At the information board
A pair of advanced wind turbines was put into operation by Janov, near Litomyšl, in the second half of 2009. The technology for both W 2000 SPG turbines with an installed capacity of 2,000 kW per unit was supplied by the Czech company Wikov Wind.
The site is located between Litomyšl and Svitavy at an altitude of more than 400 metres above sea level and has favourable wind conditions. Wind speed at 100 metres above ground reaches 6-7 m/s on average here. The production of the two turbines covers the annual consumption of about two thousand households in eastern Bohemia.
The rotor of each turbine is 80 metres above ground and the rotors have the same dimensions. Thus the total height of the turbine with a rotor blade in the top position is 120 metres. The weight of each turbine is 275.7 tonnes and the diameter of the bottom of each tower is 4.3 metres. The width corresponds to the largest diameter of the wind turbine’s steel tubular tower, which is attached to the foundation flange by a removal joint with a few dozen sturdy bolts during installation.
Visitors can see both wind turbines, the connecting road between them and the transformer booth from the information board. The wind turbines are located about 500 m from each other. In spite of the relatively short distance, the wind direction and force they are exposed to differ, sometimes by up to 2 to 3 m/s.
Wind occurs in the atmosphere due to differences in atmospheric pressure as a result of the uneven heating of Earth’s surface. Warm air rises while cold air forces its way into its place. The Earth’s rotation causes the deflection of airflow, which is also affected e.g. by landscape morphology, vegetation conditions or the presence of water bodies. As aerodynamic forces are applied to rotor blades, a wind turbine located on the tower converts wind energy into mechanical, rotational energy. This is then used to produce electricity in a generator. A wind turbine with an installed capacity of 2 MW works at wind speeds ranging from 3 to 25 m/s and at 5-20 rpm.
Erecting a wind turbine
A wind turbine can be assembled within two to three days on a prepared foundation. Trucks with turbine parts arrive at precisely defined positions, where cranes take over their load. The main stationary erecting crane with a lifting capacity of at least 500 tonnes must lift individual parts weighing dozens of tonnes to a height of more than 100 metres.
When all turbine parts are assembled, its wiring and hydraulic systems that control blade pitch are interconnected, measurement and control systems are installed and the whole device is activated and connected to the grid. And then it all depends on wind. The service life of wind turbines is at least 20-30 years. And wind turbines can be dismantled and removed as quickly as they are erected.
The depth of a foundation for one wind turbine is 2.5 m over an area of 20 m2. The foundation is made of solid reinforced concrete, which forms a counterweight to the nacelle. The nacelle can move by ±1 m at high wind speeds; the movement is compensated in part by the steel tower and in part by the foundation in the ground, which moves slightly.
An opening can be seen in the wall of the nacelle, with a crane boom with a lifting capacity of 320 kg ready behind it. It is used to lift heavy loads right into the nacelle.
One of the last steps in the erection and installation of wind turbines is connecting them to a transformer station – here with a capacity of 2,000 kW and a voltage of 690 volts. Electricity with a higher voltage produced in the generator in the upper part of the wind turbine is conducted to the bottom of the tower and underground, to the transformer station. Here the voltage is transformed into the value required by the local distribution system operator.
Inside the tower base
The base of the tower and the nacelle contain the wind turbine’s control system. Identical systems at the two locations allow the service centre to control a failed wind turbine from both positions. They also provide remote access for off-site interventions.
The ground level of the wind turbine installation can be entered by climbing six steps and passing through the entry door. You will enter a round space dominated by a lift cage for a ride to the upper part of the wind turbine – the nacelle. The lift has room for two people and a ride to the top takes about 4 minutes.
A switch cabinet and a control cabinet with an informative display are located on the left of the entry door. The space behind the lift is occupied by the generator switch cabinet, the main circuit breaker cabinet and the cabinet with the main switch for the line to the transformer station. All these devices allow you to control the power directly from the site, as required in case of an emergency shutdown, etc.
Nacelle – the rear part
The nacelle of a wind turbine houses crucial components used to generate environmentally friendly electricity from wind. The rotor blades are moved by wind lift, so wind turbine nacelles are rotated to face the wind. The rotational force is transmitted by a shaft from the rotor through a gearbox to the generator, which converts mechanical energy into electricity. Nacelle machinery includes a rotor blade pitch system serving to optimise the wind turbine’s output. It also includes a yaw control system for the nacelle. This allows orienting the wind turbine to face the current wind direction. The nacelle also includes a brake, a ventilator and possibly a cooler.
W 2000 SPG gearbox
The W 2000 SPG gearbox has a worldwide patent for controlled output speed. It is unique in that the output shaft always rotates at 1,500 ± 1 rpm, whether the rotor rotates slowly or quickly. The controlled speed allows using a synchronous generator, which supplies generated electricity into a transformer station from which it flows directly to the grid instead of the usual frequency converter.
The SPG system is an extension to the gearbox and is deflected out of the axis of the turbine’s body. Cables from the rotor run along the axis to systems in the nacelle.
Crane and control cabinets
Visitors can see the end of the generator assembly and the control box in the rear part of the nacelle. There is an opening in the wall of the nacelle, with a crane boom with a lifting capacity of 320 kg behind it. It is used to lift heavy loads right into the nacelle.
Nacelle – the front part
In the front part of the nacelle you can primarily see the rotor shaft bearing, rotor brake and the ground connection of the massive gearbox and generator assembly. The obtained power is proportional to the cube of the wind speed. The wind turbine stops automatically at wind speeds higher than 25 m/s to prevent overload. The rotor is braked and its blades are oriented with their narrowest part towards the wind.
At a wind speed of 3.5 m/s, the blades are put into their rotating position. Only then is it evaluated whether there is sufficient torque and if so, they begin to rotate. The blades only rotate in the clockwise direction. Blade pitch works as an aerodynamic brake. During a shutdown, the blades are turned into their braking position and the rotor stops within 1-1.5 rotations.
The blades have built-in lightning conductors – steel cylinders connected with cables that are terminated in the ground. When hit by a lightning, the surrounding laminate is usually burnt but it can be simply and quickly repaired by sanding and laminating.
The rotor hub (blue) and the end parts of the blades are weatherproofed by an external cover. The blades are made of fibreglass, sometimes with Kevlar reinforcement. They are 39 m long, with a total surface area of 50 m2, each weighing 6.3 tonnes. They are installed in a rotor that has a diameter of 80 metres and weighs 35 tonnes. The whole nacelle weighs 70 tonnes. The blades are hollow and their shape is designed to achieve the best aerodynamic conditions, maximum efficiency and minimum noise generation during movement. A recent innovation has seen the tips of wind turbine blades fitted with “winglets”, adopted from the wings of modern airplanes, to reduce noise and improve aerodynamic properties and thus the rotor efficiency.
Nacelle mount and nacelle entry
One of the most interesting places of the entire wind turbine: the top part of the tubular tower connecting the revolving top part – the nacelle. This shows the end of the ladder and the nacelle’s access port. It also shows a bit of the access port. It also shows a bit of the equipment allowing the wind turbine to mechanically rotate the nacelle. The yellow power cables supply electricity from the generator to the lower part of the wind turbine, from where it flows underground to the transformer booth.
View from the nacelle platform of the Janov wind turbine
The Janov wind turbines are located southeast of the village of the same name, in the countryside between Litomyšl and Svitavy.
Towards the northwest, right on the axis of the current direction of the pictured wind turbine, you can see the town of Litomyšl. The birthplace of the composer Bedřich Smetana is also famous for its Renaissance chateau, which is included on the UNESCO World Heritage List.
To the northeast from the wind turbines, right behind wind turbine No. 1, is the village of Janov and, behind it, a wooded ridge spreading across Kozlovský kopec (Kozlovský hill) with an observation tower more than 50 metres high, to the city of Česká Třebová.
To the southwest you can see the villages of Čistá, Trstěnice and Chmelík, all the way to the town of Polička.
In the southeast are the forests of Javořický Ridge. Behind it, out of sight from the wind turbine, is the town of Svitavy, the birthplace of the “Saviour of the Jews” Oskar Schindler.
The actual nacelle is fitted with wind speed and wind direction sensors on its roof. The data is evaluated by a computer that issues commands to control the nacelle yaw and rotor blade pitch according to the determined wind speed in order to achieve maximum efficiency.
Specialists from ČEZ Obnovitelné zdroje estimate that the wind turbines with their installed capacity of 2.396 MW should generate enough electricity to cover the consumption of about 640 households in central Bohemia every year.
The actual construction took place in the spring and summer of 2010.
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