| 摘要 |
PURPOSE: To detect abnormal state, e.g. disconnection of a secondary resistor or abnormal heating due to unbalance of secondary load caused thereby, in the early stage by constantly monitoring the unbalanced state of secondary current for each phase in the three-phase secondary winding output load circuit of a three-phase wound-rotor induction motor by means of a secondary current detector. CONSTITUTION: A secondary current detector for detecting the secondary current of each phase is fixed to the secondary wiring R, S, T being connected with the secondary terminal 2 of a three-phase wound-rotor induction motor 1. A secondary current detection signal is converted through a DC converter 7 into a DC signal which is delivered to a three-phase balance processing unit 8. The three-phase balance processing unit 8 determines the difference of DC signal between respective phases and operates the extent of unbalance of secondary current for each phase. When the extent of unbalance exceeds a preset upper limitΔiUL, of unbalance current, a decision is made that it represents an abnormal state, e.g. heating due to unbalance of secondary load, and the decision results are delivered to an alarm 9 where an abnormal alarm is displayed.
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