Analysis of damper winding current of synchronous generator due to space subharmonic M.M.F.

In steady state conditions, currents flow through damper windings, which create problems for losses, electro-magnetic stress, heat-evolution etc. One of the reasons for such current flows is that there are space subharmonic m.m.f.´s, which are generated when fractional slot windings are adopted for armature windings. In this paper, we describe a method of analysis on damper winding currents due to subharmonic m.m.f.´s by use of FEM. In general, the region for analyzing subharmonic m.m.f.´s is multi pole-pitches, while that for a fundamental or a harmonic m.m.f. is one pole-pitch. In this paper, we present a method for the analysis with the aid of the symmetrical co-ordinate method, in which the region for the subharmonic m.m.f. can become one pole-pitch. Numerical examples for the method are shown.