The operation of wind energy conversion systems (WECS) in cold climates suffers severely from rotor blade icing. Due to personal and environmental safety concerns WECS with iced blades may not to be operated and a reliable ice detection system is required by some jurisdictions. The RFID-based method developed by ACCM (now K2 area of LCM) detects icing directly on the blades, is cost-effective, and existing WECS may easily be upgraded with the system.
Ice detection system for wind turbines
The demand for clean and renewable energy causes a significant increase in wind energy conversion system (WECS) installations worldwide throughout the last years. A number of these were installed in cold climates, which raises the risk of blade-icing. As ice-breakage from the blades poses a severe danger to humans, animals, and the environment some authorities require the shut-down of affected WECS. This is also a sensible decision for the operator, as ice-covered blades increase the strain on the drive chain and can cause damage to the plant. Currently available ice detection systems (vibration sensor, power measurement,…) for WECS suffer from various drawbacks. In most installations no sensors are mounted directly on the blades due to the disadvantageous environment: high wind speeds and large accelerations forces, extreme temperature, and restricted access for maintenance favor indirect measurement with its reduced reliability.
The goal of this COMET K2 project was the development of a stand-alone system which can reliable detect icing with sensors attached directly to the most affected parts of the rotor-blade. In cooperation with Firma Hainzl (a major Austrian industrial systems provider) we developed and evaluated a number of concepts in terms of dependability, reliability, complexity, and cost. The decision was finally made in favor of Radio Frequency Identification (RFID). This technology is well established in industry and logistic since many years. In an RFID system small, passive (i.e. battery less) “tags” are interrogated by radio waves from a reader unit. Though typical RFID installations work over small distances and on quasi stationary targets, we could extend the parameters by utilizing special industry components and adaptions in the reading algorithm. Tags are now reliable identified over blade-tower-distances of 10-15 m (30-45 ft) at speeds up to 200 km/h (125 mph). In the current implementation a number of tags are placed on critical positions along the blade (front and backside, edge). When some tags get covered with ice, the interrogation unit needs to increase the emitted power in order to accomplish for the additional attenuation of the radio waves. This increase is used as indicator for the tag’s current environment. A patent application for this innovative system has already been filed. The advantages over other ice detection systems include multiple measurement spots directly on the blade, robustness, comparatively low price, and easy upgrade on existing wind turbines. Especially the latter might significantly increase productivity, as down-times for safety reasons or
energy-intensive blade-heating may be reduced to the lowest possible amount. A prototype of the system is currently installed in a wind park in Lower Austria. The whole test data will be evaluated by the spring of 2013. After that, ACCM (now K2 area of LCM) will decide together with its industry partner Hainzl over further development and marketing of the system.
Impact and effects
The developed ice detection system for wind turbines features low installation costs and easy upgrade in existing wind parks. This permits safe and effective operation in cold climates, where the danger of ice-breakage is omnipresent. Loss of revenue due to safety-induced shut-down time or energy-intensive blade-heating is reduced to a minimum.