Electric motor starting circuit
AssigneeEA Technology Limited
InventorsStephen Paul McDonald, Geoffrey David Baines, John Talbot Boys
Life of this patent
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Abstract
An electric induction motor can be given a kick start without excessive current drain on the supply by first connecting a unidirectional supply to a winding of the motor to build up a stationary rotor flux and then applying a starting current to another winding of the motor to produce a stator flux at an appropriate angle (between 0.degree. and 180.degree.) with the stationary rotor flux. Once the motor has begun accelerating the normal running supply can be connected. This starting current may be derived from a capacitance which is charged up during the period of establishing the stationary rotor flux.
Claims17
A starting circuit for an electric induction motor having a plurality of phase windings to be energised from an electricity supply, said phase windings having at least three terminals for connection to the supply, the circuit comprising first switching means arranged and controllable to conduct a unidirectional current derived from said supply between a first combination of said terminals to establish a stationary rotor flux in the rotor of the motor, second switching means arranged and controllable to supply a starting current between a second combination of said terminals selected to generate a stator flux at an angle between 0.degree. and 180.degree. to said stationary rotor flux, and switch control means responsive to a motor start signal to control the first switch means to conduct said unidirectional current for a period sufficient to establish said stationary rotor flux, and to control the second switching means to initiate supply of said starting current at the end of said period to provide a starting torque for the motor.
A method of starting an electric induction motor having a plurality of phase windings, comprising delivering a controlled current to the motor to establish a stationary rotor flux in the motor, and then delivering a starting current to the motor to produce a stator flux at between 0.degree. and 180.degree. to the stationary rotor flux to produce a motor starting torque.
Dependencies are inferred from the claim text.