Zinc oxide arresters are equipped with on-line leakage ammeter to monitor the operation of arresters. The on-line leakage ammeter reflects the current passing through the external insulation of the porcelain bushing and the valve plate of the arrester.

(1) The reading of on-line leakage ammeter of arrester increases abnormally. The internal damp of arrester is mainly caused by poor sealing. The sources of moisture are: in the production process of arrester, the humidity of installation environment exceeds the standard; The valve plate and internal parts were not dried thoroughly, and some moisture was retained; During assembly, the sealing ring is leaked and deviated; Or there are sundries between the sealing ring and the sealing cover of the porcelain sleeve; After a period of operation, the sealing parts were damaged, causing moisture.

(2) The reading of the online leakage ammeter of the arrester is reduced or even zero.