US Patent 7915782 Electrical machine and method of retrofitting an electrical machine

There is described an electrical machine with a rotor shaft, a slip ring, arranged on the rotor shaft, and at least two sliding contacts arranged along the circumference of the slip ring for producing an electrical connection with the slip ring. The electrical machine has one or more extraction devices arranged between the at least two sliding contacts directly via the slip ring and intended for extracting abraded material produced at the slip ring.