What does an under-excited generator do in terms of reactive power?

An under-excited generator plays a specific role in managing reactive power within a power system. When a generator operates in an under-excited state, it means that the field voltage is lower than the optimal level, leading to the generation of negative reactive power or the absorption of reactive power from the grid.

In this context, reactive power is essential for maintaining voltage levels within the power system, and the under-excited generator helps to stabilize the voltage by absorbing excess reactive power to prevent over-voltage conditions. This capability is crucial during periods when there is excess reactive power available, as it helps balance the reactive power flows and maintain system reliability.

In contrast, a generator that is excited would typically supply reactive power to the system, contributing to voltage support when needed. Understanding the behavior of under-excited generators allows operators to effectively manage the stability and reliability of the electrical grid.