How to Test an Isolation Transformer

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Nishant Commentator Join Date: Aug 2007 Location: INDIA Posts: 58	How to Test an Isolation Transformer 02/19/2009 6:44 AM
	Dear All, We have 3 phase Isolation Transformer but we have no idea, how to check isolation transformer so plz guide me. Its details as below. thanks in advance. ( Input 415 volt ac - Output 400 volt ac /frequency 50 Hz/ 15 kva / connection pri. delta & sec. Star) We are going to check transformer for its working or not working so we check voltages as below Out Put Voltages are- Phase 1 ( R ) & Neutral - 226 VAC Phase 2 ( Y ) & Neutral - 226 VAC Phase 3 ( B ) & Neutral - 228 VAC Phase 1 ( R ) & Phase 2 ( Y ) - 395 VAC Phase 1 ( R ) & Phase 3 ( B ) - 395 VAC Phase 2 ( Y )& Phase 3 ( B ) - 393 VAC Neutral & Earth - 127 VAC Phase 1 ( R ) & Earth - 330 VAC Phase 2 ( Y ) & Earth - 272 VAC Phase 3 ( B ) & Earth - 122 VAC __________________ TARGET - Where many stop thinking, some start from there. Tenacity to get target helps to WIN.
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CJMcGill Guru Join Date: Jul 2008 Location: SoCal USA Posts: 556 Good Answers: 23	#1 Re: How to Test an Isolation Transformer 02/19/2009 5:11 PM
	Dear Nishant, It would appear that you have a resistive load to earth rather than neutral on phase 3 (B). If it were a direct short, phase 3 (B) & earth = 0v, and would require a floating neutral situation or a resistor-earthed neutral. You did not indicate whether you have a solidly earthed neutral, or if your neutral is earthed through a resistor, or if the secondary neutral is earthed at all. Also if this transformer has no connected loads, and neutral has not been earthed, it indicates a problem with the phase 3 (B) leaking through a resistance to the transformer case. Either situation would require more detail about the earthing of the neutral on the Wye side. CJM __________________ I do not 'know it all', but i will admit that I would like to. CJM
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Nishant Commentator Join Date: Aug 2007 Location: INDIA Posts: 58	#2 In reply to #1 Re: How to Test an Isolation Transformer 02/19/2009 11:09 PM
	Dear CJMcGill, Thank You for perfect guidance. after your reply we check connection in that we found neutral point not connected to earth & we have no more idea about that so ignore that, but after your reply we connect output neutral point to earth & than check voltages its now ok. Thank You Sir. __________________ TARGET - Where many stop thinking, some start from there. Tenacity to get target helps to WIN.
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CJMcGill Guru Join Date: Jul 2008 Location: SoCal USA Posts: 556 Good Answers: 23	#3 In reply to #2 Re: How to Test an Isolation Transformer 02/20/2009 1:00 PM
	Dear Nishant, Thank you for sharing the outcome with us. Sadly we don't always have responses that let us know how things turn out I'm certainly happy that what we have learned, and now share can have some value for others via this forum. I accept your gratitude collectively for this fine group, many of whom could have been of the same help. It's nice to have you as a member, and I sense that you will be the one supplying a fine helpful answer to others soon. Regards, CJM P.S. you may want to check all the neutral and earth points on phase 3 (B) loads to ensure no loops have been created, since it did stand out as the earthed phase. __________________ I do not 'know it all', but i will admit that I would like to. CJM
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