Interpreting transformer phase shift in SKM PTW software 1

[rex2704]

I am a little confused with how to interpret the transformer phase shift angle value in SKM PTW software.

I want to represent a two winding, 3-phase wye-delta transformer in PTW. The details are as follows:

Primary: HV, Wye connected
Secondary: LV, Delta connected
Vector Group: Yd1 (HV voltage leads LV by 30 degrees)

For this type of connection what should the "Phase Shift Angle" be in PTW? Should it be -30 degrees or +30 degrees?

When I put a check mark in the "Link" box in the component editor of PTW, it specifies -30 degree phase shift. Is this correct for my configuration?

Thank you all in advance.

 

[davidbeach]

Put it in as 30 degrees, run a fault study. Then change it to -30 degrees and run another fault study. Compare the results. Which one gives the expected result and which one is 60 degrees wrong?

 

[rex2704]

Thanks davidbeach for your response. I will elaborate more on my problem.

I am trying to analyze a fault record available from an overcurrent relay connected to the primary side of this transformer. The fault currents on the primary side are as follows:

Magnitudes: Ia=Ic and Ib=Ia+Ic
Phase angles: Ia and Ic are in phase and Ib is 180 degrees away from them.
Our phase sequence is ABC.

I have already confirmed that this record indicates a phase-phase fault on the secondary (LV) side (it could also be a phase-phase-ground fault but we do not have voltage information to distinguish between the two).

I am finding it difficult to calculate the primary currents manually for a phase-phase fault on the secondary. So, I decided to use PTW. Now, I have run into this problem...

I get this waveform pattern for A-B phase fault when I use -30 degrees shift in PTW and I also get this pattern for B-C phase fault when I use +30 degrees shift.

It is very critical for us to determine whether it was A-B phase fault or B-C phase fault. Hence, I decided to get some expert advise.

Can you, or anyone else, help me confirm this?

Ideally, I would like to know how to calculate these primary side currents manually for such faults.

Thank you once again.

 

[davidbeach]

Actually, you don't even need a fault, a power flow case might be better. For that transformer you expect the low side to lag the high side. Which angle produces that result? I knew the answer once, but its been 6 years since I last regularly used PTW (2 jobs ago) and I just don't remember; the above is how I would figure it out again.

 

[rex2704]

Thank you once again davidbeach.

I had tried that earlier - running load flow studies. But the LF report only gave me current magnitudes and not the angles. I may have missed something.

Anyway, I called SKM and they said I should use +30 degrees for Yd1 vector group connection.

 

[EddyWirbelstrom]

For a Dy transformer, PTW defaults to Dy1.
ie. Primary ( D ) leads secondary ( y ) by 30 deg.
See +30 deg phase shift in PTW transformer dialog box.
For a Yd transformer, PTW defaults to Yd11
ie.Primary ( Y ) lags secondary ( d ) by 30 deg.
See -30 deg phase shift in PTW transformer diaglog box.
This is the default in ANSI land.
In IEC land, the default is Dy11, primary lags secondary by 30 deg.
This can be confirmed if you run a PTW Comprehensive short-circuit study and check the bus voltage angles in the automatically generated short-circuit study report.
If you apply a P-P fault on a bus on the secondary side, the Comprehensive Study report will include bus voltage and angles, and branch current and angles at buses and branches on the primary and secondary sides for phases A, B, and C.
Eg. I applied an a-b short-circuit of a 2.5 MVA, 22 / 0.415kV, 6.5% Yd1 trnasformer and got :
HV branch currents A, B, C 522.8 A, angle -21 1045.5 A, angle 159 522.8 A, angle -21
LV branch currents A, B, C 0 A, angle -0 48000 A, angle 159 48000 A, angle -21
I will confirm with manual calc later.