If the field of a synchronous motor is under excited, then the power factor will be lagging and it acts as an inductor. If the field of a synchronous motor is overexcited, then it acts as a synchronous capacitor and the corresponding power factor will be leading.
What happens when a synchronous motor is under Excited?
If (Ef=V), the synchronous motor is said to be normally excited. Under this condition, the reactive power of the motor is zero (i.e., Q = 0), that is the motor is neither absorbing nor delivering reactive power. Thus, the power factor of the motor is unity.
How synchronous machine does behave in under excitation?
Synchronous motor: … 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. Leading power factor: If field excitation is such that Eb > V the motor is said to be over-excited and it draws leading current.
How does the change of excitation over excited or under excited affect the synchronous motor?
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.
How do synchronous motors control excitation?
The excitation system can be as simple as a fixed dc power supply connected to the field of the synchronous motor or, with additional sophistication, an automatic controller can be provided with var/power factor control or voltage regulation.
What is over excited and under excited?
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..
When excitation is increased the synchronous generator operates at?
In synchronous generator, inverted V curve is drawn between field current on X-axis and power factor on Y-axis. At critical excitation the power factor is unity. If excitation is decreased, the generator operates at leading power factor and if excitation is increased, the generator operates at lagging power factor.
What are over excitation and under excitation of a synchronous generator?
The over-excitation limiter protects the generator against over-temperature caused by high field current for long time. Under-excitation limiter prevents the decrease of generator field current to the values lower than the stability margin or the thermal limit of end side of the stator core.
When load on an over excited or under excited synchronous motor is increased rate of change of its armature current as compared with that of power factor is?
V curve of synchronous motor:
When the load on an over-excited or under excited synchronous motor is increased, the rate of change of its armature current as compared with that of the power factor is less and the same can be observed by using v curves as shown below.
What will be the power factor when the synchronous motor is over excited?
If the field of a synchronous motor is overexcited, then it acts as a synchronous capacitor and the corresponding power factor will be leading. A synchronous motor running with no load will lead the current i.e. leading power factor like a capacitor.
Why does synchronous motor runs at synchronous speed?
Because of the magnetic coupling between the stator poles and rotor poles the motor runs exactly at synchronous speed.
Why synchronous motor is doubly excited?
A synchronous machine is called a doubly excited machine because both its rotor and stator are excited. To achieve magnetic locking between stator and rotor, double excitation needed. The stator of 3 phase synchronous motor is excited with a 3-phase supply while rotor is with DC Supply.
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 do you excite a synchronous generator?
To excite the field winding of the rotor of the synchronous machine, direct current is required. Direct current is supplied to the rotor field of the small machine by a DC generator called Exciter. A small DC generator called Pilot Generator supplies the current to the Exciter.
What are the special application of an overexcited synchronous motor?
Application. An over-excited synchronous motor has a leading power factor. This makes it useful for power-factor correction of industrial loads. Both transformers and induction motors draw lagging (magnetising) currents from the line.