There is described an apparatus (2) for transferring electrical power to a rotating shaft (13, 43), the apparatus (2) comprising : - a first winding (21) in a stationary part of the apparatus (2) around the shaft (13, 43); - a second winding (23) on the shaft (13, 43) adjacent to the first winding (21), characterised in that apparatus further comprises: - a sensing device (48) adapted to sense the rotational frequency of the shaft ((13, 43); and - a variable frequency drive (45) adapted to adjust an input current frequency to the first winding (21) as a function of the rotational frequency of the shaft ( 13, 43), whereby a desired output voltage and frequency in the second winding (23) on the shaft (13, 43) can be obtained. There is also described a method for transferring electrical power to a rotating shaft (13, 43).