Electric generator arrangement and method for reducing a rotor eccentricity

1. An electric generator arrangement, comprising:

a generator having a stator and a rotor mounted to said stator free to rotate, wherein the stator is equipped with at least two opposed phase windings/segments, each winding/segment comprising at least two sub-windings in series, a controlled varistor across the connections of the sub-windings of said at least two opposed phase windings/segments, a sensor for measuring the current imbalance of two opposed phase windings/segments of said electric generator and

an electronic circuit for controlling said varistor in such a way that the resistance of the varistor is increased when the current imbalance between said opposed phase windings/segments increases.

2. The electric generator arrangement as set forth in claim 1 , wherein the stator is equipped with three pairs of opposed phase windings/segments and wherein the arrangement comprises: three or more controlled varistors, each being arranged across the connections of the sub-windings of said opposed phase windings/segments,

three or more sensors for measuring the current imbalance of two opposed phase windings/segments of said electric generator, and an electronic circuit for controlling said varistors in such a way that the resistance of a varistor is increased when the current imbalance between opposed phase windings/segments connected to said varistor increases.

3. The electric generator arrangement as set forth in claim 2 , wherein the sensor for measuring the current imbalance of two opposed phase windings/segments comprises a current sensor in each branch of a phase winding/segment.

4. The electric generator arrangement as set forth in claim 3 , wherein the subwindings of a phase winding/segment have substantially the same inductances.

5. The electric generator arrangement as set forth in claim 4 , wherein the rotor is mounted to said stator with just a single bearing.

6. A wind turbine comprising an electric generator arrangement comprising:

at least one turbine blade; and

a generator having a stator and a rotor mounted to said stator free to rotate, wherein the stator is equipped with at least two opposed phase windings/segments, each winding/segment comprising at least two sub-windings in series, a controlled varistor across the connections of the sub-windings of said at least two opposed phase windings/segments,

a sensor for measuring the current imbalance of two opposed phase windings/segments of said electric generator and

an electronic circuit for controlling said varistor in such a way that the resistance of the varistor is increased when the current imbalance between said opposed phase windings/segments increases, wherein the generator is coupled to the rotor of the wind turbine.

7. The wind turbine as set forth in claim 6 , wherein the generator ( 1 ) is directly connected to the rotor of the wind turbine.

8. A method of controlling a rotor eccentricity of an electric generator arrangement, the generator having said rotor mounted to a stator free to rotate, the stator being equipped with at least two opposed phase windings/segments, each winding comprising at least two sub-windings in series, and the arrangement comprising a controlled varistor across the connections of the sub-windings of said opposed phase windings/segments, the method comprising the steps of:

measuring the current imbalance of two opposed phase windings/segments of said electric generator and

controlling said varistor in such a way that the resistance of the varistor is increased when the current imbalance increases.