Support Structure

The VHM has stringent demands for its structure, due to the high attractive magnetic forces present, the need to maintain a small airgap and the necessity of the steel sections to be laminated. The main body of the VHM thus consists of laser cut 1 mm thick steel sheets bound together. Figure 6.26 shows the relationship between manufacturing tolerance levels and lamination thickness, demonstrating the desire for sheets of less than 3 mm thickness.

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Figure 6.26: Lamination tolerances [92]

A wide machine, one which is large in a plane perpendicular to its rotor motion, results in a magnetic force acting over the stator in such a way that the system becomes a beam with a distributed load. The bending moment of this load will tend to separate the laminations of the structure, which the support structure is designed to prevent. In the laboratory prototype, the laminations were welded to ensure they did not splay apart Figure 6.27. Electrically joining the individual laminations in this manner would not be acceptable in a larger machine, as it allows the formation of power consuming eddy currents and hinders the effectiveness of the laminations.

Figure 6.27: Welding of laboratory laminations
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Figure 6.28: Skeletal Structure

The stator laminations may be supported by an external framework of fins and ribs. In this way the laminated structure is relieved of the bending moment, and each lamination only has to resist pure tensile force, Figure 6.28 shows the layout if each pole has its own rib. This section hence assumes that the skeletal structure has to react against the whole bending force, and can be designed independently of the electrical machine.

The problem can be simplified to the built in beam of Figure 6.29. Equation (6.27) describes the maximum deflection of the centre of the beam (as derived in Appendix D) in terms of its dimensions. For a maximum specified deflection, the second moment of area I, defined in ( 6.28), can be used to determine the required cross section of beam.

Figure 6.29: Equivalent beam for a VHM

Where :

C2 = ^(b4 - a4) + J-V ^(b3 - a3) 2 6L \ 2L L2 J 3L '

Where E = Young's Modulus (Pa)

If the magnetic compressive force from each pole is transferred onto a single beam in pure compression, the beam will shrink by 5 m, as given in ( 6.29).

It is now possible to design a simplified support structure for the VHM.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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