This work presents a measuring system for PDs at repetitive voltages with short rise times, based on a coupling device adapted for this kind of voltages and a method for removing contributions from the applied voltage. The potential of the system has been demonstrated through measurements of PDs around a needle in air at voltages of 5.5 kV -9.5 kV with rise times down to 10 μs. The observations obtained with this PD source prove that the measuring technique described enables detailed studies of PD properties under repetitive rapidly changing voltage waveforms in the investigated range of voltages and rise times.
The traditional method to detect partial discharges relies heavily on the use of highpass filters. Whereas this is a very effective approach for normal power voltage shapes, severe problems arise when partial discharges are to be detected under waveforms generated by modern power electronics. Therefore, a technique that utilizes the random occurrence of partial discharges for detection has been developed and used for semi-square voltages. This technique has evolved since the first publications and new applications have been found. The present paper introduces the technique and discusses the necessary analysis elements, requirements imposed as well as some examples intended to show possible application areas.
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