Development of a Hybrid Fault Current Limiter Using Liquid Metal for Large Capacity MVDC Power Systems

A hybrid fault current limiter (FCL) for medium voltage direct current (MVDC) power systems is introduced in this paper. It achieves low operation loss and high current limiting resistance through the combination of a fast mechanical switch, a magnetic induction module and a number of liquid metal units (LMUs). Firstly, the parameters of the magnetic induction module are designed to achieve a desired fault current commutation process. Then, the working principle of LMU is introduced, and its resistance properties corresponding to the liquid metal arc are studied in detail. Equations are deduced to model the V-I characteristic of LMU. Thus the current limiting performance of the topology can be simulated. To verify the feasibility of the FCL, a 5-kV/5-kA prototype is developed and laboratory tests are implemented. Comparisons with other FCLs are also conducted to demonstrate the advantages of the proposed one. It is concluded that the prototype provides the basis for further commercial product development.