Surges transferred through transformers

The lightning and switching surges can be transferred from one voltage level to another through transformer couplings. A distribution system, which may not be directly exposed to the overvoltages of atmospheric origin, but is connected to a utility system through a transformer of high turns ratio will be exposed to overvoltages on the secondary side due to overvoltages on the primary windings. The resulting stresses on the distribution system may exceed the BIL levels. The paper provides simplified expressions for the surge transfer voltages through the transformers and the results of EMTP simulations for lightning and switching surges in a typical distribution. Primary and secondary surge arresters and surge capacitors are shown to limit these overvoltages to safe levels.