Exciter Systems

Exciter system is designed to control the applied voltage, and thus the field current to the rotor, which in turn gives control of generator output or terminal voltage. Subsequently this is what provides reactive power and power factor control between the generator and the system.

Excitation response time must be fast so that the automatic voltage regulator can control the generator during system disturbance or transient in which rapid change of excitation are necessary.

Type of excitation systems

Rotating.

The basic kind of rotating exciters are motor or shaft driven and separately, self excited or bus fed system. The basic configure is a stationary armature and rotating field.

The ac output of the alternator is rectified by stationary diodes physically located off the generator and fed to the main rotor slip ring as dc current

Static

In static exciter, an external source of power is used to supply ac power to an excitation transformer. The transformer output is fed to a three phase controlled rectified bridge (SCR=silicone controlled rectifier) for conversion to dc.

The required generator field voltage is obtained by properly controlling the thyristor firing as in the rotating exciter.

Brushless

Brushless exciter consists of high frequency ac generator with a rotating fused diode assembly, a static voltage regulator for excitation control and a transformer power supply. The exciter is generally attached as an extension of the generator shaft.

Rectifier components are mounted on the diode wheel assembly, or sometimes they are housed inside the shaft. A three phase transformer, backed up by the station battery for initial field flashing support and momentary fault current support, power and regulator.



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