Calculating NGR

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Anonymous Poster	Calculating NGR 09/06/2008 7:27 PM
	how calculation of ngr and how it will work
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Sparkstation Guru Join Date: Nov 2007 Location: Christchurch, (The Garden City), South Island, New Zealand Posts: 4395 Good Answers: 230	#2 Re: how calculation of ngr 09/07/2008 12:04 AM
	Hello (First) Guest, Refer: http://www.startco.ca/library/papers/Monitoring%20NGRs.pdf That should answer your questions. Kind Regards.... __________________ "The number of inventions increases faster than the need for them at the time" - SparkY
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Anonymous Poster	#6 In reply to #2 Re: how calculation of ngr 09/08/2008 12:55 AM
	Hi Garry and Mervin This article is excellent and very useful for my job. I wish you all the best for providing this manscript in web. thanks once again and best regards Sridhar.n
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jack of all trades Guru Join Date: Sep 2006 Location: Auckland, New Zealand Posts: 8777 Good Answers: 376	#3 Re: Calculating NGR 09/07/2008 4:01 PM
	Put simply a NGR (or Neutral Grounding Resistor) is a big resistor element array placed between the star point of a transformer down to ground and is used to limit the fault current in the event of, well a phase to ground fault, to a low value allowing the protection to operate and disconnect the fault. It limits the current, gets hot and is generally made of sheets of thick stainless steel which are rather heavy and difficult to work with (as I am currently finding out with the two I am working on at the moment). These two 33kV 30 ohm 650A NGR's destined for a wind farm substation are also fitted with CT's for earth fault protection and monitioring. __________________ jack of all trades
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Sparkstation Guru Join Date: Nov 2007 Location: Christchurch, (The Garden City), South Island, New Zealand Posts: 4395 Good Answers: 230	#4 In reply to #3 Re: Calculating NGR 09/07/2008 5:24 PM
	Hello jack of all trades from me, from the Mainland. Kind Regards.... __________________ "The number of inventions increases faster than the need for them at the time" - SparkY
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Anonymous Poster	#5 In reply to #3 Re: Calculating NGR 09/07/2008 11:55 PM
	Decide how much is the NGR limiting current (mostly 400A, 30sec for MV system). IEEE 141 guides for NGR limiting current selection. For example : Voltage = 6600V Current = 400A NGR value = 6600/(1.732*400) = 9.5 Ohms Regards, A Shanmugam
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sj Active Contributor Join Date: Mar 2008 Posts: 10	#7 In reply to #5 Re: Calculating NGR 09/11/2008 4:23 AM
	Can you pl elaborate on how the 400A is selected for MV system? Is it as per any standard or an industry practice ?
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jack of all trades Guru Join Date: Sep 2006 Location: Auckland, New Zealand Posts: 8777 Good Answers: 376	#8 In reply to #7 Re: Calculating NGR 09/16/2008 3:42 PM
	<sigh> Is this a homework question or are you a clueless consultant or protection engineer? I mean really! Please have a look on the internet and Wikipedia, there is plenty of information on the basics of NGR and WHY you would select a certain fault current level for your protection. __________________ jack of all trades
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Anonymous Poster (3); jack of all trades (2); sj (1); Sparkstation (2)

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