Thermal mechanical performance test on suspended insulators for transmission line
This study described some basic performance tests and accelerated ageing test by cool-heat cycling methods and thermal mechanical performance test methods on alumina porcelain insulators (new and aged) used for transmission lines in Korea. There were no failures in electrical and mechanical performance tests such as high voltage strength, flashover voltage, impact strength, etc. in any of the samples. However in the case of accelerated ageing tests above 90 /spl deg/C temperature gradient, fracture phenomena occurred by a thermal shock in the aged samples with low aluminous porcelain body. It was found that sample A was more severely aged than other samples. According to results of the HRB test and microstructural analysis, it was reasoned that insulator bodies with the matrix reinforced with alumina crystalline phase have advantages in the suppression of crack propagation. Cool-heat aging and mechanical thermal aging tests show that a temperature gradient is more effective for acceleration of the aging than variation in the number of cycles.
Failure Trends of High-Voltage Porcelain Insulators Depending on the Constituents of the Porcelain
The aging of porcelain insulators is responsible for the failure of power utilities. Porcelain insulators from different places in South Korea, possessing various aging times and years of installation, have been investigated to carry out lifetime statistics. These samples have a mass of 36,000 lbs and are operated at 154 kV. X-ray fluorescence (XRF) and scanning electron microscopy (SEM) were performed on the porcelain bodies of the samples collected. XRF and SEM revealed trends in the weight percentage of SiO2, Al2O3, and Fe2O3 in the porcelain bodies of the collected samples. The SiO2 and Fe2O3 weight percentage reduced to 8.93% and 73.17%, respectively, in sample C compared to A. However, the Al2O3 weight percentage increased to 16.23% in sample C compared to sample A. This change in weight percentage of SiO2, Fe2O3, and Al2O3 contributed toward enhancing the mechanical and electrical properties of the insulators. Mechanical load tests with electrical voltage (M&E), thermal and mechanical load tests (T&M), and hardness tests (HRB) were performed to evaluate these characteristics. Experiments revealed an increase of 90.9% in the inequality factor (K) in sample C compared to A. The impact of constituents of porcelain on the lifetime expectancy of a porcelain insulator was reported by implementing statistical strategies, such as the Weibull distribution.
Long-Time Mechanical and Electrical Strength of Suspension Insulators
Different observers have established that conventional suspension-type insulators indicate a statistical loss of strength with time. The depreciation in insulator strength is greatest in the first few months then stabilizing at value above the normal recommended working load. Various factors contribute to this loss of strength. The author's investigations have established the deterioration of component hardware coatings as one of the principal reasons for the loss in strength.