Measuring Transformer Ratio Using Doble Ratio Test

[unclebob]

Hi all!

This one is for people who use the Doble Test Set (M4000):

A customer just bought a new dry-type transformer 2 MVA, 25000 / 600Y347 V. Nothing special...

A service group (not us) go there and does the commissioning. They used the Doble Test Set to measure the ratios of the five taps of the transformer. With that test set you can put up to 10 kV to do the measuring. My customer is worried because the results show a problem.

But when doing the same test with the ''regular'' TTR, the expected ratios are obtained.

I wasn't there so I can't say if the test set up was OK.
I personnaly never did a ratio test using the Doble M4K.

Any comments?

 

[electricpete]

The M4000 series can make TTR measurements if you have the Doble capacitor that goes with it.

If Doble TTR shows a problem and low voltage TTR doesn't, then (assuming tests were done right), it might be something like a turn fault that doesn't begin to break down until a certain voltage is reached.

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