Porcelain insulators should be exchanged periodically, but their lifetime is not clearly defined. One factor that affects service life is corrosion occurring at the pin and cap—each of which is made of iron with a zinc coating. A number of porcelain insulators used for different lengths of time in different locations are gathered, and the corrosion mechanisms of the cap and pin are investigated. The corrosion mechanism of the cap is mainly galvanic corrosion while that of the pin is primarily electrolytic and crevice corrosion as well as galvanic corrosion. Although time is an important factor in corrosion, it is found that corrosion is more influenced by geographical factors. Since the amount of acid rain and sea salt—each of which causes rapid rusting—is dependent on geographical factors, the location of where porcelain insulators are installed should be considered when predicting their lifetime. Theoretically, if there is only galvanic corrosion occurring, the expected lifetime is 56 years in an industrial area when the zinc coating has a thickness of 75 µm. Previous articles dealing with aging have predicted the maximum lifetime of porcelain insulators used in Korea to be approximately 30 years. To prolong the lifetime of porcelain insulators, further study is required in which the use of zinc alternatives, or waterproof coatings (in addition to the zinc coating), could be examined.
X-ray diVraction (XRD) studies were carried out on 2•25Cr-1Mo steel boiler tubes from a thermal power station with an objective of developing a faster method of health assessment of this steel at elevated temperatures on a routine basis. Carbide phase transformations in virgin and service exposed boiler tubes (up to ~100 000 h) were determined for plate specimens using high power X-rays. Iron and chromium rich carbides were detected by XRD at various stages of transformation towards final equilibrium. Compositional variations of equilibrium precipitate M 23 C 6 with service life or overheating in the specimens studied were monitored by a shift in the lattice parameter. T he XRD results were validated by optical and electron microscopy, hardness measurements, and particle size measurements.MST /4296
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.
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