Study on the feasibility of developing high voltage and large capacity permanent-magnet-biased fault current limiter

The fault current limiter based on permanent-magnet-biased saturation, namely PMFCL, is a preferable solution to suppress the fault current in power grids, with unique superiority and advantages in both aspects of economical investment and technological feasibility. However, the bias capability of the permanent magnet is still a pending issue as to hinder further development of the PMFCL towards high voltage (HV) and large capacity, which is yet to be clarified so far. The state-of-the-art advancement of PMFCL is firstly reviewed and its specific merits are fully accounted for. A concept of Saturation Depth Ratio is proposed and defined as to indicate that, to improve the bias capability of the permanent magnet is in effect equivalent to increasing saturation depth ratio of the iron core. With regard to a novel PMFCL topology, the mathematical relationship between the saturation depth ratio and the structural parameters is obtained through equivalent magnetic circuit analysis then verified by experiments and FEM simulation, which presents effective basis and guide to design of HV and large-capacity PMFCL. Finally, a case study of 10 kV PMFCL prototype is given. Results demonstrate that, proper adjust of section area and length of the permanent magnet can achieve preferable bias capability of the permanent magnet, and thereby show feasibility to realize HV and large-capacity PMFCL.