by by Finn Rimmer, Technology Coordinator of CEA Technologies’ Transmission Lines Asset Management Interest Group
Transmission lines have become a staple of our landscapes – they traverse an incredible range of environments, climates and terrains, leaving lasting images. Their longevity is at least partially responsible for this ubiquity. Many of the major systems currently in service were built in the 1960s and 70s, with lines installed at the turn of the century not uncommon. Due to the relatively old age of these structures, most utilities owning and operating high-voltage transmission lines encounter the same types of maintenance problems.
Maintaining reliability, extending the useful life of lines, increasing electrical energy transmission capabilities, preventing failures, and ensuring employee and public safety are all at the forefront of transmission line research and development. Wood crossarms are of particular concern as they are typically quite sensitive to climate. Likewise, climatic concerns are at the heart of the
structural integrity of towers, as atmospheric corrosion affects the galvanization of the steel.
Utilities must also cope with unforeseen events that cause electrical system disturbances, such as tree-induced cascading line failures, failed electrical protection systems, major storm damage and other component failures. As was experienced during the blackout of 2003 and the ice storm of 1998, the loss of a major transmission line shows the point at which our society is dependant on a reliable electric energy source, underscoring the need for utility engineers and managers to find effective solutions in preventing these occurrences.
To deal with these concerns, leading utilities are examining the economic impact of these problems and revisiting their planning and operations practices. Many are also heavily involved in the establishment of equipment protection standards and regulatory guidelines in the ultimate goal of minimizing the combined cost of supply and use of electricity by achieving a high degree of transmission reliability.
To facilitate these efforts, CEA Technologies Inc. (CEATI) has organized a Transmission Lines Asset Management Interest Group (TLAMIG), bringing together electrical utilities from around the world to exchange information and to sponsor technology development with the goal of optimizing the management of transmission line system assets.
The Transmission Lines Asset Management Interest Group is currently financing several key projects, including:
• Condition Assessment Methodology for H-Frame Transmission Line Wood Crossarms
• Protective Coating Maintenance Strategy for the Above-Ground Portion of Galvanized Steel Transmission Towers
• Vegetation Management in Rights of Way
Condition Assessment Methodology for H-Frame Transmission Line Wood Crossarms
One of weakest links within the transmission grid is the wood crossarm. These structures have been used for over a century to support electric transmission lines. In-service crossarms are
continuously exposed to a wide range of temperature and moisture conditions. Rainwater entrapment may cause the wood to lose much of its structural strength. Presently, the quantitative methods for evaluating the remaining strength life of in-service wood crossarms are underdeveloped. This uncertainty may lead to premature replacement as well as late action on those crossarms requiring maintenance. It is likely that because of this, utilities will be misallocating funds.
The periodic inspection and replacement of wood crossarms is necessary to ensure the
reliability of electric service to customers. However, it is difficult to assess the structural integrity of wood crossarms from the ground, meaning that, to make a qualitative assessment, it is often necessary to conduct aerial inspections. Using these visual assessments, conditions can be graded on a scale from 1 to 5. This method is however very subjective and quantifying the remaining strength and service life of crossarms remains problematic.
CEA Technologies’ Transmission Lines Asset Management Interest Group has initiated a
project to improve condition assessment and service life prediction for in-service H-frame crossarms by correlating the visual grading scale with results of detailed structural analysis and experimental evaluation of in-service crossarms. Through hydraulic actuators and pressure points, the structural analysis will identify the critical sections and potential failure modes of a crossarm structure. This will also lead to the development of an "end of life" criterion which will be an assessment of the level of wood deterioration – needed for the estimation of the remaining life. The ultimate goal is to develop a visual rating system which will be inspector-independent and will reduce the uncertainties intrinsic to the previous system.
Protective Coating Maintenance Strategy for the Above-Ground Portion of Galvanized Steel Transmission Towers
A large number of electrical transmission tower structures in North America are reaching an age at which the effects of atmospheric corrosion of the above-ground portions is now requiring significant increases in maintenance requirements in order to safely remain in service.
The degradation of the galvanizing is leading to corrosion of the underlying steel, thus reducing the structural strength of the towers, which if left unchecked will eventually lead to structural
As atmospheric corrosion rates vary
significantly with location and other factors, and towers were constructed over a large number of years, there is a need to develop a comprehensive evaluation and remediation strategy that will allow transmission utility engineers to make the most efficient use of their available funds.
In the light of this fact, CEA Technologies has launched a tower coating survey which will
determine the current practices used by electrical transmission organizations worldwide for
maintaining the above-ground portion of galvanized or coated steel transmission structures, with the ultimate goal of determining industry best-practices.
The second phase of this project will include both a qualitative assessment of the available inspection tools for determining the condition and remaining service life of towers and a tower coating test program. The test program will assess the application characteristics of each type of paint, the physical properties of each coating, the corrosion resistance of each coating and the weathering resistance of the coated panels.
In the third phase, cost analysis software to determine the exact cost of a tower coating
project will be developed. This software will take into account many important variables in its
calculation, including environmental standards, preparation and travel costs, paint cost, the
number of needed coating applications, labor costs and drying times. This software will assist utilities in managing their funds and asset management activities.
Vegetation Management in Rights of Way
Transmission line rights of way occupy many types of terrain, with the climates encountered varying from tropical to arctic. These climates greatly affect the growth rate of the vegetation seeking to take root on the land beneath transmission line conductors. Transmission lines are designed, engineered and constructed to ensure adequate clearances between conductors and any activity being carried out below. Clearance requirements take into account conductor sags (due to electric loads or ice) and other live loads, such as those from linemen, encountered during maintenance. However, if the ground vegetation is not well-managed, this may eventually lead to an arc being formed between the energized line and the vegetation below.
There are many tools and techniques commercially available to maintain the required clearances. New tools are also being developed for areas where classical tools such as herbicides and tree trimming cannot be used.
It is in light of this that CEATI’s Transmission Lines Asset Management Interest Group will be initiating a state of the art review on vegetation management. This document will contain a
comprehensive resource of practices, products, equipment, materials and their suppliers that can be used for controlling vegetation. This will facilitate the application of cost-effective means of controlling vegetation while adhering to relevant regulatory requirements pertaining to the environment and safe work practices.
Joining Together to Fund Transmission O&M Research
The Transmission Lines Asset Management Interest Group was established as one of the many "interest groups" of CEA Technologies (CEATI). The TLAMIG participants jointly sponsor
studies and research projects in the area of Transmission Line Operations and Maintenance that will benefit them, the electrical utility industry and customers at large.
Participation is open to all electrical utilities, power producers and government organizations that have an interest in transmission line operation- and maintenance-related issues. The group identifies areas of common concern and defines research objectives to solve those concerns. Individual Interest Group participants can then select to co-fund projects of interest that will be of benefit to their organizations. This flexible and collaborative approach provides substantial cost-benefit advantages to the participants.
About the Author
Finn Rimmer is a professional engineer with over 28 years of experience in transmission line
maintenance gained while working for Hydro One (formerly Ontario Hydro). His last position prior to retirement was Manager, Sustainment Programs, Lines. His experience includes high-voltage
underground transmission cables of three types—high pressure liquid-filled, gas compression, and self-contained liquid-filled lead-covered cables. Prior to his experience at Hydro One, Finn was Plant Manager at a Canada Wire and Cable plant in Saint John, New Brunswick and subsequently Corporate Process Engineer for three manufacturing plants for Canada Wire and Cable in Toronto.
Since 2000, Finn has been Technology Coordinator for the Transmission Lines Asset Management Interest Group (TLAMIG) of CEA Technologies Inc.