I. AVANTIS PM-Generator

The 690-V-generator for the AVANTIS family consists of an internally water cooled stator with 120 poles per phase (3-phase AC) of conventional build and an external, air cooled rotor that is equipped with permanent magnets. The magnets cover at least 95 % of the overall inner rotor surface. The generator concept allows for high flexibility and power output efficiency. The king tube, which supports the generator stator, allows for all design sizes of the AVANTIS turbine family. For different sizes of the generator, suitable number of core wires corresponding to the different rotational speeds of the rotor blades lead to stable voltage outputs of the system.

The generator is enclosed in such a way that no outside air stream and therefore no dirt, dust and excess humidity can get into the generator. It is also equipped with devices that prevent it from tilting during start-up or under large torques, giving a stable air gap dimension between rotor and stator.

With three big manholes in the center of the generator support, the design allows easy access per maintenance staff into the hub, independent from the position of the rotor blades. No one has to climb out of the nacelle in order to get back into the spinner again. This is very convenient especially under harsh offshore conditions.

A direct drive generating system with a variable rotor speed like the one of the AVANTIS product family allows for very high efficiency especially in partial load conditions, which is the operational mode of wind turbines most of the time. Together with the advantages of having very few different components for a whole family of turbines, this gives tremendous advantages to the customers.

It is often an argument that a large-size PM generator running at low speed costs much more to make than a conventional high-speed generator, which is much smaller. However, the higher efficiency of the whole system and the much shorter down-times of the system give a much higher advantage to the customers. "Pauli", the generator of the AV 928 - 2.5 MW, will start generating power already at 6 rpm, when it makes about 116 kW already. At partial loads, the generator runs with 97 % efficiency, and at full load and 16 rpm, with 95 %, while generating 2.860 kW. This leads to excellent power curves and to high economic yields for the customers.

The water cooling of the stator kicks in at 1,000 kW only. And even under full load, the temperature rise of the magnets is under perfect control (22 K only).