The new approach to designing HV insulation with high reliability for overhead lines and substations

To specialists, insulation coordination is well-known. The insulation level of the overhead line or the substation is determined from a distribution curve of the flashover voltage of a single insulator in the region of extremely low probabilities (flashover voltage distribution-FOV). This probability of insulation flashover, the minimum acceptable in operation, (Pperm) corresponds to a certain voltage Uo which, as a matter of fact, is the insulation level (BIL) of the line of substation as a whole. From here it follows that the possible difference in the form of the flashover distribution curve in the region of very small probabilities by calculation (a part of a curve "C", instead of a part "B") can result in a serious mistake in the design (coordination) of the insulation level of lines and substations. The author of this paper carried out research into the so-called anomalous characteristics of HV insulators of simple profiles (1998). Their main characteristics essentially, and sometimes extremely, differ from well-known characteristics in configuration, and quantitative parameters. The existence of the mentioned anomalies in common insulators with sheds (porcelain, glass and so on) also was demonstrated by the author. These anomalies are usually located in the region of probabilities considerably below achievable experimental probabilities. The paper continues the work of the previous publication and reports: the mechanism of occurrence of anomalous discharges in a compressed form; questions of insulation coordination in view of the observed effect; and new ways of designing high-voltage insulation of increased reliability.