Measuring Partial Discharges under Power Electronics Waveforms: from Slow to Ultra-fast Voltage Impulse Risetime

With increased voltage and faster switch rise time, the major issues faced while designing insulation systems for inverter-fed rotating machines is how to measure PD correctly and evaluate PDIV-RPDIV in type and qualification tests for Type I insulation. The current PD measurement techniques as per IEC 60034-27-5 involve the use of high pass filters to suppress the switching disturbance and retain the PD. This approach, however, may be not effective for fast risetime and high-amplitude voltages, where the disturbance spectrum spreads out in the higher frequency range and can overlap with the PD spectrum, rendering any frequency domain approach poorly effective. Therefore, new techniques for separation of PD from voltage switching disturbance must be investigated. This paper presents a time-domain approach for PD measurement under fast impulses and high voltage values. Results show that this approach has several advantages over the conventional one, and it can be used alone or in combination with filtering techniques.