Surge Withstand Capability of Parallel-connected Metal Oxide Varistors

Metal oxide varistors (MOVs) composed of multiple MOVs connected in parallel have benefits, including compactness and the potential to realize high surge withstand capability. On the other hand, it is absolutely necessary to control the V-I characteristics of each MOV connected in parallel to ensure uniform current flow between the component MOVs. If this current is not uniform, the component MOV having low voltage will puncture and degrade at a lower surge current than expected. In this paper, we have studied the distribution of electric field and current on the surface of a three-parallel MOV using the finite-difference time-domain (FDTD) method. Additionally, real impulse testing was conducted to confirm the surge withstand capability of three-parallel MOV. From the obtained results, we have concluded that the surge withstand capability of the three-parallel MOV is not decreased from the desired 3X individual surge withstand capability if the variation of V
_1mA
voltage between each MOV component is less than 4%.