Automatic voltage regulator simplified (AVR)

Voltage dip

• Sudden load change (large motor starting) will cause a sudden load current surges or a dip in its output voltage this effect is usually known as "voltage dip."
• Similarly, sudden load removal(stopping of a large motor) will produce an "overvoltage" at the bus bar.

AVR

• (Automatic voltage regulator) kicks in after sensing the voltage fluctuation and adjust the excitation of the generator hence the output voltage of the generator
• AVR cannot control the amount of voltage dip but can influence the speed of recovery

Recovery time

• Time taken by AVR to recover the voltage drop or increase in generator output
• Too great a voltage dip with too long recovery time will cause a momentary flicker of light and have adverse effects on running motor and sensitive electronics.

Working principle of AVR-(Automatic voltage regulator)

AVR BLOCK DIAGRAM

AVR consist of

1. Voltage sensing unit-it senses the output voltage of the generator then rectifies and smoothen it into a low voltage DC in proportion to the generator output'
2. Comparator unit-The actual dc value is compared with a set of the reference value and an error signal is produced which is then sent to the amplifier
3. Amplifier unit-Error signal is amplified by this unit and is made suitable to drive the field circuit regulating the thyristor
4. Thyristor-Is a fast-acting electronic switch which is controlled by voltage signal at its gate terminal. It rectified and regulate the field current of the generator.

Additional components

1. Rapid response time with voltage stability
2. Fair current and reactive load sharing
3. Quick voltage build-up
4. over and under current alarm/trips protection

AVR design Factor

The system is designed in such a way to limit transient voltage dip to 15% for a specified sudden voltage change to a recovery time of 1.5seconds