Electric power saving operation of the hysteresis motor using short-duration overexcitation

The hysteresis motor produces the torque by magnetic hysteresis. The short-duration overexcitation of the hysteresis motor running at synchronous speed reduces the stator current and increases the pull-out torque at the same time. This excellent effect after one-time overexcitation lasts theoretically forever. However, the sudden changes of stator voltage or load torque reduce and vanish it. The duration time of the effect after one-time overexcitation has not been clear in the continuous operation without stator voltage or load torque changes. We used the three-phase balanced voltage source and measured the duration time after one-time overexcitation under no changes of the stator voltage and load torque. It was found that the effect by one-time overexcitation lasted for two weeks of the experimental period. It seems that the effect will last forever. It is clear that electric power saving operation of the hysteresis motor using short-duration overexcitation is quite useful.