In September 2015, after two years of construction, Eneco's Luchterduinen wind farm officially commenced operation. The order to monitor the wind turbine foundations, located 23 kilometers along the North Sea coast between Zanderfurt and Nordwijk, was awarded to Zensor, a specialist in intelligent monitoring solutions. In this monitoring system, a Beckhoff CX2020 embedded controller collects data from sensors distributed throughout the wind turbine foundation structure and transmits the measured data to the cloud.
The offshore wind power industry is booming; however, it also faces many specific challenges. Regular inspections and maintenance of wind turbines are essential to ensure reliable operation, especially given their exposure to extreme weather conditions and highly corrosive environments. However, sending a technician to the site for turbine maintenance is both time-consuming and expensive. Another issue is that the ground around the turbine can subside, gradually collapse, or even sink over time. “In some offshore wind farms, the turbine towers are secured using transition sections and monopile structures driven into the seabed,” explains Yves Van Ingelgem, Business Development Manager at Zensor. “The gap between the transition section and the monopile is filled with a concrete specifically developed for this application. However, the forces of wind can cause the concrete to loosen from the steel structure, leading to foundation subsidence. Other potential problems in the turbine structure include corrosion, material fatigue, bolt and sidewall extension, and concrete cracking.”
High computing power, ultra-compact design
Zensor, a spin-off from the Free University of Brussels, primarily deals in monitoring systems for concrete and steel structures. Initially focusing on developing sensors specifically for material fatigue testing, Zensor now offers comprehensive monitoring solutions, including sensor systems, data acquisition, and reporting.
The company has installed approximately 30 sensors on the four turbines at the Luchterduinen wind farm. These sensors monitor not only various parameters of the structure itself but also the environment within the foundation and indirectly indicate seabed levels through wind turbine dynamics. The CX2020 embedded controller collects all measured data, preprocesses it, and transmits compressed data to land via fiber optic cables integrated into the wind farm's main power transmission line. "We fully leverage the performance potential of our PC-based control system," emphasizes Yves Van Ingelgem. "Other offshore wind farms use PermaZEN sensors, specifically developed by Zensor, to measure corrosion in steel foundations, requiring significant computational power." Zensor uses software written in Python and running on PCs for these calculations.
Images of corrosion are provided in voltage mode.
The PermaZEN sensor consists of a series of electrodes suspended at different water levels within the wind turbine foundation. Gori Nieubourg, a product development engineer at Zensor, explains, “A voltage is generated between the electrodes and the sidewalls of the foundation according to a specific pattern. By comparing this pattern with measured voltage and current values, we can obtain an image of the surface corrosion.”
“The performance of the software-integrated PLC was one of the main reasons we decided to choose Beckhoff,” Gori Nieubourg stated. “With a PC-based automation system, there is no need for additional hardware, as the PLC functions, visualization, and data storage can all be implemented on the Beckhoff platform. The Beckhoff platform requires fewer components and no additional interfaces, making the system more reliable. The wind turbine tower is 100 meters high; thanks to EtherCAT technology, it is easy to use “islands” of fieldbuses over longer distances to transmit sensor signals from a distance to the controller without signal loss.”
Unrestricted peripheral connections
In addition to controlling the PermaZEN sensor, the CX2020 can also control and read data from IntegriZEN—a system that tracks the current state of a concrete structure based on conductivity measurements. All relevant coefficients, such as changes in moisture, crack size, or structural pressure, affect conductivity and can be detected promptly by the monitoring system. Furthermore, the robust openness of the PC-based control system allows for the connection of virtually any type of sensor or instrument.
“We are providing a modular solution,” Yves Van Ingelgem explained. “This allows us to implement the ideal application for each project without imposing any limitations on the PC platform. For some measurements, we use standard sensors connected via analog or digital I/O or via Modbus. Whether we are using a simple temperature sensor or a sonar scanning the seabed, it is sufficient to simply add a terminal module to the system for each additional measurement type.”
XFC terminal modules with high sampling rates ensure a competitive advantage.
Most of the measured values were read through the EL3602 24-bit analog I/O terminal module. “Zensor uses XFC terminal modules with integrated oversampling technology, which have sampling frequencies up to 100 kHz. These terminal modules offer performance levels typical of high-end measurement applications, which is not typical for PLCs,” emphasized Gori Nieubourg. “The resolution of the measured values, combined with the high sampling rate, is a key factor in enhancing the competitive advantage of our solution. Another advantage is that Beckhoff provides this performance within a standard automation system that meets all the robust requirements of industrial applications. Furthermore, the fact that the PLC software runs on PC-based hardware was also a significant reason for our choice of Beckhoff: on the PLC side, we have the high flexibility of the I/O and XFC terminal modules. On the PC side, we use computing power to filter process data, perform frequency analysis, and compare measured values with predefined thresholds.”
Early detection of potential problems maximizes availability
However, Zensor's monitoring solution extends beyond the equipment within the wind turbines: all measured data is compressed within CX and transmitted via fiber optic cable to a server on land. There, a cloud solution is available for wind farm operators to monitor the system. All measured data is traceable in real time; trends and deviations are illustrated through charts. Furthermore, Zensor can specifically analyze available data to answer specific questions related to the turbine's structure, enabling regular checks and the identification of preventative measures as needed.
“Sometimes, changes in offshore weather conditions prevent us from getting close to the offshore wind turbines, making it difficult to resolve issues quickly,” Yves Van Ingelgem added. “But we can detect potential problems early on, allowing customers to prepare and plan ahead, and perform maintenance or repairs at the most appropriate time.” Therefore, intensive monitoring also helps save costs and ensures maximum turbine availability.
