Residual mechanical strength evaluation of crimping assembled composite insulators with service time of 10–14 years

Abstract

Sixteen composite insulators with service time between 10 and 14 years were sampled to conduct the specified mechanical load (SML) verification test in order to investigate whether their mechanical strength meet the criterion for continued running. Test results show that 15 out of the 16 samples pass the SML verification test. They show their failing load exceeding 1.4 times of SML, conforming to the calculation according to the mechanical strength model in the IEC 61109 standard. However, the remaining one fails to pass the test and its failing load is only 70% of SML. There are four kinds of failing modes, namely socket pulled out, ball pulled out, ball fractured and rod fractured, where socket pulled out is the most common failure mode and rod fracture mode only happens on X08 sample. The fact that X08 does not pass the test should be paid much attention since fracture of any one in the transmission lines can lead to severe transmission line accidents. Moreover, its appearance has some characteristics similar to some decay-like fracture insulators which is, inferred that the mechanical strength of composite insulators in service can be affected by the environmental stresses. In addition, it is suggested to conduct sampling test periodically for the composite insulators which have been in service more than 10 years.