When a three-phase motor is operating and loses one of its phase then, the motor will continue to operate at reduced speed and experience high vibrations. The current through its starter winding will also increase considerably in its remaining connected phases causing an internal overheating of the motor components and overloading that may result costly damage.
The damage to the three phase motor depends upon the current through the winding as well as load connected to the motor. A lightly loaded motor can run for a long time after losing a phase but heavily loaded motor may burn immediately or within few seconds. Therefore, OLR (over-load relay) is used in three phase motor to trip the supply to the motor when current rises a predetermined value .
Conclusion
Hope, you have clearly understand what happen when one phase of three phase motor is lost. Make sure to leave your opinion and suggestion about this post in the comment section below