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WIND POWER On August 26th, 1998, Australia’s first grid-connected wind farm was officially opened near Crookwell, NSW. Using eight 600kW wind turbines, the $10 million wind farm can produce up to 4.8MW of electricity, enough to meet the average demand of several thousand homes and save up to 8000 tonnes per year of carbon dioxide emissions. by LEO SIMPSON Crookwell,on onthe theSouthern Southern Tablelands Crookwell, Tablelands in in Vestas Vestas Systems more or less a turnWindWind Systems A/S A/S more or less as aasturn-key NewSouth SouthWales, Wales,isis reputedly one of the most installation. New reputedly one of the most key installation. This company supplied the eight This company supplied the eight wind consistentlywindy windyplaces places in Ausconsistently wind turbines, the computerised turbines, the computerised montralia,which whichis iswhy why it it was chosen tralia, monitoring system oversaw itoring system andand oversaw the forthis this assembly assembly of of eight 600kW for the entire project. entire project. wind turbines. turbines. Calling Calling it it a wind wind The wind turbines turbines have have been been farm possibly possibly makes makes it it sound a farm installed on aa privately privately owned owned muchlarger largerproject project than than it really much grazing property carrying carrying sheep sheep butlet letus us hope hope it it is a precursor isisbut and cattle and will will not not affect affectthe the forthe the installation installation of of many more for farming activities activities in in any any way, way, windturbines turbinesin inAustralia. Australia. wind with the bottom of of the the blade blade arc arc Theentire entire project more than 20 metres The project has has beenbeen supmetres above above the the supplied byDanish the Danish company ground. plied by the company 40  Silicon Chip Fig. 1: this cut-away diagram shows the main components inside the nacelle of the Vestas 600kW wind turbine. By any standard, these 600kW wind turbines are large and stately machines. They are installed on a 45-metre high tubular steel tower and they have three blades with a rotor diameter of 44 metres. The choice of rotor diameter depends on the prevailing wind conditions at the site. For any given power rating, higher wind speeds mean a smaller rotor diameter while lower wind speeds require a larger dia­ meter, to enable the optimum output to be obtained. While consistently windy, the Crookwell site has relatively low wind speeds so it required the largest size rotors. The 3-bladed rotor drives a planetary gearbox which steps up the nominal rotor speed of 28 revs per minute to drive the 3-phase alternator at around 1560 rpm. The alternator’s output voltage is 690V AC and this is fed to a transformer near the base of the tower where it is stepped up to 11kV AC. The generated electricity is then sent to a substation where it is stepped up to 66kV for connection to the New South Wales grid. When seen from a distance, the large rotors seem to be rotating quite slowly. After all, 28 rpm is just a little less than one revolution every two seconds. However, when you see them up close, the reality is different. Since the rotor diameter is 44 metres, the blade tips are moving at no less than 230km/h. In fact each blade makes a very audible swish as it whizzes round. From further away, say 200 or 300 metres, the wind turbines are eerily silent, any slight noise they make being drowned out by the wind that drives them. Interestingly, the wind turbines require a certain minimum wind speed before they start generating. For this Vestas model, auto start-up occurs at a wind speed of about 15km/h but the turbine does not reach full power output until the wind speed hits about 54km/h. Above that speed, the generator output stays constant until the wind speed hits 72km/h (which is a real gale, 8 on the Beaufort scale). When the wind speed exceeds 72km/h, the blades are feathered, cutting out the generator to prevent damage. Fig.2 Technical data Vestas V44-600kW Wind Turbine Diameter 44m Swept area 1,521m2 RPM 28.5 Number of blades 3 Power regulation Pitch + OptiSlip Air brake Full-feathering Hub height 45m Start-up wind speed 4m/s Cut-out wind speed 2m/s Generator Asynchronous, 1500 - 1560 rpm Nominal power output 600kW, 50Hz, 690V AC 3-phase Transmission Planetary gear/parallel shafts Control Microprocessor-based monitoring of all turbine functions, plus OptiSlip regulation of output and OptiTip pitch regulation of the blades January 1999  41 Other wind turbine installations Crookwell is not the first wind farm in Australia although it is the first to be connected to the state grid. The first Australian wind farm was installed at Esperance in Western Australia some years ago. It consists of nine 225kW wind turbines, giving a maximum output of 2MW. There is also a pair of 225kW wind turbines installed on Thursday Island and a 150kW machine is running at Coober Pedy in South Australia. We have also seen a large wind turbine running near Newcastle. By the standards of other parts of the world, the Crookwell wind farm is a small project. In Europe in particular, wind farms with ratings of many megawatts are the norm. For example, in Denmark, the 24MW Rejsby Moor wind farm employs 40 wind turbines while in Carno in Wales, 56 wind turbines are installed. There are even large offshore installations. For example, Denmark has two offshore installations with 10 wind turbines installed off the east cost of Jutland. Presently, Vestas is involved in the commissioning of a large wind farm on the northernmost tip of the North Island in New Zealand, employing 48 660kW wind turbines. This is one of the windiest sites in the world, with average wind speeds of 11m/s (40km/h). Further information on wind power around the world can be obtained from CADDET, the Centre for the Analysis And Dissemination of Demonstrated Energy Technologies. This organisation was founded in 1988 by the International Energy Agency. They have two websites: (1). www.caddet-ee.org (2). www.caddet.co.uk Further information on Vestas wind turbines can be obtained at www.vestas.dk 42  Silicon Chip Fig. 2: the power curve for the 600kW wind turbines installed at Crookwell. Computer control prevents them starting up until the windspeed, measured by an anemometer mounted on the turbine body, reaches 15km/h. They are shut down (blades feathered and braked) when the speed exceeds 72km/h. shows the power curve of the 600kW turbine. Even with the auto cut-out system for high wind speeds, wind gusts still present a big problem for a large wind turbine. Sudden gusts are extremely tough on the mechanical components of wind turbines and can cause undesirable fluctuations on the grid. This problem has been solved by Vestas with a system called “Opti­ Slip”. Combined with the “Opti­Tip” pitch adjustment system, this allows the speed of rotation of both generator and rotor to vary by as much as 10% during a gust of wind. This not only helps eliminates flickering but also minimises the strain on the main components of the wind turbine.  If you would like to view the Crook­ well Wind Farm, it is on the left side of the Goulburn to Crookwell road about half-way between Pejar Dam SC and Crookwell. Minimising the effect of windspeed changes Harnessing wind power to generate electrical power has always had to face the practical reality that the wind doesn't always blow – and when it does, it is forever changing both strength and direction. Variations are not welcome in any generating system, especially one connected to the power grid. Electricity authorities go to great trouble to keep the supply voltage as constant as possible. The mini "weather station" on the tur- bine's tail keeps the blades facing the wind, while Vestas' proprietary "OptiSlip" design can compensate for a variation in blade rotational speed of up to 10%. The graphs above show actual measurements from a Vestas 600kW Wind Turbine demonstrate the varying relationship between windspeed and generator rpm over time. Note, though, that the output remains constant at 600kW, minimising fluctuations on the electricity grid.