| 摘要 |
PURPOSE:To protect a motor by calculating power factor through detection of current variation and voltage variation then judging based on the current variation and the power factor variation whether the motor is running with no load. CONSTITUTION:When a motor 8 is running with heavy load close to rated load, values of current and power factor set in a setting section 10 are compared at a judging section 11 with those obtained when the motor 8 is running, and if there is a difference a signal is provided to an output circuit section 12 from which a stop signal is fed to a stator 4. During low load operation, no-load operation is detected based on the variation of current. By such an arrangement, no-load operation can be detected for both low load and heavy load operations resulting in protection of the motor 8. |
