Simultaneous partial discharge and current measurements in a needle-plane configuration at different pressures

Phase-resolved partial discharge (PRPD) measurement has been used for decades as a method of monitoring defects in electrically insulating materials. More recently, it has seen a renewed interest in the context of flash sintering, a novel ceramic densification process where the sample to be densified is subjected to an electric field in addition to the usual application of heat. In the context of flash sintering, the monitoring of partial discharge (PD) activity has shown that this activity increases when approaching the onset of the thermal runaway phenomenon leading to the quick densification of the material, and is influenced by environmental factors such as relative humidity or pressure. A new microcontroller-based PRPD measurement system architecture has recently been proposed as a means to explore this PD activity in further details. While PDRD measurement is traditionally carried out by comparing the measured partial discharge pattern to the waveform of the voltage applied to the device under test (DUT), we show in this work that expanding this bespoke measurement system to be able to simultaneously monitor the waveform of the current going through the DUT allows for the collection of data related to the electrical power transferred to the DUT during the process that displays peculiar features. In the present work, the DUT consists of a classical needle-plane setup. As pressure decreases down from atmospheric levels, the threshold voltage leading up to the apparition of discharges decreases following a trend similar to the classical Paschen curve. Additionally, the nature of the discharge activity transitions from low-amplitude, rapid-firing tightly packed trains of pulses to high-amplitude, longer-lasting and more spread out pulses. Simultaneous measurement of the discharges, applied voltage and current going through the DUT shows that this second type of discharge activity can be synchronous with an asymmetric, distorted current waveform having the same period as the applied voltage, corresponding to a transfer of active electrical power into the DUT. Furthermore, the width of these current waveforms expands as the applied voltage is increased progressively starting from the threshold voltage for the activation of discharge activity, indicating that the rate of total power transferred in the DUT may be tuned using the amplitude of the applied voltage. External confirmation of a significant power transfer taking place in these conditions is obtained through the observation of damage inflicted on the DUT after a period of sustained discharge activity at low pressure.