Patent GB-722876-A (GB)
Title: Improvements in or relating to dynamic braking control systems for electric driving motors
IPC: B60L7/04
Filed: 1953-02-03
Abstract: 722,876. Control of D.C. motors. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Feb. 3, 1953 [Feb. 13, 1952], No. 2995/53. Class 38 (3). For dynamic braking, the armature A1 of one traction motor is loaded on to a series field winding SF2 of another motor whilst the armature A2 is connected across the series field winding SF1, and the two circuits so formed each comprise a controlling limit relay CR or LB. These limit relays are responsive to conditions which accompany a lower than desired braking current in their respective braking circuits and are operative to prevent the progressive reduction of braking resistance in both circuits unless a low current condition exists in both relays. The provision of two limit relays has the effect of preventing unwanted reduction of resistance in one braking circuit in the event of slipping of the motor in the other circuit, which may arise if a single limit relay is used to control both circuits. The limit relay calibration is adjusted in accordance with the position of a brake handle 207 which regulates a common rheostat 206 in series with the rate coils RC, RC', of the two relays. The acceleration operation is under the control of the relay CR, the rate coil RC then being regulated by a weightresponsive rheostat 205. When a master controller MC is moved to its first on position, line switches LS1 and Glare closed and the motors are connected in series with full resistance in circuit by means of a switch JR. A brake protective relay BP prepares for the subsequent energization of the dynamic braking circuits. During the series-connection operation of the motors a fieldshunting controller FC is maintained in its fullfield position. In the second position of the master controller, a resistor R' is short-circuited, and resistors R', R', are removed in steps by the sequential closure of switches 1-2, 3-4, 9-10, provided relays CR, BP, are closed. The closure of a transition switch J then removes a last accelerating-resistance R'. Movement of the master controller to its third position closes switches M, G, for connecting the motors in parallel, the switch J dropping out. The progression of the resistance-shorting contacts S3- S10 is then re-iriitiated after which the field controller FC is moved to its weak-field position due to energization of coil FC-SF, this movement being controlled by the relay CR. The return of the master controller to its " off " position sets up a weak coasting-operation dynamic-braking circuit connection for the traction motors with resistances R', R<SP>2</SP>, R', in circuit, the switches M, G, B1, being closed for this purpose. The field controller FC is under the control of a spotting relay SR during the coasting operation. Full braking is instituted by actuation of the lever 207 to close relay BR and to move the field controller to its full-field position. The braking resistance is then reduced in steps under the control of the relays CR and LB. Each of the motors shown may be replaced by a pair of motors which are permanently connected in series. Specification 660,414 is referred to.