The high voltage problem in the saturated core HTS fault current limiter

Abstract A small model of a one-phase saturated core HTS fault current limiter was developed. It consists of an iron core, an AC coil and a DC HTS coil. The HTS coil comprised six 126 turns double-pancakes (ID 70 mm), wound after heat treatment from Bi-2223 multifilamentary tape in Ag matrix. A fault simulation circuit was set up to characterize the dynamic properties of the model limiter. The voltages and currents of the AC coil and the DC HTS coil were measured through a computer-based data acquisition system. The tests have shown that the limiter has a fast response and the first current peak can be easily limited, but a high voltage will be induced on the DC HTS coil side during the fault state. This high voltage can badly affect the DC current equipment on the DC HTS coil side. The origin and value of the high voltage can be explained using a transformer model. For a limiter with n 1 turns AC coil and n 2 turns DC coil, the largest induced voltage will be roughly close to ( n 2 / n 1 ) U , where U is the rated voltage of the limiter. To commercialize this kind of limiter, the high voltage problem must be solved. Some different designs were introduced to lower the induced voltage.