Surge transference through transformers

The article demonstrates the need for secondary surge protection on main utility tie transformers and low-voltage substation transformers. Investments in these surge protection devices are minimal and an insurance against insulation failures. A more elaborate transformer model could be used in EMTP simulations, however, the results based on the simplified transformer inductive/capacitance model are valid for practical purposes. The modeling of surge phenomena on EMTP is complex, and a modeling of all the possible surges of atmospheric origin or generated within a distribution system will be time consuming. The cost of providing secondary surge protection on unit transformers is rather small, though a coordination of the surge arrester characteristics is required. Considerations should be applied to the overvoltage withstand capability of solid-state protective devices, ASDs, and monitoring and control equipment, which is much lower than the insulation levels associated with the power equipment.