No abstract

A new non-contact drive system has been developed employing a consequent-pole type bearingless permanent magnet (PM) motor and a thrust magnetic bearing. This bearingless motor has a wide magnetic gap. The wide magnetic gap may cause a decrease in radial magnetic suspension force because of an increase in magnetic reluctance. A thrust magnetic bearing is installed at the end of the shaft, because strong thrust force exists in centrifugal pump applications. In this paper, the magnetic suspension forces and rotation characteristics of the experimental prototype are evaluated, while the rotor is magnetically suspended. Experimental results are also compared to the calculated ones using the finite element method. It is demonstrated that the developed consequent-pole type bearingless PM motor possesses sufficient magnetic suspension force for non-contact operation.

Bearingless motors are characterized by integration of electrical motors and magnetic bearings. These motors can realize magnetic suspension of rotor shafts without mechanical contacts. Recently, non-contact canned motor pumps without expendable parts by means of using these motors have been vigorously developed. In these pumps, the large magnetic gap length of about 5 mm or more is required of the bearingless motors, because fluid flows into the gap. It becomes difficult to generate sufficient suspension force for magnetic suspension, as the magnetic gap length is increased. Therefore, a novel structure of a 5-axis active control type bearingless motor which can generate the sufficient suspension force under wide-gap condition has been proposed by the principal authors. In general, thrust disks with large outside diameters are used in thrust magnetic bearings. However, in the canned motor pump application, rotational speed is limited to prevent cavitation caused by the large thrust disks. Accordingly, the proposed novel structure is equipped with a cylindrical rotor instead of the large thrust disk, and can generate sufficient suspension force in the axial direction, also. This paper introduces magnetic suspension characteristics of the proposed novel structure with experiments.Index Terms --Magnetic suspension, magnetic levitation, bearingless motors, magnetic bearings, wide gap length.

No abstract