Design of a special protection system to maintain system security at high import

Special protection systems (SPS) are widely used to enhance power system performance due to their relative low cost and ease of implementation when compared to alternatives such as transmission facility additions. Special protection systems are particularly valuable to mitigate the results of very low probability but potentially highly disastrous events. SPS may be local, system wide or involve interconnected power systems. SPS can cover single or multiple contingencies and are often dedicated to a specific purpose. For example, BC Hydro has an SPS scheme that has been specifically designed to increase export capability to the United States. The need for SPS is dependent on anticipated and recognized problems. Power system planning studies, including load flows and dynamic studies, are often used along with power system history to determine need. Even without an anticipated problem, there is often a need for SPS to cover periods where power system elements are out of service. It is important that the studies and the consequences of whatever action is taken be well understood [E. O. Schweitzer et al., October 1997]. In this paper we describe complete design requirements of an SPS system for practical application within power system of Saudi Electric Company.