Skip to main content

ADDITIONAL LOSSES IN ELECTRICAL MACHINES

Final Report Summary - ALEM (ADDITIONAL LOSSES IN ELECTRICAL MACHINES)

There are more losses in electrical machines than the conventional methods of analysis predict. These additional losses are typically about one percentage of the input power. We searched for the physical reasons for these losses. Major part of the extra losses could be associated with the deterioration of the electrical steel sheets in the production processes of electrical machines. Circulating currents in the parallel strands of stator winding may also cause significant additional losses.

Electrical steel sheets exhibit strong magneto-mechanical coupling. The sheets are cut, compressed and welded in the production processes. This causes residual strains that increase the losses. Magneto-mechanical constitutive equations for soft magnetic materials were developed based on the latest theories on electromagnetic interaction with matter. New approaches were tested to account for the hysteresis loss and stress in the magneto-mechanical constitutive laws. A novel rotational single sheet tester was developed to measure the multiaxial magneto-mechanical effects. The cutting process of electrical steel sheets was simulated to estimate the residual strains.

Cutting of the steel sheets also causes burrs at the cutting edges. The burrs make inter-laminar contacts enabling currents to flow from sheet to sheet. Random variation exists in the position and shape of the contacts. A worn-out cutting tool leads to stronger contacts. Methods of conventional and stochastic finite element analysis were developed to tackle these problems. The positions of the strands in a random-wound stator winding also have stochastic variation. This enables circulating currents to flow in the winding. Stochastic approaches were also used to model the circulating currents.

Measuring the different loss components from an electrical machine is challenging. We developed inverse thermal analysis to search for the extra losses and enhance the possibilities of validating the new loss models. Using the thermal approach, we could separate the calorimetrically measured total loss into its resistive and core loss components in the stator and rotor.