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1 Karnataka Power Transmission Corporation Limited. Office of the: Superintending Engineer, Ele., Research & Development Center, KPTCL, Kaveri Bhavan Bangalore -560 009. GUIDELINES FOR IMPROVING EARTHING OF EXISTING STATIONS Earth Electrodes: - If G.I. Pipes provided to the L.A’s/Tr. Neutral Control Panel Switch Gear/ 11 KV Feeder D.P. structures are deteriorated, additional C.I. Pipe Electrodes of size 100 mm ID, 13 mm thick, 2.75mtrs. long are to be provided as mentioned below: - Transformer Neutral - Two Nos. for each neutral connection. L.A.’s and P.T.’s - One for each phase. 11 KV Switch gear panel - Two Nos. at both ends. Control Room panel - Two Nos. 11 KV D.P.s - One for each feeder. Auxillary Transformer Neutral - One No. Power Transformer Neutral: - The Earth connection to the Transformer Neutral shall be made by running Two distinct 50 X 6 mm G.I. Flats in opposite direction from the neutral bushing to the electrode and from the electrode to the Earthmat. All connections shall be made by continuous welding. These G.I. Flats should be run on insulators with an adequate clearance from the body of the Transformer, especially Radiator for the safety of the Transformer. Lightening Arrestors and Potential Transfomers: - Each phase of the L.A.’s and P.T.’s should be connected to the individual electrodes provided for that purpose by running G.I. Flat from the base plate of the L.A. and P.T. to the electrode. The electrodes in turn shall be connected to Earthmat by welding using G.I. Flat. 2 Non-current Carrying Metal Parts: - If the existing electrode provided to the non-current carrying metal parts such as Transformer Body, Circuit Braker Body, P.T.’s and C.T.’s Body, Outdoor Structure and Isolator Structure are deteriorated, then these equipment are to be directly connected to the Earthmat using Galvanized Steel Flats with two distinct connection running in opposite direction. Power Cables: - 1. Three Core Cables: - The sheath of the cables are to be directly connected to the Earthmat at their terminations and joints, i.e., at both switchgear and terminating potheads. 2. Single Core Cables: - Sheaths of single core cable shall be earthed at only one end, preferably transformer end. The earth connection shall be made by running a Galvanised Steel Flat from the pothead structure at the top to the Earthmat & connecting the cable sheath to this Galvanized Steel Flat firmly. Wooden clamps are to be provided for Single/Three core cable in the supporting structure and metal clamps shall be avoided. 11 KV D.P. Structures: - These C.I. pipe electrodes are to be interlinked by using 50 X 6 mm M.S. flat and connected to the Earthmat by welding. If 11 KV Feeder D.P. Structures are situated outside the station yard only interconnections between electrodes are made, but shall not be connected to the Earthmat. A separate 50 X 6 mm G.I. Flat shall run from the top cross arm of the D.P.’s where strain insulators are provided for stringing of overhead line and welded. The welding shall also be done at other cross arms provided for fixing G.O.S. and pothead and to the existing ground pipe. The cable sheath shall be connected to the supporting cross arm by G.I. Bolts and Nuts. Control Room: - A separate earth bus of 50 X 6 mm Galvanised Steel Flat shall be run in the control room. The control panel earth bus shall be connected to the Earthmat through the C.I. Pipe electrodes provided around the control room. 3 The earth points provided in the control/annunciator panel and battery charger shall be connected to the control panel earth bus. Auxiliary Transformer: - The station shall have a dedicated Auxiliary Transformer installed within the station yard with its neutral firmly connected to the stat

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