What will happen when the excitation to the field of a synchronous motor is disconnected while the motor is rotating?

What will happen when the excitation to the field of a synchronous motor is disconnected while the motor is rotating?

The machine will continue to run at synchronous speed due to reluctance torque (i.e. even when field winding or armature windings are disconnected). The rotor will remain in synchronism for a short time ie.. Variable reluctance motor behaves as similar to silent pole synchronous motor unexcited.

Why must a synchronous motor never be started when DC excitation is applied to the motor?

Why must a synchronous motor never be started when DC excitation is applied to the rotor? The motor will not turn and the induced voltage on the rotor can damage to power supply for the DC excitor. The synchronous motor is not an induction motor. It does not depend on induced current in the rotor to produce a torque.

What is role of DC exciter in synchronous motor?

Synchronous motor excitation refers to the DC supply given to rotor which is used to produce the required magnetic flux. This resultant air gap flux is established by the co operation of both AC supply of armature winding and DC supply of rotor winding.

When should the DC excitation be applied?

It works as a three-phase induction motor. As soon as the motor approaches the synchronous speed, the DC excitation is applied to the field windings.

What happens to the synchronous motor when the excitation of unloaded salient pole synchronous motor suddenly gets disconnected?

When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected the motor run as a variable reluctance motor. Reluctance torque is the torque generated because the motor is moving to a position where the reluctance seen by the armature flux is declining.

What happened to synchronous motor if only field is excited?

As the Field Winding is excited by AC source, an alternating / pulsating magnetic flux will be produced. The armature conductor at Stator will not see any change in flux due to backward rotating field flux and hence no EMF will be generated in the Armature Terminal of Alternator.

What is the impact when DC exciter of synchronous motor is over excite and under excite?

If DC field excitation of a synchronous motor is such that back EMF Eb is greater than applied voltage V, then the motor is said to be over-excited. An over-excited synchronous motor draws leading current. Therefore, if the field of the synchronous motor is overexcited then its power factor will be leading.

What happens when generator loss excitation?

When a generator loses its excitation, the rotor current decreases gradually and the field voltage slowly decays as dictated by the field time constant. As a final outcome, the generator starts to consume reactive power from the power system instead of supplying it.

Will happen if generator is under Excited?

Operation in over- and under-excited modes results, as a consequence, a greater heating of some elements of the generator, i.e. the stator and rotor windings, end zone of the stator core, etc.

What is the synchronous speed of a synchronous motor?

And the speed of the rotating magnetic field is called synchronous speed. So the rotor will rotate at synchronous speed if a magnetic locking is created between the stator field and rotor field. If we give DC supply to the field winding or rotor winding of the synchronous motor then the pole created in the rotor will be constant.

Why DC is used not AC for excitation of synchronous motor?

So if we give AC supply, the rotor will stop rotating after removing the prime mover. This was the reason Why DC is used not AC for excitation of Synchronous Motor. Why DC is used instead of AC for excitation of Synchronous Alternator?

How to create magnetic locking between stator field and rotor field?

If we give DC supply to the field winding or rotor winding of the synchronous motor then the pole created in the rotor will be constant. Now we can use a prime mover to rotate the rotor initially to create the magnetic locking between the stator field and rotor field.

How does dynamically induced EMF work in rotating machines?

In rotating machines (both generator and motor), Dynamically Induced EMF works not Statically induced emf. When the flux is constant and the conductor changes its position then the induced emf is called Dynamically induced emf.