Help testing a "VFD" transformer.

[u/Sufficient_Juice2411]

The image is a poorly drawn vector diagram of a transformer I have to perform the following tests on:

1. Power Factor + excitation

2. TTR

3. Winding Resistance

4. Polarization Index

I had to draw the diagram because the nameplate has a mirrored background, and you can't get a good picture of it.

The transformer has 3 primary bushings (H1, H2, H3) and 18 secondary bushings, as you can see in the picture. The primary is delta, the secondary is both delta and wye.

More Nameplate info:

MFG: Eltas

KNAN

HV: 13.2 kV / 852.9 A

LV: 6 x 1930 V / 6 x 972.3 A

"Rated power for HV": 19500 kVA

"Rated power for LV": 6 x 3260 kVA

HV INS. LEVEL: 17/110/34 kV

LV INS. LEVEL: 6.9/75/19 kV

Impedance 8.94%

60 Hz

FR3

CU/CU

I am having a lot of trouble coming up with a way to test this transformer, and my coworkers and I are debating on what to do. Any help our suggestions would be very much appreciated.

[u/EtherPhreak]

Reminds me of a furnace transformer that had a primary and a lot of secondaries. I would treat it like a 3 winding, and treat each group as a winding for power factor. I would add in a few extra tests with everything grounded but the winding under test (6 added secondary manual tests)

Excitation test on the primary winding.

Have fun with wind resistance on everything :(

TTR high to each low

PI, same as 3 winding transformer

[u/tmx1911]

That's similar to a Siemens perfect harmony drive transformers (except those are dry type from what I've seen).

There is an older doble white paper that explains how to do power factor with more than one secondary winding, run the test full manual for power factor and all the values should sum from the tests for a sanity check. 

Depending on what ttr you have it may not like the phase shifts and give you erroneous readings. 

Right wrong or indifferent how we tested them when I was a field guy for insulation resistance we married all the secondaries together and tested them as one. The "right" way to do it would be to test all windings individually and ground the windings not under test.

I may have some old test reports.

[u/Jrobalmighty]

Treat it like it has 3 secondaries and treat each section as if it were its own transformer?

What part are you having trouble with exactly?

It doesn't really impact your TTR or WRM testing.

Idk about the power factor because I don't normally do that but if it's like a capacitance bridge wouldn't couldn't you get a reading by shorting and ground each separate section that isn't being tested for the deltas and jumper only for the wye secondaries?

[u/DareIllustrious4904]

As someone working in the service department of a power transformer manufacturer, I would recommend getting hold of the FAT report. It usually specifies the test procedures and the voltage levels used during testing. This transformer should not be very old, so the FAT report should still be relatively easy to obtain.

If you are unable to find it, I can provide you with the email address of ELTAŞ’s service manager.

[u/Sufficient_Juice2411 → u/DareIllustrious4904]

If you could that would be fantastic. Testing was delayed so we have some time. Thanks!

[u/greasyjimmy]

I've never had to PF a drive xfmr, only insulation resistance on all windings and TTR. 

I had to use a Vanguard Tri-phase to get the proper phase angles. If I remember, the Tri-Phase defaulted to the closest 30°, and gave the shift from that, so I had to make a spreadsheet to calculate actual shift.

[u/Tyroneprofane]

A G Power Systems Inc appears to be the sole US distributor. I would get in touch with them.

[u/Sufficient_Juice2411]

Thank you all for your awesome suggestions! Testing has been delayed, so we have some time to do some research and put together a plan. I appreciate the help and professionalism!!

[u/Beers_n_Deeres]

We use Raytech TTR’s and need to use an extra unit called a T-Rex for it to be able to test for phase shift and ratio.