TYPES OF EARTHING Any discussion on earthing invariably leads to a discussion on the different types of earthing and the corresponding definition of each. However, it is commonly accepted that earthing in the gas industry can be classified as either dirty or clean. Please refer to Figure 3 for a comparison of the different earthing. Dirty Earthing Dirty earthing inside the facility are typically those 120VAC, 220VAC, 480VAC power earthing that are associated with high current level switching such as Motor Control Centers (MCC), lighting, power distribution, and/or earthing corrupted by radio frequencies or electromagnetic interference. Quite often, the primary AC power coming into the plant can introduce spikes, surges, or “brownouts” that further erode the cleanliness of the AC ground. Noida, Delhi, Gurgaon, Sonepat, Ghaziabad, Manesar, Bhiwadi, Chandigarh, Dehradun, Jaiupur, Nimrana, Meruth , Clean Earthing Examples of clean earthing are the DC earthing, usually 24VDC, that reference the PLC, DCS or metering/control system in the gate station or plant. Frequently, control systems engineers from the major SCADA vendors recommend isolating these earthing from power earthing. Other clean earthing are those associated with data and communication busses that, due to the vulnerability of low-level CMOS and microprocessor circuits, must be maintained relatively free of noise interference or risk data/communications loss. Noida, Delhi, Gurgaon, Sonepat, Ghaziabad, Manesar, Bhiwadi, Chandigarh, Dehradun, Jaiupur, Nimrana, Meruth , Structural Earthing These are the earthing that physically and electrically tie the facility together and, quite importantly, complete the circuit to the 0V, ground leg of the power distribution transformer. Structural earthing can take many forms. In a ship, it is the hull of the ship; on an offshore oil/gas platform, it is the structural steel of the platform. In large petrochemical or pharmaceutical plants, a ground grid or mat is installed under the plant or the welded structural steel of the plant itself becomes the 0V electrical power ground. In the typical gas plant or gate station, the 0V ground reference is most often a heavy gauge copper wire embedded around the base of the building and tied into ground rods at the corners as well as into the AC ground feeds at critical junctures. Not only does this copper ground create the 0V reference for the station’s electrical system, it becomes part of the Faraday cage lightning arrester/arrester system that will be discussed later. Noida, Delhi, Gurgaon, Sonepat, Ghaziabad, Manesar, Bhiwadi, Chandigarh, Dehradun, Jaiupur, Nimrana, Meruth , GROUNDN-EMCC‘DIRTY’LightingCC‘CLEAN’Structural EARTHINGE Bar‘Instrument System’‘CableShields’‘PLCSystems’‘PLC’‘InstrumentMains Supply’I.S. GROUND Figure 3. Earthing Types BUILDING A PROPER EARTHING BED There are two basic elements that are used for IACS earthing systems: earthing rods and a earthing grid Using a earthing rod in a earthing bed system comprises of installing a ground rod (generally by hammering in the rod) into the earth. Earthing rods come in a variety of materials and sizes. The rods typically are made of stainless steel, galvanized steel, copper clad steel, or pure copper all yielding approximately the same lifespan. The rods generally range from ½” to 1” in diameter and from 5 to 10 feet in length. The size of the rod will vary depending on the soil conditions (sandy - high soil resistivity, rocky, silty loam - low soil resistivity, etc.) and the equipment available for installing the rods. It is best to contact a earthing rod manufacturer for help in determining the best rod to use for a given application. Typically, for the soils found in northern Virginia, 5/8” diameter by 8 feet long earthing rods are used. The goal of a earthing rod is to achieve a resistance of 25 ohms or less between the rod’s earthing conductor and the soil in the general vicinity of the rod per NEC 200. The rods are generally installed near the electric utility’s meter, in the vicinity of large above ground structures, and are tied in at various locations to the earthing grid. (see Figure 4). Noida, Delhi, Gurgaon, Sonepat, Ghaziabad, Manesar, Bhiwadi, Chandigarh, Dehradun, Jaiupur, Nimrana, Meruth Chemical Earthing in Noida faridabad Gurgaon Gurugram Delhi Dehradun Supplier of Chemical Earthing in Noida faridabad Gurgaon Gurugram Delhi Dehradun Earthing Dealer in Noida faridabad Gurgaon Gurugram Delhi Dehradun Earthing manufacturer Noida faridabad Gurgaon Gurugram Delhi Dehradun GI Earthing Electrode Supplier in Noida faridabad Gurgaon Gurugram Delhi Dehradun we supply Transformer and Generator set Special and cost effective solution of earthing Wednesday | 29 August, 2018 | 11:39 AM HOW NOT TO GROUND! Do not ground various elements of the IACS i.e., shields from field transmitters and the ROC/PLC power supply ground, to different earthing. Figure 9 shows a prime example of how not to ground. In this example, the control loop shields are grounded to a separate ground rod. Additionally, the control element power supply is grounded to the AC ground but the PLC analog input circuit is left floating. Even in a smaller station, if different instruments are connected to independent ground rods, the reference to ground will vary which will develop localized potential differences. This is a sure recipe for disaster. ww.snengineering.com www.chemicalearhingelectrode.com