Electric machine with a resistor for dissipating shaft voltages

1. An electric machine comprising:

a rotor ( 1 ) having a rotor shaft ( 2 ) and an excitation winding ( 14 );

a slip-ring group ( 8 ) arranged on the rotor shaft ( 2 ), wherein the slip-ring group includes at least one slip ring ( 9 , 10 );

a contact ring ( 13 ) mounted on the rotor shaft ( 2 ) and having a first side and a second side, wherein the inner diameter of the contact ring ( 13 ) is larger than the outer diameter of the at least one slip ring ( 9 , 10 ) and the contact ring is pushed over the slip-ring group such that at least a portion of the at least one slip ring ( 9 , 10 ) is between the contact ring ( 13 ) and the end of the rotor shaft ( 2 ) relative to a longitudinal axis ( 20 ) of the rotor shaft ( 2 ); and

at least one electrical resistor ( 24 ) for dissipating shaft voltages occurring at the rotor shaft ( 2 ), wherein the electrical resistor ( 24 ) is enclosed in the contact ring ( 13 ) between contact surfaces ( 17 , 23 , 25 , 28 , 29 ) applied to the contact ring ( 13 ), and wherein the at least one electrical resistor ( 24 ) is electrically connected via the contact surfaces ( 17 , 23 , 25 , 28 , 29 ) to the rotor shaft ( 2 ) on the first side and to the excitation winding ( 14 ) on the second side.

2. The electric machine according to claim 1 , wherein the at least one slip ring ( 9 , 10 ) includes a first slip ring ( 10 ), characterized in that a first contact surface ( 17 , 29 ) is electrically conductively connected to the first slip ring ( 10 ), which is used as a negative slip ring, of the slip-ring group ( 8 ).

3. The electric machine according to claim 1 , characterized in that the contact ring ( 13 ) has at least one contact surface ( 23 , 28 ) which is electrically conductively connected to the rotor shaft ( 2 ).

4. The electric machine according to claim 1 , characterized in that the contact ring ( 13 ) has at least one contact surface ( 17 , 25 ) arranged on a side surface of the contact ring ( 13 ).

5. The electric machine according to claim 1 , characterized in that the contact ring ( 13 ) is disk-shaped and is arranged between the rotor winding ( 14 ) and a bearing ( 5 ), in which the rotor shaft ( 2 ) is mounted, on the rotor shaft ( 2 ).

6. The electric machine according to claim 5 , characterized in that the contact ring ( 13 ) has one axially oriented and one radially oriented contact surface ( 17 , 25 ; 23 , 28 , 29 ) for making contact with the enclosed electrical resistor ( 24 ), and in that the axially oriented contact surface ( 17 ) makes contact with a connecting lug ( 18 ) of a conductor routed to the rotor winding ( 14 ) and the radially oriented contact surface ( 23 , 28 ) is disposed around the rotor shaft ( 2 ).

7. The electric machine according to claim 1 , wherein the at least one slip ring includes a first slip ring ( 10 ), characterized in that the contact ring ( 13 ) has a first contact surface ( 28 ) on an inner ring surface pointing toward the rotor shaft ( 2 ), which first contact surface abuts the rotor shaft ( 2 ), and a second contact surface ( 29 ), which abuts at least one contact segment ( 30 ) of the first slip ring ( 10 ).

8. The electric machine according to claim 7 , characterized in that the first slip ring ( 10 ) is used as a negative slip ring.

9. The electric machine according to claim 7 , characterized in that the contact ring ( 13 ) is fastened by means of a press fit in the region of contact surfaces ( 23 , 28 , 29 ) pointing radially toward the rotor shaft ( 2 ).

10. The electric machine according to claim 1 , characterized in that the electrical resistor ( 24 ) has an ohmic resistance value of between 50 ohms and 10 kilohms.

11. The electric machine according to claim 1 , where in the contact ring ( 13 ) is formed with an electrically insulating material.