Silicone Injection of Cables with Poly-isobutylene Based Water-blocked Conductor

Longitudinal water-blocking compounds were introduced into the construction of solid-dielectric cables beginning in the late 1970s. Today, over 95% of medium-voltage underground cable manufactured with stranded conductor is water-blocked with pumpable mastics or water absorbing powders and yarns. While these water-blocking materials prevent water migration along the conductor, they do not prevent radial water diffusion or water-tree growth. With the oldest cables manufactured with water-blocked conductor exceeding 40 years of age, circuit owners are faced with the challenge of how to maintain the reliability of thousands of kilometers installed without the option of conventional cable injection. This paper will review the history of cables with longitudinal water-blocked conductor and introduce a new method of cable injection to specifically address this population of cable.