PMG Exciter in Generator

The PMG is not alone. It provides the Voltage Regulator with a steady Independent power that it will use to vary the excitation of the Pilot exciter, which in turn will provide the variable current to the Main Field.

Normally, this power is taken from the Main Generator Stator windings and, therefore, will depend a lot on what is going on on the load side:

- If harmonics are present, they will probably affect the outcome of the AVR,

- If a huge demand (relative to the size of the Alternator Capacity) is made by the load, the voltage output can be depressed for a very short time or for a not-so-short time(?). This will affect the supply to the AVR. This in turn can create a snow ball (or chain reaction) that will further depress the voltage output and so on until there might not be any remanent magnetisme to restart the chain reaction in the opposite direction.This is a rare occurence but can happen and did happen ...

- A PMG will allow the alternator to provide the required Short circuit or Fault current no matter how big is the load or the fault as well as make the excitation circuit free from any harmonics or parasitic waves due to the load.

- This setup is costlier but has these advantages if required.