Patent GB-682139-A (GB)
Abstract: 682,139. Control of D.C. motors. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. March 8, 1951 [March 9, 1950], No. 5622/50. Class 38 (iii) A system for controlling the operation of a plurality of electric motors each having an armature winding and a series field winding comprises switching means for connecting the motors to a power conductor, switches for connecting the motors in predetermined combinations during motoring, additional switches co-operating with said switches to connect the motors in said predetermined combinations during regeneration, a controller having a speed control drum and a braking control drum, said drums jointly controlling the operation of said switching means and individually controlling the operation of said switches and said additional switches. A fraction control system having a main drum controller and a braking drum controller comprises motors having armatures 1-6 and series field windings F<SP>1</SP>-F.<SP>6</SP> Line switches L1, L2, and an accelerating resistor R1 are provided, an exciter E being used for separately exciting the motor field windings during regeneration. An exciter field winding EF is controlled by means of resistor R1, and resistors R<SP>3</SP>-R<SP>6</SP> provide stabilising- action during regeneration. A drum switch 39 is used for connecting the armatures of the motors to any one of a number of series and parallel combinations, a switch 40 being adapted to change the motor field windings from the series to the separately-excited connection. The braking drum controller, Fig. 2 (not shown) has a position which it occupies during normal motoring operation and in, which its contacts Bu, Br, only are closed. In addition, this drum has a special off-position regenerating-notch in which its contact Bw only is closed, as well as the usual notches for controlling the regenerative braking operation. The line-switch L1 cannot be initially energised when the braking drum is in its special offposition regenerating notch. However, once the lineswitch is actuated, it is held in, regardless of the position of the braking-drum, until the main drum controller is moved to its off-notch to open contact Mg. The first sixteen on-position notches of the main drum, Fig. 2 (not shown) are used for removal of the resistor R1, the switch 39 being in the position for series-combination of the motor armatures. In moving from notch 16 to notch 17 of the main controller the resistance Rl is restored and contact Mx closes to energise coil 39SP. The drum 39 is then moved through the first transition arrangement of the motor-combination during which motors 4, 5, 6, are first short-circuited, then disconnected, and afterwards connected in parallel with the motors. 1, 2, 3. When the main drum is being returned to its offposition after establishing regenerative braking in the series-parallel combination, the said series-parallel connection is not changed or interrupted until the main controller reaches its off-position. The coil 39P is energised by closure of contact Mz when the main drum is in the on-notches nos. 28 to 36. The switch 39 is then moved for parallel operation of the motors the full resistance R1 being re-inserted for the transition period. The short-circuited motor method of transition is again used, the final combination consisting of three pairs of motors connected in parallel. Energisation of the coil 39P is maintained whilst the main drum is being returned to the offposition after regenerative operation. The coil 40M of the change-over switch 40 is energised when the braking drum is at its normal off-position and the main drum is in any of its on-positions. The coil 40R is energised when contact Bw is closed by moving the braking-drum to its special off-position or any of its normal on-positions, and actuating the main controller from its off-position. To establish regenerative braking, the main drum is placed in its offposition and the braking-drum is advanced to its special off-position in which the line switches are held open. The main drum is then positioned for the desired motor-combination (viz. notch 1, 17, or 28). The braking-drum is thereupon moved to whatever notch is required to secure substantially zero armature current, the line switch L1 being closed and the field winding EF being energised at notch no. 1 of the braking-controller. The main controller is then advanced to remove resistor R1 and control the regenerated current. When changing to a different motor-combination during regenerative operation the braking-drum is moved to a position in which the motor armature current is substantially zero and the main drum is then returned to the off-position. The braking-drum is then moved to the special off-position notch and the main drum advanced to the first notch of the desired motor combination; after which the procedure is the same as described above. Interlocks consisting of cams and spring-pressed split-levers are provided between the shafts of the main and braking controllers. It is arranged that the braking-drum cannot be advanced from its normal off-position when the main-drum is out of its off-position. The main-drum may be moved from its off-position, however, after the braking-drum has been moved from its off-position, in which case the main drum will not lock the braking-drum even when the main drum is returned to the off-position unless the braking- drum is moved to its off-position. A second interlock prevents the braking-drum from being moved to an on-position whilst the main-drum is at its off-notch, that is, the braking-drum can only be moved between its normal off-notch and the special off-position referred to above. It is also required that the main drum must be at its off-position before the braking- drum can be returned from an on-position to either of its off-positions, or before it can be moved from the special to the normal off-position. Once the regenerative-braking connections have been completed the main drum is prevented from moving directly to a higher-speed motor-combination group.