Electrical testing of decommissioned 25 kV rail supply insulators

Partial Discharge measurements were carried out on 101 Ceramic Insulators removed from service from three different locations on a 25 kV rail supply network. Measurements were taken using a combined IEC 60270 apparent charge and RF measurement system to assess the condition of the insulators. Low level (25 – 35 pC) PD activity was observed in 15 of the samples, and was thought to be the result of voids at the terminal surfaces where delamination of the porcelain could have taken place through mechanical stress or environmental conditions. The RF and apparent charge measurement systems were comparable in their ability to detect PD activity, which indicates that it might be possible to develop a noncontact RF condition monitoring system for use with rail supply insulators.