Earthing Resistance

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FADHEL Commentator Join Date: Sep 2012 Posts: 58	Earthing Resistance 10/22/2012 9:51 AM
	Dear all We have existing auto transformer 400/132/11kv the tertiary winding (11kv) delta connected and this delta connected earthed across 21hom resistance. Now when we need to buy new auto transformer with suitable resistance the supplier tell us the new auto transformer not need to earthing resistance. The Question Is When we can install the earth resistance and when we can not. Please I have known that when the tertiary winding feeding any external load the earthing resistance must be install and when the tertiary winding not feeding any external load the earthing resistance must be not install. Is this true? Regards
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#1 Re: Earthing Resistance 10/22/2012 10:10 AM
	If it is an auto-transformer, then it is earthed upstream either at the windings or the star point of the supply point. Being an autotransformer means that its downstream earth reference is the upstream earth connection as the downstream windings and the upstream windings are connected. Therefore the downstream windings do not need an earth connection because they have one already. So the supplier is correct. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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FADHEL Commentator Join Date: Sep 2012 Posts: 58	#2 In reply to #1 Re: Earthing Resistance 10/22/2012 4:32 PM
	Dear sir What do you mean by upstream windings & downstream windings Did you mean high voltage & low voltage side regards
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#4 In reply to #2 Re: Earthing Resistance 10/23/2012 3:26 AM
	On the basis of the information provided in the original posting, upstream and downstream are the only labels that one can apply to the circumstance, because the voltages each side of the transformer have not been detailed sufficiently to convey further meaning. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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pnaban Guru Join Date: Jun 2010 Location: srilanka Posts: 2725 Good Answers: 5	#3 Re: Earthing Resistance 10/23/2012 12:08 AM
	Write to the manufacturer of old transformer and ask him why they connected to earth. __________________ pnaban
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#5 Re: Earthing Resistance 10/23/2012 3:27 AM
	It may be quicker to use the telephone, particularly as additional curiosity and meaning can be conveyed by voice exchange that will not come through in the written word. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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FADHEL Commentator Join Date: Sep 2012 Posts: 58	#6 In reply to #5 Re: Earthing Resistance 10/24/2012 6:23 AM
	Dear Mr. pwslack Tried to contact the company,but i do not successful. please could you help me to answer question below I have known that when the tertiary winding feeding any external load the earthing resistance must be install and when the tertiary winding not feeding any external load the earthing resistance must be not install. Is this true? I am very sorry to repeat the question, but I am hoping that helps me. Regards
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#7 In reply to #6 Re: Earthing Resistance 12/04/2012 5:32 AM
	#3↑. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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FADHEL (2); pnaban (1); PWSlack (4)

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