New technologies, standards, and maintenance methods in spacer cable systems

Abstract

The overhead distribution lines with bare conductors for medium and low voltage circuits are being substituted due to their failure rate and security level, and not meeting customer needs, particularly in adverse areas, i.e., heavy trees and high isokeraunic levels. The failure rate in CEMIG's medium voltage overhead distribution lines, in urban areas, is 0.9 failure/km-year. More and more customers ask for better services and lower costs. These types of systems are greatly influenced by external causes such as lightning, rain, trees, collision, and vandalism. In Brazil, based on the US experience, the aerial spacer cable system has been shown as the best system to improve its reliability. The low maintenance cost, easy operation, high security level and the attractive cost-benefits have justified its use, mainly in urban areas, by CEMIG, a Brazilian Utility. In the MV spacer cable system were included other technologies, such as CSP transformer, SF/sub 6/ switch, medium and low voltage polymeric arresters, low voltage multiplex cable, and wedge and piercing connectors. CEMIG's spacer cable system has been getting an average failure rate of 0.04 failure/km-year. This paper describes the line design, equipment, standards and also, the maintenance methods in live-line and field experiences of spacer cable system in our company, with the technical support of Hendrix Wire & Cable and Wirex Cable, Brazil. Other utilities in Brazil are now using this system, to meet one of the government's requirements of improving reliability. It is a good alternative for companies searching for high reliability for their distribution electrical system.