Impact of charge accumulation on insulation films subjected to unipolar and bipolar square waves

The paper presents the results of surface charge measurements on insulation film samples with different surface resistivities. Polytetrafluoroethylene (PTFE) and Nylon 6 (PA6) as well as mica paper subjected to unipolar and bipolar square waves at different switching frequencies. The experimental data are presented to explain the differences observed in the times-to-failure of turn insulation when aged using unipolar and bipolar square waves. Time-to-failure experiments and COMSOL
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simulations are used to estimate the accumulated charge on the surface of insulation films with different surface resistivities.