Assessing the electrical and mechanical integrity of composite insulators prior to live working

Many electric power utilities routinely employ composite or nonceramic insulators (NCI) on overhead transmission lines. NCI offer numerous advantages, including low weight and ease of handling, features that are important for live working and replacement of NCI using live working procedures. An essential requirement for ensuring worker safety when performing live work with NCI is to confirm the short-term (i.e., for the duration of the work) electrical and mechanical integrity of both the installed and the replacement NCI. Unfortunately, there are no simple methods of testing the integrity of either installed or replacement NCI prior to executing live work. This has caused many utilities to curtail live work with NCI, and in some cases utilities have even decided not to employ NCI because their integrity in service could not be verified. This paper reports on a project conducted by EPRI. To assess defects in NCI that could create unsafe conditions for live working, i.e., defects that can cause electrical and mechanical failure during live work. NCI defects were categorized and analyzed in terms of their likelihood to cause catastrophic failure during live work. The ability of current NCI evaluation techniques to detect defects is assessed and detection techniques are discussed