In this paper

fault analysis is done for the explosion of two cable outlet 110 kV composite bushing metal oxide arresters（MOAs）with no gap and the same type occurred in Shanghai Power Grid.By visual inspection

electrical diagnostic test and anatomical analysis

and combined with the factors such as the weather at the fault time and under the operating conditions

the MOA faults are caused by internal damp.Internal damp during the operation causes are as follows: 1)the end air seals of the upper and lower flange exists defects;2)the process of silicon gel by penetrating causes defects to form the air gap.In addition

there is a phenomenon that the silicone rubber composite sheath is not tightly bonded with the epoxy cylinder.For two of the six MOAs burned and exploded during the operation

only one meets the operational requirements under the electrical diag-nostic tests of the remaining four MOAs

the familial defects of this type MOA are submitted in accordance with the relevant departments.