| 摘要 |
1. A protective circuit for an electric motor (1 and 2) in series with the circuit breaker (10) controlled by a phase angle control means, comprising a fuse (12) to cut off the supply to the motor in the event of a permanent short circuit of the controlled circuit breaker, and a second controlled circuit breaker (16), such as a triac or a thyristor, which is turned on when it has detected a permanent short circuit of the first circuit breaker (10) and is arranged in such a manner as to fuse the fuse in such case, characterized in that the circuit is so operated that the time between transfer into the conducting condition of the second controlled circuit breaker (16) and the instant of fusing of the fuse (12) is sufficiently large to ensure that a short tripping of the second controlled circuit breaker does not fuse the said fuse (12). |
