Design of a Test Method for Investigating the Influence of Zero Crossings on the Breakdown Voltage for Medium-Frequency Voltage Stresses

The increasing usage of power electronic components in the energy supply system creates new requirements for the insulation materials used. The insulation inside power electronic transformers (PETs) for example, is mainly stressed with square-wave voltages of higher frequencies in the range of several kilohertz. In cascaded topologies, an additional dc offset can occur. One key parameter of the insulating materials is the short-time breakdown voltage, which exhibits a significant frequency dependence. However, the causes for the decreasing breakdown voltage with increasing frequency and the influence of individual parameters of the voltage shape, such as the influence of zero crossings, are insufficiently investigated in detail. There exists no standardized procedure for the investigation of such influences. This paper therefore presents a test method and a test voltage waveform which takes into account the special requirements of testing with dc offset and, in particular, allows for the investigation of the influence of zero crossings.