Inrush current protection for wind turbines and wind farms
A wind turbine is provided. The wind turbine includes a transformer having a low-voltage side and a high-voltage side. The transformer is configured to step up a voltage of the low-voltage side of the transformer to a voltage of an external grid. The wind turbine further includes an electrical power generating unit which is connected to the low-voltage side of the transformer and configured to feed an ac-power to the low-voltage side of the transformer. A charging device of the wind turbine is connected to the low-voltage side of the transformer and configured to charge the low-voltage side of the transformer when the generator does not feed ac-power to the low-voltage side of the transformer.
1. A method for connecting a transformer to a grid after a grid failure, comprising:
detecting a recovery of the grid;
buffering energy of the grid;
charging a low-voltage side of the transformer with the buffered energy while a high-voltage side of the transformer is disconnected from the grid so that the high-voltage side of the transformer is substantially in phase with the grid; and
connecting the high-voltage side of the transformer and the grid.
2. The method of claim 1 , wherein charging the low-voltage side of the transformer comprises ramping a voltage of the low-voltage side of the transformer up to a predefined value.
3. The method of claim 1 , wherein connecting the high-voltage side of the transformer comprises causing closing a switch connected between the grid and the high-voltage side of the transformer after charging the low-voltage side of the transformer by a charging device.
4. The method of claim 1 , further comprising synchronizing a generator with the low-voltage side of the transformer.
5. The method of claim 4 , wherein the generator is a wind turbine generator.
6. The method of claim 1 , wherein detecting the recovery of the grid comprises measuring a signal of a low-voltage side of an additional transformer connected with its high-voltage side to the grid.
7. The method of claim 6 , wherein the additional transformer is a voltage transformer of a switch gear.