Design of a Bearingless Canned Motor Pump

Motors of pumps used in aggressive environments have to be protected from the fluid. A common approach is to enclose both the rotor and the stator with a metallic can: a canned pump. In today's systems the rotor is held in position with slide bearings. In this paper an approach with magnetic bearings is described. The shaft of the rotor is thereby levitated magnetically with one conventional 3-phase AC bearing, a bearingless motor and a semiactive axial bearing. Positioning and field probes sense all through the metallic can; there is no direct contact between any sensor and the medium. The pump is of centrifogal design, rated 0.6 kW and delivering 60 llmin against a pressure of 16 bar. To supply the pump, conventional industrial switched power converters are used and controlled by a digital multiprocessor system. The application of the pump is planned in the pharmaceuticallchemical industry. A prototype was built to prove the principle of a bearingless canned motor pump.