| 摘要 |
PURPOSE:To prevent a burnout defect from occurring at an inverter due to the resistor overheat by measuring a time of feedback power from an induction motor to flow to a resistor and breaking an electromagnetic contactor when it exceeds a predetermined time. CONSTITUTION:An inverter 13 which operates an induction motor 3 in an arbitrary frequency is composed of a power reactor 1, a power inverter 2, a resistor 4, a resistance controlling transistor 5, a rush current suppressing resistor 6, a driving circuit 10 of an electromagnetic contactor, a coil 11, a contact 7, a controller 8, a voltage detector 9, and a smoothing condenser 12. A coil 15 of an electromagnetic contactor B and its contact 14 are provided. Thus, power is fedback from the motor 3 to a DC side to charge the condenser 12 at the time of braking the motor 3, and the voltage across the condenser is raised. This voltage is detected by the detector 9. When its value becomes a predetermined value or higher, the resistor 4 is consumed by the controller 8. The time at this time is measured by the timer of the controller 8. If it is longer than the predetermined time, an abnormal signal is output to break the contactor B14.
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