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Transformer Positive Seq Calculations

Transformer Positive Seq Calculations

Transformer Positive Seq Calculations

(OP)
I am an electrical engineer in training working in the area of power system.
I have been given a transformer test report from a manufacturer.
The transformer has the following information:
Rating: 24/32/40 MVA.

Voltage: 138 KV HV (wye) – 34.5 KV LV (wye) – 7.2 KV Tertiary (Delta)

Impedance at 24 MVA (I believe that would be the positive impedance):
HV – LV: 10.01% at HV Tap position 1
HV – LV: 9.60% at HV Tap position 9
HV – LV: 9.56% at HV Tap position 17

Transformer Test report includes the following information for Zero Sequence Impedance:

1st Term -       2nd Term -    Taps-    Base(MVA) - Meas Vol(KV)  Meas Curr(A)    Z0 (Ohm/ph)    Z0 (%)
H1-H2-H3-H0 , X1-X2-X3-X0   1/-         24                1.833          143.88               38.22            3.98
H1-H2-H3-H0    N/A                 9         24                 4.62             143.88             96.33             12.14
H1-H2-H3-H0    N/A               17          24                4.596           142.08              97.04             15.1

Do you know how above impedance values got calculated?

I have been asked to determine:
1. above impedance values based on 100 MVA power base.
2. Positive Sequence impedance values based on 100 MVA power base.

I would appreciate it if you could pick one of above values as an exmaple.
Thanks

so0774

RE: Transformer Positive Seq Calculations

If you are a new graduate, then I would assume you have a power systems textbook.  Please take a look at the per unit chapter.  If not, Google it.


Mike

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