Application of a variable-reactor/capacitor combination for reversing and controlling the speed of polyphase induction motors

By introducing a variable reactor paralleled with a fixed capacitor in one of the supply lines of a 3-phase induction motor, the speed and direction of rotation can be controlled, by controlling the value of the the external effective reactance. Applying the method of symmetrical components, both the starting and running performances of such a motor are analysed. If the external reactance is made to vary automatically with speed, this gives a method of controlling, and reversing with dynamic braking, the speed of the motor.