What causes over excitation in generator?

What causes over excitation in generator?

If the voltage is trending higher, the regulator reduces the excitation, and if it trends lower it will increase the excitation. Over excitation happens when the regulating circuit puts too much power into the field, causing over voltage and excessive current.

Why a field current excitation is necessary for the alternators operation?

Without the excitation system the AC alternator would have no way of building its voltage as it starts to rotate, nor would not be able to regulate its voltage to the pre-set nominal level while running at its rated speed. So, without an excitation system, an AC alternator would be useless for its purpose.

Why excitation system is required?

The main requirement of an excitation system is reliability under all conditions of service, a simplicity of control, ease of maintenance, stability and fast transient response. The amount of excitation required depends on the load current, load power factor and speed of the machine.

Is the rotor excitation current AC or DC?

1. Magnetic flux: Magnetic circuit is placed in the rotor. Required magnetic flux is created in the rotor by supplying DC (Direct Current) to the rotor circuit. This Direct Current (DC) is called excitation current.

What is excitation voltage in generator?

An excitation voltage or current is the amount of electric energy ( D.C ) feed into the field winding of an alternator rotor to produce magnetic flux / field. Conventionally a D.C generator synchronized and coupled with the alternator on the same shaft is used for this purpose.

What is excitation current in power system?

Excitation current is the current flowing into the high voltage winding with the low voltage side open. This current should be proportional to the No-load acceptance test but with the difference resultant from the use of test voltages different from nominal values.

How is field excitation generated in DC generator?

For D.C generators or exciter the field excitation is generated only when the poles posses some some residual magnetism. Upon rotation of generator shaft the residual magnetism generate a small voltage in the armature. This lead to generate even more field strength and so more output voltage and so on and so on. Q.

How is current induced on an exciter in a generator?

The current is induced onto the stator for load output. The biggest drawback to this system is the AVR is impacted by the load the generator is powering. When the load increases the voltage begins to decrease and the AVR must provide more current to the exciter to support the demand.

Why is an excitation system not allowed in a power plant?

This is due to the voltage drop / dip in the winding of a generator. An unregulated excitation system would be thus unacceptable / UN-feasible for maintaining power output at variable load. On ship and land based plants there is a regular fluctuation in the load demand; if remained unregulated this would destabilize the generators.