Method of operating a wind turbine
A wind turbine has a generator ( 7 ) with a connected rotor ( 3 ) having a hub ( 4 ) and blades ( 5 ) rotatably connected to the hub for adjusting the pitch angle. In a method of operating such a wind turbine under climatic conditions, where there is a risk of icing on the blades and no or weak wind, the generator is used as a motor for driving the rotor and the pitch angle of the blades is adjusted to ensure that the resulting wind substantially hits the leading edge of the blades. It is thus ensured that any icing only occurs on the leading edge of the blades. Any ice formed may be removed by means of de-icing in a known manner.
1. Method of operating a wind turbine including a generator ( 7 ) with a connected rotor ( 3 ) having a hub ( 4 ) and blades ( 5 ) rotatably connected to the hub ( 4 ) for adjusting the pitch angle characterised in that under climatic conditions, where there is a risk of icing on the blades ( 5 ) and no or weak wind, the generator ( 7 ) is used as a motor for driving the rotor ( 3 ), the rotational speed and pitch angle of the blades being adjusted such that icing occurs in areas of the blades where an ice abatement means is provided in form of a de-icing system or a surface structure or surface coating providing a water- and ice-repellent surface.
2. Method according to claim 1 , wherein the rotational speed and the pitch angle of the blades are adjusted to allow the resulting wind to hit the leading edge ( 10 ) of the blades at an angle of incidence of between −30° and +30° along the majority of the length of the blades.
3. Method according to claim 2 wherein said angle is between −12° and +12°.
4. Method according to claim 2 , wherein the pitch angle of the blade is adjusted so as to minimise the power consumption used for rotating the rotor.
5. Method according to claim 2 , wherein in the leading edge areas the blades are provided with a de-icing system being activated at intervals for removing the formed layers of ice.
6. Method according to claim 2 , wherein in the leading edge area of the blades have a surface structure or a surface coating providing a water- and ice-repellent surface.
7. Method according to claim 2 , characterised in that by using the generator as a motor the rotor is made to rotate at the same constant rotational speed.
8. Method according to claim 2 , characterised in that the generator is intermittently used as a motor to make the rotor rotate at a predetermined first rpm, the generator/motor then being disconnected from the supply grid to allow the rotor to idle freely, until a predetermined second rpm is reached, the generator subsequently being used as motor, until the first predetermined rpm is reached once again.
9. Method according to claim 1 , wherein the pitch angle of the blade is adjusted so as to minimise the power consumption used for rotating the rotor.
10. Method according to claim 1 , wherein in the leading edge areas of the blades are provided with a de-icing system being activated at intervals for removing the formed layers of ice.
11. Method according to claim 10 , wherein the intervals between the activation of the de-icing system are determined on the basis of the thickness of the formed layer of ice.
12. Method according to claim 10 , wherein the intervals between the activation of the de-icing system are determined based on the climatic conditions.
13. Method according to claim 12 wherein said climatic conditions include wind, temperature, humidity and precipitation.
14. Method according to claim 10 , characterised in that the intervals between activation of the de-icing system are fixed.
15. Method according to claim 1 , wherein in the leading edge area of the blades have a surface structure or a surface coating providing a water- and ice-repellent surface.
16. Method according to claim 1 , characterised in that by using the generator as a motor the rotor is made to rotate at the same constant rotational speed.
17. Method according to claim 1 , characterised in that the generator is intermittently used as a motor to make the rotor rotate at a predetermined first rpm, the generator/motor then being disconnected from the supply grid to allow the rotor to idle freely, until a predetermined second rpm is reached, the generator subsequently being used as motor, until the first predetermined rpm is reached once again.
18. Method according to claim 1 wherein said areas are leading edge areas of the blades.