Automatic Voltage Regulator • 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 any motor/machinery will drop considerably. • When any new load is given to an un-regulated AC Generator, the V drop is more substantial V time
Automatic Voltage Regulator …Why do we need them? • Close control of generator volatge is required to prevent such dips in V. • This control is achieved by an Automatic Voltage Regulator (AVR) • The real need of the AVR is to deal with the voltage dip following the sudden connection of extra load and to restore the rated Voltage without undue overshooting and regeneration(i.e. volatge hunting)
Automatic Voltage Regulator How does it work? V time • There are two stages that follow when the extra load is connected. • Transient Stage(followed by recovery) • Steady state condition • Response time for restoration within 3% of voltage dip is 1.5seconds • Steady state voltage regulation at any p.f. within rated p.f. and unity p.f. Is +/-2.5%
Automatic Voltage Regulator How does it work? There are three basic parts to an AVR Error detecting element Correcting Element Stabilizing Element
Automatic Voltage Regulator Block Diagram
Automatic Voltage Regulator Block diagram • The AVR senses the DG output voltage and acts to alter the field current to maintain the output voltage at its set value • The 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 actual generator voltage. • This signal is compared with the set value at the COMPARATOR • The ‘error’ signal from the Comparator is used to control the excitation current through ERROR AMP. and CONTROLLER.