Patent GB-289475-A (GB)
Title: Improvements in and relating to automatic switching systems
IPC: H02H3/06
Filed: 1928-04-27
Abstract: 289,475. British Thomson-Houston Co., Ltd., (Assignees of Anderson, A. E. and Bany, H.). April 28, 1927, [Convention date]. Systems depending on two or more machines. -One of two current sources is automatically connected to a load circuit by circuit-breakers controlled by co-operating selecting devices responsive to the voltage of each source and a known timing device adapted to make a predetermined number of attempts at predetermined intervals to re-close an open circuit-breaker, overload responsive means being provided to trip the circuit-breakers. A preferred source is selected when both sources are alive. The emergency source is connected when the preferred source fails and the latter is restored, when again effective, before cutting out the emergency source, should this be operative, but after tripping its circuit-breaker should it not be operative. The system is applicable to direct current sources and to single and polyphase sources. When sources 1, 2 are energized simultaneously, time delay relays 14, 15 lift. Relay 16 thus lifts, but relay 17 is prevented by an interlock on relay 16. Relay 18 also lifts. The motor 26 of a timing device is energized when one of the relays 16, 17 is lifted and the other down; so is a magnet 21 if the proper circuit-breaker is open, in this case 4, the source 1 being preferred. Magnet 21 releases the timing device which closes contacts 31 to energize a time-delay-opening relay 20 also controlled by the position of the circuit-breaker. This relay closes contacts 50 in a maintaining circuit independent of contacts 31 and in the circuit of a hesitating relay 12 which is closed at contacts 32 through interlocks ensuring that circuit-breakers 4 and 5 are open and relay 16 lifted. Relay 12 completes the circuit of the closing coil 6 through interlocks on the relays 16 and 17, so connecting source 1 to the load circuit 3. When the source 1 fails, source 2 being energized, relays 14 and 16 drop and allow relay 17 to lift. The timing device is started as before, but contact 32 now closes the circuit of trip coil 10 through interlocks on the closed circuit-breaker 4 and lifted relay 17. A contact on the open circuit-breaker 4 energizes the hesitating relay 13 through interlocks on the circuit-breaker 5 and relay 17, and this closes the circuit of lifting coil 7 through an interlock in the relay 17. When source 1 is restored while source 2 is energized, a contact on the lifted relay 18 replaces the interlock on closed circuit-breaker 5 in the circuit of relay 12 made by the timin device so that the source 1 is switched into parallel with source 2. The closing of circuitbreaker 4 makes a circuit of the trip coil 11 through interlocks on the relays 16 and 18 and the closed circuit-breaker 5; source 2 is thus disconnected. Should source 2 not be energized when source 1 is restored though the circuitbreaker 5 is closed interlocks on this switch and the dropped relay 18 cause the contact 32 to close circuit for trip coil 11 and the relay 12 is energized by the opening of circuit-breaker 5 so that the circuit 2 is disconnected before the source 1 is switched on. Overload on the circuit 3 operates the current trip coils 8, 9 and the opening of either circuit-breaker under the conditions energizes the magnet 21 setting the timing device in operation; if the circuit is not properly closed when this device reaches its original position the magnet 21 will remain energized and a notch 30 will engage a stop 29 and lock it against further operation until manually re-set. In a modification when the source 2 is supplying, an extra contact on circuit breaker 5 holds the relay 17 energized when relay 16 lifts on restoration of voltage on the preferred source, thus maintaining the emergency supply until it fails or is cut off by overload or other means. A momentary failure of voltage does not result in opening the circuit-breaker 5 in this case, since the relay 15 re-energizes the relay 17 before the timing device can operate.