GB829032A - Improvements in or relating to the protection of electrical distribution systems - Google Patents

Abstract

829,032. Protective cut-out arrangements. WESTINGHOUSE ELECTRIC CORPORATION. Jan. 21, 1957 [Jan. 26, 1956], No. 2114/57. Class 38 (5). A power-directional relay controlling a circuit-breaker 13 positioned between a network 1 and a transformer 9 supplied by a feeder 7, comprises a rotor 19 rotatable between circuit-breaker tripping and closing positions and a stator structure with voltage windings 43a, 45a energized by two-phase voltages from the network side of the circuitbreaker, a voltage winding 47a energized by the remaining phase voltage on the transformer side of the circuitbreaker, current windings 37a, 39a, 41a energized by the phase currents and phasing windings 37b, 39b, 41b energized by the voltages across the circuit-breaker contacts, the current and voltage windings producing a torque which moves the rotor 19 to close contacts 25, 27 to trip the circuit-breaker in the event of reverse power flow from the network to the transformer and the voltage and phasing windings producing a torque effective to close contacts 25, 29 to close the circuit-breaker when the voltage conditions are such as to permit power flow from the feeder to the network. A spiral spring 29 assists the current and voltage windings to produce circuit-breaker tripping when the reverse power flow is only that due to transformer magnetizing currents taken from the network when the feeder is de-energized. The effect of voltage variation on the torque resulting from reverse magnetising currents is minimised by shading rings 69, 71, 73. To improve the operating characteristics of the relay impedances 75, 77, 79, 81, 83, 85 are connected in series with the phasing windings, short-circuiting contacts 87, 89, 91 for the impedances 77, 81, 85 being provided on the circuit-breaker. A leaf-spring 99 carried by the rotor 19 cooperates with a fixed stop 101 to provide an initial torque in the circuit-breaker tripping direction. The relay may have a cup-shaped conductive rotor 19, and internally and externally positioned electromagnetic elements, as shown.