A Static Var Compensator Using a Superconducting Coil

A superconducting coil has virtually no losses for a dc current. To utilize this feature in a static VAR compensator application the conventional conversion equipment between the three phase system and the coil must be modified to obtain variable ac currents with a constant coil current. In the description of a recently introduced control scheme of a bridge converter it is shown that by the method of variable free-wheeling the line currents of a converter can be made variable while the coil current remains nearly constant [1]. In this paper the novel static VAR circuit, called SAVAR (Superconductor Application for VAR control) is analyzed, and some derived voltage and current shapes are compared with experimental results. A 40 MVA SAVAR system, including the appropriate harmonic filters, is designed and compared technically and economically with a conventional static VAR generator. It is concluded that the dynamic characteristics of the SAVAR circuit satisfy the requirements of the voltage support operation in electric utility systems. At this time the economic advantages of a SAVAR system are marginal. However, continuing improvements in thyristor ratings and expected increases in energy cost are factors which could give additional economic benefits to SAVAR in the future.