Analysis of an anisotropic nonlinear electric field with a discussion of dielectric tests for converter transformers and smoothing reactors

Oil-immersed insulating materials have anisotropic and nonlinear conductivity. A new calculating method for the electric field in such materials is developed for the insulation design of power converter transformers and smoothing reactors. Flashover voltages estimated from the results very closely approximate measured values. Dielectric test methods are discussed based on calculated electrical stress in each part of the power converter transformers for various applied voltages. Alternative tests are proposed instead of the combined AC-DC voltage and polarity reversal tests.>