System performance characteristics of superconducting alternators for electric utility power generation

The application of superconductors in the field windings of large steam-turbine generators appears to offer a number of significant economic and operational advantages. The principal advantage offered by such machines appears to be a potentially large reduction in size, weight, and cost for a given power rating. In addition, superconducting alternators also appear to have a number of unique and potentially advantageous operational characteristics, most of which are a consequence of the relatively low per-unit synchronous reactance that is characteristic of these machines. This paper reviews the reasons for the low synchronous reactance attributable to the use of superconducting field winding, and compares the expected performance characteristics of a superconducting alternator in the 1000 MVA range with those of a conventional power system generator of comparable rating. Among the specific topics discussed are performance with regard to dynamic stability, transient stability, voltage regulation, and excitation control. The principal operational advantages of a superconducting alternator appear to be 1) the absence of a dynamic stability limit within its MVA capability, 2) significantly greater transient stability when operating at leading power factors, 3) superior voltage regulation, and 4) no degradation of dynamic stability due to automatic voltage regulator action. Consequently, superconducting alternators appear to be ideally matched to modern power system applications that require operation of generators at leading power factors.