Accelerating aging of transmission line porcelain suspension insulators by autoclaving

Porcelain suspension insulators aged for 1, 5 and 10 years on Korean transmission lines and new insulators are tested for autoclave expansion. The compressive strength of the insulators aged in an autoclave with conditions of 250°C and at 20 atm for 30 minutes, was about 7.6 kgf/mm², which is close to that measured on insulators aged for 10 years in the field. From simulation results, the cement displacement changed linearly with temperature. At a temperature of 200°C, the shear stress was approximately 7 kgf/mm²; a stress that is brought about by a 0.07% expansion of the cement. It is evident that the cement would fracture at a 0.07% expansion, because the cement has about 7 to 9 kgf/mm² flexure strength. A turning point in the shear stress with mechanical load occurred at 0.02% cement expansion. From an analysis of the porcelain body it is shown that there is sufficient margin of strength to guard against fracture of the porcelain body even for a cement expansion more than 0.12%.