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A BRIEF DESCRIPTION OF THE OA100 (100 kW) WTG of SKYROS ISLAND
(by Prof.N.Athanassiadis, Dr.K.Michailidis)
 


 

                                       Fig.1 View of the nacelle                                              Fig.2 The whole unit

The Picture 1 shows a view of the nacelle along its vertical plane of symmetry.Fig.2 shows the whole unit and
a part of the room where the electrical-electronic control components are installed.
The electrical panels, the main desk, the P.C  and a UPS unit are housed in a room besides the tower.
The main dimensions and the operation characteristics of the mechanical components of the unit shown in Fig.1 and Fig.2 as well as of the electrical-electronic equipment are as follows :
 
 

 
The rotor is an up-wind 3/fixed blade type of a 20m diameter, its axis being at a 24m height. 
 The blades (type WPX20) are of the firm AERPAC (Netherlands).The rotor hub is of 
 special cast iron GG40.2. It follows the hydraulic low speed shaft disc, 914 mm dia. X 25.4 mm of special cast iron fixed between the flange of the rotor hub and  the flange of the low speed shaft  of the unit. The latter is of 31 NiCr 14 alloy steel. It has a total length 1580 mm and a diameter of  240 mm to its front bearing (spherical roller bearing type), which is then reduced to 180 mm and  to 160 mm at its rear bearing (paired face-to-face bearing). 
 
 
The gear box of the USA firm BYRNE GEAR CORP., is a 2 stage planetary type, (size                1500-20000) of 1:26 speed ratio, connected to the main low speed shaft with a flexible coupling, 
Citroen -Winflex type, size 28T. 
 
 
The generator is of squirrel cage type, 3-phase, 380 VAC, 175 kW at 1520 RpM, of the firm         ABB. It is connected to the gear box high speed shaft trough a second flexible coupling on  the 
front part of which is fixed the electrical fail-safe brake disc (515 mm diameter X 12.7 mm). 
A pulse generator placed on the rear shaft end of the generator gives its speed at any moment 
and for safety reason, a centrifugal switch for emergency stop situations if an over speed condition occur. 
 
The major mechanical system is assembled on a two-INP360 beam frame and is housed in the nacelle, the yawing of which is achieved by an electrogear box of 1150:1 reduction speed ratio.
The nacelle is fixed on a crane type ball bearing with internal toothing. A flexible coupling with a regulated max value of the transmitted torque is placed between the crane type bearing and the electrogear box, in the motor of which is embodied an electromagnetic disc brake.
The crane type bearing sits on the top of the steel tower of the unit. The 23m high cylindrical tower has a bottom diameter of 2000mm and an intermediate part of a diameter of 1200 mm .
The last upper part of the tower has a length of 10000mm and a dia. of 1000mm.
The main innovation in the design of this unit is that the rotor - generator system works under programed variable speed control according to the wind speed and the electrical conditions of the network of the island.
To this end we provided an electric-electronic equipment, diagrammatically shown in Fig.4.



 
 

                              Fig. 3. OA 100 (100 kW) . Nacelle assembly



This equipment consisted (inter alia ) of :
 
 
An  inverter AC/DC/AC current source type of 6 and 6 thyristors, (ABB Veritron 144 kW, 315A ). 
The inverter is followed by the necessary electronic equipment for the regulation of its programed operation  and safety conditions. There are also a power factor correction unit with harmonic filter and a multimeasuring instrument type Dranetz 808.
 
A programmable logic controller (PLC), Siemens, S5115U, which acting on the inverter electronic unit that controls the frequency of the generator AC circuit by changing also its AC voltage, enables  the generator to run at programed variable speed.
 
 The PLC calculate the ref. speed of the unit starting at low 5.5 Hz frequency in order to keep a low value of the starting voltage.
Then, increasing the frequency by a programed ramp to about 20 to 50 Hz and therefore the speed of the generator
(about 600 to 1520 RpM) monitoring the best operating efficiency and securing its safety against strong whirling winds, keeping under control the load in the permissible level by reducing on time the speed of the unit as much as needed.
After the first period we fixed the cut-in wind speed at 4.5 m/s and the cut-out at 25 m/s.
In addition to the above operation, the PLC plays an equally important role since it is programed to inspect the operation of each subsystem, to indicate any abnormal condition and keeping the safety of the unit.
To this end we have chosen 110 key positions on the mechanical and the electrical systems, the sensors of which are connected to the PLC.
The later, by a continuous sweeping over these 110 points at 0.1 sec to 0.5 sec, depending of the importance of each one, shows the course of the operation and any abnormality for which gives a stop  command.
In such a case, by some failures (e.g. network abnormality's) the PLC is programed to restart automatically the unit after the start conditions are normally again.
 
A UPS unit 5 kVA ,220 V, 50 Hz, single phase, to supply the PLC, the electrical fail-safe brake and the sensors  of the unit . 
The UPS keeps the control system and, the hydraulic brake and the yawing  motor in operation for emergency reasons when a network error occurs.
 
A main desk for the manually operation of the unit and checking the operational condition of its components. 
Also it will be used by inspection and correction of parameters inserted to the PLC, since the unit OA100 is a prototype model under test.
 
The electrical equipment, already described, is housed in one-room small building near the tower of the WTG.
The assembly of the anemometer - wind vane indicator, is placed on the top of a mast at a height of 24 m , about
30 m to the west of the tower. 


Fig.4. OA100.Main electrical-electronic equipment



 
Sample 
 
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