Electrical and mechanical properties of service-aged medium voltage porcelain support insulators

The aging of insulation materials is of great importance in determining useful lifetime of electrical equipment. Mechanical and electrical tests were conducted on aged 6 kV porcelain support insulators, which were in service for 70 years in an indoor substation. The mechanical tests included compression, tension and bending of the insulators until failure. The electrical tests included application of standard lightning impulse voltages and determining the 50% probability flashover voltage for both positive and negative polarities and determining 50 Hz AC flashover voltage. In electrical tests, puncture did not occur. Across all of the tests, the insulators were found to conform to the initial parameters specified by the manufacturer. It was found that the deterioration of the porcelain insulator had not reached an excessively high level despite the substantially long service time.