Long-Term Mechanical Properties of High Voltage Composite Insulators

The extensive use of composite insulators for transmission lines can ultimately be justified only on long-tern qualification tests. The results after three years of long-term evaluation of composite insulators subjected to uniaxial tensile loads are presented. Three insulator designs with maximum failing loads in excess of 450 kN were investigated at temperatures from -25°C to 100°C. Based on the extrapolation of the time to rupture results of the approximately three years of testing, all three designs would, under similar conditions, exceed the expected daily loadings. The slope of the time to rupture versus load line on semi-log plot varies from 12 kN to 25 kN per decade of time depending on the insulator design.