Discharge properties and diagnosis of gas pressure in vacuum interrupter

Vacuum circuit breaker (VCB) is widely used in medium voltage distribution system to control and protect power lines and equipments. The internal pressure of vacuum interrupter (VI) is one of the most important parameters for VCBs´ performance. If the slow leak cannot be detected and timely solved, VI will cause serious faults. Therefore, a high sensitivity and reliable detecting device is essential. In this paper, the signal intensity of the discharge signal caused by the discharge occurring inside the VI whose degree of vacuum could be varied was measured. The partial discharge inception voltages plotted against the internal pressure of the VI showed a convex downward curve. Increasing the internal pressure to atmospheric from 10^-3 pa for simulating the process of leak, we had stored the discharge waveforms by using digital oscilloscope under various pressures. Furthermore, by altering the probe´s material, designing the signal conditioning circuit and optimizing criterion algorithm, the anti-interference ability of the equipment had been improved. A large series of experiments had been executed in this paper and certified that the device could be applied not only as a alarm system but could also be used to develop a diagnosis system that could estimate the vacuum degree of a VCB by analysis of the discharge pattern.