Patent GB-187337-A (GB)
Title: Improvements in and relating to electric distribution systems
IPC: H02J3/06
Filed: 1921-07-20
Abstract: 187,337. British Thomson - Houston Co., Ltd., (General Electric Co.). July 20, 1921. Protective arrangements.-In distribution svstems in which a group feeder supplies a distributing bus-bar connected to individual feeders, each feeder is protected by a time element circuitbreaker of relatively low interrupting capacity to deal with moderate overloads, a quick-acting main circuit-breaker of relatively high interrupting capacity being connected in the group feeder circuit to respond to overloads above the capacity of the feeder circuit interrupters. Opening of the main circuit-breaker on the occurrence of a short-circuit in a feeder introduces a resistance into the group feeder circuit thereby reducing the current to allow the faulty feeder to be interrupted, the consequent rise of potential cn the distributing bus .bar closing a voltage relay to complete the reclosing circuit of the main interrupter. In Fig. 1 for alternating current working the supply 1 is connected to the distributing bus 3 by a group feeder 2 having a main interrupter 5 which normally short-circuits a resistance 7. Each of the feeders 4 has an interrupter 6 having a tripping magnet 23 the circuit of which is completed by a time element relay 20 energized by a series transformer 19 in the feeder 4. The main circuit-breaker 5 has a trip magnet 16 energized by the control supply 12, 18, the tripping circuit being completed by a quick-acting relay 9 supplied by a series transformer 8 in the group feeder circuit 2, the setting of the relay 9 being higher than the setting of relays 20. In the event of a moderate overload the relay 9 is unaffected, the circuit-breaker 6 in the faulty feeder 4 being opened after the delay caused by the time limit relay 29. On heavy overloads above the capacity of the feeder interrupters 6 the instantaneously-acting relay 9 operates causing the tripping of the main interrupter 5. The consequent introduction of the limiting resistance 7 allows the tripping of the faulty feeder interrupter 6 to be completed, when. the rise of potential on the distributing bus-bar operates the voltage relay 25 through the potential transformer 24 to complete the circuit of a time element relay 30 which in turn closes the circuit of the reclosing coil 36 of the interrupter 5. The time element of relay 30 enables it to bridge its contacts for a time sufficient to enable the reclcsing to be completed. In a modified form shown in Fig. 2, the trip magnet 16 of the interrupter 5 is controlled by quickacting relays 38 in series with the operating coils 20 of the feeder relays. With a heavy overload on a feeder the corresponding quick-acting relay 38 operates to bridge conductors 42, 45 thereby completing the circuit of the tripping magnet 16 and causing the group feeder circuit-breaker 5 to open. The operation of the relay 38 which is provided with upper and lower contacts automatically prevents the completion of the circuit for tripping magnet 23 until the relay 38 is released by the diminution of current caused by the introduction of the resistance 7. The interrupter of the faulty feeder can now operate and the group feeder reclose as in Fig. 1. In a further development shown in Fig. 3, the circuit of the tripping magnet 23 of the interrupter 6 is independent of the relay 38, the time delay action of the relay 20 being relied upon to ensure that with heavy overloads the relay 38 operates in advance. Modified for direct current working as in Fig. 2, the series transformers 8, 19 are replaced by series resistances 54, 66 in the group feeder and individual feeder circuits respectively, the function of the potential transformer 24 for the reclosing circuit of the main interrupter 51 being obtained by connecting the voltage relay 72 between the distributing bus-bar 49 and ground when the interrupter 51 is in its open position. In this modification the individual feeders 50 are provided with interrupters 52 having tripping magnets 69 controlled by time-element relays 65.