Abstract: The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

Abstract: Wind turbine installation (1) comprising a tower (2), a nacelle (3), —a liquid immersed power electrical device (6) having an expansion vessel (7), an air dehydrating breather (8) comprising a moisture absorbing agent (9), and a conduit (10) fluidly connecting the expansion vessel (7) and the air dehydrating breather (8), wherein the wind turbine installation (1) comprises a barrier (11) separating a restricted zone (12) from a non-restricted zone (13) in said wind turbine installation (1), wherein the electrical device (6) is located in the restricted zone (12), wherein the air dehydrating breather (8) is located in the non-restricted zone (12) and wherein the conduit (10) extends through the barrier (11) and a method of maintaining a wind turbine installation (1).

Abstract: Wind turbine installation (1) comprising a tower (2), a nacelle (3), —a liquid immersed power electrical device (6) having an expansion vessel (7), an air dehydrating breather (8) comprising a moisture absorbing agent (9), and a conduit (10) fluidly connecting the expansion vessel (7) and the air dehydrating breather (8), wherein the wind turbine installation (1) comprises a barrier (11) separating a restricted zone (12) from a non-restricted zone (13) in said wind turbine installation (1), wherein the electrical device (6) is located in the restricted zone (12), wherein the air dehydrating breather (8) is located in the non-restricted zone (12) and wherein the conduit (10) extends through the barrier (11) and a method of maintaining a wind turbine installation (1).

Abstract: The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

Abstract: The invention relates to a method for controlling a wind turbine configured with an on load tap changer transformer which enables adjustment of a current ratio of a primary side current of the transformer and a secondary side current of the transformer. The method comprises detecting that a network voltage on the primary side or secondary side of the transformer is outside a pre-determined voltage range, and in response determining a current reference for the primary side current based on the detected network voltage. The power converter of the wind turbine is controlled to generate an increase of the primary side current towards the current reference, and the current ratio of the transformer is adjusted towards a higher ratio of the current ratio.

Abstract: The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

Abstract: The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

Abstract: The invention relates to a method for controlling a wind turbine configured with an on load tap changer transformer which enables adjustment of a current ratio of a primary side current of the transformer and a secondary side current of the transformer. The method comprises detecting that a network voltage on the primary side or secondary side of the transformer is outside a pre-determined voltage range, and in response determining a current reference for the primary side current based on the detected network voltage. The power converter of the wind turbine is controlled to generate an increase of the primary side current towards the current reference, and the current ratio of the transformer is adjusted towards a higher ratio of the current ratio.

Abstract: A transformer assembly for a wind turbine is described. The transformer assembly includes a liquid-filled main transformer and an auxiliary transformer connected on the high-voltage side of the main transformer. The auxiliary transformer benefits from improved power quality in this configuration.