Influence of pollution on the performance of metal oxide surge arresters

Surge arresters are used as key equipment to protect costly substation and transmission line equipment against atmospheric as well as switching over voltages. Reliability of surge arresters has been the subject matter of many studies. Elimination of series gaps in metal oxide surge arresters (MOSA) avoids variation in protective levels caused by erratic gap spark over. MOSA has extremely stable protective characteristics and is very fast acting device, offers lower protective levels at high rates of discharge current. But, in the presence of contamination and moisture, there is the possibility of flow of leakage currents internally and externally both of which may distort the uniformity of voltage distribution across the MOSA. Nonuniform voltage distribution may cause voltage stress and lead to stress degradation. Internal leakage current may also raise temperature around metal oxide discs and lead to thermal run-away. Stress degradation and initiation of thermal run-away process may affect the stability and energy absorption capability of the MOSA. In this paper, an effort has been made to suggest an algorithm with the help of which voltage and current distribution, inside and outside the polluted MOSA could be studied and flashover conditions be achieved. Dynamic surface resistance change during formation and quenching of dry bands due to leakage current has been considered.