Characteristics of Oil-Solid Surface Discharge Under Microsecond Pulse Voltage Using UHF Method

Oil-solid surface discharge (OSSD) is a pivotal concern in the oil-immersed pulse power equipment withstood microsecond pulse voltages (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPVs). The detection method and characteristics of OSSD under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV are important for the equipment’s condition monitoring and fault diagnosis. In this article, a partial discharge (PD) detection system using ultrahigh frequency (UHF) method is set up under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV. The characteristics of OSSD under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV with different voltage polarities and voltage levels are studied, and the influence mechanism of voltage polarity on OSSD characteristics is analyzed. The results show that UHF method has high sensitivity and sufficient pulse time resolution to effectively detect OSSD under <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV; the PD initiation voltage (PDIV) of OSSD under positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV is higher than that under negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV, and they are both lower than those under the same polarity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPVs in pure oil gap; the voltage polarity has significant effects on the PD sequence characteristics and PD patterns of OSSD. Positive PD is hardly detected under positive <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV, but the reverse PDs always exist. Negative PDs and reverse PDs exist simultaneously under negative <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV, and the PD distributions change significantly with the increasing voltage. The obstruction effect of solid interface resulting in a decrease of oil volume near the needle tip where streamer can initiate, and significant change of streamer propagation direction and the corresponding residual charge distribution in discharge channel, as well as the different discharge mechanisms of oil under different polarity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPVs are responsible for those differences. A simple method for evaluating OSSD in actual pulse power equipment is proposed by the polarity effect on PD pattern of OSSD. The findings provide valuable insights into the application of UHF-based PD detection for condition monitoring and fault diagnosis of oil-immersed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>sPV equipment as well as the oil-immersed power equipment under lightning and switching overvoltages.