OPEN PHASE DETECTION METHOD AND DETECTION DEVICE IN SLIP RING OF THREE-PHASE WOUND-ROTOR INDUCTION MOTOR

摘要

PROBLEM TO BE SOLVED: To provide an open phase detection method and device in a slip ring of a three-phase wound-rotor induction motor capable of preventing the motor from being burnt by generation of an overload current by detecting, on an early stage, a defect of contact with the slip ring with wear-out of a brush or an open phase caused by setting error or the like of the brush.SOLUTION: When detecting an open phase of a slip ring for a three-phase wound-rotor induction motor in which phases of a three-phase secondary-side winding output line and a secondary resistor are connected via the slip ring and a brush which is in contact with the slip ring in a slidable manner, current values of phases are measured mutually between the slip ring and the secondary resistor, an unbalance factor of the measured current values is calculated and in the case where the unbalance factor does not satisfy a predetermined condition, an abnormal signal is outputted.