| 摘要 |
843,767. Control of several D.C. motors. ENGLISH ELECTRIC CO. Ltd. April 11, 1957 [April 17, 1956], No. 11616/56. Class 38 (3). If the wheels driven by either of the traction motors M1, M2 should slip, the coils of a relay WSR1 become unbalanced and the relay closes its contacts WSR1a to connect a tap on resistor 13 directly to the negative terminal of rectifier 17. This renders rectifier RT1 non-conducting whereby the motor-group M1, M2 operates only on half-wave rectification, so reducing the current drawn by the motors. When the slipping wheel regains adhesion, the voltage balance is restored, and the wheel-slip relay opens its contacts, again to provide full-wave rectification. The grids of rectifiers RT3, RT4, are similarly maintained normally at a positive potential with regard to their cathodes by connecting each grid to the positive terminal of rectifier 20 and each cathode to the negative terminal of the bridge rectifier. A wheel-slip relay WSR2 is associated with motor group M3, M4, and is arranged to render rectifier RT4 non-conductive in the event of wheel-slip on either of these motors. In an alternative arrangement, each wheel-slip relay blocks not only a rectifier associated with the group containing the slipping motor, but also the rectifier, associated with the other group, which is connected to the opposite end of winding 10b. This prevents D.C. magnetization of the transformer core. The wheel-slip relays may open with time-delay to allow a longer period for restoration of normal conditions. An overload relay OL1 closes contacts OL1a if the current through rectifier RT2 exceeds a predetermined value. This results in a negative bias being applied to the grids of both the rectifiers RT1, RT2. A similar relay OL2 is connected in circuit with rectifier RT4. The rectifiers RT1- RT4 may be connected in a bridge circuit, and the wheel-slip relays may be effective to render non-conducting the rectifiers of one half of the bridge circuit only. When the motors are connected in parallel, the wheel-slip relays detect unbalance in the current between pairs of motors. Wheel-slip may be detected by means of tachometer generators. |
