J & P Transformer Book, 13th Edition

Appendix 6: A symmetrical component study of earth faults in transformers in parallel

The behaviour of transformers in parallel under earth fault conditions is governed largely by the neutral point earthing of the circuit in which the fault occurs. The current and voltage distributions may be determined in a direct and simple manner by the application of symmetrical components, and the present study demonstrates the procedure and shows the influence of the neutral point earth circuits.

For example, a typical three-phase, 50 Hz, duplicate transformer grid substation of the smaller type is chosen; from the secondary busbars of this are fed two duplicate step-down transformers supplying a factory load, as shown in Fig. A6.1. The specifications ...