Design of Rotating Electrical Machines, 2nd Edition

4

Inductances

In rotating electrical machines, the total flux consists of the main flux Φm and the leakage flux Φσ components. The main flux (air-gap flux) of the machine enables electromechanical energy conversion but the proportion of the total flux called the leakage flux does not participate in energy conversion. From the physical point of view a machine has only, for example, the total stator flux, or corresponding (total) stator flux linkage which is the integral of the voltage supply (ψs = ∫ (us − Rs is)dt). Also in case of finite element analysis the total flux will result from the calculations and extra work is needed to segregate the flux components. There is, however, a long tradition in electrical machine design according to which the flux components are calculated separately.

The main flux has to cross the air gap of rotating machines; an important function of the main flux is therefore to electromagnetically connect both the stator and the rotor. In this sense, an air-gap flux Φm creates an air-gap flux linkage Ψm in the investigated winding, and consequently connects different parts of the machine. The leakage fluxes of the stator and rotor do not generally cross the air gap. They contribute to the generation of the total flux linkage of the winding by producing a leakage flux linkage Ψσ component to it. Flux leakage occurs in both the stator and the rotor winding. The corresponding leakage flux linkages are the flux leakage Ψs σ of the stator and the flux leakage ...