could you explain briefly the reaction of an induction motor if one phase is out of phase?

Answer 1

It will "Dither" back and forth when it reaches the "missing" step signal.

If you want a more technical explanation email me 8-)

Answer 2

1. If the motor is stopped and one phase is out when you try starting, it will not run. It does not run because the two existing phases will oppose each other (cancel each other) and therefore the stator of the motor will only over heat. However if something was to turn the shaft of the motor in any direction (clockwise or anti-clockwise) the motor will start and operate at a lower capacity at same speed and everything. It would be able to operate at full load because one phase is out and therefore this will mean that the other two has to carry some addition load.

2. If the motor was running and one phase went out the motor will continue running in the same direction. However may overheat depending on the load it is carrying.

With two phases only the motor is like a single phase motor without a capacitor to give a phase shift and produce a rotating magnetic field.

I hope this helped.

Answer 3

The intuitive answer is that it would vibrate as if it were out of balance mechanically Graph the (assumed) three phases on the same coordinate system to get a visualization of this. Picture the ball in a ball vibrator or ball whistle. The vibration would not be that pronounced unless the offending phase was severely out of phase. Current draws will be unbalanced, also, of course, and in the extreme, will burn the motor out.

This is not the same as the phenomenon known as single phasing, where two phases are lost due to a broken wire or blown fuse.