Methods for Determining Dielectric Stresses in the Windings of a Transformer Subjected to Lightning Impulse

In this paper there are presented two methods for determining the dielectric stresses occurring in the tap winding of a lightning pulse transformer. The first method is to implement the equivalent circuit using the ATP / EMTP program, and the second method consists in testing the transformer at a low voltage impulse before being put into the tank. The design of the transformer was done taking into account the results obtained with ATP / EMTP. This fact allowed the design of the winding structure as well as their location in space to obtain uniformly distributed overvoltages along the axial and radial direction of the coil assembly. The results of the laboratory tests performed on the transformer, validated the results obtained with ATP / EMTP.