Rotor for an electric machine and method for retrofit

1. A rotor for an electric machine comprising a shaft, a spider on the shaft, a laminated drum on the spider,

wherein the spider has a plurality of spaced part elements defining ducts between each other for conducting cooling axially air through the spider,

wherein the laminated drum has a plurality of radially extending cooling channels connected to the ducts for conducting the cooling air radially form the ducts through the laminated drum,

further comprising at least one cooling air throttle element configured either within one of the ducts or within one of the cooling channels extending from the duct through the laminated drum.

2. The rotor according to claim 1 , wherein the throttle element is provided within the duct.

3. The rotor according to claim 2 , wherein the throttle element is located within the duct so as to divide the duct into:

a first zone of the duct connected to a first group of cooling channels having a first air volume flow therethrough, and channels, and

a second zone of the duct connected to a second group of cooling channels having a second different air volume flow therethrough.

4. The rotor according to claim 2 , wherein the throttle element is a plate provided in the duct, the plate defining a passage for a gas passing through the duct.

5. The rotor according to claim 4 , wherein the passage is defined by a hole in the plate.

6. The rotor according to claim 1 , wherein the throttle element is configured with an individual cooling channel within the duct to throttle cooling air moving into the cooling channel from the duct.

7. The rotor according to claim 6 , wherein the throttle element is housed in duct and is connected to an end of the cooling channel.

8. The rotor according to claim 6 , wherein the throttle element includes:

a wall movable to relative to the laminated drum,

apertures on in the wall,

an activation system for the wall.

9. The rotor according to claim 1 , wherein the throttle element includes a throttle valve.

10. The rotor according to claim 9 , wherein the throttle valve is an electrically, hydraulically or pneumatically controlled throttle valve.

11. A method for retrofitting a rotor for an electric machine, the rotor comprising a shaft, a spider on the shaft, a laminated drum on the spider,

wherein the spider has a plurality of spaced apart elements defining ducts between each other,

wherein the laminated drum has a plurality of radially extending cooling channels connected to the ducts,

the method comprises

providing a cooling air throttle element either within one of the ducts or within one of the cooling channel extending radially form the duct.

12. The method according to claim 11 , further comprising

operating the rotor before the throttle element is provided, and

detecting one or both of air circulation losses and temperatures while operating the rotor,

wherein the throttle element is provided on the basis of the detected air circulation losses or temperatures.