Under the operations of poly phase induction motor sometimes breakage of one phase is realized because of many factors. The question that arises under such a scenario is whether the motor will continue to operate or not? Providing a limit of 57.7% not to be exceeded by the load the motor will still operate. It is also mandatory to maintain the same temperature allows same temperature rise. On three phase induction motors carrying rated load.
Talking about wound rotor induction motor a breakage in one phase will not allow the operation of the motor because of the high speed. But if the speed can be monitored under successful conditions before opening a circuit the operation of the motor is possible under reduced load.
The effect of operating condition is examined when the load increases. Under this condition the torque also increases subsequently till the time it reaches the maximum torque value.
If you increase the load further, the rotor will come to stand still position as the driving torque decreases with the falling speed.
Unbalancing of supply voltage effect:
Generally the unequally heating under the operating conditions is realized when the supply voltage is unbalanced. Since it produces rotating field that response to non uniform rate and strength which results into unbalanced currents in the winding of stator.
Line frequency and line voltage variation effect:
The major componance of operating conditions like starting current, full load current, starting at maximum torque long with required temperature made of the various parts of the motor of the machine are affected by any variation in supply frequency and voltage resulting into unbalancing and un satisfactory results.