The performance of zinc oxide (ZnO) surge arresters has been considered in the present work, in particular, the effects of preconditioning on their protective level. The work involved development of laboratory experimental set-ups and theoretical modelling. The effect of single and double impulse stresses on ZnO surge arresters has been investigated using the constructed double impulse test facility which provides means of testing surge arresters with two successive 50kV, 5kA impulses of similar, and for the first time, opposite polarities. The time interval between both impulses can be as...