Design of dependable and secure system integrity protection schemes

System Integrity Protection Schemes (SIPS) are traditionally designed with an emphasis on dependability. This ensures they operate when required to preserve system integrity and as a result, most SIPS are implemented as fully duplicated schemes. However, as the complexity and uncertainty of power systems increase, enhancing the security of SIPS becomes vitally important. This prevents spurious operations, which have a detrimental impact on system reliability. A procedure for designing SIPS that achieve an effective tradeoff between dependability and security is proposed in this paper. The proposed method uses fault tree analysis and the theory of minimal cut sets to break down the reliability analysis of the complete SIPS into the analysis of the individual operational phases of SIPS, which simplifies the analysis. Then, this study determines the minimum reliability requirements of each component, i.e. Mean Time To Failure (MTTF) and Mean Time To Fail Spurious (MTTF^spurious) and the optimum design of SIPS for realizing the desired level of dependability and security. It is illustrated using the Dinorwig Intertrip Scheme, which is located in North Wales and operated by National Grid (Great Britain transmission system operator).