Breakdown of polymer dielectrics at high direct and alternating voltages superimposed by high frequency high voltages

This paper deals with the measuring of the breakdown voltage of polymeric insulation materials stressed by high direct voltages and power-frequency high-voltages superimposed by high-frequency voltages. High-frequency highvoltage stress results in an intense heating caused by higher dielectric losses commensurate to the frequency, the permittivity and the dielectric loss factor of the materials. The raised thermal stress leads to an influence on the breakdown voltage. The aim of the paper is to make a statement regarding to the influence of superimposed high frequency voltages on dielectrics in steady state operation. The test voltages up to several 10 kV are realized by a test system consisting of an innovative high-frequency high-voltage generator combined with conventional AC- and DC-test equipment. A constant sinusoidal high-frequency voltage up to 50 kV in a frequency range from 1 kHz to 50 kHz is superimposed on a high 50 Hz alternating voltage or a high direct voltage in different ratios. The analysis of the measured breakdown voltage leads to a mathematical approach to calculate the breakdown voltages of different superimposed voltage forms.