The failure of string fracture and core breakdown of composite insulator could pose serious threat to the safe and stable operation of transmission lines. In this paper

the failure case of the string fracture and core breakdown of composite insulators in Zhejiang Province since 2016 is statistically analyzed

including failure overview

product situation

failure configuration

performance test

failure cause and related recommendations and measures.It is shown by the result that the failure of string fracture and core breakdown of composite insulators occurred totally8 times in Zhejiang Province since 2016

including six decay-like fracture

one brittle fracture and one core breakdown. Among them

the brittle fracture is mainly due to weak end seal

penetration of external moisture and the stress corrosion generated under action of long term high electric field. The decay-like fracture is mainly due to weak bonding between core and housing

degradation and deterioration of epoxy resin matrix in the core under common influence of damp

discharge and mechanical stress. While

the core breakdown is due to insufficient partial bonding of the interface

damage of the housing or the end seal

penetration of moisture along the interface or the defect of the core

causing partial discharge

forming carbonization channel and developing gradually into penetrating breakdown. In view of above statistical failures

it is recommended that the boron-free fiber and acid-proof core with good stress and corrosion resistance performance is used for the composite insulator. The coaxial multiple direction clamping for the assembly of end accessories is adopted. The high temperature vulcanized silicone rubber injection is sued for the end sealing and the adhesion strength between the core and housing is assured. At the same time

the infrared nd ultraviolet live detection of the composite insulators is strengthened during the operation and maintenance period.