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Presented By:Rajarshi Ghose Dastidar.Roll no. 149

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Why do we need them???? It is known that Voltage(V) of a power supply

system must be maintained at a constant value.

Other wise the performance of anymotor/machinery will drop considerably.When any new load is given to an un-regulated

AC Generator, the V drop is more substantial

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Close control of generator voltage isrequired to prevent such dips in V.

This control is achieved by an AutomaticVoltage Regulator (AVR)

The real need of the AVR is to deal with thevoltage dip following the sudden connection

of extra load and to restore the rated Voltagewithout undue overshooting andregeneration(i.e. voltage hunting)

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There are two stages that follow when the extraload is connected.

Transient Stage(followed by recovery) Steady state condition

time

V

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How does it work?There are three basic parts to an AVR:

Error detecting element

Correcting Element

Stabilizing Element

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Block Diagram

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The AVR senses the DC output voltage and acts to alterthe field current to maintain the output voltage at its

set valueThe excitation voltage can be set by the hand trimmer

The VOLTAGE SENSING unit transforms down,rectifies and smoothes the generator output voltage.

This produces DC signal proportional to the actualgenerator voltage.

This signal is compared with the set value at theCOMPARATOR

The error signal from the Comparator is used tocontrol the excitation current through ERROR AMP.and CONTROLLER.

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