Although wind turbines are huge, generating electricity through the turning of their 79 m long rotors, they could not function without the many minuscule sensors which are constantly monitoring their health, allowing them to function in extreme environmental stresses.
The Role of Sensors in Wind Farms
Sensors reduce the danger and the cost of wind farms, whilst boosting the reliability and durability by providing data on every single turbine. Windfarms are examples of loT in action, with networks of sensors joined by Ethernet cables.
Historical operating data can also benefit the wind farm, particularly data such as wind speed, yaw angles, power, gearbox temperature, and other metrics. From this, workers can generate a model that can forecast what mechanisms to inspect. All the data can then be observed and controlled a smartphone or computer.
Figure 1: The basic components of a wind turbine within the nacelle and some of the types of sensors and where they’re placed. (Source: TE Connectivity brochure)
These sensors are vital as wind turbines are intricate, with more than 8,000 individual components. Their vast blades and tower assemblies are affixed to platforms composed of hundreds of tons of steel, gaging 30-15 m across and 6-10 m deep. The gearbox that converts the sluggish rotating speed of the blades to a quicker speed is contained within a vessel above the tower (called a nacelle), weighing around 45 T (tonnes).
Figure 2: Burbo Bank Offshore Windfarm with North Wales in the distance. (Source: Wikipedia)
The world’s biggest producer of wind power is the UK, with a national volume of 5.3 GW that powers >5,000,000 houses. DONG Energy recently added 32 turbines on Liverpool Bay in the Irish Sea, markedly becoming the first commercial use of 8 MW turbines which have twice the productivity of original turbines. These novel turbines are approximately 195 m high, with 80 m rotors, powering a single home for 29 hours following a single revolution of a single rotor.
The greatest-capacity conventional-drive turbine is presently the Vestas 164 (Vestas Wind Systems) with a productivity of 9 MW. It is comprised of a 178 m rotor (which weighs 32 T) is 219 m high and overall weighs more than 1800 T.
Figure 3: A turbine blade convoy meandering through Edenfield to the Scout Moor Wind Farm, the second largest onshore wind farm in England. (Source: Geograph)
The Crucial Role of Sensors
There are numerous dissimilar types of sensors utilized in wind turbines. These function to:
- Sense, analyze, and transfer information about constraints
- Evaluate levels of vibration
- Analyze changes in temperature, weight, and mechanical stresses
Eddy Current Sensors
Eddy current sensors (aka Foucault currents) are currently one of the most frequently used sensors in wind turbines. These sensors monitor alterations in the electricity formed when a conductive material arrives within a motile magnetic field, translating this data into variations in distance.
These sensors can be applied to wind turbines, analyzing the lubricating space of the shaft and ensuring the presence of a thin oil layer. These sensors can resist oils, pressure, and temperature, dependably analyzing the oil gap under aggressive circumstances. This analysis is important as if the space becomes too big the shaft can seize up. Furthermore, they can monitor the rotation of the shaft, ensuring the minimal run-out and allowing the turbine to shut down for maintenance if this value is too high. Finally, they can also monitor the torque administered to the nacelle (a result of tremors and excessive wind) which can damage the internal structure of the turbine, thereby ensuring rotor safety.
Numerous displacement sensors are utilized to assess mechanical integrity. The platforms needed to maintain the placement of wind turbines require a huge volume of concrete. Due to the vast structure at the top of the towers, the “top-loaded” structure must be analyzed constantly to ensure that it is stable. This can be carried out by laser displacement sensors, which can monitor minute movements in the foundation.
They emit a beam of light to a receiver, and deviations in the light can be converted into units of distance. Furthermore, Laser triangulation sensors can be utilized, set up with a sensor, transmitter, and receiver. Very small movements can be detected and therefore an error can be detected before it becomes a dangerous hazard.
The capacitive type is another type of displacement sensor which monitors the space between the stator and the rotor within the turbine. This space is typically called the generator air gap. These sensors work based upon electrical capacitance between conductive surfaces, with the theory that capacitance will be altered proportionally to the space between the two surfaces.
Furthermore, draw-wire displacement sensors associate a spring-loaded wire coiled onto a spool-type transducer. The wire can be very long and so these sensors can be useful in measuring a faraway object. Spool rotations are monitored and used to calculate the change in the electrical signal.
When applied to wind turbines, they monitor the flow of air by analyzing the air flaps position. These sensors can be paired with numerous rotary transducers, such as potentiometers, Hall-effect sensors, and analog or digital non-contacting sensors.
Figure 4: This draw-wire displacement sensor from Bourns shows the spring-loaded spool on which the cable is wound and a rotational sensor mounted to the enclosure. Several types of sensors can be used depending on the requirements of the application. (Source: Bourns)
For example, Bourns AMS22B5A1BHASL334N non-contacting analog rotary sensor utilizes magnetic technology and is resilient to shock, tremor, liquid, and dust. It can also function over a temperature range of -40-125 °C, with a 12-bit output resolution and linearity of ±0.3 percent.
Vibrations within the main, yaw and slew bearings can be measured in wind turbines by accelerometers. This data can then be compiled and utilized to assess alterations over time and forecast future problems.
For example, ADXL1001 and ADXL1002 MEMS accelerometers are excellent examples as they quantify tremors with good resolution and minimal noise density. They are very stable, and resilient from shocks up to 10,000 mps, with combined self-diagnostic functions and an over-range gauge, operating at a frequency range of greater than -40 °C-125 °C.
Both mechanical and ultrasonic wind sensors are positioned above the nacelle. Ultrasonic sensors are becoming increasingly popular in areas where maintenance is not easy, as they do not need calibration once set up. These sensors monitor distance through sound waves, broadcasting low-frequency sound waves and analyzing the wave following reflection by the focal object. Analysis of the time between sound generation and return, the distance can also be calculated.
For example, the Texas Instruments PGA460/PGA460-Q1 ultrasonic processor contains a Digital Signal Processor (DSP) core with a signal conditioner, sending output to an analog-to-digital converter. The converted signal can then be processed for object analysis utilizing thresholds of various time-scales.
Overheating can also be detected by temperature sensors. For example, TE Connectivity's PTF Platinum temperature sensors measure temperature in the wide range of -200 °C to +600 °C, with temperature sensors which utilize thin-film resistors as the sensing element. They are minute and light, don’t drift, and have a minimal time constant for speedy feedback.
If the sensors themselves fail, set up with several sensors can be used to compensate. However, this backup approach must meet requirements including broad operating temperature ranges and certification to IP67 or IP68 for defense from dust and liquid.
Overall, sensors are a fundamental component of the reduction of failures. Use of these sensors is vital for assessing turbines and maintenance requirements.
This information has been sourced, reviewed and adapted from materials provided by Mouser Electronics.
For more information on this source, please visit Mouser Electronics.