Modeling and practical investigation of the efficiency and operational behavior of induction machines with die-cast copper rotor

The increasing standardization requirements in DIN EN 60034-30 with higher efficiency demands on rotating electrical machines necessitates the exploitation of new power reserves for the classical induction machine. The principle of reducing the rotor losses by the application of a copper cage is known in the power range of very big as well as very small machines. In this contribution a new technology of copper die-casting for standard motors is introduced which gives the possibility of loss reduction and the achievement of a higher energy efficiency class without increasing the active volume. Specifically developed copper alloys own a favorable electric conductivity at simultaneously gained mechanical yield strength. Without rise of the external dimensions a higher power density is accessible in the end. The modeling of the machine for FEA calculations, the specific features of the geometry with copper rotor and the effects on the operational parameters are presented. The development of analytical and numerical models for the description of the electromagnetic behavior includes the influence of the bar form and the slot design, the variation of the slot shape as well as the effects on initial torque and breakdown torque. Special attention is paid on the effects of the changed saturation conditions, rotor losses and additional rotor losses. The calculated data and characteristic curves are verified by measurements on a range of 15 kW standard motors. In this project phase always the same stator geometry has been used for comparability. The rotors have identical sheet cross sections with different cage material. Due to the higher efficiency and better mechanical properties new application fields are opened to the induction machine with die-cast copper rotor at middle power area especially in electric mobility and high-speed applications.