A study of interfacial pressure behavior for two types of thermally cycled coldshrinkable joints

Joints are generally known to be the weakest link of underground distribution lines. One of the most common failure modes is attributable to the occurrence of dielectric breakdown at the cable-joint interface. Interfacial pressure is known to be a key factor in the interfacial breakdown strength: a high interfacial pressure leads to good dielectric breakdown strength whereas a lower pressure leads to poor long-term-performance.The present work shows the behavior of two different types of distribution cable joints: ethylene-propylene rubber (EPR) based coldshrinkable cable joint and silicone rubber (SR) based coldshrinkable cable joint. Interfacial pressure was monitored for thermal cycles at three different temperatures: 75, 90 and 130°C. The cycling protocol is based on an existing IEEE standard for cable joints for use with extruded dielectric cables rated 5-138 kV. A preliminary theoretical model has been developed and compared to the obtained data.