Determining the reliability requirements of system integrity protection schemes

System Integrity Protection Schemes (SIPS) are one of the most widely used solutions to the challenges in operating and protecting large and highly complex power systems. Therefore, it must be ensured that their performance meets the reliability requirements of electrical utilities. This paper suggests the use of Safety Integrity Level (SIL) for determining the range of acceptable SIPS reliability, as expressed using the probability of failure on demand (PFD). SIL is a reliability metric widely used in the process control industry. A procedure based on SIL and fault tree analysis is proposed for determining the minimum reliability required by the SIPS individual components for achieving the predetermined desired reliability level of the protection scheme. The theory of minimal cut sets is used for this purpose. The proposed methodology is illustrated using the Dinorwig intertrip scheme, which is located in North Wales, UK, and operated by National Grid.