Development of a condition assessment model for transmission line in-service wood crossarms

Abstract

Wood transmission structures, such as H frames, have been extensively used to support electrical transmission lines throughout Canada. The transmission infrastructure is in general aging, and fungal decay of wood crossarms poses a significant risk of failure under adverse weather conditions. A crossarm failure in the transmission system can result in forced outages and customer disruptions that lead to significant economic losses. This paper presents a condition assessment model to prioritize the replacement of transmission crossarms that are near the end of their service life. The proposed standard involves a visual condition rating system, which is validated by results of full-scale testing of a sample of in-service crossarms. Aerial inspection of transmission lines using the proposed visual rating system is a simple, economical, fast, and effective method of assessment. The proposed approach would ensure a more consistent compliance with the condition-based replacement standard specified in the Canadian (Canadian Standards Association Standard CSA 22.3 No. 1-01) and North American (US National Electric Safety Code 2002 edition) standards.Key words: transmission structure, wood crossarms, decay, condition assessment, full-scale testing, visual rating system, statistical data analysis, bending strength.