Behaviour of zinc oxide surge arresters under pollution

Results of pollution tests with AC voltages which were carried out with a multiunit zinc oxide arrester are presented. The interaction between the polluted porcelain housing and the inner varistor column due to capacitive coupling has been found to be responsible for the temperature rise of varistor elements. Different voltage distributions inside and outside the arrester cause a high radial electric field which can lead to internal discharges if the radial insulation system is not properly designed. These internal discharges may damage varistor elements which are not adequately coated and may cause the total destruction of the arrester. The shape of the internal and external currents due to discharges is analyzed. A test method for comparing different arrester constructions under severe pollution is proposed. The method can also be used to demonstrate the absence of discharges for a certain arrester design under extreme conditions of pollution during type tests