Three-dimensional computed tomography and composition analysis of porcelain insulators for 154 kV power transmission lines

Porcelain insulators were removed from 154 kV power transmission lines from three locations that were installed between 1969 and 1977. Visual inspection, three-dimensional computed tomography (3D-CT), and X-ray fluorescence (XRF) analyses were carried out. The 3D-CT analysis shows the presence of a number of pores. It was found that the insulating resistance of the porcelain insulators decreases with increasing number of pores and total pore area. Since most of the pores are located in the cement area, it is expected that the decrease in insulating resistance is related to the deterioration of the cement. The XRF analysis reveals that a high percentage of Fe exists in the cap. The Fe
₂
O
₃
content, which indicates corrosion, is the highest at 95.7% in Region C (48 years), followed by 88.4% in Region A (40 years), and 81.65% in Region B (38 years). High levels of Al
₂
O
₃
and SiO
₂
were detected in Regions B and C where the number of yellow dust days is high. In the case of the cement, the water-absorbing CaO component is 62.87% on average. In Region C where the insulators are the oldest, higher CaO is detected. This shows water absorbion greatly affected the insulation deterioration of the porcelain insulator. It was found that the Al content of the porcelain insulator from Region C, for which the main material is cristobalite, is lower than that from other areas using alumina. The components found by XRF analysis are dependent on the age, the main materials, and the environmental conditions where the insulators were installed.