Degradation characteristics on MOV of surge arrester used for 6.6kV power distribution line

In Japan, porcelain-housed internally gapped lightning surge arresters are applied for 6.6kV distribution lines. A lightning surge arrester is composed of Metal Oxide Varistors (MOVs) and an internal gap, which are installed in a porcelain housing having sealing structure. It is well known that a dominant degradation factor of a surge arrester is follow current interrupting ability of a MOV. This paper is focused on follow current interrupting ability of a degraded MOV due to lightning current. The degradation characteristics of a MOV due to lightning surge is examined by measuring the reference voltage of the MOV after lightning impulse currents are applied to a MOV. The variation of the reference voltage in the negative direction voltage was bigger than that of the positive direction voltage. Therefore, it should be evaluated by checking the reference voltage using both positive and negative direction during the degradation test.