High-speed drag-cup induction motors for turbo-molecular pumps applications

This paper investigates the behaviour of induction motors for high vacuum pump systems, through a coupled modelling and experimental approach. Particular attention is focused on the optimisation of drag-cup motors, aimed at reducing the rotor losses. This analysis is carried on in comparison with the performances of a squirrel-cage induction motor, in order to put in evidence advantages and drawbacks. The numerical model, based on a time-stepping finite element procedure, couples electromagnetic field and circuit equations, allowing the analysis of electronically driven motors. Magnetic hysteresis is included and magnetic losses are computed by the loss separation theory.