Cognition on the current-limiting effect of saturated-core superconducting fault current limiter

As the level of short-circuit fault current gradually approaches the maximum value that the breaker can cut off, effective ways to limit it have to be found. The saturated-core superconducting fault current limiter (SCSFCL) is a kind of current-limiting device based on the nonlinear activity of the steel core. The SCSFCL is set in series with the transmission line. In the steady state of power grid, the core is driven in the deep saturation region of B-H curve by large DC in superconducting coil. So the SCSFCL has low reactance and little influence on the normal operation of the grid. When short-circuit fault occurs, the SCSFCL should effectively limit the fault current by cutting off the DC excitation. As the core is driven by the fault current and works in both linear and saturation region, the current and voltage waveforms are not sinusoidal any more. How to define or even recognize the current-limiting effect needs correct answer. At present, the ways of defining it are not unique. By analyzing the port property in limiting state, the limiting effect described by equivalent reactance, induced voltage, and current reduction rate is compared in this paper to give cognition on it.