SMES for enhanced flexibility and performance of FACTS devices

This paper reviews the possible utility industry applications of SMES and discusses a number of technical issues and tradeoffs resulting from the design optimization process for SMES utility applications. The power electronics interfaces are discussed. Among the potential performance benefits are improved system reliability, dynamic stability; enhanced power quality; transmission capacity enhancement; and area protection. SMES devices may also have a positive cost and environmental impact by reducing fuel consumption and emissions through reduced losses and reduced generation availability for frequency stabilization. FACTS (flexible AC transmission systems) which handle both real and reactive power to achieve improved transmission and distribution system performance are multi-MW proven electronic devices now being introduced in the utility industry. In this environment, SMES is a logical addition to the expanding family of advanced power devices. The design of the SMES coil and power conversion system are very much dependent on the application. Although coil refrigeration and thermal insulation at low temperature present design challenges, the cryogenic system comprised of a refrigerator and cryostat storage vessel is a function primarily of the coil refrigeration requirements and consequently are sized for each application. Designing the SMES to operate at the voltages used by utilities can further reduce the cost of the power conversion system and related interfaces and the superconducting coil. An attractive option is the addition of energy storage to existing FACTS and Custom Power