his technical report reviews the state-of-the-art in composite system reliability (CSR) evaluation. Reliability assessment methods for composite generation and transmission systems have been developed in recent decades. However, maintaining an adequate level of reliability of the modern power grid is particularly challenging today due to many causes such as increasingly frequent extreme events (e.g., failure of multiple physical components, extreme weather events, and other natural disasters), high penetration of variable energy resources (VERs), and the increasing complexity of energy system infrastructure. Despite the numerous reliability analysis methods that exist today, including enumeration (analytical) methods and Monte Carlo methods, the computational burden is still a major obstacle to applying CSR analysis in an actual large-scale composite system, especially in the area of operations. Organizations and utilities in North America (including the North American Electric Reliability Corporation or NERC), Europe, Asia, and other places in the world have been searching for appropriate methodologies and computing tools.
Based on extensive discussions and experience sharing among task force members from research organizations, utility companies, software developers, and regulatory bodies, the Composite System Reliability Task Force (CSR TF) has focused on some of the most commonly seen concerns and issues related to the adequacy and operational reliability of a composite system. The TF has attempted to address these concerns by gathering best practices from published literature and users of probabilistic tools in the electric power industry.
The objective of this report is to provide guidelines and suggestions for power industry professionals who are considering applying probabilistic methods in CSR analysis. This report, therefore, also investigates other factors that affect the use of probabilistic techniques by electric utilities.
Finally, the report provides useful references for the development of NERC guidelines and standards relevant to CSR adoption in the industry.

Composite Power System Reliability is defined as the computational procedure that quantifies the probability that the power system will perform the function of delivering electric power to customers adequately, on a continuous basis and with an acceptable quality. This definition leaves many details undefined and exemplifies the ambiguity in reliability analysis. The increasing deployment of wind and PV creates additional uncertainties that make reliability analysis a rather complex issue. Because of increased uncertainty the need for composite reliability analysis and utilization of results in power system planning is critical. New approaches are emerging for dealing with these problems from the operational point of view, including demand response programs, tapping on customer and distributed resource flexibility and new control approaches. The key question to be addressed is: how the new operational paradigms affect composite power system reliability. This paper presents the ongoing work of the IEEE Composite System Reliability Task Force of the IEEE PES Reliability, Risk, Probability Application (RRPA) Subcommittee.