Transformer Neutral Earthing

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spradhan Power-User Join Date: May 2010 Location: Bhilai,Dist.-Durg,Chhattisgarh,INDIA Posts: 104 Good Answers: 5	Transformer Neutral Earthing 06/16/2011 3:23 AM
	During inspection of electrical installations envisaged under a modernisation project in a steel plant in India,prior to charging, the concerned Electrical Inspector from CEA made an observation that the Neutral of the 6.6/11 kV ,7.5 MVA,DELTA/STAR Transformer should be connected to two separate Earth Electrodes through 50mmX6mm copper strip in place of galvanised steel strip even though the relevant regulation of CEA does not specify the material of the earth conductor. My question is whether it is technically OK ? If yes, What should be the arrangement for connection between the copper strip and the galvanised steel clamp welded to the 100 mm dia G I pipe electrode in order to ensure proper contact with minimum resistance ? Whether any bimetalic strip comprising of copper on one side and GI on the other side is available in the market ? If not,can a bimetalic strip of copper & aluminium be recommended for such application ? Thanks in advance. __________________ Learning is a never-ending process.
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hithuanand Power-User Join Date: Apr 2010 Location: Asia/India Posts: 365 Good Answers: 1	#1 Re: Transformer Neutral Earthing 06/16/2011 9:37 AM
	The EAF that i studied in our steel complex limited has four tap positions in which 1,2 positions are in star-star and 3,4 positions in star-delta(5MVA,11KV/250V)power transformer.Phase to Phase arching is done on molten metal bed.There was Amplidyne controlled and Thyristor controlled EAF.Don't know about earthing material dimensions.
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electricalexpert65 Guru Join Date: Oct 2009 Posts: 2061 Good Answers: 169	#2 Re: Transformer Neutral Earthing 06/16/2011 10:26 AM
	The CEA is grossly incorrect in demanding a Copper Strip in place of a GI Strip. Indian Standard IS 3043 recommends Copper or Aluminium or Steel as Earthing Conductor or Protective Conductor Material - as long as appropriate sizing is done. You can quote from IS 3043 to the CEA Inspector. But, the problem is these Inspectors think that they have jumped from heavens and you cannot argue with them. To satisfy his ego, you can tin or silver plate the Copper Strip and connect it directly to the GI Clamp, without any Bimetallic Washers.
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spradhan Power-User Join Date: May 2010 Location: Bhilai,Dist.-Durg,Chhattisgarh,INDIA Posts: 104 Good Answers: 5	#4 In reply to #2 Re: Transformer Neutral Earthing 06/18/2011 5:17 AM
	Thank you electricalexpert65 ! __________________ Learning is a never-ending process.
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Vinu_Answers Commentator Join Date: Mar 2011 Location: Noida, (U.P.), India. Posts: 99 Good Answers: 6	#3 Re: Transformer Neutral Earthing 06/18/2011 5:06 AM
	As Per IS-3043, Earthing electrode when made up of GI or steel shall be not less than 6.3mm in thickness and when made up of Copper (Cu) shall be not less than 3.15mm in thickness. In your case, You have used copper strip of size, 50mmX6mm, then there will be no problem. Also I agree with ee65, that you can apply tin or silver paint on Copper Strip. Vinu_Answers Sure_Answers __________________ Sure Answers Always
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