Hydro-Quebec multiple SVC application control stability study

A report is presented on the SVC (static VAR compensator) control stability studies undertaken as part of an overall system improvement project. It is shown that for an all-shunt network, a regulator setting of T_r=0.5 s would be stable for many contingencies, but some contingencies would require gain-supervisor action and transfer-trip automatisms to ensure system security. The transfer-trip automatisms would be complex and require much study to identify. Thus, from the perspective of SVC voltage regulator stability, the all-shunt option is the least desirable. For a mostly series network, a regulator setting of T_r>0.25 s provides good stability margin for all system contingencies. This means that system security is not dependent upon a complex set of transfer-trip automatisms. A few new design considerations for the power system have been identified, due to adding series compensation. The major new phenomenon is a low-frequency oscillation between shunt reactors and the series capacitors, which has very little natural damping. The SVC voltage regulators will decrease the damping of these modes, and may cause them to become unstable. To insure against such instability, it is proposed that high-pass filters with a break frequency of 20 Hz be applied to all SVCs