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Anonymous Poster

Winding Resistance and Tap Condition Measurement

01/30/2011 1:29 PM

I need to confirm winding resistance and the LTC "make before break" of 138kv/13.8, 18mva transformer. I am using megger MTO210 or AVTM-830280.

- while I am changing the tap, is the instrument detects if the switch breaks before make, how fast it detects and indicates.

- for winding resistance test, how do we determine the max. test current? the option on the instrument (10mA, 100mA, 1A, and 10A)

- During the Y neutral gnd. test do we have to remove the gnd connection on the X0 bushing, while performing this test?

- Is there any other concerns, I should be careful of

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Look to see if you tap changer is making its new tap position before breaking the old tap position. Let us know what you find.

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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1604 Good Answers: 63	#1 Re: Winding Resistance and Tap Condition Measurement 01/30/2011 1:36 PM
	http://cr4.globalspec.com/thread/65319/Transformer-Voltage-Sag Is this your post?
	Reply

Anonymous Poster	#2 In reply to #1 Re: Winding Resistance and Tap Condition Measurement 01/31/2011 9:35 AM
	yes, do you have any comment. thanks
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wareagle Guru Join Date: Jun 2008 Location: Alabama Posts: 1604 Good Answers: 63	#3 Re: Winding Resistance and Tap Condition Measurement 01/31/2011 2:23 PM
	My comments were in the other post.
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PeterT Guru Join Date: May 2010 Location: Liverpool, NY Posts: 961 Good Answers: 131	#4 Re: Winding Resistance and Tap Condition Measurement 02/01/2011 3:42 PM
	Winding resistance should be measured at the highest possible current your test set can provide, within constraints of the circuit. For DC winding resistance of transformers, my firm typically uses a 3A DC power supply and measures the voltage across the winding with a calibrated digital multimeter, then use Ohm's Law to calculate resistance. Works well. As for the "make before break" timing, if there is any problem, you really need to do an internal inspection (drain the oil, open the LTC tank, and inspect/operate it manually). You will probably find some problem with contacts that have burned/eroded away to the point that they don't make proper contact at the leading edge of their travel, and need to be replaced anyway. If you are having a problem with tap changes, that is likely. If that's the problem, there is no way around replacing them. __________________ To get the right answers, first you need to ask the right questions.
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Anonymous Poster (1); PeterT (1); wareagle (2)

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