A Novel Topology of a Liquid Metal Current Limiter for MVDC Network Applications

A liquid metal current limiter (LMCL) utilizing a fast switch and a parallel connecting path and consisting of several serial current limiting elements (CLEs) has the potential for use in a dc system. The current commutation ability is vital to the reaction time and the current limiting efficiency of this LMCL. In this paper, the characteristics of a natural current commutation driven by the arc voltage between contacts are first revealed; this method can only be applied in a low-voltage system. To fulfill the demands of a medium-voltage direct current system, an innovative LMCL topology is recommended due to the forced current commutation driven by an auxiliary magnetic induction module. A specially designed structure of magnetic coupling coils with a high coupling coefficient is proposed to improve the current commutation ability. The forced current commutation characteristic is analyzed via simulation and verified experimentally. Furthermore, the arc V-I characteristics of CLEs are deeply discussed to guide the selection of serial quantity of the CLE. Finally, a prototype for the complete LMCL is designed, assembled, and tested in the laboratory. The current limiting coefficient of the LMCL is less than 0.464, the peak value of arc voltage is approximately 6.3 kV, and the current limiting reaction time is 1.53 ms.