Effects of Rotational Inertia and Bearing Force on Stability of Permanent Maglev Rotator

Abstract

The authors’ former works demonstrated that a passive magnetic (PM) rotator supported merely by PM bearings has a minimal speed, above which it can stabilize its equilibrium, under the function of a so-called Gyro-effect. It is unclear, however, by which factors is this minimal speed determined. This paper investigated the factors affecting the minimal stable speed of permanent maglev rotator, namely, the rotating inertia and PMB force. Two novel permanent maglev turbine models were designed: Model A---one stator and three rotors which have the same size but different rotational inertias; Model B---one rotor and one stator, but the stator has been devised with three different passive magnetic bearings: 1. a pair of small magnetic rings; 2. a pair of big magnetic rings; and 3. both of the two pairs of magnetic rings. Four Hall sensors distributed evenly at the turbine’s stator were used to detect the rotor’s eccentricity, and the speed sensor measured rotating speed. The calculated models of rotor’s eccentricity were established respectively for the two turbine models; the rotor’s eccentricity measuring system was built up and the rotor’s eccentricity of the two turbines was measured. The experimental data demonstrated that the rotational inertia of three rotors in the model A is 6.293×10-5 kg•m2, 1.074×10-4 kg•m2 and 2.081×10-4 kg•m2 respectively, and the corresponding minimal speed for suspension are 4597rpm, 3030rpm and 2222rpm respectively; in the model B, the magnetic force between the stator and rotor in the three cases is 92.12N, 123.48N, 212.66N respectively, corresponding to the minimal speed for suspension---3730rpm, 3120rpm and 2195rpm respectively. The results exhibited that same as the permanent maglev heart pump, permanent maglev turbines also have gyroscopic effect, which makes the rotors maintain stable suspension. And the minimal speed for suspension has a negative correlation with the rotor’s rotational inertia, namely, the bigger the inertia of the rotor, the smaller the required speed for suspension; the minimal speed for suspension also has a negative correlation with the magnetic force between the stator and rotor, that is, the larger the magnetic force, the smaller the rotating speed for suspension. Smaller minimal speed means better stability of the system, thereafter larger inertia or larger bearing force means better stability; besides, larger difference between minimal speed and performance speed of the rotator means better stability, it’s suggested permanent maglev be applied in high speed rotary machines.