GB669607A - Improvements in the remote control and protection of electric motors - Google Patents

Abstract

669,607. Protective cut-out arrangements. BROOKE, W., and BALDWIN, H. T. Jan. 10, 1950. No. 592/50. Class 38 (v). A remote control protective system for the control of an electric motor B supplied by means of a trailing cable V ... Z such as in mines, has a relay K with a coil K2 shunted by a large capacity condenser n (e.g. of 500 microfarads) to enable the satisfactory operation of the relay on a low voltage half wave rectified supply. The motor B is started when a remote control switch G is moved from the "off" position r1 to the "start" position r2 so as to complete a circuit from a transformer secondary winding g2 through the coil K2 and condenser n, through pilot conductor Z, half wave rectifier m, switch G and earth continuity pilot conductor Z. The coil K2 is fully energized and closes relay contacts K1 to energize the closing coil d of the contactor C. The switch G is then moved into the "run" position r3 where it inserts a resistance p into the control circuit to reduce the excitation of the relay K to a level sufficient to keep it closed, but insufficient to reclose it should it have been opened. by a fault. In the event of the earth connection becoming unsatisfactory as indicated by a resistance a, the relay K opens to stop the motor. Should the pilot and earth conductors Y, Z become short-circuited or should an earth fault develop on conductor Y, the rectifier m is no longer in circuit and alternating current is applied to the coil K2 and condenser n. Under this condition the relay coil has a high impedance relative to the condenser and the excitation of relay is reduced so causing contacts K2 to open. The transformer g may be supplied by means of a voltage stabilizing transformer h and a current-limiting resistance b may be inserted in the control circuit. It is stated that the use of a large condenser n, which may have a capacity of 500 microfarads, permits the satisfactory operation of the relay in conjunction with the half wave rectifier from an alternating current supply of from 1 to 4 volts. Specifications 644,058 and 665,570 are referred to.