While the wind-swept ridge tops of the West Texas plains are ideal for generating wind power, harsh site conditions can degrade turbine blades due to erosion from dirt, hail, lightning strikes, insects, and other airborne particles. Plus, fatigue from the sun’s UV rays and other natural elements leave hairline cracks and gouges in the leading edge. If not mended, water can seep through these minute cracks and cause damage that could require major blade repairs in the future. After years of service and millions of blade rotations, one company decided it was time for some major inspection and maintenance on the turbine blades of their large wind farm near Sweetwater, Texas.
The management company decided to perform a complete inspection and leading-edge refurbishment on all blades on the farm, rather than repair blades on an individual case-by-case basis. Performing maintenance in this manner would minimize shutdown time and reduce the likelihood of major problems that require shutdown for extended repair in the near future.
The first phase of inspection and refurbishment began on a group of 1.5-MW turbines in an area damaged by a violent lightning storm. Because a typical 1.5-MW turbine outputs upward of 36 MW of power per day, the cost to shut one down can run $800 or more a day. Minimizing downtime and keeping turbines running efficiently are critical factors in maximizing ROI. Also, having a clean, refurbished leading edge on the blades lets the turbine perform at a higher output and maximizes long-term blade performance due to reduced friction when the blades move through the air.
The refurbishment required workers to physically inspect all blades on site, document required work, and then repair and refurbish the leading edge as well as other areas on the blade. First, workers sanded the blade, then filled any cracks and gouges with putty. They applied two layers of a leading-edge protectant and finished the area with two top coats of polyurethane. Two different colors of protectant (first red, then white) were used so when blade erosion occurs, it will be easier to determine the extent of repair needed when viewed from ground level.
When the first phase of the project went out for bid, the management company contacted a number of contractors to determine the most thorough and economical way to perform the work. In addition to cost, minimum turbine downtime was also considered. There were a number of ways to inspect and repair the blades such as working from suspended scaffolding, rappelling down from the nacelle, or using a basket suspended from a crane. The companies used a combination of all techniques.
After the contract was awarded and work began on the site, the contracted company performed most of the inspection and refurbishing from suspended scaffolding. However, to keep the work running on schedule, they chose TGM Wind Services of Abilene, Texas (tgmwind.com) to help. TGM specialized in this type of work but used a different technique to access the overhead areas: aerial work platforms. Aerials are relatively new to North American wind farms. However, they have been used to maintain turbines in Europe and globally for many years, and time-tested in harsh conditions. With the extra productivity the aerials provided on the job, progress proceeded on schedule.
When it was time to solicit bids on the refurbishment of blades in the next phase of the overall project, site management remembered the aerial work platforms they had seen in the initial phase and added TGM Wind Services to the list of companies to whom they sent requests for quotations. The project included inspecting and refurbishing the blades on 25, 1.5-MW GE turbines.
The machines management saw TGM operating were Bronto Skylift Model S-90 HLA truck-mounted aerial work platforms. TGM owns four of the large aerials and has used them on towers since they took delivery of the first two machines in 2010, with two additional units earlier this year. Through their experience and knowledge from earlier work on the site, TGM knew they could meet management’s expectations and agreed to submit a bid.
Mounted on a 6-axle Kimball chassis, TGM’s 90-m working height Bronto machines can drive directly to a turbine. Also, advanced outrigger controls and one-button automatic leveling allow positioning, setting up, and elevating the machines to the overhead area in 15 to 20 minutes, or less, from the time they arrive on site. This can save considerable time and lower transportation and set-up costs when compared with some other methods on a multi-tower site.
The machines can withstand winds speeds up to 12.5 m/s (28 mph) when elevated. They can lift up to 1000 lbs of men and materials in an 8-ft by 3-ft, enclosed platform to a 90-m maximum working height with a maximum horizontal outreach of 33m.
TGM’s Bronto S-90 HLA machines are also equipped with electrical, pneumatic, hydraulic, and water lines that run inside the telescoping boom from the ground to outlets in the platform. The lines let technicians easily operate power tools and washers from the platform. This saves time and is much safer because it eliminates lines or hoses running down from the overhead platform to ground level, thereby reducing the chance of accidental contact by workers or passing vehicles.
These capabilities result in faster, safer inspection and maintenance of turbine exteriors and blades at a lower cost than other currently used methods. Some methods, such as suspended scaffolding, require fastening cables inside the nacelle and letting down from a hole in the nacelle body. But aerials are non-invasive and don’t require any access inside the nacelle to reach the blades.
Aerial work platforms can also be safer to operate, which was a major concern of site management. The aerial device’s platform is mounted on a telescoping boom affixed to a ground-level turntable and operated directly from the platform, so technicians have greater control in platform positioning. Also, unlike platforms suspended from overhead cables, the lifts are not as susceptible to wind forces. So techs can get up close to the blades and maintain that position while working. All TGM technicians have been factory certified to operate the aerials and received training in first aid, CPR, and other disciplines as required by the wind-farm management for all workers on site.
Because of Bronto’s aerial work platform capabilities and TGM Wind Services’ experience with similar projects, VP of TGM Kevin Darby provided site management with a fixed price quote per blade no matter what repairs or supplies were required. In addition, Darby said that TGM would inspect and refurbish an average of one turbine (three blades) per day depending on favorable weather conditions. Most other companies that provided quotes based their costs on time and materials or per diem rates.
The platforms let TGM offer a competitive package. With a fixed price, less turbine downtime, and a lower overall cost, site management couldn’t pass it up and awarded TGM the contract. Not only did TGM perform as promised, they exceeded their commitment.
Filed Under: O&M