three phase motor to single phase supply

The motor may not start (unless some tricks are applied); but if it is already running, it may still continue to run even if one phase is lost.

In a motor, the rotor rotates due to the 3 Phase rotating magnetic field which is generated as a result of electromagnetic induction (Faradays law of electromagnetic induction for Induction motor). It needs to be understood that the motor cannot rotate without this rotating magnetic field. This magnetic field is generated as a result of the 3 phase winding (which are equal in magnitude and separated electrically by 120Deg in time) which are wound on 3 structures which are physically separated by 120 deg . These structures are called the stator. The 3 sets of stator winding generates a rotating field which interacts with the rotor condutors and produces a force (as per Lorenz law) which gneerates a torque to move the rotor and hence the shaft.

So when single phase supply is appled to a 3 phase motor, no rotating field is created and hence the motor shaft will not rotate. Normally for 3 phase motors, single phasing protection is provided which trips the motor in case of loss of any one phase.

as against the 3 phase motors, single phase motors has only one set of winding in the stator and this generates a stationary field in space but alternating intime. Here the net torque generated is 0 and hence the rotor does not rotate unless special means are applied to start the motor.These includes split phase, capacitor start, permanet split capacitor start and so on....

Rgds

does the motor winding will burn or will damage when a single phase supply is applied?

Possibly. It depends on what protective devices are present (e.g., fuses, circuit breaker, overload relay, phase loss detection relay).

If they have been set up correctly, the circuit protection device(s) will operate, disconnecting it.

If you apply single-phase voltage to a three phase motor at standstill, it would not start. If during the regular operation of the motor, if the motor is subjected to single phasing conditions, then be ready to loose the motor, unless you have an effective protection device in the motor feeder to protect the motor under such situations.

The answer is:

D. All of the above.

Dear Mr.ir,

The motor will not start, as single phase supply does not produce sufficient torque in one direction. It oscillates, and the inertia of the rotor is large and hence the motor will not start.

That is why for ceiling fans etc., condenser is provided to split the phase and provide sufficient torque. same may not be possible in 3 phase motor.

Humming noise, will be there, fuse may get blown or the circuit may trip, or else winding may get damaged.

DHAYANANDHAN.S