Patent GB-247222-A (GB)
Title: Improvements in and relating to automatic electric switching systems
Filed: 1926-02-08
Abstract: 247,222. British Thomson-Houston Co., Ltd., (Assignees of Bany, H.). Feb. 6, 1925, [Convention date]. Switching systems; running generators in parallel. - In automatic systems for switching alternative sources of power, including synchronous converters, motor - generators, static transformers prime-moverdriven dynamos and other generating or transforming units, on to a circuit in a selected sequence, failure to connect one source automatically results in the connection of another. Failure of the mains voltage supplying a transforming unit will have a like result where the units are supplied from independent mains. Means are included to change the sequence of operation at will and at any time without affecting operating plant. The Figure shows two rotary converters 1, 2 supplied from separate mains 3, 4 through automatic starters 12, 14 and with circuitbreakers 15, 16 to switch them on to a supply circuit 5 through resistances 19, 23 automatically controlled by the circuit breakers and overload coils 20, 25. Master relays 11, 13 control the starters 12. 14 and the circuit breakers 15, 16, switches 17, 18 preventing loading when voltage and polarity are incorrect. The master relays are controlled by protective relays 41, 42 and time-delay lock-out switches 44, 47 which set a starting-time-limit. The system is shown set for operation in the sequence 1, 2, but a handswitch 10 is provided to change the sequence, and this may be operated during running by simultaneous use of a switch 53. Relays 50. 52 change the connections automatically if the master relay of the leading machine should not operate within a snort period, or upon the functioning of the starting-time-limits 44, 47, whilst an under-volt relay 54 will operate the relay 52 if the mains voltage of the leading machine should fail. A voltage relay 6 is the master element of the leading machine and controls two time-delay relays 28, 29 so that this machine cannot be started or shut down until the load condition has persisted for a predetermined time. An overload relay 8 is the master element for the trailing machine. and with the time-delay relays 37, 38 controls this machine in a similar manner. The system operates when the voltage on the circuit 5 falls to a predetermined value, whereupon the master element 6 opens its contacts 7 and closes its contacts 31. Relay 29 closes at once and relay 28 after an interval. Two circuits are thus closed from the transformer 55 (or 64) supplied by the mains of the leading machine. One circuit includes the coil 11 (or 13) and the other contacts 87 of the under-volt relay 54 and the coil 50. The last, after a short time-delay, will operate relay 52 to put the trailing machine in operation if the master relay 11 (or 13) of the leading machine should not function. The starting-time-limit relays 44, 47 are always energized except when their respective master relays 11, 13 are functioning. Should the actuation of the latter not result in placing their machines on load within a predetrmined time they will be de-energized by the opening of contacts 43 or 46 and the relay 50 will function as above. The ultimate closure of the circuit-breakers 15, 16 on' successful starting re-energizes the relays 44, 47. So long as the output of each machine exceeds a predetermined value relays 34, 35 close circuits shunting the contacts 31 of the master element 6 of the leading machine, but at a lesser output this circuit is opened and, when one machine only is running, the relay 29 de-energized, whereupon the master relay of that machine becomes de-energized after a time interval and the' machine is shut down.