Investigations on electro-thermal ageing of metal oxide surge arrester elements: a realistic laboratory simulation

The ageing of metal oxide surge arresters (MOSAs) under field operating conditions caused by a combination of electrical and thermal stresses is simulated in the laboratory in an attempt to characterize the degradation phenomena as well as to identify the significant indices of such a degradation. Other than the widely adopted leakage current index, the prospects of parameters such as barrier height, capacitance, tan delta, nonlinearity coefficient, and area ratio as sensitive degradation indices are studied. Also, the effect of electro-thermal aging on the V-I characteristics as a whole, up to the breakdown voltage of the MOSA, is presented. The simulation is carried out on a `one day=one year´ (of the arrester´s field life) basis. The accelerated aging for this purpose followed an empirical transient electrical stress pattern, while the IEC guidelines were followed for selection of continuous operating voltage of the arrester and the scheme of thermal stresses