4.9 EXCITATION
The field voltage and current may be specified by a dc generator driven by a motor or by the shaft a of turbine generator. These units are called exciters and the complete voltage controls system, including error detection and various feedback loops is called an excitation system or an automatic voltage regulator (AVR).
4.9.1 Exciter system block diagram
The following figure represents a simplified excitation system. The control input is Vref. Then Vref is raised while generator terminal voltage |Va| initially remains the same. Ve goes up, VF increases and |Ve| tends to increase.
A new equilibrium reached with a higher |Va|. If |Va| changes because of a change in load, we also get a correcting action (See Fig. 4.12)
Fig 4.11 ...
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