Patent GB-445142-A (GB)
Title: Improvements in or relating to protective arrangements for alternating-current distribution systems
IPC: H02H7/28
Filed: 1935-04-02
Abstract: 445,142. Protective cut-out systems. WESTINGHOUSE ELECTRIC & MANUFACTURING CO., East Pittsburgh, Pennsylvania, U.S.A.-(Assignees of Parsons, J. S. ; 7632, Westmoreland Avenue, Swissvale, and Harrison, G. 0.; 724, Kelly Avenue, Wilkinsburg, both in Pennsylvania, U.S.A.) April 2, 1935, No. 10250. Convention date, May 19, 1934. [Class 38 (v)] In an alternating current system comprising a feeder circuit 3 and a network circuit 5 interconnected through transformers 4 and network protectors 6, with means for controlling the operation of the latter, means responsive to an abnormal relationship of voltages between the feeder and network circuits are provided for creating an artificial fault or otherwise modifying the electrical condition of the feeder circuit, in order to prevent closure of the network circuit breakers when the said abnormal relationship of voltages exists. The feeder circuit 3 is connected to a grounded-neutral source 1 through a feeder circuit-breaker 2, which is provided with back-contacts 2a or other means for earthing one conductor of the feeder 3 when the breaker 2 is open. Normally-open switches 8 are also provided for earthing the same conductor of the feeder when the breaker 2 is reclosed if an abnormal relationship exists between the feeder and network voltages, due, for example, to crossed phases or other incorrect connections after repairing a fault. In one form of network protector 6, shown in Fig. 2, a circuit-breaker 10 is controlled by an electrostatic relay 11 connected through a condenser 12 to a high-voltage terminal of the transformer 4. The relay has a movable contact member 11a which engages a front contact 11b if the feeder voltage is approximately 90 per cent normal, and engages a back contact 11c in response to an undervoltage condition of approximately 30 per cent normal. The front contact 11b is connected in circuit with a timing relay 13 which effects closure of the circuit-breaker 10 after an interval when the feeder voltage conditions are approximately normal, and the back contact 11c is connected to the trip coil of the circuit-breaker. With this arrangement, the circuit-breaker 10 trips open when the voltage in the feeder conductor connected to the earthing switches falls below 30 per cent normal, and recloses with a time delay when the voltage is approximately normal. The earthing switches 8 are controlled by a voltage responsive relay 14 and a negative phase sequence voltage relay 15, connected as shown in Fig. 3. The relay 14 is connected across the main contacts of the nearest network circuit-breaker 10 and is designed to close at a voltage of approximately 130 per cent normal phase-to-earth voltage of the network. The object of this relay is to trip the switch 8 to closed position in the event that all three conductors of the feeder have been rotated 120‹ or 240‹ in repairing a feeder fault. The relay 15 is connected to a negative phase sequence filter 16 comprising an autotransformer 16a, inductance 16c and resistance 16b, and trips the switch 8 if any two conductors of the feeder have been transposed, or if any conductor has been left open. In a modification, Fig. 4 (not shown), the electrostatic relay of Fig. 3 is replaced by an electromagnetic control system comprising instantaneous under-voltage and over-voltage relays, and an induction type relay adjusted to close with time delay action. In another arrangement, Fig. 5, relays 21 trip the network circuit-breaker 10 in response to phase-to-phase voltage conditions below a predetermined value, and a separate relay 23 effects closing of the circuit-breaker when voltage conditions are approximately normal. In addition, a ground-detecting relay 24, connected to one conductor of the feeder 3 through an impedance 25, trips the circuit-breaker and prevents the operation of the closing relay, whenever a ground exists on any phase of the feeder. The switch 8, in this arrangement, is controlled by voltage-responsive relays connected across the contacts of the nearest network circuitbreaker, Fig. 6, (not shown). In another arrangement, Fig. 7 (not shown) the electromagnetic relays of Fig. 5 are replaced by electrostatic relays.