Surge withstand capability of metal oxide varistors for 10/350 µ s waveform

Lightning protection using surge protective devices (SPDs) have an important role for reliability of power delivery in current advanced information technology society. SPDs are categorized by 3 test class (Class I, II and III) according to IEC 61643-11) [1]. Especially, because class I SPDs intend to install at the entrance of power line according to IEC 61643-12) [2], it is important how big current SPD withstands. As components of SPD in Low voltage power distribution system, metal oxide varistors (MOVs) and/or spark gaps (GDT) were mainly used. SPDs with MOVs are voltage limiting type and have some merits as follows compared to that with GDT. • Capability of cut off the follow current • Lower residual voltage • Quickly response However, from surge withstand capability of the view, it is easy for MOVs to degrade its electrical characteristics by surge current because it translates from surge energy to heat itself. This point is a drawback for MOVs. This study describes the degradation mechanism of MOVs by surge impulses and the approaches for high and stable surge withstand capability through 10/350us impulse test results.