GB748120A - Improvements in or relating to electric motor control systems - Google Patents

Abstract

748,120. Control of D.C. motors. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Nov. 19, 1954 [Dec. 7, 1953], No. 33563/54. Class 38(3) Relates to a series-parallel control system for an even number of series-wound motors, for example traction motors, which are adapted to be over-driven by the load to act as generators. In the arrangement shown, a first motoring position of a master controlled provides a connection with armatures 1-6, field windings F1-F6, and accelerating resistors R1, R2, R3, in a series circuit between the supplyline and earth. In this connection, and in all the subsequent connections, the accelerating resistors are on the highpotential side of the armatures and the field windings are on the earth side, so that the insulation requirements of the motor field windings are reduced. Further movement of the controller reduces the accelerating resistance, introduces field shunting, and provides the transition circuits for a series-parallel grouping of the motors. In this grouping, the resistors R1, R2, R3, are connected in parallel with each other and in series with a first motor circuit comprising armatures 1, 2, 3 and field windings F1, F2, F3. A second motor circuit is connected in parallel with the first and comprises the. remaining motor armatures and field windings. After reduction of the acceleration resistances, the final series-parallel grouping is attained in which three parallel circuits each comprise two series-connected motors. The accelerating resistors are again connected in parallel with each other between the supply-line and the motor circuits. To introduce dynamic braking operation, the 'master controller is moved backwardly, from the "off" position to the first braking-position whereby the line and powerearth connections are interrupted. The braking-connectios has three parallel-connected branches, the first branch comprising resistor R1, motor armatures 1, 2, 3, and field windings F4, F5, F6, of the other motors. The second branch comprises resistors R2, and the third branch armatures 4, 5, 6, and field windings F1, F2, F3. A terminal A2' is held at earth potential due to a high-resistance connection 73 to earth, and, since the motor voltages are all substantially equal, a corresponding point A6<SP>1</SP> is also near earth potential. This arrangement again reduces the earth-insulation requirements of the motor field windings. In the remaining braking operation controller-positions, the resistors R1, R2, R3, are cut out in suitable steps, the operative portions of the resistors R1, R3, being kept equal in order to maintain a balanced dynamic braking circuit.