Transformer Positive Seq Calculations

[so0774]

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

 

[mpparent]

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