Voltage Equivalence of Partial Discharge Tests for XLPE Insulation Defects

Abstract

Partial discharge (PD) is an important factor leading to insulation deterioration and fault of power cables. Due to large cable capacitances, power supplies should provide high reactive charging currents during field tests; common PD test methods of power frequency (PF) voltage or alternating current resonance (ACR) voltage cannot meet the field test requirements with the increase of cable voltage levels and line lengths. At present, the equivalence between PF-like (PFL) voltages, such as damped alternating current (DAC) voltage, very low-frequency sine (VLF-Sine) wave voltage, or very low-frequency cosine rectangular (VLF-CR) wave voltage and PF is still unclear. In this article, four kinds of defect flat models of the needle tips, air gaps, metal particles, and moisture are made. The PD tests are carried out under different voltage waveforms [DAC, sine, and cosine rectangular (CR)] and frequencies (0.1&#x2013;1000 Hz). The PD inception voltages (PDIV), phase-resolved PD (PRPD) spectra, and PD amplitudes of various defects are studied. The PDIV&#x2019;s equivalent coefficient <inline-formula> <tex-math notation="LaTeX">${K}_{\text {PDIV}}$ </tex-math></inline-formula>, total discharge amplitude&#x2019;s equivalent coefficient <inline-formula> <tex-math notation="LaTeX">${K}_{\textit {W}}$ </tex-math></inline-formula>, and PRPD&#x2019;s statistical operators are proposed to characterize the PD equivalence between PFL and PF quantitatively. The results show that <inline-formula> <tex-math notation="LaTeX">${K}_{\text {PDIV}}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">${K}_{W}$ </tex-math></inline-formula>, and PRPD&#x2019;s statistical operators can better evaluate the PD discovery abilities, PD severities, and PD-type recognition abilities of different voltage types. This study provides a technical basis for selecting the appropriate test voltage types and ensuring the test scientificity and reliability of cable PD tests in the field.