PURPOSE: To predict the life expectancy of a vacuum bulb which is in the state of being mounted on a vacuum circuit breaker, by controlling to a specific range the rising time constant of the pulse electric current of a large electric current pulse power source generating a magnetic field at a solenoid coil surrounding the vacuum bulb.
CONSTITUTION: A vacuum pressure measuring device 2 is equipped with electrodes 4, 5 which are in a vacuum bulb 1 mounted on a vacuum circuit breaker 3, a control circuit 7 that maintains a lag time during which high voltage impressed from a DC high pressure power source 6 reaches the predetermined voltage, a large electric current pulse power source 8 which is actuated through the circuit 7, and a solenoid coil 9 at which a magnetic field is generated by means of the output of the power source 8 and which surrounds the vacuum bulb, and measures vacuum pressure by measuring the crest value and integration value of an ion electric current flowing between electrodes 4, 5 by means of a detecting circuit 10. The probability of ion electric current generation becomes high by controlling the pulse electric current rising time constant of the above large electric current pulse power source at 0.1-5mS, and a measuring range can be expanded to 10-7Torr, so the prediction of the life expectancy of the vacuum bulb under the condition of being mounted on the vacuum circuit breaker, and the transport and fitting of it can easily be done.
KURODA KATSUZO
ISHIGAMI KOREHIRO
