Effect of Thickness and Frequency on Square Wave Breakdown of Epoxy Insulation for Solid-State Transformers

The dielectric breakdown of insulating materials by high-frequency non-sinusoidal waveform voltage stress with high dV/dt is a new problem in the design and application of high-power electronic equipment. Here we discuss the frequency dependence of breakdown strength experiments. We constructed an insulation breakdown test platform at high frequency non-sinusoidal voltage, including high frequency and high voltage power supply, breakdown signal detection and boost unit. Measure measurement of specimens of different thicknesses (30 μm-100 μm) at different frequencies (50Hz-20 kHz). The results show that under the bipolar square wave, the dielectric breakdown strength ($E_b$) of epoxy resin film decreases with the increase of frequency, and the rate of breakdown field strength decreases with the increase of frequency; the breakdown field strength ($E_b$) decreases with the increase of thickness, showing a trend similar to the exponential rule. At the low frequency, with the increase of sample thickness, the breakdown field strength decreases and then increases. In addition to the internal local discharge and high dielectric heating, the spatial charge, trapping and polarization at the interface also play an important role under high-frequency stress. Further studies should focus on the interfacial effects behind the disruption mechanism.