AVO New Zealand

Abstract

Utility companies worldwide are striving to reduce the life cycle costs of their medium voltage distribution systems in response to economic and environmental drives. The use of tree retardant XLPE insulation has allowed utilities to achieve long cable service life under severe operating conditions. This has lead to improved life cycle economics and minimized social and environmental issues resulting from cable replacement activities.

This paper will discuss the multitude of accelerated cable aging tests, implications and current global trends for both the TR-XLPE and the Copolymer XLPE insulations. It will review the experience with TR-XLPE in North America, experience with Copolymer XLPE and TR-XLPE in Europe as well as the growing interest and usage of TR-XLPE in Asia. As the long life performance expectations for the MV underground cable system increase, movtivation towards using TR-XLPE as the insulation of choice to achieve these objectives is increasing.

Keywords - crosslinked polyethylene, tree-retardant XLPE, copolymer XLPE, accelerated wet cable testsI.

Full Paper (579KB PDF)

INTRODUCTION

Utility companies worldwide are striving to reduce the life cycle costs of their medium voltage distribution systems in response to economic and environmental drives. The use of tree retardant XLPE insulation has allowed utilities to achieve long service life under severe operating conditions. This has lead to improved life cycle economics and minimized social and environmental issues resulting from cable replacement activities.

When extruded cables with XLPE insulation started to replace the older paper cables in the early 1970’s, there was an expectation that those cables would provide long life with no electrical property degradation. However, in the late 1970’s, it was recognized that XLPE, as well as other polymers, undergo a degradation process, called water treeing, when exposed to moisture and an electrical stress. Two different approaches were used, at about the same time, to solve this problem. In North America, a novel additive formulation approach was used to impart water treeing resistance. The resulting product, called additive TR-XLPE or “TR-XLPE” was introduced in the early 1980’s and has shown excellent field service performance. In Europe, blends of polyethylene with ethylene alkyl acrylate copolymers were used to impart resistance to water treeing degradation. This product, called “Copolymer XLPE”, was also introduced in the early 1980’s and has had excellent field service performance.

This paper will discuss the global experience with tree retardant XLPE cables in medium voltage cable systems. It will review the cable aging test results for both the TR-XLPE and the Copolymer XLPE products as well as review the experience with TR-XLPE in North America, experience with Copolymer XLPE and TR-XLPE in Europe as well as the growing interest and usage of TR-XLPE in Asia.