Design of Rotating Electrical Machines, 2nd Edition

Damper Winding

Next, the resistance and the leakage inductance of a damper winding are investigated. The simplest damper winding is a solid-rotor construction, in which eddy currents can be induced. The calculation of such a solid body is a challenging task, which cannot be solved analytically. However, if we assume the rotor material is linear, we are able to derive equations analytically for the material. Figure 7.31 illustrates the observation between the stator winding and the surface current.

Figure 7.31 Application of Ampère’s law between the surface currents and the stator currents. Note that boldface l indicates the general integration route, not the length of the machine. The field strength Hr0 is measured at the very surface of the solid rotor surface.

Now, Ampère’s law H · dl = ƒS J · dS is applied to the area between the stator and rotor surfaces along the integration path of Figure 7.31 for the determination of the impedance of the solid material of the rotor, observed from the stator. When the rotor surface moves at a speed that is different from the current linkage harmonic of the stator, currents are induced in the solid rotor. A field strength Hr caused by the damper currents acts upon the rotor surface. The corresponding additional current of the stator is detectable ...