Assessment of available transfer capability and margins

Available transfer capability (ATC) calculation is a complicated task, which involves the determination of total transfer capability (TTC) and two margins-transmission reliability margin (TRM) and capacity benefit margin (CBM). Three currently used methods of TTC determination are presented and compared in this paper. Besides these methods, transfer-based security constrained OPF (TSCOPF) method is proposed in this paper as a replacement of conventional SCOPF method, for use in the deregulation environment. Both TRM and CBM, which account for reliability of the system, are seldom mentioned in the papers associated with ATC. This paper presents a probabilistic method to assess TRM, proposes rules and a procedure to allocate CBM and two methods of incorporating CBM into ATC. A modified IEEE RTS is utilized to demonstrate the proposed methods and the results show that the values of ATC are quite different when margins are taken into account and the methods of incorporating ATC affect the ATC value significantly.