What is the effect of under excitation and over excitation on the synchronous motor?
Conclusion: An overexcited synchronous motor operate at leading power factor, under-excited synchronous motor operate at lagging power factor and normal excited synchronous motor operate at unity power factor.
What happens if generator is under Excited?
Under excitation occurs when less than design current is supplied to the field winding. The net result is that magnetizing current for the machine must come from the load. The pullout strength between rotor & stator is reduced, which makes the machine unstable under transient load conditions.
What happens when synchronous motor is under Excited?
Synchronous motor: 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.
What happens when excitation of synchronous generator fails?
If the excitation of the generator fails, suddenly there will be no more magnetically locking between rotor and rotating magnetic field of stator. But still the governor will supply same mechanical power to the rotor due to this sudden magnetic unlocking; the rotor will be accelerated beyond the synchronous speed.
Why do synchronous generators need excitation?
Excitation in an electrical machine means production of magnetic flux by passing current in the field winding. In order to excite the field winding on the rotor of the synchronous machine the direct current is required.
How an over excited synchronous machine improves power factor?
By varying the DC excitation of the motor, the power factor of the motor can be varied widely. Overexcited synchronous motors operate at leading power factor and provide reactive kVAR-like capacitors. This yields an improved power factor for the power-supply system.
What is the cause of over excitation in generator?
Over excitation happens when the regulating circuit puts too much power into the field, causing over voltage and excessive current.
What is excitation system of a synchronous generator?
The word Excitation means the production of flux by passing current in the field winding. 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 will be the power factor when the synchronous motor is over excited?
leading
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.
What is excitation in synchronous generator?
What happen if synchronous generator is behave as induction generator?
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. The machine will start to generate power by induction and hence will work as Induction Generator.
What are the effects when exciter for alternator fails?
Again when loss of field occurs due to failure of exciter but not due to problem in the field circuit (field circuit remains intact) there will be an induced current at slip frequency in the field circuit. This situation makes the relay to pick up and drop off as per slip frequency of the induced current in the field.