| 摘要 |
<p>This loss-of-vacuum detecting means for a vacuum circuit breaker utilizes input information derived from the current transformers of the overcurrent-sensing means typically present in medium voltage switchgear. In this overcurrent-sensing means, the current transformer secondaries for the respective phases of the switchgear are connected in parallel with each other across a shorting conductor; and in series with each secondary is the operating coil of an overcurrent relay. Connected in the shorting conductor is an "a" switch that is closed when the vacuum circuit breaker is closed and is opened when the circuit breaker is opened. Rectifying means is connected across said switch for developing a d.c. voltage when said switch is opened and one or more of said secondary windings is energized. Time-delay relay means is arranged to be energized by said d.c. voltage and is operable when the voltage thereacross exceeds a predetermined level for a predetermined minimum period following opening of said switch. Operation of said relay means is indicative of a loss of vacuum in one of the vacuum interrupters of the vacuum circuit breaker.</p> |
