Review of available transmission capability (ATC) calculation methods

In last few years, transfer of bulk electrical power over long distances has increased in order to have a reliable and economical electrical supply. For example, hydroelectric power generated in Canada can be transferred to consumers and industry in United States using the high voltage transmission system. But only limited amount of power can be transferred over the transmission system subject to thermal limits of transmission lines, bus voltage limits, dynamic stability and voltage stability limits. The maximum power that can be transferred over the existing amount is called the available transfer capability. To operate the power system safely and to gain the benefits of the bulk power transfers, the transfer capabilities must be calculated and the power system planned and operated so that the power transfers do not exceed the transfer capability. The purpose of this paper is to explain concepts and calculation methods used to calculate available transfer capability and also discuss advantages and disadvantages of each. The methods reviewed in this paper are based on DC and AC Power Transfer Distribution Factors (PTDF), Continuation Power Flow (CPF) and repeated AC Power Flow. Simulation results are presented for each method on IEEE 6-bus and 39-bus system.