# Experimental analysis on force and correction factor of an active magnetic thrust bearing

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## Abstract

Active magnetic thrust bearing (AMTB) is a device which is used to support an object by controlling the magnetic field. In practice, there is lot of difference between theoretical force and actual force developed between the stator and rotor of an AMTB. This difference is mainly due to fringing, leakage, variation in material properties, misalignments, vibrations, and temperature effects, etc. The difference is also varying with the air gap between stator and rotor and the current supplied. In this work, an experimental approach has been proposed to study the loss factor and efficiency of an Active Magnetic Thrust Bearing. A prototype of AMTB has been made and experimented at different air gaps. Based on the study of single acting actuator, the control performance of a double actuator has been studied. From the study of single acting actuator efficiency and double acting actuator control performance, an optimum air gap has been suggested.

## Keywords

Active magnetic thrust bearings Correction factor Magnetic levitation Control system Air gap## List of symbols

- \(A_{\text{g}}\)
Area of air gap (m

^{2})- \(B\)
Magnetic flux density

- \(F_{\text{a}}\)
Actual Force developed (N)

- \(F_{\text{h}}\)
Position stiffness (N/m)

- \(F_{\text{i}}\)
Current stiffness

- \(F_{\text{p}}\)
Force on one pole face (N)

- \(F_{\text{pre}}\)
Predicted force (N)

- \(F_{\text{th}}\)
Theoretical force (N)

- \(h_{\text{c}}\)
Axial length of stator (mm)

- \(h_{\text{t}}\)
Axial length of stator pole with base (mm)

- \(i_{\text{c}}\)
Control current (A)

- \(i_{\text{in}}\)
Input current (A)

- \(i_{\text{ut}}\)
Utilized current (A)

- \(k\)
Correction factor

- \(k_{\text{D}}\)
Derivative gain

- \(k_{\text{p}}\)
Proportional gain

- \(k_{\text{av}}\)
Average correction factor

- \(l_{b}\)
Axial length of stator base (m)

- \(l_{\text{d}}\)
Axial length of thrust rotor (m)

- \(h\)
Height of an air gap (m)

- \(n\)
Number of readings

*N*Number of coil turns

- \(v\)
Voltage supplied

- \(\varepsilon_{\text{th}} \%\)
Percentage of error between theoretical force and actual force

- \(\varepsilon_{\text{pre}} \%\)
Percentage of error between predicted force and actual force

- \(Ni\)
Magneto motive force

- \(\phi\)
Magnetic flux

- \(\mu_{0}\)
Permeability of free space 4π × 10

^{−7}H/m

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