Cognition on the Current-Limiting Effect of Saturated-Core Superconducting Fault Current Limiter

The saturated-core superconducting fault current limiter (SCSFCL) is an important facility for limiting the short-circuit fault current of the power grid. However, the cognition or the judgment on the current-limiting effect, which is the key indicator of the SCSFCL, is not unique. This is because the nonlinear property of the steel cores in the limiting state makes the voltage on the SCSFCL and the current passing through the SCSFCL not sinusoidal any more. In this paper, it is presented that the equivalent limiting reactance, which is commonly used currently, cannot reflect the current-limiting effect, nor is the induced voltage. It is pointed out that for a certain SCSFCL, the current-limiting effect is not fixed, and it depends on the parameters of the power grid as well as the position, where the SCSFCL is installed. It is clarified that only the current reduction rate by comparing the short-circuit fault current before and after the installation of the SCSFCL in a certain power grid can correctly reflect the current-limiting effect. Certainly, the calculation for the current-limiting effect must be conducted by the field-circuit coupled method, where the field concerns the property inside the SCSFCL and the circuit concerns the property of the power grid. This paper does not mainly focus on the simulation method, but provides the means of judging or evaluating current-limiting effect of the SCSFCL.