A Review of Resistive Compounds for Primary URD Cables

Olefinic copolymers heavily loaded with high-structure conductive carbon black, used as conductor and core screens for primary feeders in underground distribution are discussed. These materials may be either thermoplastic or cross linked. Electrical and mechanical characteristics of these compounds and the manner in which they are affected by the type of base resin and by the type and quantity of carbon black are reviewed. The process of electrical conduction through the boundary layer and through the body of the compound is treated in some detail. Processability is an important consideration and orientation induced by the extrusion process can lead to anisotropic electrical properties. Reference is made to the influence of various environments which the cable may encounter in service. The value of resistivity required in cable constructions is also briefly discussed. Attention is drawn to the need for a specification of the required performance of a resistive compound. It is also recommended that cables using these types of covering that have been in service for a number of years should be examined to study the changes in properties that may have occurred.