| 摘要 |
<p>1,144,188. Control of A.C. motors; protective arrangements. ROTORK ENG. CO. Ltd. 8 Dec., 1967 [15 Dec., 1966], No. 56165/66. Headings H2J and H2K. A polyphase motor-operated actuator 20 having a reversing starter circuit which forms an integral part of the actuator assembly, has a control circuit 31 which prevents energization of the starter circuit if the phase sequence of the supply A, B, C is incorrect. The control circuit comprises a relay 19, the voltage across which is made dependent upon the phase sequence by its being star connected with a resistor or other impedance 15 and a capacitor 18. A contact 32 of the relay is closed if the phase sequence is correct, thus permitting operation of forward or reverse contactors 27, 29 by push-buttons 38, 41. 37 and 44 are limit switches and the object of the invention is to prevent wrong rotation of the motor, when the limit switches would be ineffective. The starter circuit is energized from the two phases not connected to the relay 19 so that the motor cannot be started unless the supply is present on all three phases. The relay may also operate an indicator lamp and to accommodate various supply voltages the resistor 15 may be tapped and the starter circuit energized via a tapped transformer or a separate supply. The relay may be electromagnetic, thermal, thermionic or semi-conductor type, the contactors 27, 29 may be replaced by semi-conductor switches, the limit switches may respond to position and/ or torque, there is an overload switch 34, and the actuator may operate a valve.</p> |
