Transformer Tripping When it Rains

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TSIKA Participant Join Date: Mar 2012 Posts: 3	Transformer Tripping When it Rains 10/27/2014 10:53 AM
	We are having 40MVA 88/22kV transformer and the substation is built inside chrome mine, apperantly when it rains or cloudy weather with lightnings the TRfr trips with Diff and MV REF. Investigation were done and it was found that NEC oil was full of carbon & the was some arcing on Red phase of the NEC, NEC was replaced then the trfr was energised it tripped again on diff. We did diff stability on a trfr and all routine tests on the trfr. It was found to be okay. What are the possible failures that can cause this trfr to trip on diff more especially when it rains? if the problem is with transformer what are the possible tests i can perform. Kind regards Tsika Protection Technician
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PeterT Guru Join Date: May 2010 Location: Liverpool, NY Posts: 961 Good Answers: 131	#1 Re: Transformer Tripping When it Rains 10/27/2014 3:58 PM
	Some possible causes: - Diff relay and REF relay CT circuits are wired wrong. - Diff relay and REF relay settings are wrong. - Contamination from mine dust and moisture is causing tracking on cable jackets, and relays trip to protect the cables. - Contamination from mine dust & moisture is causing tracking on transformer bushings, and the relays trip to protect the transformer. - Shields of high-voltage cable are grounded incorrectly, so Diff or REF is sensed when it shouldn't. You need to do some investigation - Best to hire someone competent to do this rather than blunder around in the dark (literally!). I don't know what an NEC is, but it may or may not be related. However, if it was full of carbon and had arcing problems, you need to determine what caused that and correct it, or it will happen again! __________________ To get the right answers, first you need to ask the right questions.
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IQ Guru Join Date: Feb 2013 Posts: 2004 Good Answers: 31	#2 In reply to #1 Re: Transformer Tripping When it Rains 10/28/2014 4:53 AM
	NEC used to mean Neutral Earthing Compensator. Nowadays it could mean anything but this.
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welderman Guru Join Date: Sep 2007 Posts: 1601 Good Answers: 58	#3 Re: Transformer Tripping When it Rains 10/28/2014 9:41 AM
	You might try replacing or cleaning the contaminated oil, and dehumidify the substation. I also suggest you try placing an electrostatic particle precipitation device in the substation. HV bushings can be coated with teflon or equivalent to prevent wetting of the terminals.
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IQ Guru Join Date: Feb 2013 Posts: 2004 Good Answers: 31	#4 In reply to #3 Re: Transformer Tripping When it Rains 10/28/2014 9:59 AM
	On the last trip this should all have been done, (in an ideal world). Dielectric test on oil. Moisture content, CFC content, acetlyene content and signs of polltion in the oil, (copper carbonising and iron). Clean the bushing, check for cracks by 'ringing them' and check all connections. That is the first step in ensuring the fault does not lay with the Tfx.
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