Effect of profiles on ac contamination flashover performance of large-tonnage suspension disc insulators

From field experience and laboratory experiments, it was indicated that the flashover performance of contaminated insulators was significantly influenced by the insulator geometry. In the paper, insulators with three different profiles including seven types of deep under-ribs disc insulator, three types of two-shed disc insulator and three types of three-shed disc insulator were tested in an artificial climate chamber to investigate the influences of insulator profile parameters on the flashover performance of large tonnage disc insulators. The artificial contamination test results indicated that 50% flashover voltage stress (E_50%) decreased with the increasing insulator diameter and creepage distance. The influence of salt deposit density (SDD) was also investigated, and it was found that E_50% of alternating-shed insulator decreased more rapidly than that of deep under-ribs insulator with the increase of SDD. An empirical expression was proposed, by employing the least-square method, to describe the relationships between E_50% and insulator configuration parameters as well as SDD. Through analyzing the generalized fitting coefficients (r) of the equation and the standard error of estimate (s), it can be concluded that the calculated results are in good agreement with the experimental data. Moreover, special attentions were also paid to the influence of the under-ribs and the ratio of shed overhang distance to the shed spacing on flashover performance respectively. This work can enrich the investigation of insulators parameters and may provide useful reference for performance evaluation and selection of insulators in EHV and UHV transmission lines.