Dynamic Resistance and Inductance of Slot-Embedded Conductors

The effective resistance and inductance of electric machine armature conductors differ considerably from their direct current values. Their determination is of interest especially in connection with machines operated from nonsinusoidal power sources and large induction machines. This paper describes a new and very general method of finding the normal modes of current flow in a conductor of arbitrary cross section placed in an arbitrarily shaped slot. The method is based on finding Green's functions for the slot region, including the air gap, by a numerical technique, and subsequent solution of the resulting integral equation to find the normal modes. The modal solution may then be used to find any desired steady-state or transient performance characteristics or field distributions in the conductor and slot with ease. A computer program employing this technique is described. Steady-state characteristics of a few particular conductors are shown to illustrate the method. It is found, among other things, that the presence of insulation in the slot can have a marked influence on the effective resistance and inductance of the conductor.