Critical monitoring of wind turbines

The future is very encouraging for wind power. The technology is growing exponentially due to the current power crisis and the ongoing discussions about nuclear power plants. Wind turbines are becoming more efficient and are able to produce increased electricity capacity given the same  factors.

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Worldwide installed wind power per year in MW. (Source GWEC)

Converting wind power into electrical power:

A wind turbine converts the kinetic energy of wind into rotational mechanical energy. This energy is directly converted, by a generator, into electrical energy. Large wind turbines as shown in the picture, typically have a generator installed on top of the tower. Commonly, there is also a gear box to adapt the speed. Various sensors for wind speed, humidity and temperature measurement are placed inside and outside to monitor the climate. A controller unit analyses the data and adjusts the yaw and pitch drives to the correct positions. See the schematic below.

Wind Turbine
Schematic of Wind Turbine Systems

The formula for wind power density:

W   = d x A2 x V3 x C  where :

d: defines the density of the air. Typically it’s 1.225 Kg/m3 This is a value which can vary depending on air pressure, temperature and humidity.

A2: defines the diameter of the turbine blades. This value is quite effective with its squared relationship. The larger a wind turbine is the more energy can be harnessed.

V3: defines the velocity of the wind. The wind speed is the most effective value with its cubed relationship.

In reality, the wind is never the same speed and a wind turbine is only efficient at certain wind speeds. Usually 10 mph (16 km/h) or greater is most effective. At high wind speed the wind turbine can break. The efficiency is therefore held to a constant of around 10 mph.

C: defines the constant which is normally 0.5 for metric
values. This is actually a  combination of two or more constants depending on the specific variables and the  system of units that is used.

 Why measure the local climate?

To forecast the power of the wind over a few hours or days is not an easy task.

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Off shore wind farms

Wind farms can extend over miles of land or offshore areas where the climate and the wind speed can vary substantially, especially in hilly areas. Positioning towers only slightly to the left or right can make a significant difference because the wind velocity can be increased due to the topography. Therefore, wind mapping has to be performed in order to determine if a location is  correct for the wind farm. Such wind maps are usually done with Doppler radars which are equipped with stationary temperature and humidity sensors. These sensors improve the overall accuracy.

Once wind mapping has been carried out over different seasons, wind turbine positions can be determined. Each turbine will be equipped with sensors for wind direction and speed, temperature and humidity. Using all these parameters, the turbine characteristics plus  the weather forecast, a power  prediction can be made using complex mathematics.

The final power value will be calculated in “watts” which will be supplied into power grids, (see schematic on the right).  Electricity for many houses or factories can be powered by the green energy.

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Not ideal energy generating conditions!

Why measure inside a wind turbine?

Wind farms are normally installed in areas with harsh environments where strong winds are common. Salty air, high humidity and condensation are daily issues for wind turbines.

Normal ventilation is not sufficient to ensure continuous operation. The inside climate has to be monitored and dehumidified by desiccant to protect the electrical components against short circuits and the  machinery against corrosion. These measurements are required to ensure continuous operation and reduce maintenance costs.

What solutions can Rotronic offer?

Rotronic offers sensors with  exceptional accuracy and a wide range of products for meteorological applications and for monitoring  internal conditions.

Low sensor drift and long-term stability are perfect in   wind energy applications where reduced maintenance reduces operational costs.

The wide range of networking possibilities including RS-485, USB, LAN and  probe extension cables up to 100 m allows measurements in remote or hard to reach places. Validated Rotronic HW4 software makes it easy to analyse the data or it can be exported into MS Excel for  reporting and further processing.

The ability to calibrate  accurately using humidity standards and portable generators on site ensures continued sensor performance!

Comments or queries? Please do get in touch!

 

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