| 摘要 |
An electrical switching circuit for a multi-phase a.c. supply uses semiconductor rectifier switches SCR1 to 5 to reversibly switch power to a multi-phase electric motor so that the motor can be run in a forward or a reverse direction. The SCRs are provide in two sets, one for switching power to forward run the motor, and the other set for reverse running of the motor. Inductor elements DELTA L are connected in series with the SCRs. The inductor elements comprise coils which include a non-linear permeability core, for example of ferrite or permalloy, which are operative to suppress voltage transients at switch on of the motor. These transients would otherwise produce spurious firing of the SCRs and could produce a short circuit across the input phases of the a.c. supply. The circuit is used in a valve actuator. Improved torque limit switches and position limit switches are disclosed, which operate a low voltage and which use Reed and wall effect switches. |
