Frequency and system damping assistance from HVDC and FACTS controllers

HVDC transmission systems have led the way in providing assistance to power system stability from a source other than a generator. Since 1972 when the Nelson River transmission entered service in Canada, the DC system controls have been used to modulate the DC power to help stabilize the power frequency at either end of the link and to dampen power oscillations between weakly connected areas of the AC system. The principles developed at Nelson River have not only continued to give good service, but also have been applied elsewhere. In India, DC connections between separate electrical areas have been built to encourage energy trading. The systems they interconnect are relatively weak. An example DC back-to-back project illustrates how suitable DC power controls can assist both frequency stabilization and damping of power oscillations within the AC systems. FACTS controllers can assist too. The static VAr compensator (SVC), though leveraging only reactive and not real power, can Increase the power transfer capability of an AC system by stabilizing the voltage. It is also possible to vary the voltage control setting to provide additional damping.