In power system studies, the reliability of protection systems has a considerable effect on the reliability of supply, and hence appropriate reliability models must be incorporated. A majority of studies conducted assuming perfectly reliable protection systems, and hence do not take into account the effects of failure scenarios in their operation.Modelling of the failure modes in protection systems associated with their dependability and security features is essential for comprehensive evaluation of power system reliability. There are relatively fewer works in the literature on power system reliability accounting for the impact of protection system. In this paper, common mode failure operations such as dependability failures of protection of neighbouring lines in a Power System network is considered. In an existing method, only first order and second order failures of transmission lines are considered, whereas, failure modes using higher order Cutsets are not considered. Expressions for reliability analysis are developed and software has been developed using MATLAB. The results for sample systems are obtained and analysed. From the results, it can be concluded that although probability of failure indices are increased as compared to an existing method, the proposed method is more general, realistic and approximate analysis can be carried out for any system having higher order dependable failures.