Evaluation of a PD measuring system for repetitive steep voltage waveforms

Measurements of partial discharges (PDs) at high frequency voltages is important but not a straightforward task. In this paper a PD measuring system developed for use at repetitive, steep voltage waveforms is presented, which is based on electrical detection using capacitive decoupling of the PD signals. The system utilizes only a low order filter and allows the presence of significant remnants of the applied voltage in the signal used for PD detection. Analytical calculations that estimate the reachable sensitivity of this method are presented, and for an example with a test object of 100 pF capacitance, a sensitivity in the range of 1 - 10 pC/kV at 1 μs rise time was obtained. Further, the transfer function of the measuring system has been measured and used for reconstruction of the voltage across the test object, the latter consisting of both the applied square-like voltage and voltage drops due to PDs. This is an attractive possibility since the applied high voltage signal at the test object can be recalculated from the same signal as is used for PD detection. In addition, the reconstruction of the PD voltage drop could provide information about the PD processes, provided that the sampling frequency is high enough.