PERFORMANCE OF ZINC OXIDE-VANADIUM PENTOXIDE VARISTORS IN MEDIUM VOLTAGE SURGE ARRESTERS

Abstract

Metal oxide varistor (MOV) discs (Ø28 mm × 12 mm) made of 97.5 mol.% zinc oxide (ZnO), and 0.5 mol.% each of vanadium pentoxide (V2O5), tin (IV) oxide (SnO2), antimony(III) oxide (Sb2O3), cobalt(II, III) oxide (Co3O4), and chromium(III) oxide (Cr2O3) additives were produced using powder metallurgy. The obtained MOVs were polycrystalline with high density. This study focused on analyzing the microstructure and mechanical and electrical properties of the MOVs. The developed MOVs had a fine-grained microstructure with an average ZnO grain size of about 10 μm. The Ag-coated MOV discs tested in a range of 100 – 1300 V ac exhibited a leakage current of 0.033 – 1.420 mA and a minimum varistor voltage of 2.37 ± 0.15 kV. After conducting functional tests on Ag-coated MOVs installed in polymer-housed surge arresters, it was found that they are suitable for use in medium voltage arresters with a nominal voltage (Un) of 25 kV, a continuous operating voltage (Uc) of 12 kV and a leakage current (IL) of 1 mA.