Reactive Power Flow and Control
The utility companies operate with an agreed voltage level at inter-tie connections, and provide for their own reactive power compensation to meet the requirement. It can be said that there are no true hierarchical structures in terms of reactive power flow. Static var controllers are ideally suited to control the varying reactive power demand of large fluctuating loads and dynamic overvoltages due to load rejection and are used in high-voltage dc (HVDC) converter stations for fast control of reactive power flow. Synchronous generators are primary voltage-control devices and primary sources of spinning reactive power reserve. A synchronous condenser provides stepless control of reactive power in both under-excited and overexcited regions. Synchronous condensers have been used for normal voltage control, HVDC applications, and voltage control under upset conditions with voltage regulators. The arrangement provides discrete leading vars from the capacitors and continuously lagging vars from thyristor-controlled reactors.