Transfer of bulk electrical power over long distances is routine in North America 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 Los Angeles using the high voltage transmission system. But the transmission system has a limited capability to transfer power. The maximum power that can be transferred is called the 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 operated so that the power transfers do not exceed the transfer capability. The calculation of transfer capability depends on many factors and the purpose of this web site is to explain and illustrate the calculation of transfer capability.