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WORKING LIVE ON TRANSMISSION LINE STRUCTURESDeveloping protective coating maintenance strategies

BY GEORGE JUHN & ALEX MOGILEVSKY, CEATI International

Aging of the electrical transmission infrastructure has resulted in an increased need for maintenance to ensure a reliable supply of power to customers who have higher expectations than ever before.

Further complicating the situation is an increase in electrical congestion and the financial implications of shutting down a supply or network line for extended periods of time to carry out the required maintenance. In response to these system, financial, and customer demands, many utilities are led to perform maintenance on energized transmission lines.

As one travels throughout North America and takes a close look at the many transmission structures, it is evident that there is, or will be, a necessity to invest in reinstating protective coating to prevent any further deterioration. The potential consequences of performing this “live line” work has led to a need to document and collate technologies, methods, and approaches for recoating transmission structures without having to schedule a line outage. Note that many utilities have initiated transmission line structure coating programs based on in-house research without the availability of industry standards for many of the situations addressed.

Leading utilities in the industry recognize the benefits of collaborative efforts among peers to respond to industry issues of this type, and through the Centre for Energy Advancement through Technological Innovation (CEATI) International commissioned a study entitled “Transmission Line Structures – Recoating While Energized”. The study was completed in 2010 by Quanta Technology, an expert in the field of transmission line asset man-agement, along with the support of AltaLinkLP, BC Hydro, Bonneville Power Administration, Hydro One Networks Inc., Hydro-Québec TransÉnergie, Manitoba Hydro, and Transpower New Zealand Ltd.

In addition to this study, participating utilities in one of CEATI’s twelve transmission focused programs (the Transmission Line Asset Management Interest Group), undertook related studies that included the development of protective coating maintenance strategies for steel transmission towers and methods to assess the condition of structures and coatings. Furthermore, working groups led by the National Association of Corrosion Engineers

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WORKING LIVE ON TRANSMISSION LINE STRUCTURES

(NACE) and the Institute of Electrical and Electronic Engineers (IEEE) are in the process of developing a standard for corrosion control of existing electrical transmission structures by coating systems.

The “Recoating While Energized” study incorporated information pro-vided by a number of utilities and coating service providers. Additionally, the report examined methods and procedures for recoating/repainting trans-mission line support structures while energized with an emphasis on safety. The study includes a description of the methods and procedures in sufficient detail to allow interested parties to review, contact, and initiate discussions with potential service providers. As well, a number of the avail able coating materials are highlighted and automated equipment, such as robotics, is included as a key focus area.

Corrosion related to the loss of galvanization for steel-based transmission line structures is a primary concern in the application of protective coatings.

VARIATIONS IN UTILITY PRACTICESThe report highlights significant variations in practices for painting structures while transmission lines are energized. About 54 percent of the responding utilities have painted or recoated transmission line structures while the lines were energized. Some utilities would paint the entire transmission line structure while the lines are energized as standard practice, while others paint only sections of the structure (typically up to the conductor level). Certain utilities do not paint any part of the structure while energized, with restrictions due mainly to safety and/or labour regulations.

A few utility participants rely on outside contractors to do the work and use them as their standard mod el; this is the case particularly for U.S.-based utilities. Still others develop their own staff before an out side con tractor can be utilized; which is the case particularly for Canada-based utilities.

The utilities confirmed the use of painters or app rentice linemen to per-form this work. No utilities iden tified trained linemen for coating towers, as they gen erally lack the painting skills necessary.

Study results that can be applied to everyday operations• Offer an understanding of current utility and service

provider practices regarding painting/recoating energized transmission line structures, thereby providing the backdrop for improved planning and work procedure development.

• Identify potential risks and mitigation measures as well as provide for review/assessment specific planning considerations by maintenance engineers and managers to manage work of this type more effectively. Specific planning considerations include: 1) factors that influence a method/procedure; 2) training and experience of the crew; 3) structure types and access to the structure; 4) environmental issues; 5) weather; and 6) equipment needs.

• Gain knowledge about types of protective coatings and surface preparation methods in use.

• Assist in the development of detailed procedures to paint/recoat energized transmission line structures.

• Outline information on service providers to initiate communications about potential contracts to paint/recoat energized transmission line structures.

• Educate utility personnel regarding alternative methods to paint/ recoat transmission line structures.

PRACTICAL APPLICATIONS

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One promising alternative approach to the methods de-scribed in the full report is the use of robotic tech nologies. Ground-based robots could be used to separate the live conductors from the structure, there fore allowing more distance for a crew to safely paint 115 kV to 500 kV struc-tures. There are indications that util izing ground-based ro-bots would allow for the de velopment of more efficient tech-niques, but most ser vice providers do not consider util izing this technology be cause they are not in the util ity business. There is a high degree of electrical ex per tise required to utilize ground-based ro botics, yet service providers at this time primarily employ painters trained to work near energized equipment without the necessary engin eer ing and line main tain er expertise. ET

George Juhn (Technical Advisor) and Alex Mogil evsky (Senior Program Manager ­ T&D) are aff liated with CEATI International, a global organ­ization composed of 120­plus electrical utilities.

COMMENTS: alex.mogilevsky@ceati.com

FAMOUS LAST WORDS

Additionally, service providers reported varying practices regarding the painting of structures while transmission lines are energized. Particularly in the U.S. market, some service providers paint the entire transmission line structure while energized as a core business. Up to 80 to 90 percent of their business is paint ing structures while energized, and they estimate that about 90 percent of the transmission (115 kilo volts and above) structures in the U.S. can be com pletely painted while energized.

Other service providers, particularly in the Can adian market, only paint sections of the structure—typically up to the conductor level—while en-ergized, and other service providers do not paint any part of the structure while energized. Qualified service pro viders are numerous in the U.S. while there are only a few currently operating in Canada.

SAFETY OF PARAMOUNT IMPORTANCEIn order to carry out the task safely, painters receive train ing in climbing, electrical safety, personal pro tective equipment, and other aspects needed to carry out the work. The electrical minimum approach distance is the key factor that determines if a structure can be painted while energized. Responses from util ities and service providers indicated that it might take several years to develop staff capable of painting near energized areas such as a structure’s arm. Service providers shared guidelines for the job execution and these aspects are described in the report.

Safety is of paramount importance, making pain ting/recoating ener gized transmission line struc tures a high risk and labour intensive job. Detailed procedures must be written by the personnel that will be at the field site, either working, or supervising the crew op erations. Skilled and experienced personnel are a pre-requisite for developing safe and efficient work pro cedures.

A method for painting/recoating a 161 kV steel monopole transmission line structure is presented. The structure was divided into six zones with in-creasing levels of risks. The minimum approach distance for this structure was identified and used to conclude that, in this particular case, the section at the structure arms could not be painted while energized due to violations to the minimum approach distance.

The report summarizes a variety of responses showing the extent to which a tower can be painted while energized, and concludes that this is a function of the utility or service provider’s understanding of live line work, the skill set of the personnel involved, the risks that they are willing to take, and the safety procedures developed for executing the job.

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138 kV tower upgrade