I. Introduction
The objective of the system operators is to ensure power balance supply in the event of any contingency on the system. Transmission line outages are most commonly occurring disturbances in the power system and can have the great impact on system reliability. In extreme circumstances, when system security is at stake, load curtailment becomes an obligatory action by the system operators in order to maintain power balance. Failures due to such disturbances in a composite power system can cause small to large (catastrophic) scale interruptions to customers. Therefore, reliability cost analysis becomes a crucial evaluation in composite power system in order to highlight the severity of disturbance to the load points [1], [2].