Appendix C: Fault Calculations

In this appendix, asymmetrical fault calculations for a transformer are given. A single-line-to-ground fault on the LV side is considered. The neutral terminals of the LV and HV windings are solidly grounded. Two distinct cases are considered: with and without fault in-feed from the secondary (LV) side. For each of these two cases, two conditions are considered: with and without stabilizing tertiary winding (TV). The effects of omitting the tertiary winding are illustrated with these cases.

Transformer Data

Rating (S) = 25 MVA, Core construction: three-phase three-limb

Voltage ratio: HV/LV/TV, 132/11/11 KV, star/star/delta

Leakage sequence impedances (based on 25 MVA base):

HV/LV : Z1 = Z2 = 12%, Z0 = 10.2%

HV/TV ...

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