Reliability assessment of transmission and distribution schemes

This paper presents a further step in the development of accurate and consistent techniques for the reliability evaluation of transmission and distribution systems. A theoretically accurate Markov approach⁶is limited in application because of computer storage requirements and the rounding errors which occur in the solution of relatively large systems. This paper extends the modified approximate technique presented in reference (P) to permit evaluation of the contribution to the system reliability indices of different modes of component outage. The equations developed give results which compare very closely those predicted by the Markov approach. A three state weather model is developed to illustrate the effect of severe adverse weather periods on the system reliability performance. The load point failure modes considered are those which arise due to component permanent, temporary, maintenance and overload outages.