lightning Protection System Following checks should be carried out at regular interval – once every 06 months: Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 115/124 Version 2.0 8.4.4.1 Inspection of Air Terminal Physical inspection of air terminal and functionality checks with air terminal test meter. 8.4.4.2 Inspection of Down-conductors  Check for corrosion  Continuity testing by continuity tester, across all types of conductors in lightning protection and grounding system. The resistance should be strived to be as less as possible preferably less than 5.0 ohm.  The down conductors are routed, located and electrically bonded as required. 8.4.5 Periodic Check for Earthing System:  Earth resistance will be checked at the interval of 6 months with the standard process of measurement (Three point method) and recorded. If the measured value is beyond specified standards, corrective action must be taken.  Earth termination systems are interconnected. Where a conductor is totally hidden, its electrical continuity should be tested.  In case specified standards of earth resistance are not met, ground conductivity may be improved by  Refilling of earth pit with electrolytic compound for electrolytic grounding system where provided.  Recharging of earth pits in case conventional grounding system is installed.  Physical inspection of connection between ground rod and down conductor near grounding system for corrosion, bad contacts followed by corrective action. 8.4.6 Inspection of Surge Protection devices:  All surge protection devices should be checked at an interval of 3 months for their functionality. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 116/124 Version 2.0  Indications provided with surge protection system should be monitored and recorded on daily basis.  Faulty devices should be replaced. 8.4.7 Earthing System Inspection Chambers Inspection Chambers of each earthing system should be maintained properly. Grass and other wild growth should be regularly cleared around inspection chamber. Whenever grading or other civil works takes around these chambers, they should be protected properly and should not be allowed to be lost during such works. 8.5 Special Total System Inspection: In the event of occurrence of major lightning strike around the Terminal building and other CNS facility as observed or monitored on the strike record counter, all the aforesaid inspection should be carried out and if need be, the corrective measures to be taken immediately so that LPS is maintained in its optimal effectiveness. 8.6 Inspection Regarding Modifications / Repairs of the Protected Structures While carrying out the periodic maintenance particular attention should be paid, besides earthing and corrosion, to alteration or extensions to the structure that may affect the LPS. Examples of such alterations or extensions are:- a) Change in the use of building; b) Installation of fuel oil storage tank near to building; c) Erection of radio aerials; and d) Installation or alteration to electrical, telecommunications or computing Facilities within or closely connected to the building. 8.7 Records The following records should be kept on site, or by the person responsible for the upkeep of the installation:- a) Scale drawings showing the nature, dimensions and position of all components and Parts of the LPS. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 117/124 Version 2.0 b) The nature of the soil and any special earthing arrangements. c) Date and particulars of salting, if used. d) Test conditions, date and results. e) Alterations, additions or repairs to the system. f) The name and contact details of the person/s responsible for the installation or its upkeep. 8.8 Maintenance Schedules A coordinated programs of inspection and maintenance of the lightning and surge protection systems have been designed in the form of preventive maintenance schedules as given below to ensure its serviceability. 1. Weekly Preventive Maintenance 2. Monthly Preventive Maintenance 3. Inspection after Lightning 4. Pre Monsoon/Pre Winter Maintenance. 8.8.1 Weekly Preventive Maintenance Schedule Visual Inspection (Corrosion, loose connection, dry solder) Surge Protective Devices Status Remarks Air Terminal Down Conductors Connectors of Earth Pit Air terminal & Down conductor Down conductor & Earth Electrode Self diagnostic type of Surge protectors. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 118/124 Version 2.0 8.8.2 Monthly Preventive Maintenance Schedule Surge Protective Devices Status (Resistance of GDT element should be very high) Earth Resistance Value observed Earth Resistance Value of site at the time of Installation Tightness of Connectors of Visual Inspection as given in table at 8.8.1 Air Remarks terminal & Down Conductor Down Conductor & Earth Electrode 8.8.3 Inspection after Lightning Status of surge protector(Resistance of GDT element) Visual Inspection as as given in table 8.8.1 Earth Air Resistance Remarks Terminal & its Connection Down Conductor & its Connection Earth Pit Rx path Tx path Power strip Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 119/124 Version 2.0 8.8.4 Pre Monsoon/Pre Winter Maintenance Earth Resistance Loop Resistance of Air terminal & Down conductor Tightness of Connectors of Greasing of Connectors of Visual inspection As given in table 8.8.1 Equipotential Bonding status Value at Installation Value observed Value at Installation Value observed Air terminal & Down conductor Down conductor & Earth electrode Air terminal & Down conductor Down conductor & Earth electrode Air terminals Down conductor ------------------------------------------------ Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 120/124 Version 2.0 Chapter -9 DEFINITIONS and ACRONYMS 9.1 DEFINITIONS In this Manual, the following definitions shall apply.- 9.1.1 Lightning Flash: Electrical discharge of atmospheric origin between cloud and earth comprising one or more impulse of many kilo amps 9.1.2 Lightning Strokes: The single distinguishable current impulse of a flash. 9.1.3 Lightning Protective System: The whole system of conductors used to protect a structure from the effects of lightning. 9.1.4 Air Termination (Air Termination Network):That part of a lightning protective system which is intended to intercept lightning discharges. 9.1.5 Down Conductor: Conductor that connects an air termination with an earth termination. 9.1.6 Bond: A conductor intended to provide electrical connection between the lightning protective system and other metalwork and between various portions of the latter. 9.1.7 Joint: A mechanical and/or electrical junction between two or more portions of a lightning protective system. 9.1.8 Testing Joint: Joints designed and situated so as to enable resistance or continuity measurements to be made. 9.1.9 Earth Termination (Earth Termination Network) :That part of a lightning protective system which is intended to discharge lightning currents into the general mass of the earth. All points below the lowest testing point in a down conductor are included in this term. 9.1.10 Earth Electrode: That part of the earth termination making direct electrical contact with earth. Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 121/124 Version 2.0 9.1.11 Ring Conductor: Earth termination or electrode fixed to a structure above or below the earth or within or under foundations. A ring conductor may be used alone as an earth termination network or in conjunction with metal rods as an interconnection conductor. 9.1.12 Indicating Plate: A plate detailing the number and position of earth electrodes. 9.1.13 Reference Earth Electrode:An earth electrode capable of being completely isolated from an earth termination network for use in periodic testing. 9.1.14 Log Book:A record of tests and inspections of a lightning conductor installation. 9.2 Acronyms A : Ampere ASR : Airport Surveillance Radar ARSR : Air route Surveillance Radar ANSI : American National Standard Institute ATM system : Air Traffic Management System BS : British standards BIS : Bureau of Indian Standards cm : centimeter CNS : Communication Navigation Surveillance CNS-OM : CNS –Operation & Maintenance Deg. : Degree dia : Diameter DME : Distance Measuring Equipment ES : Earthing System EES : Earth Electrode System IS : Indian Standards (Bureau of India Standards) IEC : International Electro technical Commission IEEE : Institute of Electrical and Electronics Engineers LA : Lightning Arrestor Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 122/124 Version 2.0 LLZ : Localizer LPS : Lightning Protection System Ft : Feet GP : Glide Path kA : Kilo Ampere kmph : Kilometer per hour kV : Kilo volt M(m) : Meter mm : millimeter ms : mill second MIL –STD : Military Standard EEB :Equi-potential Earth Bus bar MEEB :Main Equi-potential Earth Bus bar NDB : Non Direction Beacon NF : Near Field NFPA : National Fire Protection Association MV : Mega Volt RF : Radio Frequency SMR : Surface Movement Radar UL : Underwriters Lab. V : Volt VLSI : Very Large Scale Integrated Circuit ---------------------------- Airports Authority of India CNS Manual Vol. V Ver. 2.0 Lightning, Surge Protection and Earthing System for CNS Installations ------------------------------------------------------------------------------------------------------------------------------------------------------------------ April 2014 Page 123/124 Version 2.0 ******End of CNS Vol. V Ver. 2.0 *****