What is PMG and AREP excitation system in generator
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Answer Posted / suryaa
Electrical Power
Output
Sense
Main Stator Exciter
Stator
Exciter
Rotor
Mechanical
Rotational
Power Input
Diode
Bridge
Main Rotor
Set Reference
Output
AVR
Power
Auxilliary Coils
(Series and Shunt)
to give constant
power source
AVR14 – AREP
EXCITATION SYSTEM
The AREP excitation system improves the
voltage response of the generator during
transient load application, such as motor
starting. AREP also provides a sustained shortcircuit current for the operation of protective
devices. This option requires the standard selfexcited generator be replaced by a generator
that has been fitted with auxiliary AREP coils.
These coils provide excitation power to the AVR,
giving both shunt and compound (booster)
characteristics. Isolation of the excitation power
ensures that regulation is not affected by nonlinear distorting loads.
The Permanent Magnet Generator (PMG) is normally used
as a secondary exciter to supply constant voltage for an
Automatic Voltage Regulator (AVR). Because the PMG is
separately mounted on the generator shaft, the terminal
voltage will not affect the input voltage of the AVR, and it
can get stable energy without regard to the synchronous
generator.
• Improved transient performance
When the terminal voltage of a generator is reduced by appliying a significant load, the AVR input voltage is reduced
as well if a SHUNT excitation system is used. Therefore
sometimes the input energy is not enough for the AVR
to increase field current. However the PMG will provide
constant voltage for the AVR so that the field current can be
increased quickly to ensure the voltage dip is minimal and
remain within an acceptable range.
• Provide >300% sustaining short-circuit current
Under short-circuit conditions, it is necessary to sustain a minimum value of current in a sufficient time to ensure operation of
the system’s protective devices. Sustained short-circuit current
is achieved by the PMG excitation system.
• Increased non-linear loading ability
The non-linear load may produce harmonics for the generator
terminal voltage. These harmonics will affect AVR firing if the
AVR is supplied by terminal voltage. PMG is a separate generator, electrically isolated from terminal voltage, thus it can improve
AVR operation condition.
• Ensure remanence voltage to black starting
The permanent magnet mounted inside the PMG rotor can keep
a strong magnetic field for a long time. In generator black starting conditions, voltage can be built up by the PMG without
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