The STX 93 turbine has a direct driven multi-pole synchronous PM generator which is fully integrated in the structural design. The advantage of this design is:

• A minimum of moving parts unlike a conventional turbine with a gearbox,
• Low maintenance needs,
• High efficiency due to the use of permanent magnets (no rotor losses and adherent cooling systems),
• Weight reduction.

Use is made of a single multiple row roller bearing on which the hub is mounted on one side and generator carrier and -rotor on the other side. The stator is mounted on the opposite side of the carrier which on its turn is mounted on a compact casted nacelle frame. The advantage of this design is the best stiffness to weight ratio possible.

The rotor speed during power production is variable. The matching between the available aerodynamic torque and the produced electromechanical torque of the generator is determining the rotor speed. The torque-speed curve is programmed in the frequency turbine control system and the inverter is adapting the generator stator current in response to the measured generator power frequency.

The AC-DC-AC converter located in the tower base allows the generator to operate with a variable speed while the power is fed into the grid with a constant frequency of 50Hz (or 60Hz for the countries where this applies). It furthermore assures an average constant power output for wind speeds above rated. The power factor at the grid side is controllable at standstill as well as operating. Above rated wind speed, the blade pitch control maintains a more or less constant rotor speed between admitted boundaries.

The control system of the STX 93 is built up in a modular manner. The control and safety functions take place in the same area or space where the needed measurements and control or safety actions are performed.

The control system of the STX 93 is built up in a modular manner. The control and safety functions take place in the same area or space where the needed measurements and control or safety actions are performed.