GB490948A - Improvements in and relating to methods of dynamic braking of electric motors - Google Patents

Abstract

490,948. Control of A.C. motors, BRITISH THOMSON-HOUSTON CO., Ltd. Feb. 25, 1937, No. 5690. Convention date, Feb. 26, 1936. [Class 38 (iii)] Non-regenerative braking.-A squirrel-cage induction motor is braked by disconnecting it from the normal supply generator, connecting an impedance across its primary winding, and exciting it from a separate synchronous dynamo-electric machine at a gradually decreasing frequency. When a switch 16 is thrown from its left to its right-hand position, the motor is disconnected from the supply and impedance 17 connected across its primary windings 11. A machine 13 which normally operates as a synchronous condenser connected to the motor and improving the power factor remains connected to the primary windings 11 and excites the motor at a frequency which gradually decreases as the machine 13 runs down, Thus the motor is braked and the slip remains low throughout the braking period, excessive heating in the secondary 10, which has a low resistance winding, being avoided. The braking may bo controlled by varying the impedance 17 or the excitation of the machine 13. In a modification, Fig. 2 (not shown), the machine 13 is connected to an additional primary winding on the motor, and is provided with an adjustable mechanical brake whereby its rate of deceleration may be controlled. The machine 13 may not run during normal running operation of the motor but is self-started just before a braking operation. In a further modification, Fig. 3 (not shown), the machine 13 is loaded by a small adjustable speed motor, and supplies a tapping on the primary of the main motor. Specification 190,488, [Class 38 (iii)], is referred to.