Sample Analysis of Failed Large Tonnage Porcelain Insulators on UHV DC Overhead Transmission Lines

Ultra-high voltage (UHV) AC and DC transmission lines are important carriers for long-distance power transmission in China and play a vital role in the development of China’s national economy. Large tonnage insulators of 420 kN and above are used in large quantities in UHV overhead transmission lines. The competent unit of power grid operation in China attaches great importance to the safe operation and maintenance of large tonnage insulators in UHV lines. In this paper, 11 pieces of large tonnage triple-umbrella type porcelain insulators were collected from a ± 1100 kV UHV DC transmission line in northern China. These insulators were found to be defective insulators with severely reduced resistance during overhead line inspection. In order to determine the failure causes of these insulators, a series of sample tests were conducted, including dissection, electromechanical test, thermal-mechanical test and microscopic detection. The test results showed that the defects in the manufacturing process of porcelain insulators were the main cause of failure. Specifically, excessive pores and large particle impurities could cause the increase and expansion of microscopic cracks in porcelain insulators. Therefore, high-quality raw material preparation and strict manufacturing process should be very important for large tonnage insulators. However, due to the high insulation safety standard of UHV lines in China, a small number of defective insulators do not pose an immediate danger. Improvement suggestions were made for the manufacturing process of large-tonnage porcelain insulators. The potential risk analysis and maintenance recommendation were discussed at the end of this paper.