AUTOMATIC VOLTAGE REGULATOR(AVR)


Automatic voltage regulator (AVR) maintains the
Generator terminal voltage at a given value
automatically by changing the excitation current to
the Generator field.
The AVR supplies the required D.C. to the Generator
field depending on the load, power factor etc. to
maintain a constant terminal voltage.
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CONTROL SYSTEMS OF AVR
1. Auto control
2. Manual control
2
TYPES OF AVR
1.Single channel AVR
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
Two controllers one is automatic and
the other is manual
Both the controllers are fed from the
same supply
3
2. Dual channel AVR system
 One automatic voltage controller and
one manual controller
 Different power supply, gate control
and pulse amplifier units for each of the
controllers
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3.Twin channel AVR system

Two automatic voltage regulators
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Function of AVR



compares the Generator terminal
voltage with a preset reference voltage.
If the Generator terminal voltage is less
than the reference voltage, the AVR
increases D.C. voltage across the
Generator field.
Maintaining the constant voltage as per
the setting.
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EXCITATION AS A CLOSED LOOP CONTROL SYSTEM
If
Synchronous
Vg
Generator
Grid
Excitation
System
The automatic voltage control system
OPERATIONAL AMPLIFIER
FEED BACK
GAIN
7
I
N
P
U
T
6
2
OP AMP
3
REF
OUTPUT
4
Block diagram of AVR
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AVR inputs


Generator voltage feedback signal
Generator voltage reference
AVR provides the following functions
and signals


Summing and amplification of signals to
provide the exciter rectifier firing angle
control signal.
A signal for manual follow up.
10
AVR Action



Two inputs are of opposite polarity.
When the magnitudes are equal, the
net input is zero.
When unequal-the error is amplified
and reversed to obtain a correction
signal which goes to the
GPG(gate pulse generator)
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AVR CIRCUIT
12
+-50 V SUPPLY

To power the regulator amplifier as well
as the optional accessories such as
manual follow up and power integral
stabilizer
13
Regulator auxiliary card

3 phase voltage from the generator PT’s
are stepped down and applied to the
regulator auxiliary card which converts it to
ripple free dc voltage suitable for the input
of regulator amplifier.
Balance Voltmeter

A 30-0-30 V dc voltmeter is connected
across the output of regulator amplifier to
read the magnitude and polarity of the
output voltage of OP-AMP at any instant.
AVR Voltage Setting

From the +-50 V source ,-50 V is applied
and taken across a motorized
potentiometer which can be operated from
the control bench board. The variable
output from the pot. is applied to the
input of the regulator OP-AMP.
Manual Voltage Control


In the absence of AVR the voltage can be
manually controlled.
The stabilized 15 V from the MPS is
applied across a second potentiometer.
The variable output goes to the GPG
together with output of the regulator
OP-AMP.
MANUAL FOLLOW UP

When there is a noticeable output from
the regulator OP-AMP, depending on its
polarity, either of a pair of relays is
automatically closed to drive the manual
potentiometer motor in the required
direction.