Importance of materials in composite conductors

Abstract

Composite conductors offer exceptional sag-reduction benefits and increased capacity when compared to conventional conductors. They are therefore increasingly considered for overhead transmission line thermal upgrades. There are two types of fiber composites used in overhead conductors: polymer matrix composites (PMCs) and metal matrix composites (MMCs). PMCs are limited by their polymer matrix which can age and degrade under environmental and high temperature conditions. Two predominant polymer aging mechanisms are thermal oxidation near the glass transition temperature, and water absorption in hot-wet environments. Both aging mechanisms are specific to PMCs and can severely deteriorate the shear, bend and compressive strengths. Poor bend and shear strength can lead to failure when the PMC is subjected to off-axis loading such as during installation and in connectors. MMCs used in transmission lines consist of fibers embedded in an aluminum matrix. They are generally heavier and have a slightly lower sag performance than PMCs. The shear and compression properties in MMC conductors are governed by the aluminum matrix. The aluminum matrix strength is stable under aging at high temperature and is not affected by moisture. MMCs retain good tensile, bending, and compressive strengths after environmental exposure at high temperatures.