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 250degC 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 200degC, 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%.