An Online VCB’s Vacuum Degree Detecting Method Based on HFID

Vacuum degree is one of the important parameters of the working condition of the vacuum circuit breaker (VCB). The real-time detection of the vacuum degree is the guarantee of the safe and stable operation of the vacuum circuit breaker. A coupling capacitance method is proposed to detect the vacuum degree of the interrupter on line, which is based on the principle of partial discharge measurement. If the withstand voltage strength between the live contact of the vacuum interrupter to the middle shield decreases due to the decrease of vacuum degree, when the power frequency voltage rises from zero to a certain value, the equivalent capacitance between the live contact and the shield generates electricity. The partial discharge signal can be monitored online by two partial discharge probes located between the shield and the grounding box shell. By capturing the high frequency pulse of discharge, we can indirectly monitor the change of the potential at the shield of the interrupter, so as to accurately understand the vacuum condition of the interrupter. The on-line vacuum monitoring device designed in this paper can meet the requirements of DL/T 403, that is, to capture the discharge signal at the initial stage of pre discharge, and adjust the sensitivity switch of the front panel to make it suitable for the on-line vacuum monitoring of various high, medium and low voltage vacuum circuit breakers, with the monitoring range of more than 10^-1 Pa.