Comparison of Different Voltage Waveforms for Partial Discharge Measurement in Medium Voltage Cables and Accessories

Partial discharge (PD) measurement is commonly used to identify weak spots in medium voltage (MV) cables and accessories, as an acceptance and a maintenance test procedure. A PD event leads to the continued accelerated aging of a cable or an accessory and does not heal itself. In this background, PD testing can spot localized issues in the cable insulation such as voids, air gaps and electrical trees, and workmanship problems at the cable accessories (due to misalignment, improper cutbacks, etc.). PD is a frequency-dependent phenomenon and is influenced by the rate of rise of the test voltage, especially at the point of zero-crossing. It is therefore important to analyze if the nature of the voltage waveform used has a significant effect on the PD measurement test results. This paper aims to evaluate the performance of different voltage waveforms, such as the power frequency (sinusoidal AC – 60 Hz), damped alternating current (DAC), and sinusoidal very low frequency (VLF) (at 0.1 Hz) for PD measurement in MV cables and accessories. The paper will demonstrate the sensitivity of the aforementioned offline PD measurement technologies in identifying defects in MV cable samples through a laboratory investigation when various voltage waveforms are applied. The PD measurement sensitivity in terms of the background noise level, localization capability as well as the identification of the partial discharge inception voltage (PDIV) and partial discharge extinction voltage (PDEV) values will also be highlighted.