Safety start
AssigneeAuckland Uniservices Limited
InventorsJohn T Boys, Udaya K. Madawala
Life of this patent
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Abstract
A starting circuit for an induction motor is provided whereby a stationary rotor flux is established then a stored charge supplied to a motor winding in order to provide a starting torque. Before applying a mains power supply to the motor after the starting torque has been applied, a back EMF is sensed, directly or indirectly, to provide an indication that the rotor is turning before the mains supply is connected to the motor. This provides a reliable and simple method for ensuring that a mains supply may be safely connected to the motor.
Claims16
A starting circuit for an electric induction motor having a plurality of phase windings to be energised from an electricity supply, the phase windings having at least three terminals for connection to the supply, the circuit comprising
- a first switching means arranged and controllable to conduct a uni-directional current derived from the supply between a first combination of the terminals to establish a stationary rotor flux in the rotor of the motor,
- a second switching means arranged and controllable to supply a starting current between a second combination of the terminals selected to generate a stator flux at an angle to the stationary rotor flux,
- switch control means to control the first switch means to establish the stationary rotor flux and to control the second switching means to initiate supply of the starting current to provide a starting torque for the motor, and
- back EMF sensing means to sense a back EMF generated by rotation of the rotor to sense whether the rotor has turned sufficiently to be in a condition to connect the motor to the supply.
A method of starting an electric induction motor having a plurality of phase windings, the method comprising the steps of
- delivering a uni-directional current to the motor to establish a stationary rotor flux in the rotor of the motor,
- delivering a starting current to the motor to produce a stator flux at an angle to the stationary rotor flux to produce a motor starting torque,
- detecting the back EMF produced by rotation of the rotor in response to the starting torque, and
- determining whether one or more characteristics of the detected back EMF indicates that the motor is in a condition for connection to an operating supply.
Any novel feature or combination features disclosed herein.
Dependencies are inferred from the claim text.