Describe the effect of change of excitation and mechanical input of an alternator
Answers
Exciter can be of three types DC exciter, AC exciter and Static exciter.
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
energised through a permanent magnet AC generator, the three-phase output of which
is converted to DC through rectifiers. Example of DC excitation system is IEEE type
Limiting and
protecting
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Power
System
Voltage Exciter
Regulator
Generator
Voltage
transducers
Power system
stabilizer
Rate
Feedback
4.2
DC1A [1], [2]. 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 replaced with electronic
regulators.
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 converted to DC through rotating rectifiers, as the armature is now rotating at the
main generator rotor speed, and the output is directly connected to the main field
winding. The filed of the AC exciter generator itself is energised through a pilot
permanent magnet AC generator whose three-phase output is converted to DC
through rectification. Example IEEE type AC1A.
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. Example IEEE type ST1A