Abstract
Overhead transmission lines are usually equipped with suspension insulators for keeping insulation. The suspension insulators are subjected to harsh environments in service for a long time. Long-term reliability of the insulators is required for both mechanical and electrical performances. We studied long-term reliability of mechanical strength on the suspension insulators. S P T (Strength, Probability & Time) characteristics, were obtained by testing the suspension insulators loaded at considerably high tensile stress for a long time. Based on these characteristics, we studied the method predicting failure risk at normal loads in service. Change in cement properties with time affected mechanical strength of the suspension insulators. Predicted failure risk was unrealistically low when using the S P T characteristics on the insulators with not aged cement. Increase in failure risk was estimated from the data on the cement-aged insulators. It was also verified that quality suspension insulators showed very low calculated failure rate under normal loading conditions in the field, which can ensure the long-term reliability of the insulators.
