a magnetic core (58);

a first winding (W_ab) of insulated wire having a number of turns wound on said magnetic core; and

a second winding (W_cd) of insulated wire having the same number of turns as the first winding wound on said magnetic core,

wherein,

the turns of each winding (W_ab; W_cd) are numbered consecutively; and

the turns of each winding (W_ab; W_cd) are arranged in at least two layers, of which a first layer (L₁) of turns is wound directly on said magnetic core and a second layer (L₂) of turns is wound around a section of said first layer,

characterized in that

the first and second layers (L₁, L₂) of each winding (W_ab; W_cd) are arranged such that the difference between the highest number of a turn in the second layer (L₂) and the lowest number of a turn in the section of the first layer (L₁) on which the second layer (L₂) is wound is less than or equal to 50% of the number of turns in the first layer (L₁) of that winding and

the first layer (L₁) consists of turns having consecutive numbers from turn number one to the number of turns (N₁) in the first layer (L₁);

the second layer (L₂) consists of turns having consecutive numbers higher than the number of turns (N₁) in the first layer (L₁); and

the section of the first layer (L₁) on which the second layer (L₂) is wound comprises the highest numbered turns of the first layer (L₁).