WHAT IS THE EFFECT OF UNDER VOLTAGE ‎ON 3 PHASE INDUCTION MOTOR ?‎

this issue depending on the actual absorbed load torque, for example if the load is half of FL motor torque the motor will run w/o problem.
it's like variable voltage control for AC motor.

Over Load, because the motor power is constant, if voltage goes down, current goes up.

Motor gives abnormal sound and not work on its full load

The effect of under volatge on three phase motor is running not normally because the power motor not optimal so if the load increase can effect to the motor overload (trip)

Over current, because the motor consume the same power

It causes the currents to be increased which means will heat the winding coils.
a good protection should trip the motor in case of under voltage