Influence of high voltage harmonics on partial discharge patterns modulation

Typically, in laboratory and diagnostics tests focused on measuring partial discharges, a pure sinusoidal voltage waveform is assumed. However, in practice the spectral content of the applied voltage is rarely so ideal and additional spectral components have a significant impact on the discharge behavior in electrical insulation systems. In this paper the influence of voltage harmonics on partial discharge behavior and pattern evolution is analyzed. The presented experiments were conducted on specimens representing various defects in high voltage insulation system, in the form of protrusion, inclusion, delamination. The experimental results showed that various harmonic compositions superimposed on the fundamental sinusoidal waveform have a significant impact on PD intensity and maximal charge. In consequence, PD pattern phase and amplitude distributions are distorted and calculated statistical parameters are changed. The rough parameters reflecting the waveform spectral quality, such as THD, are rather superficial and do not provide a unique and reliable signature of the applied voltage in terms of phase angle variations. In certain environments, neglecting harmonic content in the voltage may lead to a misleading interpretation and assessment of partial discharge severity. A complete knowledge of harmonic content is essential and critical in conducting a proper assessment of the impact of PD, including acceptability criteria and compatibility with the standards.