Inter-laminar Contacts and Losses in Cores of Electrical Machine

Abstract

This dissertation deals with the modeling of inter-laminar contacts in the cores of electrical machines. A series of punching and pressing processes forms random burrs at the edges of electrical sheets. These burrs form random inter-laminar galvanic contacts when pressed.

Several numerical formulations based on finite element method were developed. A surface boundary layer model is implemented in a 2D finite element analysis of the electrical machine. An efficient stochastic model to account for random inter-laminar contacts is proposed and validated. Eddy current loss due to inter-laminar contacts in a laminated core was obtained experimentally, and the effect on eddy current loss coefficient was studied. Based on 3D FE simulations, and obtained eddy current loss, an iterative method was developed to estimate the equivalent conductivity of the laminated core. Finally, a measurement setup was designed to perform a short-circuit and thermal test on the inter-laminar contacts.

A statistical study of random inter-laminar galvanic contacts at the edges of the stator of an induction machine showed a 7.7 % increase in mean electromagnetic losses. An efficient stochastic method was implemented to account for random inter-laminar contact that reduced computation time by 76 %. The eddy current loss coefficient due to inter-laminar contacts was increased by 2 % in the case of one limb fault of the EI core and 2.7 % in the case of two limb fault. Finally, the measurements from thermography test were used to estimate the size of the inter-laminar contacts and the finite element method validated the results.