Wind turbines and methods

A system comprising:

• an electrical grid with a main voltage;
• a bus bar, the electrical grid providing electrical power to the bus bar;
• a main transformer;
• an auxiliary wind turbine transformer, the main transformer configured to connect the bus bar to the auxiliary wind turbine transformer;
• a service voltage transformer;
• a wind turbine, the wind turbine further comprising:
• a generator;
• one or more power converters arranged between the generator and a point of connection to the main transformer,
• one or more of wind turbine electrical components configured for connecting to the auxiliary wind turbine transformer;
• and
• wherein a selection of the wind turbine electrical components are configured for connecting to the bus bar through the service voltage transformer when the main transformer is disconnected from the bus bar.

A method for connecting a disconnected wind turbine main transformer to a grid, the method comprising:

• connecting the grid to a primary winding of a service voltage transformer via a bus bar to supply power to a pre-charge circuit;
• pre-energizing a secondary winding of the main transformer with the pre-charge circuit while a primary winding of the transformer is disconnected from the grid;
• and
• connecting the primary winding of the main transformer to the grid when the primary winding of the transformer is substantially in phase with the grid.

A wind turbine, comprising:

• a generator;
• one or more power converters arranged between the generator and a point of connection to a main transformer, wherein the main transformer is configured to connect a bus bar to the converters, wherein the bulbar is configured to receive electrical power from an electrical grid with a main voltage;
• a pre-charge circuit configured to be connected to the bus bar through a service voltage transformer when the main transformer is disconnected from the bus bar;
• and
• wherein the pre-charge circuit is configured to apply electrical power to a DC bus of the converter such that a secondary winding of the main transformer is pre-charged and a primary winding of the transformer is substantially in phase with the grid.