Wind can not only howl and whisper, but also hum and creak. Wherever oscillations and vibrations are involved, Wölfel contributes its decades of expertise in vibration monitoring and reduction. Together with Phoenix Contact, the company has taken a closer look at structural monitoring and ice detection on wind turbines.
The clouds pile up on the horizon. The first gusts of wind whip across the land. A thunderstorm is approaching. Sebastian Obermeier and Nils Lesmann don’t notice a thing. This is because they are active in the base of the blade of a wind turbine. Together with other experts, they test a sensor update and set up a wireless connection to transmit data to the wind nacelle. To reach the Bluetooth module in the 56-metre-long blade, Lesmann climbs a good ten meters into the narrow blade. It is already the second of the three blades that are on today. Suddenly the command comes: “Get out of the wing, get off the turbine.”
Get down from the tower!
The thunderstorm has come threateningly close. On the way back to the gondola, the engineers can already see the first sparks of the electrostatic charge at the weather station. It crackles audibly. But the safety engineer, who maintains contact down in front of the wind turbine, has ordered the team to retreat in good time. The team reaches safe ground. If you want to catch the wind, you have to withstand it. And moving air can be very fickle. Sometimes it’s a gentle breeze that blows around the rotor blades, sometimes it’s violent gusts, like today during a thunderstorm, that can exert enormous forces on the tower. Sometimes it is mechanical wear and tear that puts a strain on the turbine. And not so rarely it is freezing water that causes unwanted imbalances.
All of these influences can drastically reduce the service life and yield of wind turbines. It therefore makes sense to keep an eye on the condition of the asparagus-shaped energy generators – the more precise, the better. And a dream team has come together in this field. The company Wölfel specializes in detecting structural changes and using sophisticated data analysis to track down potential weak points and negative influences. Phoenix Contact contributes the appropriate hardware and expertise in sensor technology and automation.
Listened and analyzed
Today the thunderstorm has won and it’s back to the office. Sebastian Obermeier is an expert in algorithm development for wind turbines at Wölfel and explains what vibrations do to wind towers: “You can think of it like a musical instrument – the rotor blade vibrates at its very own frequencies – but not audible to the human ear. However, these vibrations reveal a lot about the structure, potential ice build-up or any damage that may have occurred. We differentiate between the natural frequencies of the rotor blades themselves and vibrations caused by external influences or operating loads.”
For more than 50 years, the engineering company based in Höchberg, Lower Franconia, has been focusing on vibrations and acoustics. Founded by Professor Dr. Horst Peter Wölfel in 1971, today around 170 employees at five locations develop solutions for earthquake engineering, vibration protection, noise immission control, vibration reduction and structural health monitoring of wind turbines. The location for wind power-related topics is Hamburg, where a stiff breeze is known to blow much more frequently than in Lower Franconia.
Sebastian Obermeier explains the contribution that continuous vibration measurement can make to wind turbines: “Undetected cracks, material fatigue or ice build-up – all of these can become noticeable through changes in vibration patterns. If you listen at an early stage, you can prevent damage and significantly increase the availability of the turbine. Continuous vibration monitoring, especially of the rotor blades, therefore makes operation more efficient and safer.”
Nils Lesmann, one of the experts in Phoenix Contact’s wind team, describes the collaboration between the two companies: “We have been developing modern condition monitoring systems together for several years. It’s not just about being able to measure precisely. It is important to integrate the data into the control systems of wind turbines. This is why the structural health monitoring (SHM.Blade) and ice detection (IDD.Blade) developed by Wölfel have also found their place on the open platform of PLCnext Technology from Phoenix Contact and are integrated into the complete rotor blade monitoring system Blade Intelligence.”
Treachery in detail
This integration is based on years of joint development work. What previously worked smoothly in the laboratory or on the computer is pushed to the limits of functionality – or beyond – in practice on the tower or in the blade. The devil is often in the detail. For example, do metal components in the nacelle shield the wireless transmission? How are the sensors attached so that they can reliably report data to the controller for many years? How does the necessary data transfer from the sensor to the controller take place?
“After all, a malfunction only becomes apparent when a turbine is back in operation after installation. This means that in the event of error messages, the wind turbine has to be stopped again for improvements and expensive downtimes are incurred by the developers, as downtimes naturally have to be paid for,” says Sebastian Obermeier. “That’s why developments for the offshore sector, for example, are so complex and costly. You can’t just drive up in a van and climb the tower.” Precise planning, sound specialist knowledge and a great deal of experience are necessary to ensure that tight development budgets are not exceeded.
The years of cooperation are paying off for both companies, as Nils Lesmann explains: “The result is a powerful plug-and-play solution: the sensor data flows directly into the open control platform – for maximum transparency, flexibility and connectivity in the park network or towards the cloud. Wölfel’s monitoring and analysis expertise is ideally complemented by Phoenix Contact’s connection technology and control expertise. This enables us to offer a modular structure for monitoring wind turbines that is unique in the entire wind energy sector.”
