Abstract: Detection of degradation of the degree of vacuum in a vacuum interrupter suffers from poor sensibility because of mixed presence of various noises other than that due to discharge resulting from degradation The present invention allows accurate detection of degradation of the degree of vacuum by detecting the continuity of discharge produced between an electrode and a shield due to degradation of the degree of vacuum and the duration of discharge. The continuity of discharge is detected in accordance with a time slightly longer than 1 cycle time of a power-source voltage, and the duration of discharge is detected in accordance with a time sufficiently longer than 1 cycle time.

Abstract: Detection of vacuum degradation in vacuum circuit breakers has been low in detection sensitivity owing to the presence of various noises besides electric discharge. Accurate detection of vacuum degradation is made possible by detecting the continuity of electric discharge occurring between the electrode and the shield as vacuum degrades, and the duration of electric discharge. It is arranged that the continuity of electric discharge is detected as a somewhat longer period of time than one cycle time of power source frequency and the duration of electric discharge is detected as a sufficiently longer period of time than one cycle time.

Abstract: A vacuum monitor for a vacuum interrupter which can detect poor vacuum pressure at high detection sensitivity from the outside of the interrupter, on the basis of the impulsive electromagnetic wave signals generated when vacuum pressure increases within the vacuum interrupter. The vacuum monitor according to the present invention comprises, in particular, a detector terminal of capacitor coupler type or inductor coupler type disposed near a high voltage conductor for receiving impulsive electromagnetic wave signals, a signal level discriminating section, and a diagnosis section for improving the reliability of the monitor, particularly when the detected signal level of the electromagnetic wave signals is low.

Abstract: An abnormally high vacuum pressure of a vacuum interrupter is detected from outside of the interrupter in response to electromagnetic wave signals generated by an electric discharge derived in response to a voltage difference and depending upon Paschen's law. Since the above-mentioned electric discharge is quite different from so-called partial discharge, even when the fixed and movable contacts are closed (i.e., under hot-line condition), it is possible to detect poor vacuum pressure on the basis of the electric discharge existing between the fixed and movable contact rods including two contacts and the main shield, as well as when the two contacts are open. The vacuum monitor according to the present invention comprises a rod or loop antenna fixedly or movably disposed near a conductive material of or connected to the vacuum interrupter and a detection section including, in particular, a 2 to 20 KHz band-pass filter.