Surge transfer through 3-phase transformers

ALTHOUGH a low-voltage circuit, connected to the system by a transformer, has no direct exposure to lightning, lightning surge voltages can be produced in this circuit as a result of surge voltage impact on the high-voltage side of the transformer. Even though a lightning arrester is connected on the high-voltage side of the transformer, surge voltages transferred to the low-voltage side can be dangerous especially to lower BIL equipments such as rotating machines and dry-type transformers.