Voltage distribution studies on ZnO arresters

The voltage distribution in a zinc oxide (ZnO) surge arrester under normal operating conditions has been observed to be non-uniform. The discs at the top are subjected to a higher voltage and hence thermal stresses, leading to a faster thermal ageing of these highly stressed discs. Therefore, efforts are generally made to make the voltage distribution as uniform as possible. The voltage distribution in the arrester is governed by the geometry as well as the electrical properties of the materials used. To improve the voltage distribution, some changes in geometry are relatively easier to implement. The authors employ a numerical field computation approach to ascertain the influence of the geometry of different components of the arrester on its voltage distribution. Practical geometries of a 220 kV and a 400 kV class arrester are considered under both clean and uniformly polluted conditions. Some optimum values for the geometry of the components are obtained