Blade monitoring in wind power equipment: "Reducing downtime by up to 80%"
We interviewed Dr. Daniel Brenner, Head of Monitoring Systems at Weidmuller, and Dr. John Reimers, Head of Marketing, regarding the application of the BLADEcontrol® system in wind turbine icing monitoring and blade condition monitoring.
How does icing form in wind power equipment? Where does it form?
Generally, icing can form anywhere, especially during rainy or snowy weather. However, the resulting ice layer is usually very thin. When wind turbines are running, ice is often seen forming on the leading edge of the blades. Ice forms when ice particles in the air are too large to be converted into airflow around the blades. In other words, ice particles collide with the leading edge of the blades and accumulate to form an ice layer. The thickness of the ice formed on the leading edge varies depending on the density of the particles, which in turn depends on temperature and air pressure. The ice on the leading edge causes ice to accumulate on the surface as much as possible, thus forming a thick ice layer. This is why the conservative BLADEcontrol® model focuses on solving the problem of ice accumulation.
The temperatures at which ice forms vary. What are these different temperatures? What climatic conditions cause them to form?
Ice typically forms at temperatures around zero degrees Celsius. If the temperature is far below zero, there is almost no moisture in the air, meaning only a small amount of ice can form. The conditions for ice formation depend on a large number of different parameters. Because the size of ice particles is impossible to measure, ice formation is sometimes unpredictable.
What problems can icing on wind turbine blades cause ?
Ice at the leading edge alters the airflow around the blades, thus reducing energy output. Different blade profiles are sensitive to ice formation to varying degrees.
There is a risk of ice falling from the blades during wind turbine operation, posing a hazard to the surrounding area, and is therefore generally prohibited. Sometimes, ice blocks may impact and damage the next blade, so the wind turbine itself is also susceptible to damage from ice. Furthermore, if ice blocks fall unevenly from the blades, it can cause imbalances in the wind turbine's drive system, increasing the load and reducing its lifespan.
What consequences will this have on the economic viability of wind turbines?
Icing reduces wind turbine power generation due to decreased performance and increased downtime. Depending on the location of ice freezing, the type of icing detection is a significant factor in downtime and can potentially reduce the overall profitability of the project.
What risks do ice layers pose to people?
Ice accumulation on the blades is particularly critical, as the high speeds at the blade tips (up to 250 km/h) mean ice can be thrown a considerable distance. The oldest and most conservative formula for calculating the theoretical throwing distance is 1.5 times the sum of the hub height and rotor diameter—devices that were much smaller then. Whether this formula still applies to wind turbines twice that height is unclear. However, the risk radius of a rotating system is always higher than that of a stationary system, which is why German approval authorities prohibit the use of wind power equipment during freezing events. In such cases, ice thickness is considered "serious" once it poses a risk to the surrounding area. Generally, ice thickness is assumed to be 1.5 to 2 centimeters.
What solutions does Weidmüller offer to prevent ice formation on blades?
The Weidmüller BLADEcontrol® blade monitoring system detects icing on blades and shuts down the equipment before falling ice poses a threat to the surrounding area. This system does not actively prevent ice formation. Depending on the wind turbine's location and climate conditions, it is wise to stop the turbine when ice forms to prevent further freezing. The turbine restarts when external conditions change. However, in Germany, the standard approach is to automatically signal (shut down) at the initial stage of ice formation that could pose a risk to the surrounding area. A significant advantage of this system compared to systems that measure icing on the turbine casing is that it continues to measure icing even when the turbine is stopped and stationary. This means that once the ice melts or falls, the turbine can be automatically restarted (when safe conditions are met). With other detection systems, even when the turbine reports no ice, a visual inspection of the blades is still required to ensure the absence of ice, followed by manual restarting, which obviously increases downtime.
Is BLADEcontrol® suitable for all types of wind power generation equipment? Where is the system installed?
BLADEcontrol® is available from various manufacturers. Its most important prerequisite is power supply in the hub. This is true in all modern wind turbines, except in certain sub-megawatt models. Specific turbine operating data, such as wind speed, power, and pitch angle, must also be transmitted to BLADEcontrol®. Accelerometers inside the blades measure the signals, which converge in the hub and are then transmitted to the analysis unit via WiFi or slip rings. The analysis unit connects to the turbine, enabling the exchange of measurement results and installation data.
How accurate is ice detection? What measurement principle is it based on? And how does it determine the formation of different levels of ice?
The formation of ice increases the weight of the blades. This increased weight reduces the natural vibrational velocity of all elastomers, including the blades. The relative change in frequency is inversely proportional to the relative change in mass. BLADEcontrol® measures this change. The system is sensitive enough to detect ice layers significantly below dangerous limits. Based on assumptions about the mass distribution on the blades, this ratio determines the change in mass and the thickness of the ice layer. If the actual distribution of ice on the blades deviates from these assumptions (e.g., in rainy or snowy weather), the wind turbine will shut down prematurely when it detects ice layers thinner than those posing a safety hazard. In this case, shutdown is advisable to prevent imbalances in the turbine.
What commands does the system send to the wind turbine control unit?
BLADEcontrol® sends signals only to the turbine control unit; how the turbine responds is the operator's responsibility. By default, signals include ice formation status, such as mild or severe freezing, and functional information about the system, interfaces, network, and other parameters. If blade damage monitoring is used, signals are also transmitted in cases of severe damage, which are responded to by shutting down the turbine. The signal range can be adjusted and extended to meet customer requirements, such as including freezing index transmissions with accurate information on ice formation.
Is there data to demonstrate that BLADEcontrol® improves the economic profitability of wind turbines?
Compared to systems that measure ice formation on the nacelle casing, BLADEcontrol® measurements show that it can reduce downtime by up to 80%. This depends on the turbine location, meaning the cost of installing this system can be recovered within a single winter. BLADEcontrol® can detect early blade damage through blade damage monitoring, thereby reducing blade maintenance costs. We can also demonstrate that blade condition monitoring can prevent maintenance costs of up to six figures caused by blade breakage.
Besides wind turbines, where else can this system be applied? Is it possible to conduct research or further develop it in this field?
The application of natural vibration analysis is significant in many fields. However, Weidmüller Monitoring Systems focuses its attention on the wind power industry. Our focus is primarily on expanding the system's functionality in two ways: firstly, this technology can also be used to monitor future towers and foundations; secondly, expanding the sensor platform for more precise analysis that can help improve wind turbine power generation. Methods here include slant flow analysis, which indicates that the turbine is not in its optimal power generation position, as well as detecting pitch angle errors, mass imbalances, and aerodynamic imbalances.
This page contains advertising content.
