What happens 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 happens when synchronous generator is over excited?

An over excited synchronous generator generates reactive power as its excitation is increased (over excited ) means the magnetic field strength of the stator winding of the synchronous generator is now increased more by increase in DC excitation , so in such a case more flux will induce in stator winding and when this …

When synchronous motor is under excited that means?

A synchronous motor is capable of operating at all types of power factor i.e. either UPF, leading, or lagging power factor. Lagging power factor: If field excitation is such that Eb < V the motor is said to be under excited and it has a lagging power factor.

Will the synchronous motor starts with field excited only?

Synchronous motors are inherently not able to self-start on an AC power source with the utility frequency of 50 or 60 Hz. Once the rotor reaches a speed close to the synchronous speed (>95\%) through some starting means, the field winding will be excited, so the motor locks into synchronization.

What happens when excitation of synchronous motor fails?

When the excitation fails the power delivering capacity of machine suddenly reduces. So the mechanical power input is greater than electrical power output. This imbalance will accelerate the rotor and force it to run above synchronous speed. The circulating currents and then magnetic field are created.

What is over excited and under excited generator?

Over excited means more voltage is fed back to produce more flux as oppose to under excite which means less voltage thus producing less flux.. In synchronous motor being over or under excited does not have much effect as it is automatically being regulated by a counter acting flux producing slips..

Why synchronous motor is excited?

CASE 3: If the field current is more than the normal field current, motor is said to be over excited. This excess field current produces excess flux (flux set up by DC supply rotor winding – resultant air gap flux) which must be neutralized by the armature winding. This is called V curve of synchronous motor.

Why exciter is essential for synchronous motor?

The exciter provides the power to the electromagnets that form the poles on the rotor that in turn follow the rotating magnetic field from the system.

How is a synchronous motor excited?

Synchronous motor excitation refers to the DC supply given to rotor which is used to produce the required magnetic flux. When the synchronous motor is working at constant applied voltage V, the resultant air gap flux as demanded by V remains substantially constant.

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

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 is meant by under excited synchronous motor?

An under excited synchronous motor has a lagging power factor. Over Excited Synchronous Motor If DC field excitation of a synchronous motor is such that back EMF E b is greater than applied voltage V, then the motor is said to be over-excited. An over-excited synchronous motor draws leading current.

What is the leading power factor of a synchronous motor?

Standard synchronous motors are available rated either 100\% or 80\% leading power factor. At 80\% power factor, 60\% of the motor-rated kVA is available to be delivered to the system as reactive kVA for improving the system power factor. This leading reactive kVA increases as load decreases.

What are the advantages and disadvantages of synchronous motor?

The advantages of the synchronous motor are the ease with which the power factor can be controlled and the constant rotational speed of the machine, irrespective of the applied load. Synchronous motors, however, are generally more expensive and a d.c. supply is a necessary feature of the rotor excitation.

What are the V curves of synchronous motor?

The plot of power factor against the field current of synchronous motor is known as V curves of synchronous motor. The V curves at different power inputs are shown in Figure. With an increase in load, the V curves get shifted upwards, as shown in Figure.