Help Identify Transformer Vector Group

[trips123]

Good PM,

We are Planning to replace the old electro mechanical differential relay with numerical one. Problem is we cant identify the tranformer vector group because its name plate data was already lost.

Oher information taken from the previous test result is shown below:

1.5Mva
Delta-Wye
34.5/.480KV
50/5 -CT(HV)
2000/5 - CT(LV)
help or any TIP to identify the said vector group.........Tnx

 

[dpc]

If this is a normal transformer was made in the US in the past 80 years, you can assume, with 95% certainty that the low side will lag the high side by 30 degrees. (If it is connected per the nameplate that you don't have. H1 - A, H2 - B, H3- C with positive phase sequence). This rule applies regardless of delta-wye or wye-delta configuration.

This has been the ANSI standard since the earth was still cooling. There can be exceptions, but they are rare.

We hayseeds here in the US don't know nuthin' 'bout no vector groups.

 

[ScottyUK]

Energise the HV side with a three phase LV supply. You should be able to verify the phase relationship using a 'scope and isolation amplifier.


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Sometimes I wake up Grumpy.
Other times I just let her sleep!

 

[isquaredr]

Disconnect the y neutralfrpm earth and connect A-a together, then energise A, B & C with a three phase lv supply, measure volts as follows :-
A-b, A-c, B-a, B-b, B-c, C-a, C-b, C-c

Draw the D & y on top of each other both in the 11 & 1 o'clock positions (assuming its Dy11 or Dy1) not forgetting to tie A & a together and see which measured voltages fits the diagrams.
Its a while since ive carried out this procedure but it is standard vector varifacation.

 

[jghrist]

If your existing CTs and differential relay work correctly and are connected like this,

then your transformer is standard US Dyn1 with the low voltage lagging the high voltage by 30 deg.

 

[PUNGLU]

With a three phase low voltage source and your multimeter you should be able to verify the vector group.Assume the 11 o'clock or 1 o'clock configuration when drawing your vector diagrams.Apply the test three phase voltage on the phases A B C (With A-a or B-b or C-c tied together and the earthing on the Y neutral delinked). Comparing the vectors A-b, A-c, B-a, B-b, B-c, C-a, C-b should be able to give you acceptable results.