The thickness of the iron lamination sheets varies between about 0.05 and 0.5 mm in most electrical machines. The choice of lamination thickness depends on a balance between performance and cost.
Since the eddy-current losses are approximately proportional to the square of the lamination thickness, it is a good idea to choose thin iron laminations. Especially for switching frequencies in the range of several hundred Herzt and above or when there is a requirement for low iron core losses, a thin lamination thickness is a requisite. What is mainly limiting the use of very thin lamination thicknesses are the cost and the technical feasibility:
- Reducing the lamination thickness does generally also reduce the stacking factor. As a consequence, the machine length has to be increased for the same rated power and the conductor losses do increase accordingly.
- One reason that contributes to the reduction of the stacking factor is the fact that the very thin coating, which provides insulation between two lamination sheets, represents an increasing percentage of the total lamination thickness for very thin lamination sheets.
- Another reason that contributes to the reduction of the stacking factor is due to the physical imperfections of the lamination sheets. The thiner the lamination sheets, the more layers that can have irregular gaps between them and reduce the stacking factor.
- Generally, thinner iron laminations are also more expensive to purchase than thicker lamination sheets.
- In addition, manufacturing, i.e. punching and stacking of the lamination sheets, gets also more expensive with the larger number of lamination sheets that have to be handled with thinner lamination sheets. It is also much more difficult to punch very thin lamination sheets, and the quality and maintanance of the punch tools has to be high quality.
As a consequence, the choice of lamination thickness is a compromise between performance and cost. Nowadays, electrical machines are more often bought considering their life-cycle cost and not just their purchase price, which results in a trend towards thinner and higher quality iron laminations.
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