Estimating reactive margin for determining transfer limits

Currently, system operators refer to written operating procedures to establish transfer limits across major interties. These procedures tabulate predetermined intertie limits for critical contingencies on the system. Under this approach, transfer ratings are typically conservative, as studies are based on highly stressed system conditions, and incomplete, as studies cannot analyze all combinations of equipment out-of-service. One approach to improve the use of the offline studies is to track results and interpolate for unstudied cases. In this paper, the authors look at estimating reactive margins based on such schemes. The procedures for calculating reactive margins under the WSCC criterion are followed. Numerical tests on the New England 39 bus system indicate the potential of the approach