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).