Ice detection for wind turbines

1st February 2013

Labkotec Oy has introduced an ice detector to support the needs of wind turbine operations for more reliable operation, consistent performance, reduced maintenance and improved safety. To prove the performance of its latest generation ice detector, the LID-3300IP, Labkotec Oy subjected the device to a rigorous independent testing regime to ensure that it would meet the standards of modern wind energy operators.

Efficient ice detection brings safety to arctic wind turbines. So, for operational, maintenance and safety reasons, ice detection is a desirable feature for wind turbines located in harsh environments. Icing of wind turbines is a common issue in northern latitudes and at elevated sites, building up on rotor blades, weather sensors and power lines, for example. As well as its effect on energy production efficiency, ice build up on rotor blades can cause damage to buildings and people near the wind turbines.

Until now, there have been no set standards or certification tests to prove the performance and set best practice for ice detection. Labkotec Oy has collaborated with VTT Technical Research Centre of Finland, the largest multi-technological applied research organisation in Northern Europe to establish performance criteria. VTT is a part of the Finnish innovation system under the domain of the Ministry of Employment and the Economy and is a non-profit-making research organization. VTT has developed methods to evaluate icing of detectors for wind turbines based on detection time in standard icing conditions. With Labkotec Oy, it has established a pre-certification process which may be a precursor to the development of formal certification rules, standards and best practices for icing or ice detection tests.

Labkotec Ice Detectors have been specially designed for the detection of ice on the rotor blades and are capable for detecting in-cloud icing and freezing rain. Ice detectors are compact and easy to install and no calibration is needed making them suitable both for old and new wind turbines and are easy to connect to wind turbine control systems. Congealment status, alarms and parameters can be monitored and adjusted through an in-built web-based user interface. The unit allows for two analogue output signals so that both external temperatures and freezing conditions can be measured.

For the pre-certification, an LID/ISD ice sensor plus the LID-3300IP Ice Detector control unit was chosen. This device is based on ultrasonic signal detection where the output signal weakens in the presence of ice. When a set alarm level is reached, ice detector then gives a signal to turbine control system to either heat the rotor blades or stop the turbine operation.

The ice detectors were tested by VTT by measuring detection time in standard icing conditions. Icing measurement tests were done in VTT’s icing wind tunnel in several phases and using acceleration by using increased rate of icing. The purpose of conducted tests and studies was to evaluate the suitability of the device for wind energy related ice detection, especially to define the response time of the ice detector, how quickly icing is detected after icing conditions have started.

The icing rate is strongly affected by numerous parameters such as: wind speed, dimensions of structure, temperature, water content and droplet size. The simulation tests were based on a 44 metre wind turbine rotor blade, and the standard ice alarm response time of the ice detector corresponds to an ice accretion on the leading edge of the blade which increases the chord length by 1.3 cm at 85 per cent of the maximum blade radius.

Standard icing conditions are defined as: temperature -5°C, droplet size 17µm and wind speed 10m/s. The droplet size has been defined based on RMC –measurements (Rotating Multi Cylinder). The standard icing conditions are representative for in-cloud icing and resulted ice type is rime ice.

Thanks to the pre-certification work carried out by VTT in collaboration with Labkotec Oy, there are now an established set of tests and measurements that can be used to define ice detection performance. In its research report, VTT has stated: “The LID-3300IP Ice Detector is applicable for wind turbines and meteorological weather stations. Based on the assessment the device is capable for detecting in-cloud icing and freezing rain. The functionality of the detector is dependent on settings and the operative performance can be optimised for each weather conditions and purposed by adjusting the settings.”

For Labkotec Oy, the importance of the testing regime developed by VTT is that the company is able to demonstrate that its LID-3300IP Ice Detector can meet all official requirements and building permit standards set against a defined and clear set of performance criteria. The ability to show improved turbine production reliability and radically reduced risks caused by ice formation in arctic conditions.

Fig. 1. The LID-3300IP is the latest generation of ice detectors from Labkotec Oy for use in wind turbine applications.
Fig. 2. The LID-3300IP Ice Detector has been developed to support improved wind turbine reliability and enhance safety close to structures.

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