Effect of the dielectric constant of the insulation layer: An insulation layer is normally used to cover the lateral surface of ZnO blocks in a surge arrester assembly. The dielectric
behaviour of the insulation layer plays an important role in determining the ZnO varistor withstand capability towards surface flashover. By reinforcing the insulation strength on the varistor surface, deterioration because of the partial discharges or moisture
ingress could be prevented. In this study, the effect of the dielectric constant of the fibreglass layer on the maximum discharge energy was examined. It was found that increasing the
dielectric constant of the insulation layer results in insignificant changes in the energy discharged by the arrester. The maximum electric field intensity in the arrester because of the variation of the dielectric constant of the insulation layer was also computed, as shown in Fig. 11. Increasing the dielectric constant decreases the maximum electric field inside the arrester, especially on the lateral surface of the ZnO blocks. Owing to higher permittivity of the
insulation layer, the electric field can be aligned easier within the material which will result in lower electric field intensity. This justifies the importance of the insulation layer in preventing the ZnO surface against deterioration.