If the transformer has OLTC in HV side is advisable to perform the Excitation Current test in all taps.
If in MV also has NLTC, for having a benchmarking test the contact resistance of all taps (usually 5 taps)
IEEE-STD 62-1995 (I think so) is a good reference.
Insulation power factor including capacitance test is advisable also.
This tests will be important as zero test (benchmarking) for future diagnostics.
okay. We have a 5MVA, 88/33kV transformer that we want to put in service. It was bought around 1985 (Iam told)but was neverput in commission.Over time the nameplate was removed and no one seems to have the details except that it was to be used to step down from 88/33kV at one of our stations. The transformer was stored undressed and blanked nicely. Initial tests indicated that the winding insulation is okay. Now we want to establish its vector group. How can this be done on site? And assuming we did not know the rated voltage ratios, how this be determined? (just to be sure). I would appreciate some guidelines or literature on this.
Vidima, have you considered energizing the primary with low voltage {380Y/220?}; then making ratio and vector-group checks with a voltmeter and phase-angle meter? It may then be possible to energize the transformer at 33kV or some intermediate voltage for an idling period before placing into full service.
Vector group and voltage ratios are easily determined with a Turns Ratio Tester, such as those manufactured by Biddle. The voltage used by the TTR is only about 10 volts. You should be able to determine who built the transformer by checking bushing nameplates, transformer prints, purchase orders, by comparing with other transformers, and possibly by examination of auxiliary equipment on the transfomer. Transformer manufacturers normally maintain records of their products and you should be able to get a replacement nameplate, test data, copies of the original drawings, etc.
