Weather Monitoring 19 Winter Icing Conditions Test Turbine Controls and Project Reliability
A turbine control anemometer acts as the eyes and ears of any wind turbine. Turbine control and project SCADA systems rely on this relatively small component to direct the turbine into the prevailing wind for optimal efficiency. Winter in the northern latitudes is a windy time and can also be a stressful time for many turbine operators. Unfortunately, atmospheric icing conditions can frequently occur in windy locations. A wind turbine anemometer cups or ultrasonic sensors can freeze over, stopping all data transmission to the turbine controls, bringing operation to a halt. It is critical that a wind turbine ceace operation if communication with the anemometer is interrupted. If a turbine continues to operate when it is not pointed into the wind, the shear across the turbine blades can cause damaging mechanical strain on the machine.
Any power that is produced during the time before a turbine shuts down for a met failure is not recorded by the SCADA control system. This means decreased wind farm reliability and significant lost profits for owners and utilities. “Icing events are not only bad for the owner. They are a nightmare for the utility” said one large Colorado Utility representative. “With more wind than ever feeding into the grid, this is true now more than ever.” The industry’s eyes are turning to sensor reliablity as linked to project reliability.
The end of 2009 brought increased interest in offshore wind development in the United States. Over 700 people were in attendance at the American Wind Energy Association workshop on offshore development last December in Boston, Massachusets to discuss the exciting challenges ahead for the North American wind industry in offshore wind development Anemometers, both for assessment and turbine control are an essential part of the offshore equation. Anemometers positioned on turbines offshore are exposed not only to extreme icing, but also highly corrosive salt water. For this reason it is critical that anemometers chosen for offshore use are not only heated but are built of a non-corrosive material and extensively tested to perform in such an environment. Annodised aluminum is an example of a common construction material to find when procuring turbine control anemometers. Leaving a natural finish on an allumium alloy will also prevent corrosion. A common lab test for corrosion, which is said to simulate offshore conditions is the MIL-STD-810 Method 509.3 corrosion chamber test.
Many turbine manufacturers offer cold weather packages now to accommodate for wind turbine projects operating in cold weather environments. Offered in either ultrasonic or cup style, there are a handful of cold weather products on the market today. Wind industry accumulative knowledge and field experience have demonstrated few are without some problems.
Due to increased concern and awareness of icing issues both off-shore and on-land, there is some movement away from the traditional cup and vane anemometers over to ultrasonic technology.
Ultrasonic anemometers are generally preferred for turbine control due maintenance free operation and longer life cycles, but until recently have been a second choice of wind profilers. This is primiarily due to the percieved high cost. Because ultrasonic sensors have no moving parts, they cost less to maintain and have longer life cycles than traditional cup and vane sensors. Future ultrasonic anemometers with intelligent interfaces will deliver added values such as electronic compasses and barometric pressure sensors. In 2005, all Automated Surface Observing Systems (ASOS) in the United States switched over to Ultrasonic wind speed and directional sensors. ASOS systems serve as the nation’s primary surface weather observing network. Wind developers will often use ASOS wind data as reference data when determining the feasibility of a project site. In today’s uncertain economy and competitive industry climate, downtime due to met failure is not an option for any project owner. To assure customers of reliable project life, turbine manufacturers are requiring rigorous lab field testing prior to accepting a new brand of anemometer into its supply chain. An example of a lab test is a freezing rain simulation test, which is meant to simulate environmental conditions during extreme icing. The MIL-STD-810F, Method 521.2 test is the accepted test for ice free operation. This test requires a certain chain of events that is meant to simulate extreme icing conditions in the field.
The test begins with a one hour cold soak followed by thirty minutes of high wind within a sealed chamber. Over the next three hours the chamber temperature is reduced to 1.4o
test’, or any similar testing proceedure, will help identify the most durable turbine anemometers. When asked about the MIL-STD-810F test, one anemometer manufacturer said; “This test has really helped us contribute to the industry and improve our manufacturing plan. We came into the test with a certain level of heating and left the test with plans to change to a much higher powered heater. Our entire production line was changed to be able to meet industry standards. You just need a higher heating capacity using a standard 24V power supply if you are going to survive in those type of conditions”
In environments where extreme icing is present, a higher power heater is required. Sources vary on exactly what that power level must be, but “somewhere over 220W would appear to be sufficent”. Most importantly, a sensor must be tested in the field before it is installed for turbine operational control. The MIL-STD-810F test is a common and accepted standard for simulation of wind turbine field conditions.
Winter field testing is completed by most turbine manufacturers before they can accept and integrate a new anemometer. The lab can not tell you everything. A winter day in the midwest can be quite unpredictable. Hoarfrost off the coast of Rhode Island or ice rime near Lake Ontario simply cannot be simulated in the lab. Manufacturers typically spend up to a year reviewing and testing new equipment. Other tests that are common for anemometers are the IEC 60945 vibration analysis test and the MIL-STD-810, Method 509.3 corrosion test.
Turbine downtime due to inclement weather need not be a concern on the long worry list of a project owner. The coming offshore market can learn from the experiences of onshore developers as well. An anemometer with a powerful enough heater that has performed and tested well in the lab and field will be an effective eyes and brain of any turbine, no matter if it is installed in Palm Springs or Idaho Falls.
For more information contact Lufft (USA). Reader Reply Card no 53 C while the sensor is hit with cold water through a wind tunnel at approximately 14m/s. This ‘icing
Meteorology RH / Td / T
Relative Humidity Dew Point Temperature Air Temperature
best accuracy ±1.3% RH and ±0.2°C (±0.36°F)
proven long term stability
high reliability due to unique sensor protection coating
heated probe technology for best performance near condensation
traceable calibration certificate
The Sound of the Weather – Campbell Station Drives Musical Art Installation
Campbell Scientific (UK) have supplied weather stations for a wide variety of diverse applications over the years but, until now, art installations was never one of them. Marketing Manager, Iain Thornton said “The invitation to sponsor such an unusual project was irresistible; typically weather data is processed and visualised in tables or graphs not used as the basis for musical composition”
The project, named Variable4, is the brainchild of sound artist & composer, James Bully and colleague artist, composer and software engineer, Daniel Jones. The event is funded by the PRS for Music Foundation and sponsored by Campbell Scientific and is scheduled to take place on May 22nd this year, on Dungeness headland in Kent, UK.
Here is how Daniel Jones describes the event: “Variable 4 will transform weather patterns into a living musical composition with the same instability and unpredictability as the elements themselves. Using meteorological sensors connected to a custom software environment we have developed, the wild weather conditions of the Kent coast-land will be used to generate new combinations of musical forms, heard through a field of speakers embedded invisibly into the landscape.”
A Campbell Scientific BWS200 weather station is being supplied which will be recording wind speed and direction, precipitation, air temperature, relative humidity and solar radiation.
The integrated CR200 data logger will process the data and talk to the Variable4 computer system via a MD485 multi-drop interface. Sensors will be sampled in near real time so that even subtle changes will affect the music.
“We have all heard the wind before but not like this, and certainly not in chorus with temperature, sunshine and rainfall – it will be an interesting event and I would urge anyone with an interest in the weather to come and experience it ” Commented Iain Thornton.
Reader Reply Card no 54
E+E operates an accredited-by-state calibration laboratory and holds "Austria's National Standard for Humidity"
E+E sensor technology is used by national weather institutes worldwide
ISO 9001:2008 ISO TS16949:2009 certified
A-4209 Engerwitzdorf · Austria
T: +43 7235 605 0 · F: +43 7235 605 8
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Reader Reply Card no 55
May/June 2010
IET
we take up the challenge
Sensor Technology
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