Automatic Voltage Regulators

As you may be aware that voltage produced in an alternator is function of speed in RPM and the magnetic field.

Since the frequency of AC power generated is fixed and decided by the speed of the prime-mover, such as diesel engine or turbine, the voltage is decided solely by the magnetic field

Demand of the magnetic field varies with the load in KW / MW and the power factor of the load. In any captive power station, the load and Power Factor are never stable and this variation greatly reflects on the output voltage of the alternator. Therefore, an AVR has to measure a sample of this voltage every 20mili-seconds and send a command to raise of lower the excitation current of time-based control to take care of some vital factors, such as intertia of magnetic fields of the alternator & exciter plus, reactive load current etc to maintain the voltage with acceptable limits - with our AVRs it is +/- 1.0%