Condition Assessment and Reliability Evaluation of Utility Wood Poles Using Fuzzy Logic and Monte Carlo Simulations

摘要

Hydro One currently has close to 2 million utility wood poles in service. The majority (close to 1.7 million) are distribution poles supporting low voltage wires up to 44 kV, while the remainder support high voltage wires up to 230 kV. This massive network of wood pole lines was built over 100 years ago. Many of these structures are still in service beyond their original design life of 35 to 40 years. To establish an efficient maintenance and replacement program, it is important to first evaluate existing wood pole damage states through periodical inspections and assessment. The damage assessment of existing wood pole structures is, however, a difficult task due to the lack of accurate information (visually collected information) and the complex nature of wood pole deterioration. Currently, there is no well-established procedure for wood pole inspectors to follow when assessing the combined effects of multiple deterioration or damages on a wood pole structure. Consequently, the evaluation of an existing utility wood pole is based on a highly subjective procedure, and usually suffers from imprecision and personal bias. Different wood pole inspectors may assess a given pole differently. Characterization of the uncertainties inherent in wood pole lines and their operating environment is complicated by the presence of time. As soon as the line becomes energized or operational, it begins to age. As the system ages or goes through various maintenance and upgrades, the inherent uncertainties will also undergo continuous change. As time passes the microstructure will evolve, microorganisms and insects will invade the wood and strength will deteriorate. The objective of this paper is to examine the application of fuzzy logic for condition assessment and Monte Carlo simulations for reliability evaluation of wood pole structures when subjected to multiple deterioration symptoms. A number of factors that affect the condition of a wood pole are examined. These include cracks, surface rot, mechanical damages, bird damages (woodpecker holes) etc. A wood pole expert system (WPES) was developed for condition assessment and failure probability of wood pole lines. For condition assessment, a fuzzy condition rating model for combining the visually observed symptoms of failures is developed. The use of fuzzy set theory to model the deterioration symptoms of transmission structures was introduced by Hathout [1]. The model developed in this paper is based on a fuzzy computational technique called resolution identity of fuzzy sets where a fuzzy set is decomposed into non-fuzzy level sets by slicing the fuzzy set at different a-levels or membership levels [2]. The strengths of the wood pole structures are calculated as functions of their wind speed resistance just before collapse. The fuzzy condition assessment is then introduced to calculate the actual or damaged wind resistance of the wood pole structures. Monte Carlo simulations are then performed to calculate the probability of failure of a wood pole line using the actual wind resistance of the structures and wind speed records from the nearest weather station. Case studies are included to illustrate the proposed models. These models are expected to reduce the subjectivity inherent in the visual inspection and assessment of existing wood pole structures. They will allow engineers with no background in damage assessment to accurately predict the failure of wood pole structures subjected to multiple deterioration symptoms.