Zero Sequence CT to be Used at Transformer Neutral

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hisham.i Active Contributor Join Date: Oct 2014 Posts: 14	Zero Sequence CT to be Used at Transformer Neutral 01/01/2015 6:03 AM
	The principle of operation of zero sequence current transformer, that it detects the difference of the summation of the magnetic fiels generated by the 3 phases, and in case there is a ground fault the summation will not be zero, and hence it will generate a secondary current which will flow into the proper relay and trip the breaker. Based on this principle of operation, i am thinking of using same zero sequence current transformer to detect the current on the neutral line of the delta star transformer. The only thing that i found that will be affected is the ground fault maximum current compared to the CT ratio. Please advise if i can use the zero sequence CT on the transformer neutral.
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Noudge79 Guru Join Date: Feb 2011 Posts: 1119 Good Answers: 11	#1 Re: Zero Sequence CT to be Used at Transformer Neutral 01/01/2015 12:11 PM
	Then, what are your plans? __________________ " To infinity and beyond" - Buzz Lightyear
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4wsilver Power-User Join Date: May 2013 Posts: 351 Good Answers: 22	#2 Re: Zero Sequence CT to be Used at Transformer Neutral 01/02/2015 7:15 AM
	There is no such thing as a zero sequence CT. There are only CT's. That is the usual location in Y windings. A "zero sequence CT" is simply a name for an application for a CT. What you need to do is to look at what currents can exist and then pick a Ct that will give you the signal you need without saturation. Your question indicates that you really have no understanding of CT's or their applications.
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JRaef Guru Join Date: Sep 2006 Location: California, USA, where the Godless live next door to God. Posts: 4665 Good Answers: 803	#3 In reply to #2 Re: Zero Sequence CT to be Used at Transformer Neutral 01/03/2015 11:50 AM
	I agree with 4wsilver, "zero sequence" is an application method for using a CT. That said, there are special types of CTs often used in zero sequence applications, called "core balanced" CTs. They are different from phase CTs in that they are more precise and operate at lower secondary currents, but because you will be passing all 3 phases with or without the neutral though it, it's difficult to control the conductor position within the window, so the CBCT must be made in such a way as to avoid nuisance tripping of the GF relay on non-fault related phase current imbalance. So it makes no sense to use a CBCT on just the neutral of a transformer. But I'm not sure what you think you will be accomplishing with that. Read this, it might help you here. http://www.gedigitalenergy.com/products/support/f60/get8390.pdf __________________ All I every really wanted to be, was... A LUMBERJACK!.
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4wsilver (1); JRaef (1); Noudge79 (1)

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