A strong tailwind
Modern wind turbines are extremely efficient: If a new turbine is built today, it produces around 20 times more electricity than those built 20 years ago. Optimized and automated power control is one of the main reasons for this increase in efficiency. Balluff position measuring systems are used worldwide for power control – including at Shanghai Electrics, one of the largest operators of offshore wind farms in China.
Why are today’s wind turbines so much more efficient? In addition to the changed size of the turbines, optimized power control also plays an important role in the increase in performance. Even in low wind conditions, the blades of modern wind turbines still turn. If the wind speeds fluctuate strongly, the modern control system ensures the generator is utilized as evenly as possible. In the event of storms or gale-force winds, the wind turbine speeds are reduced or they are brought to a complete standstill for their own protection. The position of the rotor blades plays a central role, as it determines how much force is applied to the blades – and ultimately how fast the wind turbine turns. The optimum position of the rotor blades is achieved by means of the pitch adjustment. This involves changing the pitch angle of the respective rotor blade, which can lead to deceleration or even a stop. Modern turbines use two different methods of power control: Hydraulic and electric adjustment.
The right choice
Shanghai Electric – a leading global manufacturer of power generation equipment and related infrastructure from China – was also faced with the choice of the appropriate power control technology. “When we started planning the offshore wind farms off the coast of China, we considered both hydraulic and electric adjustment,” explains Jun Miao, vice president at Shanghai Electric Wind Power Group. Both approaches have their advantages and disadvantages. In order to provide the required torque for today’s systems with electric pitch adjustment, motors of an appropriately large size must be used.
If the power ever fails, batteries ensure that the turbine receives the torque for its primary setting and can start up again. “A battery has to be charged or replaced regularly. This leads to additional maintenance costs and the environmental impact of batteries is also under criticism,” explains Industry Manager Kris Xin of Balluff, who advised Cheng’s team on the selection of the appropriate power control system. “Even in the event of a power failure, the hydraulics of the accumulators have sufficient power reserve to provide the torque for start-up. Another advantage is that the hydraulic mechanism has a dampened principle of operation and is therefore gentle on moving components.” In the end, the arguments in favor of hydraulic pitch adjustment were convincing, because it requires little maintenance and has a longer service life.
China focuses on wind power
Wind energy is experiencing a real boom in China. According to the Chinese energy authority, wind turbines with a total capacity of almost 72 gigawatts were installed in 2020. The country has advanced to the top of the world in this sector internationally. Shanghai Electric is striving to become China’s largest provider of offshore wind energy.
Worldwide, the company is ranked among the top 10. Since 2018, Balluff has been supporting the company in the realization of more than 50 offshore wind farms. The nacelles required for the wind turbines are assembled in Shanghai and then installed along the southeastern coast of China. Once all the wind farms are completed, around 3000 wind turbines with a total output of around 800,000 MW will be running.
“Our goal is to effectively reduce the total life cycle cost of offshore wind farms,” explains Zhengxuan Xuan, head of control systems at Shanghai Electric responsible for the entire energy sector. “This can be achieved only if all components are extremely reliable and feature fail-safe performance.” The combination of excellent customer service, experience in the field of industrial automation and industry knowledge for offshore wind farms convinced the company to choose to work with Balluff.
Long service life
To date, a total of around 1000 wind turbines have each been equipped with three magnetostrictive linear position sensors (BTL). These monitor the tilt angle of the rotor blades. The system has been specially developed for use in hydraulic cylinders, because the space-saving housing design of the electronic head allows it to be integrated directly in the cylinder. Thanks to its contactless operating principle, the solution is wear-free and has a long service life. “Balluff not only supplies individual components, but also supported us in finding a solution,” says Yuan Cheng, development manager at Shanghai Electric. “The expert advice helped us decide on a hydraulic pitching solution, which makes Balluff an ideal partner for us.”