Wind Energy Converters
I-WEC has selected a reliable 2.5 MW design from German WEC design house aerodyn Energiesysteme Gmbh. This design represents the largest capacity WECs that can currently be transported and installed within the existing South African infrastructure.
The design is classified for the prevalent wind conditions over the Southern African region, and is certified by the TÜV Nord 3rd party inspection organization to international standards such as Germanishe Lloyd and the IEC 61400. This ensures that each WEC will be insurable and bankable.
The rotor blades are a complex composite construction over 50 m in length, and non-conventional methods must be used to achieve the desired quality. Glass fibre is used for a high strength and low weight sandwich construction, bound together with epoxy resin to ensure the necessary impact resistance of the completed blades.
Once installed, the blade tip’s reach is over 130 m, therefore each blade features an integrated lightning protection system. This allows for the transfer of current from lightning strikes at either the blade tip or centre to the earthed tower, and thus ensures continued safe operation of the blades.
The wind energy converter is a construction of 5 major component groups:
- The 3 rotor blades, each over 50 m long and weighing in excess of 12 tonne.
- The rotor hub, connecting the blades to the rotor shaft. It is a single casting weighing over 10 tonne.
- The nacelle, housing the drivetrain. It is a complex construction of steel and composites weighing over 90 tonne when completely assembled.
- The tubular steel tower. It is a high precision construction between 70 and 80 m in height and weighing approximately 190 tonne, and is designed to withstand extreme static and dynamic loads for over 20 years.
- The foundation, acting as anchor and lightning connection for the tower, with a combined structure of concrete and steel weighing over 60 tonne.
All components are designed and constructed according to the exacting international standards adopted by the SABS.
The drivetrain is the central arrangement where the slow rotation of the rotor is converted to the high rotational speed required for efficient power generation.
The system consists of a forged steel rotor shaft supported by a specialized configuration of two rotor bearings. This configuration is designed in such a way as to completely eliminate any axial force on the gearbox.
The gearbox itself is the most critical component in the drivetrain, and a variety of designs serve to ensure optimal operational conditions for it. The 24 tonne gearbox is a high efficiency multistage machine with gear ratios between 80 and 85, thus providing the generator with optimal rotational input to ensure efficient power generation.
Power is sent to the converter for synchronized supply to the local grid connection.
Data is gathered by more than 20 sensors, and processed by a combination of PLCs and an industrial PC. This information is used for real-time control of the WEC and stored for further performance calculations. The data and control functionality of the WEC is available remotely, and monitored continuously for safety and preventative maintenance purposes.
Also included in the control system are the yaw- and pitch-control systems, which ensure the optimal performance of WECs for varying wind conditions:
- The yaw system rotates the nacelle 360° to face into the wind at all times.
- The pitch system adjusts the angle of the blade relative to the wind flow to ensure a constant rotation speed of the rotor. It also acts as the primary breaking device by feathering the blades, thus turning the blades parallel to the wind direction. (This effectively eliminates energy transfer from the wind and adds aerodynamic resistance to rotation).
Power is generated using a permanent magnet synchronous generator and full converter combination. This enables power generation at lower wind speeds and results in a higher energy yield than comparable doubly fed induction generator systems.
Each WEC will deliver up to 2.5 MW at a 690 V output voltage, which is stepped up to 11 kV by the on-site transformer for cost effective power distribution. If it is deemed necessary, the further connection and distribution to the national grid can be negotiated as part of the scope of supply.