Affiliations: [a] School of Mechanical Engineering, University of Science and Technology Beijing, Beijing, China | [b] State Key Laboratory of Technologies in Space Cryogenic Propellants, Beijing, China | [c] Technical Institute of Physics and Chemistry of Chinese Academy of Sciences, Beijing, China
Correspondence:
[*]
Corresponding author: Li Wang, School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China. E-mail:liwang@me.ustb.edu.cn
Abstract: Magnetic flux leakage inevitably occurs between an axial
electromagnetic bearing and a rotor because of the structural arrangement of
the former. The effects of magnetic flux leakage of the axial
electromagnetic bearing on an active electromagnetic bearing system are
studied in this research. Despite the occurrence of a magnetic flux leakage,
the axial electromagnetic force produced by the axial electromagnetic
bearing is greater than that without magnetic flux leakage at a smaller air
gap ratio K (K = 1, 2, 3; where K is the ratio of the air gap between the
stator and the rotor to the air gap between the stator and the thrust
plate), and the axial electromagnetic force decreases continuously with the
increase in air gap ratio K. When air gap ratio K increases to 4, the axial
electromagnetic force with magnetic flux leakage is less than that without
magnetic flux leakage. In addition, a deviation is noted between the centers
of the rotor and the axial bearing because of machining precision,
installation error, or change of running state, and the axial
electromagnetic bearing produces additional radial forces on the rotor. The
resultant radial force produced by axial electromagnetic bearing increases
from 2.1 N to 9.18 N as the radial deviation of the rotor increases from 0.1
mm to 0.4 mm in our simulation conditions. The direction of radial force is
the same as that of the radial deviation, which increases the control
current of the radial electromagnetic bearing control system and the joule
heat of the radial electromagnetic bearing coil. Hence, the additional
radial forces produced by axial electromagnetic bearing must be considered
in the optimal design of a radial electromagnetic bearing control system.
The joule heat of the radial electromagnetic bearing increases from 0.38%
to 17.1% because of the additional radial force produced by the axial
electromagnetic bearing, which increases the control current of the radial
electromagnetic bearing control system. Such increase has an adverse effect
on the refrigeration expander, particularly on the cryogenic expander
systems in which the bearing is used.
Keywords: Finite element analysis, magnetic flux leakage, radial force, nonlinear
