Patent GB-190613691-A (GB)
Title: Improvements in Electric Motor Control Systems and Apparatus.
Filed: 1906-06-14
Granted: 1907-05-30
Abstract: 13,691. British Thomson-Houston Co., [General Electric Co.]. June 14. Switches. - In a control system for electric railways, a time-interval relay, consisting of two electro-magnetic switches operated by shunt and series coils, is employed, by means of which a smooth acceleration is obtained by cutting out resistances, the rate of cut-out varying with the load. The relay is here described in conjunction with a controller of the kind described in Specification No. 19,573, A.D. 1904. Master-controllers K, K<1> are connected in parallel to the train-wires l<1> ... l<4>. The governing-device W consists of two electro-magnetic relays w, w<1>, provided with series coils 2, 4, shunt coils 1, 3, and dash-pots 5, 6, the dash-pot 6 causing its core to fall more slowly than the other 5, while both are provided with check valves. The relay is so proportioned that, when the coil 1 is de-energized and the current valve in the coil 2 is not above that best adapted for acceleration under heavier normal loads, the core is free to drop and close the contacts 7, while the relay w<1> is free to close the contacts 8 at the valve at which it is desired to accelerate at normal loads. When the main switches X, X' are closed and the controller K moved so as to bring the movable contacts into engagement with the fixed contacts along the line a-a, the switches T<1> ... T<4>, S are closed, and the motors are connected with the source in series with each other and with the resistances R<a> ... R<g>. When the master-controller is moved into its second position, the circuits previously made remain, while an additional branch passes from the train-wire l<4> through the contacts 7, 8, coils 1, 3 of the relays, upper contacts of the interlock on the switch S, lower contacts of the interlock r<10>, contacts q of the relay Q, actuatiug-coil of the switch R', and the interlocks r<2> ... r<4> to the ground. The switch R<1> is accordingly closed, cutting out the resistance R<a> from the motor circuit, and shunting its actuating-circuit from the lower contacts of the interlock r<10> to the upper contacts, through the lower contacts of the interlock r<20> and the actuating- coil of the resistance contactor R', and shifting the actuating-circuit for the series contactor from the lower contacts of the interlock r<1> to the upper contacts, and thereby maintaining the circuit for the contactor R'. In the meantime, both relays are lifted, interrupting the actuating-circuit so that the contact R' is not immediately closed. If the motor current is not great enough to cause the coil 2 to maintain the core of the relay raised, the contacts 7 and consequently the contactor R' are closed. If, however, this current is great enough to maintain the relay w lifted, and the current falls sufficiently before the slow-moving core of the relay w<1> has completed its descent, the controlling action of the governor is still entirely due to the relay w. When an abnormal load is placed upon the motors, the current rises to such a value that, not only is the relay w held in its operated position, but the relay w<1> is also prevented from closing, thus causing the time between the closing of one contactor and the next to be longer. The remaining resistances are cut out in a similar manner. Fig. 2 shows a modified form of the governor W, the relay w being the same; the second relay w<2>, however, has only a single coil 9 arranged in the motor circuit, the latter relay controlling a shunt about the coil 2 of the relay w, which shunt contains a resistance 11. The dash-pot 12 of the relay w<2> is arranged to retard the upward movement of the core. and has an inwardly-opening check valve. The resistance 11 is so proportioned that, when the current of the motor circuit rises too high, sufficient current flows through the coil 2 to hold the relay w up, thereby preventing the cutting out of more resistance while the current remains too high.