In this article we will discuss about the types of exciter . we will also know about the ac and dc exciter.
Excitation system provides the current required for the field winding of a synchronous generator to produce the rated terminal voltage at the generator terminals.
Types of Exciter
Exciter can be of three types:
(1) DC exciter
(2) A.C. exciter
(3) Static exciter
(1) DC exciter
In this type of exciter a separately or self excited DC generator driven by a motor or connected to the same shaft as that of the main generator rotor is used. In case of separately excited DC generator the field winding of the DC generator is energized through a permanent magnet AC generator, the three-phase out of which is converted to DC through rectifiers. This type of excitation was widely used up to 1960 but now-a—days AC excitation or static excitation is being used. For older generating stations where DC excitation is still used the voltage regulator alone is replace with electronic regulators.
(2) AC exciter
In this type of exciter the AC generator whose armature is mounted on the same shaft as that of the main generator, with its field stationary, is used for supplying field current to the main generator field winding. The output of AC exciter generator is converting to DC through rotating rectifier, as the armature is now rotating at the main generator rotor speed, and the output is directly connected to the main field winding. The field of the AC exciter generator itself is energized through a pilot permanent magnet AC generator whose three-phase output is convert to DC through rectification.
(3) Static Exciter
In this exciter the output of the main synchronous generator is converted from AC to DC through static rectification and then the output is supplied to the main generator field winding through slip rings.
4. Voltage transducers
Voltage transducers measure the three-phase terminal voltage through potential transformed and convert them and filter them to DC which is compared with the reference voltage and the error signal is used to control the main exciter field winding current through the exciter.
5. Voltage Regulator
The voltage regulator can be of magnetic amplification type or digital amplification type. At present digital amplifies the error signal generated by voltage transducers and the output of the voltage regulator is used to control the pilot excitation there by controlling the main generator field winding through the DC/AC excitation system
Limiting and protection circuit:
Limiting and protection circuits are used to limit main generator field winding current over excitation, udder excitation, terminal voltage, volts-per Hertz etc.
Problems in D.C.excitation system:
(1) Large time constant
(2) Communication difficulties.
Hence these are basic types of exciter and their working . If you will find any incorrect in above article you must comment below in comment box.