Reluctance network for analysing induction machines

Abstract

This thesis presents the components, the construction rules and the equations of the reluctance network used in the analysis of an electrical machine. It defines the equations to form the components of a single-phase electric equivalent circuit from the results of a reluctance network. As part of the study, a computer program has been developed to solve a two-dimensional reluctance network. As a result, the flux and current distributions are calculated for a cage induction motor. The rotor construction with a single-cage and double-cage winding is studied. From the analysis results, a single-phase equivalent circuit is defined to calculate the locked-rotor current of the motor in the steady-state period after the inrush current, at the moment when the rotor starts to rotate.

The target in the study is to develop a single-phase equivalent circuit for a starting motor with the effects of iron saturation and eddy-current losses included. The leakage-flux paths of the core in the rotor have their own reactances and iron-loss resistances in the single-phase equivalent circuit. The cumulative influence of the main and leakage fluxes on the magnetic saturation of the machine cross-section is taken into account by using a reluctance model covering the whole cross-sectional area of the machine. The components for the equivalent circuit are defined from the energy distribution over a period in steady-state condition.

In the analysis program, damping caused by leakage reactance of the end-windings in the stator and rotor is excluded from the model equations. Only the resistances of the windings are included to limit the supply current.