Effects of Annealing on Magnetic Properties of Laminated Stator Cores and Efficiency of Induction Machines

Steel laminations for electric machines are commonly manufactured using punching or laser cutting. The cutting process leads to degraded magnetic properties and therefore reduces the efficiency and the performance of electric machines. This paper presents an experimental approach for quantifying the influence of the manufacturing process as well as the influence of annealing on electrical steel laminations. The magnetic properties of three electrical steel grades are reported for laser cut toroidal cores and for punched stator core laminations. The stator laminations are used to produce three identical induction machine prototypes with a rated power of 4 kilowatt. The machines are measured according to IEC 60404-2-1 and IEC 600404-2-3. We present the influence of material selection on the machine efficiency and we show that the annealing process recovers the magnetic properties of the original material and increases the efficiency of the machine prototype.