Multilevel frequency converters and noise reduction for pratial discharge tests

This paper presents the usage of multilevel frequency converters for partial discharge tests and an approach for noise reduction. The comparison of the background noise generated by square wave (2-level) and 5-level frequency converters with the frequency of 200 Hz is presented. The testing frequency of 200 Hz is necessary for partial discharge test of transformers because of avoiding saturation effect of the iron core. Therefore, the frequency converter must be generated the voltage with the frequency of more than two time of the power frequency. The comparison of background noise and output voltage waveform generated by the developed converters is presented. Both frequency converters with the noise reduction technique (applied a low pass filter) have very low background noise, and the generated voltages are closed to pure sinusoidal waveform when the frequency converters supply to PD test circuit.