Patent GB-395112-A (GB)
Title: Improvements in and relating to automatic re-closing circuit breaker systems
IPC: A43D69/02
Filed: 1932-04-14
Abstract: 395,112. Protective cut-out systems. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Fitzgerald, A. S. ; Warwick Road, Wynnewood, Pennsylvania, U.S.A.) April 14, 1932, No. 10721. Convention date, April 17, 1931. [Class 38 (v).] An a.c. supply 11 is connected, through a transformer 12 and valves 13, 14 to a d.c. load, the valve grids being energized through a transformer 15 and reactance device 17, 18, 19 from the supply 11 so that their potentials are normally in phase with those of the anodes, but can be made in phase opposition by saturating the reactance 19 by means of a winding 20, whereby the valves cease to be conducting. A current transformer 28 on overload overcomes the - bias of batteries 31, 32 whereby valves 25, 26 pass fully-rectified current from the supply 11 to a condenser 23 and shunt resistance 27. The potential of the latter overcomes the bias of battery 22a to render valve 22 conducting, so energizing the winding 20 through transformer 21 from the line 11. The valves 13, 14 now cease to conduct, the transformer 28 is no longer energized, and condenser 23 discharges through the resistance 27, so that the valve 22 again becomes non-conducting and the valves 13, 14 conducting. This cycle is repeated if the overload persists, but the number of attempts to restore the line is restricted (say, to three) by means of a condenser 33, which receives an increment of charge from the transformer 34 across the line 11 every time the condenser 23 is charged, the charging current of the latter setting up a potential across a resistance 38 which overcomes the bias on the grid of a valve 35. When the condenser 33, after three increments, becomes fully charged, it overcomes the bias on the grid of a valve 39, whereby the latter becomes conducting, so that the potential across a resistance 40 renders the valve 42 conducting, and, provided the hand switch 44 is closed, the battery 43 maintains a flow of current through resistance 27 and condenser 23 even after the load is disconnected bv the permanent energization of winding 20 by the non-conducting valve 22. Reconnection can now only be effected by opening switch 44. In the modification shown in Fig. 2, the reclosing of the line 10 is made dependent on the resisrance of the line, which is connected so as to form one arm of a Wheatstone-bridge 50 energized from the line 11 and supplying through a rectifier 59 and winding 57 a saturable impedance 58 in a further bridge 62. Normally the bridge 50 is unbalanced in the direction to maintain 58 unsaturated so that the bridge 62 is balanced, but on the load 10 becoming disconnected, the unbalance of 50 is reversed and 62 becomes unbalanced, thereby setting up a potential across a resistance 63 which renders a valve 65 conducting. A current is sent through resistance 27 in the same direction as that from the rectifiers 25, 26 and valve 22 is maintained conducting to keep the line 10 disconnected as long as the fault exists or until the switch 44 is opened. The bridge 62 is for providing increased sensitivity but may be dispensed with, the resistance 63 being then connected directly across the bridge 50. By reversely connecting the valves 13, 14 in parallel, the circuit 10 may be adapted to supply an a.c. load.