Design and direct liquid cooling of tooth-coil windings

This paper presents the design and analysis of fractional-slot concentrated-windings for use with direct liquid cooling. To achieve considerably higher torque density than state of the art of electrical machines, recently patented cast coils that allow slot fill factors up to 90% are considered as basis for further enhancement. The sensitivity of large conductors to high losses due to current displacement as well as the implementation of direct liquid cooling of every single conductor is discussed. Two innovative coil designs are developed and compared, in consideration of current displacement using finite element methods, with basic trapezoidal cast coils. The heat dissipation capacities of the new coil designs are tested analytically as well as by measurement. Additionally, different cooling mediums are compared for their suitability for direct liquid cooling of coils. The proposed coil designs lead to possible current densities of $$100 \frac{\mathrm {A}}{\mathrm {mm}^2}$$100Amm2 and to a reduction of the additional losses to about $$50 \%$$50%.