Purpose of Neutral Grounding:- Neutral of a3 Phase Star Connected Transformer is to be Earthed Properly to Enable Earth-Fault protection for STATOR Windings & associated Systems & also to Limit Transient Over-voltage during Fault in System or Switching, Lightning, or Heavy Load through-off or long time Unclear fault in the System etc.etc. In such Faults it limits the Earth fault current to less than Full load Current , for a terminal Earth Fault. It gives System stability, by providing easy path for Unbalance system Current/Voltage into the ground during fault Condition, thus System got Stabilized.. These are process of Grounding the Neutral :- 1. Connect Neutral with Ground / Solid Earthing ( Small Distribution trafo) 2.Resistance Grounding : - Connect Neutral with Ground through Metal-Grid type Resistor. For Large or Medium Voltage Transformer.Resistors are short time tated for30 seconds. 3.High Impedance Grounding:- Neutral is Earthed through Primary winding of a distribution Transformer & A loading Resistor is connected across low voltage secondary. 4. Ziz-zag- or Star/Delta transformer in the Tertiary Winding to Neutralise Earth fault current into the Ground. Necessary Relaying against different faults in System When System Neutral is Grounded:- 1) Connect CT in the Neutral of Proper Rating ( Say100/1, 25/1 according System design). Standby-Earth fault Protection, gives100% protection against Earth-Fault. 2) Connect3 PT in Open-Delta , PT Open_Delta is the Sensing of Neutral displacement Relay. VDG-14. In normal condition Open-Delta point Voltage will be Zero, but in case of Fault There must be some voltage in Open-Delta-point. Typical setting5-20 Volts. 3) Instantaneous Earth Fault Relay. Chemical earthing Supplier in Noida