Estimation of Internal Pressure of Vacuum Interrupter by Measuring Partial Discharge Current

Abstract

Loss of vacuum in vacuum interrupter (VI) is becoming an interesting theme for VI used in medium voltage range beyond its lifetime of typically 20–30 years. The early detection of abnormality in the vacuum insulated equipment must be important for the development of higher voltage vacuum circuit breakers (VCBs), such as cubicle type gas insulated switchgear (C-GIS) with compressed gas and/or insulation gas. In the present study, for the purpose of diagnosing the vacuum pressure in VI by a partial discharge (PD) measurement, PD characteristics in medium vacuum range of 1 Pa to 100 Pa were investigated. As a leakage gas, air was sealed into the VI, and its pressure was regulated from 2.2 Pa to 100 Pa, which corresponds to the left region of Paschen curve. From PD current waveforms by detecting resistor connected to plane electrode outside the VI, the charges, occurrence frequency and phase characteristics of PDs for each applied AC voltage and internal vacuum pressure were determined. It was concluded that a number of occurrence of PD and PD charges would be dominant parameter for determination of the internal pressure of VI.