Measurement and evaluation of partial discharges at higher-frequency sinusoidal and impulse test voltages

In this work, four instruments are investigated and compared concerning the measurement of partial discharges under highfrequency sinusoidal and impulse test voltages in a laboratory environment.The chosen instruments, typically employed for detecting partial discharges under voltages with high dV/dt-ratios, are a high-frequency current transformer, a D-dot probe, a detection capacitor connected in series to the test object, and a photomultiplier.Initially, the sensitivity of the instruments is assessed for discharges taking place over a single period of a sinusoidal test voltage (1 kHz) and during a positive, unipolar, slow-rise impulse.Next, individual instrument signals in response to either a single weak (units of pC) or a moderate (hundreds of pC) partial discharge are analysed in detail, and the suitability of the instruments for the construction of a phase-resolved partial discharge pattern is evaluated (sine, 10 kHz).Ultimately, the performance of the instruments for steep-flank (~375 kV/μs) impulse test voltages is studied.Analog filters are employed to improve the instruments' detection capabilities, and an overview of the instruments' strengths and weaknesses is presented.The detection series capacitor instrument is shown to have the best overall performance for the studied aspects of partial discharge measurement.