The number of emergency stops during a 20-year service life of a wind turbine is typically between 500 and 1,000 stops. This means a durable and reliable braking system in a wind turbine is essential to its safe operation. Effective wind-turbine brakes must perform two critical functions: maintain the stability of the nacelle when it turns and as it orients toward the wind.
Wind turbines are equipped with numerous safety devices to ensure safe operation. One essential safety component is the braking system. Yaw brakes are used to stop and hold the rotating nacelle in position once the rotors have been turned to face into the wind.`Wind turbines are equipped with numerous safety devices to ensure safe operation. One essential safety component is the braking system. Yaw brakes are used to stop and hold the rotating nacelle in position once the rotors have been turned to face into the wind.
Wind-turbine brakes are critical for managing risk and protecting assets in the case of high wind speeds. The integrity and safety of a wind turbine relies heavily on this system and if it is damaged, repairs and component replacements can be challenging and costly. Wind towers are dozens of meters above the ground, making wind-tech safety another important consideration.
One idea is a portable tool that can be mounted directly to a wind tower, allowing for easier onsite reparations of the yaw disc.
Brakes uncovered
The braking system consists of a set of hydraulic clamps and calipers set up around the braking or yaw disc. The job of the caliper is to slow the disc by creating friction. When the brake is activated, a piston placed inside the caliper essentially squeezes the brake pads against the braking disc. This applied pressure generates frictional force in the opposite direction of the rotation, causing the nacelle or rotors to stop.
However, the disc brake must meet specific parameters for an ideal function. For example, the surface finish and track flatness are important features, and small imperfections may lead to wear or poor performance. The distance from the track to the brake may also affect performance if misaligned. In fact, even slight deviations from these parameters overstress the components and create a lack of traction in the brakes that put a wind turbine at risk of damage or failure.
Hold the brakes
Should the brake calipers become damaged in a wind turbine, replacement is fairly simple because they are relatively small and light components (of course, minus the time and cost of the work up-tower). However, the brake discs tell a different story. These discs are heavy and big — typically more than two meters in diameter. What’s more is that they are commonly embedded between the tower flange and nacelle frame, making it extremely difficult to disassemble and move during repairs or replacement.
To complicate matters, wind farms are typically in remote locations that are difficult access. Wind towers are dozens of meters above ground with limited space in the nacelle for movement, making a relatively simple disc repair costly and complex. When a yaw disc is damaged, however, the conventional repair procedure is to completely exchange the damaged braking track for a new one. This requires a safe and (ideally) spacious work area.
A portable repair
One company — in collaboration with turbine manufacturers and wind-farm owners — has been working to fix the challenges of up-tower brake disc replacements. iZanda Portable Machine Tools, an engineering and machinery company, says it has analyzed the problems that occur during such procedures over several years and developed specialized portable machinery to address up-tower challenges.
iZanda Portable Machine Tools recently released a case study about the effectiveness of a new up-tower brake disc repair tool that the company has engineered for wind turbines. The aim is to avoid costly crane use, disassembly or dismounting of a turbine nacelle, and the expense of a brand-new yaw disc. These images show the damage of a braking disc track before repair (left) and after use of iZanda’s new, patent-pending tool (right).
“This portable tool can be hoisted and mounted up to the wind tower without the use of a crane to perform onsite reparations of the yaw disc,” explains Marta Díaz International Manager with iZanda. “It is specifically designed to work in the small and cramped space of the nacelle, and can be mounted by screws in the frame or reinforced with welding if necessary.”
According to Díaz, the tool means a full disc repair can occur in about three or four days, rather than one week or longer. “We’ve also recently modified the machine to increase its efficiency by improving the cutting tools and reducing the weight of its components for easier assembly.”
“It’s an advancement in the industry that allows a quick, cost-effective repair — which more often than not avoids the replacement of a damaged component for a new one,” she adds.
Filed Under: Components, News, O&M
