Development of a Pulsed High Frequency Source for Testing Cellulosic Insulation Material for High Voltage Solid State Transformer Applications

Solid state transformers (SSTs) are believed to play a major role in the near future due to their additional features compared to conventional transformers. SSTs are a combination of power electronics and a conventional transformer. The function of this device is to commute the signal into the kHz range before it is transformed to another voltage with the conventional transformer within the SST. Many different topologies for the power electronic part in SST applications have been implemented and presented in literature. Many newer publications use SiC MOSFETs due to their high achievable blocking voltage and fast switching speed. The transforming element in SST applications, where a higher amount of power is needed, will still be a conventional transformer with conventional insulation. Thus the oil paper insulation system has to be investigated experimentally in respect of the higher frequency stress. For these investigations a source is needed that can deliver voltage stress which is present in SST applications. Thus a pulsed high frequency (HF) source had to be developed to be able to test and study the insulation in detail. In this publication we show the development and function of such a pulsed HF source for voltages up to 5 kV. Also first measurement results of tests at 20 kHz and 40 kHz are presented and compared with 50 Hz measurements.