Which of the following is categorized as a static reactive reserve source?

A static reactive reserve source is characterized by its ability to provide reactive power support in a stable manner, which does not fluctuate significantly with changes in system conditions. When evaluating the correct choice, a static VAR compensator in automatic mode fits this definition perfectly.

This device operates by adjusting the reactive power in response to the system's voltage levels and demands, allowing it to stabilize voltage without significant dependence on dynamic conditions or inherent system changes. It helps maintain the voltage profile of the system by providing or absorbing reactive power almost instantaneously, yet remains classified as a static source because its outputs can be predetermined and controlled without relying on moving parts or real-time dynamic adjustments that characterize dynamic sources.

In contrast, while capacitor banks with automatic control can also be considered static support sources, they typically operate based on preset conditions. They are contingent on operational thresholds and are generally considered to be an asset rather than a reserve. Dynamic reactive power support differs because it deals with real-time adjustments and responses, which can fluctuate significantly. Shunt reactors primarily serve to absorb reactive power and stabilize voltage but are also not categorized as reserves in the same context as a static VAR compensator operating in automatic mode.