The results of excitation-current tests 1

[Sbastionn]

Hi.

I was using M4100 to do a excitation-current tests to a double winding double winding transformer.
When I read the the results, there is few things that I want to figure it out.

The first one is about the result of "Measurement %PF" is way larger than the result that I was doing to insulation test.
The %PF of excitation-current tests is about 70%, and the insulation test one is about 0.2%.
So i was wondering what is the result of excitation-current tests which can be considered to "good results"?

Another question is also in the result of excitation-current tests, I found that column "Capacitance/Inductance" is a inductance value.
So is this result means if I get a larger value, it can considered to a better result?
Also I want to know how this result be calculated.
I know the insulation test one, the result is a capacitance value, we can calculate a similar value by "test voltage divided by specimen test current". (Assume there is no leakage resistance because of the good %PF). So I was wondering can we calculate a value that is similar to inductance value?

 

[thermionic1]

In this test, you are not looking at insulation quality, only the pattern of currents between phases. It's generally a pattern of two similar, but higher currents on the outer phases and a lower current on the center phase. The test set is reporting data for (% PF), but I don't recall an instance where this is used in evaluation of this test and because you are not shorting all the HV/LV windings, a much higher %PF would be normal. The (Cap/Ind) should indicate (Ind), if the test is performed correctly.

I don't have my Doble literature in front of me at the moment, but you should be able to access the manuals / help in the Doble M4100 software. There will be a discussion of the excitation current test, as well as how to connect the test set for Wye/Delta winding configurations. If I recall correctly, a shell form unit requires a more detailed analysis of results.

If this is a routine test, you can leave the NLTC in the as found position. If the transformer has an OLTC, it is recommended to test in the full raise, full lower, N and +/1 tap positions. If this is an acceptance test it is recommended to test in all OLTC positions and often all NLTC positions.

The test is sensitive to turn to turn shorts, as well as OLTC problems.

If you are leasing the M4100 or are a Doble client, you can certainly call them to discuss.