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KWASI BIMPONG
Associate

Join Date: Jan 2012
Location: Tema
Posts: 25

Transformer Differential Relay Operation

02/16/2014 7:51 AM

Team, please what will be the cause for a differential relay of a transformer to operate any time it is been energised.However it always holds after two or three attempt of trying to close.
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RAMConsult
Guru
Engineering Fields - Power Engineering - New Member

Join Date: May 2007
Location: NYC metropolitan area.
Posts: 3230
Good Answers: 444
#1

Re: Transformer differential relay operation

02/16/2014 5:26 PM

You're very lucky that "...it always holds after two or three attempt(s)...", at least that you proved(?) that the transformer is not(?) faulty! Your relay is not properly set, the wrong type, or the CT's were not properly chosen.

The magnetizing inrush is either saturating the CTs or the transformer, causing enough zero sequence current to fool the relay at its current setting. Get a professional out there to help correct the problem.

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Instruform
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Join Date: Feb 2009
Posts: 35
#2

Re: Transformer Differential Relay Operation

02/17/2014 7:01 PM

I also had this problem before in 1975 on 3x1Phase electromechanical transformer differential relays.

It was eventually found that the delta interconnecting bias magnetic circuit between the 3 single phase relays was not connected.
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