Investigation on the Effects of Magnetic Saturation in Induction Machines During Transients

Magnetic saturation in electrical machines is of major influence on the operating characteristics during transients. For induction machines, the assumption of linear magnetic behavior of the iron core in classical machine models may be adequate for the calculation of steady-state rated operation. In operating points or during transients following a short-circuit or out-of-phase synchronization, where currents can reach values as high as 25 pu, especially the magnetic paths of the leakage fluxes are highly saturated, leading to a significant raise in currents and machine torque. Therefore an investigation on the effect of magnetic saturation has been performed by comparing inductances calculated by analytical methods for assumed linear magnetic behavior with results of static finite-element-method (FEM) models taking magnetic saturation into account. These results are subsequently converted into simplified current-depending parameter functions that can be used in transient machine models. Therefore, based on an enhanced space phasor approach, a newly modified machine model is presented, where the parameters can be used according to the dependencies worked out in the paper in order to identify deviations with the classical approach using constant inductances. Furthermore the newly acquired set of current-depending machine inductances is validated by simulating a series of transients using dynamic FEM calculation, showing a significant improvement in accuracy compared to sets of constant parameters