AVR in Island Condition
When the generator is in island mode which means it is separated from the grid and supplying electricity to a local load the AVR uses Voltage Mode.
Because there is no external voltage reference from the grid the generator must maintain a constant voltage under these conditions.
The AVR regulates the excitation to maintain the output voltage constant so it remains stable even when the load changes.
The priority in this mode is on sustaining voltage therefore reactive power (or) power factor management are not a priority.
AVR in Grid-Connected Condition
When the generator is connected to the grid it provides a reliable voltage reference.
In this condition, the AVR operates in PF/VAR mode controlling the generator’s reactive power output.
The generator must control reactive power in order to maintain the power factor and run in sync with the grid.
Reactive power that is not appropriately balanced might cause grid instability. As a result the AVR modulates excitation to regulate reactive power and ensure grid stability.
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