Thermographic Measurement and Simulation of Power Losses Due to Inter-laminar Contacts in Electrical Sheets

Ferromagnetic cores of electrical machines and transformers are constructed from laminated electrical sheets to reduce eddy current losses. Burrs are formed at the edges of electrical sheets during punching and cutting. These burrs deteriorate the insulation of adjacent sheets, make interlaminar contacts and cause interlaminar currents to flow across the stack. It is essential to know the interlaminar conductivity and the size of the contacts to estimate additional losses in the electrical machine. In this paper, the size of the interlaminar contacts formed by the burrs is estimated using a novel thermographic measurement method and an analytical method. The initial temperature rise of the contacts is used in the analytical model to estimate the contact size. The electromagnetic and thermal finite element formulations validate the results obtained from the analytical method. Moreover, the results obtained from the measurement, the analytical method, and the finite element method are compared. The study shows that the initial temperature rise method can be used to estimate the interlaminar contact size and electromagnetic losses if the temperature is measured immediately after energizing the sheets.