Incorporating deterministic criteria in the probabilistic framework for composite generation and transmission systems

A reliability study of bulk power systems is of utmost importance. Conventional bulk power system reliability indices typically do not reflect the ability of the system to withstand, without resulting in load curtailment or other violations, the abrupt loss of system components. A system well-being evaluation method was proposed that divide the generation and transmission facilities into several states depending on the level to which adequacy and security constraints are satisfied. The security constraints to be specified are generally up to the discretion of the utility. The well-being indices, which are the probabilities of the system being in the healthy, marginal and at risk state as designated by deterministic criteria can provide important and intuitively interpretable information for system planning and operations. This paper presents an approach to evaluate the composite system well-being indices under a security constrained well-being framework. The method is based on an algorithm that determines first the healthy state probability based on a contingency listing that could be as detailed as computation limitations could tolerate. The healthy state probability provides an extra index for system planners or designers to decide whether or not the power system is capable, based on the deterministic criteria, to withstand unplanned outages of system components without violation of specified constraints. Together with the at risk and marginal state probability, this kind of well-being analysis provides a more comprehensive view of a bulk power system's reliability. Studies on a hypothetical system were done to confirm the validity of the method, and to examine the effect of load characteristics, system component maintenance and addition on the well-being indices, with emphasis being placed on the healthy state probability. The studies also show how appropriate load curtailment philosophy can be applied to preserve the well-being of essential load buses within the bulk power system.