BCT polarity testing
BCT polarity testing
(OP)
A thread a while back strayed into the subject of testing BCT polarity while installed on a power transformer. I cannot find the thread anymore. Red flagged for some reason? Anyway, I mentioned performing such a test a few years back and claimed I didn't remember shorting the unused power transformer windings. I had occasion to do a similar test this past week, and the instructions were clear that the unused power transformer windings were to be shorted. The test set involved is a Multi-Amp ratio, excitation and polarity tester. I believe Multi-Amp is now Megger. The set applies a voltage to the CT secondary, and displays the primary voltage added to or subtracted from a fraction of the secondary voltage. When switched from add to subtract, reading will drop if polarity is correct and increase if reversed. We were able to quickly correct a REF protection scheme, and increase our confidence in a bus differential scheme.
Just wanted to clear up any misunderstanding I may have caused.
Just wanted to clear up any misunderstanding I may have caused.






RE: BCT polarity testing
It was my thread - I think it is still there somewhere. Thanks for the update: I've got a generator transformer with a probable reversed neutral CT to test when it comes down for outage in the summer, and this method sounds considerably easier than a primary injection test. It's good to get some feedback from a user of the Megger unit rather than hearing the sales pitch.
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RE: BCT polarity testing
http://www.geindustrial.com/products/manuals/GEH-230AF.pdf
for the polarity importance
RE: BCT polarity testing
Is this the instrument you've used?
http://www.advanced.co.th/products/spec/CTER91.pdf
Ralph
RE: BCT polarity testing
RE: BCT polarity testing
Yes.
j,
C57.13.1 describes some of the tests this instrument performs, but this particular polarity test is not described.
RE: BCT polarity testing
ANSI/IEEE Std C57.13-1978 An American National Standard IEEE Standard Requirements for Instrument Transformers,
Section 8.4 Polarity addresses three methods commonly used for determining CT polarity.
RE: BCT polarity testing