Foreword : Onshore and offshore wind turbines typically use more than a dozen sensors that can perform their tasks correctly and withstand extremely harsh environmental conditions.
Wind turbines are not only exposed to the natural environment, but must also operate absolutely reliably under the harshest conditions. Even after 20 or 30 years of operation, they are expected to maintain optimal performance in any weather, providing the highest economic benefits and minimizing downtime. Achieving these goals requires sophisticated sensor technology with both safety and performance reliability. Incremental sensors and tachogenerators play a key role, and they must simultaneously meet stringent requirements for reliability and durability. Onshore and offshore wind turbines typically use more than a dozen sensors that can perform their tasks correctly and withstand extremely harsh environmental conditions.
Just as wind turbines vary in size, performance, and structure, the requirements for the sensors they employ also differ. Success in this market requires consideration of the diverse structural, maintenance, and operational needs of wind turbine manufacturers and owners. Baumer's extensive product portfolio, combining its rich technical expertise and years of professional experience, fully meets these requirements. The Baumer Group's Motion Control Products division offers suitable products for various applications in the wind energy industry, meeting current and future requirements (Figures 1a and 1b).
Figure 1a: More than a dozen encoders and tachogenerators play an indispensable role in ensuring the safe, reliable, economical, efficient and long-term stable operation of wind turbines.
Figure 1b: One-stop solution: For many years, Baumer has worked closely with renowned wind turbine manufacturers to develop customized solutions. Its extensive product selection can meet virtually any application requirement.
Rotor speed and position feedback
To ensure wind turbines achieve top performance and optimal efficiency, rotor speed must be adjusted according to wind force and direction. Incremental sensors used to monitor rotational speed can be mounted directly on the rotor hub or on the wind turbine's drive system to obtain the current rotor speed and transmit the information to the main controller.
Absolute encoders provide rotor position feedback at any time, with a maximum resolution of 17 bits, and often employ parallel incremental channels to obtain redundant speed feedback. More high-performance products include the new HDmag series of bearingless magnetic encoders, which can also accurately perform generator feedback tasks. Thanks to their extremely compact design, they allow for large axial and radial tolerances during installation. Bearingless encoders for highly dynamic applications can be directly mounted on rapidly rotating generator shafts, completing over 25,000,000,000 revolutions over 20 years. This clearly exceeds the capabilities of ball bearings. Encoders with a maximum through-bore diameter of 740 mm are mounted directly on the hub (Figure 6). Bearingless encoders generate over 500,000 pulses per revolution, and this high resolution allows them to accurately acquire relatively low rotor speeds.
Figure 6: A bearingless incremental or absolute encoder with a maximum through-hole diameter of 740 mm is directly mounted on the rotor hub.
Rotor blade positioning: A challenge for absolute encoders
The pitch angle of the rotor blades is crucial to the power generation efficiency of a wind turbine. To maximize the use of wind power from different wind directions, the windward side of the rotor blades must be aligned with the wind direction. Because absolute encoders (Figure 3) can also retain position values during power outages and serve as a reference cycle when redundant generators restart, they are the preferred products for position feedback.
Figure 3: Rotor blade pitch control: a perfect challenge for absolute encoders using SSI, CANopen or any other fieldbus interface and Ethernet technology.
Absolute encoders are available in through-hole and shaft designs. They are integrated into the pitch system and move with each rotor blade under the action of the yaw mechanism, thus enabling redundant measurements. The acquired values are transmitted to the wind turbine's main controller via optional SSI, CANopen, Ethernet, or other fieldbus interfaces.
Encoder for generator feedback
Generator speed is a crucial factor in the operation of wind farms: firstly, it ensures a stable power supply from the grid, and secondly, it enables emergency shutdown of the turbines when the maximum speed limit is exceeded. Incremental encoders have proven to be a reliable choice for these applications. Since overspeed switches can act as emergency stop triggers when speed thresholds are exceeded (Figure 4), incremental encoders can be used in conjunction with them, playing a key role in the profitability and operational safety of wind farms.
Figure 4: Since the overspeed switch can be used as an emergency stop trigger when the speed threshold is exceeded, incremental encoders or tachogenerators can be used in conjunction with it, playing a key role in the profitability and operational safety of power plants.
Heavy-duty encoders with through-hole diameters up to 150mm can deliver up to 10,000 pulses per revolution. For example, the HOG131 encoder series features excellent vibration resistance and superior weather resistance, making it a perfect product for applications in high-salinity air and harsh marine environments (Figure 2).
Figure 2: For example, the HOG131 encoder series features excellent vibration resistance and superior weather resistance, making it a perfect product for applications in high-salinity air and harsh marine environments.
The shaft encoder employs a special seal to meet robustness requirements. With integrated lightning protection, an operating temperature range of -40°C to +100°C, and special surface protection, reliable operation is ensured even under extreme conditions. Integrated condition monitoring (Figure 5) functions as a fault warning system, significantly reducing the risk of unexpected failures. Because potential errors are eliminated during regular maintenance, intolerable power plant downtime due to sensor malfunctions is avoided.
Figure 5: Enhanced security through integrated condition monitoring (EMS – Enhanced Monitoring System): Unacceptable power plant downtime due to sensor failures is avoided as potential errors are eliminated during regular maintenance.
Cabin motion control: Precise positioning achieved by absolute multi-turn encoders
To optimally utilize the prevailing wind and ensure maximum power generation efficiency of the wind farm, the nacelle must rotate and align with the current wind direction. This so-called azimuth positioning requires simultaneous acquisition of both the rotation direction and position. This task is typically accomplished by an absolute multi-turn encoder (Figure 7) via optical or magnetic sensing. The compact design, extremely high shock and vibration resistance, and wide operating temperature range ensure the long-term reliability of absolute multi-turn encoders. Baumer's patented encoder solution can withstand continuous shocks up to 500G and employs an electrically insulated shaft to effectively prevent the influence of shaft current.
Figure 7: Precise cabin motion control: For so-called azimuth positioning, the direction of rotation and position must be obtained simultaneously, which is usually accomplished using an absolute multi-turn encoder.
We offer a wide selection of products, including standardized products and customized solutions, taking into full account the resolution and interface requirements, field installation conditions, and durability and robustness requirements for both onshore and offshore applications, to suit the specific technical and structural characteristics of each wind turbine.
The Baumer encoder series, which meets stringent safety requirements, includes a wide range of absolute and incremental encoders with different mechanical structures (Figure 8), all of which comply with SIL3 (IEC 62061) and PLe standards (EN ISO 13849-1).
Figure 8: The Baumer encoder series, which meets stringent safety requirements, includes a wide range of absolute and incremental encoders with different mechanical structures (Figure 8), all of which comply with SIL3 (IEC 62061) and PLe standards (EN ISO 13849-1).
Figure 9: Impressive wind turbines require a large number of reliable sensors to ensure a long-term, efficient, and safe supply of renewable energy.
