AUTOMATIC VOLTAGE REGULATOR(AVR)

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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

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TYPES OF AVR

• 1.Single channel AVR
• Two controllers one is automatic and the other is
  manual
• Both the controllers are fed from the same supply

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• 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
The automatic voltage control system


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OPERATIONAL AMPLIFIER
GAIN
FEED BACK
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I N P U T
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2
OP AMP
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OUTPUT
REF
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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.

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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
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-50 V SUPPLY

• To power the regulator amplifier as well as the
  optional accessories such as manual follow up and
  power integral stabilizer

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Regulator auxiliary card

• 3 phase voltage from the generator PTs 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.

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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.

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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.

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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.

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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.