|This paper presents two methods for determining the dielectric stresses occurring in the tap winding of a lightning pulse autotransformer. The first method is to im-plement the equivalent circuit using the ATP / EMTP pro-gram, and the second method consists in testing the auto-transformer at a low voltage impulse before being put into the tank. The design of the autotransformer was done tak-ing 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 over-voltages along the axial and radial direction of the coil as-sembly. The results of the laboratory tests performed on the autotransformer, validated the results obtained with ATP / EMTP.