Influence of voltage harmonic phenomena on partial discharge behavior at HVDC

Abstract

Insulation is a critical component of any electrical power system, which, when subjected to excessive stress, may lead to premature ageing and eventual failure. Partial discharge (PD) measurement is a well-developed insulation diagnostic method, particularly under alternating voltage (AC), for quality assessment and condition monitoring of power apparatus. However, this technique is still immature when applied to DC operating equipment, especially high voltage direct current (HVDC) systems where rippled and distorted voltage waveforms appear at the output terminal of the converters. This paper presents the results of experimental PD measurements and analysis for commonly encountered PD sources: corona, surface and void discharging defects under the application of DC and DC superimposed with harmonics. The results show that PD activity under rippled voltage is different than that under pure DC. PD occurs with higher repetition rate, and is - in varying degrees - influenced by the relative magnitudes of the harmonics, depending on the PD source. Since it appears that PD is more severe under the influence of harmonic voltage ripple, the results should be of interest to network operators and will contribute to understanding of the phenomena in HVDC insulation diagnostics.