Electric motor starting circuit with gradually increasing power supply - has resistors corresponding to respective phase lines switched at rate according to required start=up curve

摘要

The starting circuit has n resistors (1-4) connected into each of the motor's phase lines and switched (5-8) in combinations each in series with the motor (13) by a control (9). The motor is started by gradually increasing the number of resistors that are switched in parallel with one another. The rate at which resistors are switched in is decided by the required start-up curve. A relay (12) short circuits the resistor network once the motor has reached the required speed. The resistors can be relatively small as each carries only a fraction of the total current initially. The circuit enables motors with high loads to be started with very fine regulation and small current variations.