Developing a Surge Resistant Fuse for Power Systems in Telecom Facilities

Metal oxide varistors (MOVs) are commonly mounted as a lightning protection measure (LPM) in power systems such as the 48 V DC system in telecom facilities. However, degradation in the performance of the MOVs causes electric leakage of 50 Hz commercial AC power. In order to prevent such electric leakage, it is recommended that a fuse be connected in series with the MOVs for short-circuit protection. However, because the fuse is connected in series with the MOVs and a lightning surge will flow through it, such fuses must not be blown out by the lightning surge. Therefore, the authors propose a fuse with a dual structure: an outer conductor through which the lightning surge current and some of the overcurrent from commercial power will flow, and an inner conductor through which the overcurrent from commercial power and some of the lightning surge current will flow. In this study, authors evaluated whether the proposed fuse can control the current flow or not. First, by measuring the lightning surge currents that flowed through a prototype, which was installed on small coils, it was found that the proposed fuse can control the lightning surge current flow, which favors higher frequency current flow through the outer conductor. Second, by simulating the current separation rate (CSR), which is the ratio of current flow through the outer and inner conductor, it was found that the efficiency of current separation can be improved by changing the thickness and diameter of the outer conductor.