Evaluation of test methods for longitudinal water blocked cables

Longitudinal water blocked cable designs have gained popularity among many electrical utility and rural cooperative users in North America. These types of cables are used for primary underground distribution which tend to operate in wet environments where the harmful effects of water, especially water tree deterioration of the insulation and corrosion of the metallic components, are of primary concern. In the case of radial water ingress through external damage or other mechanism, the swellable agents and water blocking tape will swell upon contact with water resulting in the formation of gel and restricting longitudinal water propagation to a minimum. This paper investigates proposed test methods in determining longitudinal water penetration of water blocked cables and discusses the results of tests performed on a typical cable design. Longitudinal water penetration testing has been performed under various conditions including hydrostatic pressure applied on unconditioned cable specimens as well as cable under temperature cycling under specific durations. Investigations into the compatibility of the key water blocking components of the cable constructions have encompassed studies of the water swellable agents in both the dry and gelled state under a variety of thermal conditions