Patent GB-393577-A (GB)
Title: Improvements in and relating to protective apparatus for electric systems
IPC: H02H7/30
Filed: 1931-11-26
Abstract: 393,577. Protective cut-out arrangements. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. -(Assignees of Traver, O. C.; 1015, Childs Avenue, Drexel Hill, Pennsylvania, U.S.A.) Nov. 26, 1931, No. 32836. Convention date, Nov. 26, 1930. [Class 38 (v).] Under fault conditions in a circuit 10, 11, 12, a power directional starting unit 20 operates to open contacts 56 and close contacts 61, and if the fault is within a certain minimum distance the coil of a relay 74 and a circuit-breaker trip coil 14' are energized in series through contacts 44, 45 on an ohmmeter 19, and the circuitbreaker is quickly opened. The relay 74 maintains itself closed and supplies the coil 14 independently of contacts 61, 44, 45. If the fault is within a higher distance range, the .contact 44 of the ohmmeter 19 takes up a position intermediate the contact 45 and another fixed contact 46, so that the coils 74 and 14 are not immediately energized, but a timing device 18 energized through contacts 61 closes contacts 21, 37, and energizes the coils 74 and 14 over contacts 79 of a transfer relay 80, to trip the circuit-breaker after a time t1. If the fault is within a still higher distance range the contacts 44, 46 of the ohmmeter 19 are closed and the transfer relay 80 is energized to open its contacts 79, so that the circuit-breaker is not tripped when the contacts 21, 37 of the timing device 18 are closed, but only when its contacts 21, 38 are closed after a time t2. A leaf-spring 8 is provided on the contact arm 44 which normally holds the contact 44 away from the contact 45 so that the circuit-breaker is tripped quickly with short distance faults only when the current flowing is high. At the same time better discrimination between short distance and higher distance range faults is obtained. In a modification shown in Fig. 4 two separate time elements 18<1>, 18<11> are used, and a solenoid 84 connected across the voltage coil 49 of the ohmmeter 19 through contacts 56, 56<11> of the starting device 20, is used to maintain the moving contact 44 of the ohmmeter 19 away from the fixed contact 45. On current reversal contacts 56, 56<11> of the starting device 20 are opened, to de-energize the solenoid 84, and if the fault is within the minimum distance range, contacts 44, 45 of the ohmmeter 19 quickly engage and the coil 14 is energized to trip the circuit-breaker. If the fault is within a higher distance range, the contact 44 takes up a position intermediate the contacts 45, 46, and when, after a time t1, the timing element 18<1>, energized by the closing of contacts 56<1>, 61 of the starting device 20 closes its contacts 37<1>, the circuit-breaker is tripped. If the fault is within a still higher distance range, contacts 44, 46 of the ohmmeter 19 close, and short-circuit the timing element 181 through a resistance 86, so that the circuitbreaker is tripped by the closure of contacts 381 of the timing element 18<11> only after a time t2. In a further modification, Fig. 5, the ohmmeter 19 and the starting device 20 are formed as a single unit 19<1>. The timing device 18 is energized through contacts 87 normally kept open by the contact arm 85 of the element 191. On reversal of current the-contact arm 85 is moved in the direction of fixed contacts 89, 88, closing the contacts 87, and energizing the timing device 18. If the fault is within a minimum distance range the contact arm 85 engages the contact 88, so that a circuit is completed through coils 74 and 14 to trip the circuit-breaker quickly. If the fault is within a higher distance range the contact 85 engages the contact 89 and energizes an auxiliary relay 90 which maintains itself closed, and also connects a fixed contact 37 of the timing device 18 so that the circuit-breaker is tripped only after a time t1, when the contact 37 is engaged by the moving contact arm 21. If the fault is within a still higher distance range, the contact arm 85 of the element 19<1> does not reach the contact 89, and the circuit-breaker is tripped only after a time t2, when the contact 38 of the timing device 18 is engaged by the arm 21. In a modification of the arrangement shown in Fig. 1, the current coils of the ohmmeter 19 and the starting device 20 are energized by the difference between the currents in the two phases across which the voltage coils of these devices are connected. Specifications 307,806, 319,637, 320,968, and 324,056, [all in Class 38 (v), Electric switches &c.], are referred to. Reference has been directed by the Comptroller to Specification 326,890, [Class 38 (v), Electric switches &c.].