Dielectric performance of interfaces in premolded cable joints

Great progress has been made in developing high-quality insulating materials, in maintaining consistent manufacturing processes, and in designing cable joints for easy installation. However, little attention has been given to the interfaces in cable joints. Greases are generally used as a lubricant for installation of premolded cable joints (excluding heat-shrink and cold-shrink splices), and are therefore always found at these interfaces. Analysis of field-aged cable joints has revealed two common problems related to greases: dry and sticky interfaces causing great difficulties in power disconnection, and interfacial discharges (or surface tracking) leading to dielectric breakdown. The focus of this study is on the dielectric performance of interfaces in cable joints. Measurements of breakdown voltage and pressure were carried out at interfaces of both new and field-aged cable joints. The effect of surface conditions was also investigated. Results show that the dielectric performance at interfaces is intimately related to the surface conditions, and a distinct long-term behavior is found for each type of interface in cable joints. The significance of the results and their implications are discussed.