Diagnostics For Vacuum Degree Of Vacuum Interrupter Based On Partial Discharge Mechanisms Under Medium Vacuum Level

A loss of vacuum in vacuum Interrupter (VI) can lead to a crucial failure in vacuum circuit breaker (VCB). The purpose of present research is to develop the continuous monitoring and diagnostic technique for degradation of vacuum degree in VIs. The loss of vacuum originates from a natural slow leakage, corrosion at flange face, mechanical damages at bellows or flanges, etc. during long-term operations. The partial discharge (PD) phenomena, occurring in the VI under lower vacuum level from 0.1 Pa to 100 Pa, have been focused on, and its characteristics and mechanisms have been discussed. A glass VI with close contact state was used as a specimen, whose vacuum degree could arbitrarily be kept by connecting vacuum pumping systems. PDs inside the VI could be detected with a detecting resistor connecting to a plane-round electrode located 50 mm from a vapor shield of VI. Applied voltage and electrical potential of the floating vapor shield were also measured with a voltage divider, a capacitive voltage divider directly connecting to the vapor shield of VI. Furthermore, to determine the PD location in the VI, framing images light emission of PD were measured by digital camera with image intensifier, whose exposure time and its timing were controlled by gate pulse from a pulse generator. The present study found out the characteristics of first PD, which can be measured in degradation process of VI. The pressure range corresponds to the Paschen left region. The differences in PD polarities were clarified through above measurement, and temporal change of charge potential of vapor shield was calculated. From the above results and discussion, the applicability of PD detecting for vacuum degree deterioration to operating VCBs in the field and its method including sensing and signal processing were proposed.