Journal of American Science 2010;6(9) http://www.americanscience.org editor@americanscience.org 1 Comparative Analysis of ATC Probabilistic Methods Mojgan Hojabri 1 , Hashim Hizam 1 , Norman Mariun 1 , Senan Mahmood Abdullah 1 1 Department of Electrical and Electronic Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, Malaysia mojgan.hojabri@gmail.com Abstract - The price of power transfer between two areas is a key issue between buyers and sellers in the power market which is directly related to the ATC deal and security. ATC deal is computed by Deterministic methods and ATC security presented by probabilistic methods. Since the ATC is used for operation or planning of power system, ATC can be determined by Deterministic or Probabilistic methods. In this paper, existing probabilistic methods which could predict ATC for power system planning are reviewed and compared. [Journal of American Science 2010;6(9):1-4]. (ISSN: 1545-1003). Keywords: Available transfer capability (ATC), Transmission capability margins, Power market, Power system planning. 1. Introduction ATC is an evaluation of the remaining energy in the physical transmission network for future commercial activity over and above already committed utilities (NERC, 1996). ATC should represent accurate and practical knowledge information on the ability of interconnected networks to reliably increase the transfer of power between two sites, and it is a function of increase in power transfers between different sites in the interconnected network (Cornière et al., 2000; Tsai and Lu, 2001). Mathematically, ATC is defined as the total transfer capability (TTC) less the transmission reliability margin (TRM) the sum of the capacity benefit margin (CBM) and existing transmission commitments (ETC), which includes pre-transfer base case flows without contracts and the flows caused by existing contracts. In other words, ATC can be expressed as: ETC CBM TRM TTC ATC - - - = (1) Transfer capability essential necessary to secure that the interconnected transmission network is certain under a reasonable range of uncertainties in system situation determine the transmission reliability margin (TRM). Capacity benefit margin is specified as that quantity of total transfer capability reserved by load serving entities to certain access to generation from interconnected systems to meet generation reliability necessities. TRM accounts for the intrinsic uncertainty in system situations and the necessity for operating flexibility to certain reliable system operation as system conditions change. There are several approaches proposed to achieve this (Sauer, 1997): 1) Repeated computation of TTC using variations in the base case data 2) A single repeat computation of TTC using limitations reduced by a fixed percentage (i.e., 4%). 3) TTC reduced by a fixed percentage (i.e., 5%). 4) Probabilistic approach using statistical or other systematic reliability concepts. 5) First order sensitivity method to take the effect of changes in load and simultaneous transfer on ATC Gravener and Nwankpa , 1999). Utilities would have to determine sufficiently their ATCs to certain that system reliability is maintained while serving a wide range of transmission transactions. ATC would be continuously calculated and updated in planned power transfers between or among the areas. The ATC principles are stated as follows: 1) Give a reasonable and dependable indication of transfer capabilities. 2) Recognize time-variant conditions, simultaneous transfers, and parallel flows. 3) Recognize the dependence on points of injection / extraction. 4) Reflect regional coordination to include the interconnected network. 5) Conform to NERC and other organizational system reliability criteria and guides. 6) Accommodate reasonable uncertainties in system conditions and provide flexibility (Sauer and Grijalva, 1999). In the most case, determination of transfer capability and other related margins has been coordinated by the North American Electric Reliability Council (Ejebe et al., 2000; NERC, 1999). And operating studies commonly seek to determine limitations due to the following types of problems: 1) Thermal overloads Limitation 2) Voltage stability Limitation 3) Voltage limitation 4) Power generated Limitation 5) Reactive power generated Limitation 6) Load Power Limitation