Life extension of an existing transmission line

The Ontario Hydro Grid System has been built up over the past 89 years and currently consists of 29,000 cct. km (18,000 cct. miles) of 115, 230 and 500 kV lines. Some of the oldest 115 kV lines, constructed in 1906, are still in-service today with most of the original components. By the year 2000, more than one-third of the transmission lines will exceed their 50 year design life. As virtually all these lines are needed indefinitely, they need to be refurbished or replaced to ensure a safe, reliable and economic operation of the transmission line system. The purpose of this paper is to present a process of assessment and evaluation of an existing overhead line and to provide some practical guidelines for life extension of old transmission lines.