| 摘要 |
Apparatus for protecting and starting a three-phase motor uses the three-phase field rotation torque produced by three voltage coils, connected to a three-phase power supply, spaced 120 degrees apart from each other, acting on an aluminum disk having a limited range of rotation. When a start button is pushed connecting the voltage coils in wye configuration, the tendency of the disk to turn is converted to an electrical signal for starting the motor. The apparatus prevents the motor from starting if phase energization is abnormal or phase rotation is not in a predetermined direction. The present apparatus also provides continuous monitoring of the motor with three-phase rotation torque produced by three current coils, which are connected in series with the motor and, in one embodiment, may be wound around the same cores as the voltage coils. The current coils generate torque tending to rotate the disk in the same direction as the torque generated by the voltage coils, thereby maintaining the motor in an energized condition, even after the start button is released. If a phase-failure or phase-reversing condition occurs while the motor is running, the invention deenergizes the motor before the motor overheats and an overload relay trips, thereby prolonging the useful life of the motor.
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