Patent GB-171009-A (GB)
Title: Improvements in and relating to electric distribution systems
IPC: H02H3/06
Filed: 1920-09-16
Abstract: 171,009. British Thomson - Houston Co., Ltd., (General Electric Co.). Sept. 16, 1920. Cut-out arrangements.-In an overload cut-out system, the operation of the cut-out operates to connect a source of relatively low potential to the load circuit, and when the current from this source falls to a predetermined value due to an increase in the impedance of the load circuit upon the removal of the short-circuit, means are provided to close the cut-out. The system may be applied to alternating or direct current systems and the auxiliary source may be a transformer, a battery, or a generator. The operating-coil 7, Fig. 1, and resetting-coil 8 of an overload cut-out 6 are energized from direct-current mains 9, 10 and the circuits of these coils are controlled by switches 15, 17 operatively connected with the circuit-breaker 6. Upon the occurrence of an overload, a relay 11 completes the circuit of the coil 7 through the contacts 13 of the switch 15. The operation of the circuit-breaker 6 causes the switches 15, 17 to bridge contacts 14, 16. The closure of contacts 16 connects a relay 21 to the secondary winding of a step-down transformer 18, and the relay 21 operates, after a time interval, to connect the load circuit 31 to the transformer 18 through the relay 21 and a resistance 22. The operation of the relay 21 opens the contacts 27 and 24 and closes the contacts 34 to place the winding 33 across the mains 9, 10 through the contacts 14 of the switch 15. The relay 21 allows a testing-current from the transformer 18 to flow through the load circuit 31. When the impedance of the load circuit reaches a predetermined value, due to the removal of the short-circuit, the current through the relay 21 is insufficient to maintain it in its raised position and the transformer 18 is disconnected from the load circuit at the contacts 28 and the contacts 27 are bridged to place a relay 40 across the mains 9, 10. The relay 40 operates to bridge contacts 41 to place the closing coils 8 across the mains 9, 10. The closure of the circuit-breaker 6 opens the contacts 14 to de-energize the relays 33, 40 and the apparatus returns to the position shown. In the modification shown in Fig. 2, the opening of the circuit-breaker 6 causes the switch 15 to bridge the contacts 14, thereby energizing the coil 42 in series with a resistance 45. The contacts 28 are bridged to connect the transformer 18 to the load circuit 31 through a retaining-coil 21, and the contacts 34 are bridged to energize the winding 33 in parallel with the winding 42. As the resistance of the winding 33 is much less than that of the winding 42, the latter is practically short-circuited. When the impedance of the load circuit reaches a predetermined value, the winding 21 ceases to hold the contacts 28 bridged and the transformer 18 is disconnected from the load circuit. Under this condition the contacts 27 are bridged to complete the circuit of the relay 40, which operates to close the circuit of the closing-coil 8. In a modification, the system is applied to a three-phase system. In a modification shown in Fig. 4, a load circuit 70 is connected to direct-current bus-bars- 58, 59 through an overload circuit-breaker 60 normally held closed by a coil 63. When an overload occurs, a relay 65 operates to open the circuit of the coil 63, and an auxiliary switch 68 is closed. The closure of the switch 68 connects a battery or the low-voltage generator of a motor-generator 71 to a relay 21, which operates to connect the generator to the load circuit 70. The operation of the relay 21 opens the initial circuit of the relay 21 at contacts 24 and closes contacts 34 to energize a retaining-winding 33. When the resistance of the load circuit reaches a predetermined value due to the removal of the short-circuit, the winding 21 fails to retain its core in its raised position and the contacts 27 are closed and the contacts 28 opened. The coil 63 is thereby energized to close the circuit-breaker 60, and the lowvoltage generator is disconnected from the load circuit.