Abstract
Electrical machines contain stationary and moving parts coupled by an electrical or magnetic field. The field acts on the machine parts and plays key role in the process of electromechanical conversion. For this reason, it is often referred to as the coupling field. This chapter presents the most significant principles of creating a force or torque on the machine moving parts. In all the cases considered, the force appears due to the action of the electrostatic or magnetic field on the moving parts of the machine. Depending on the nature of the coupling field, the machines can be magnetic or electrostatic.
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Notes
- 1.
The right-hand rule requires thumb and forefinger to assume right angle. The middle finger should be perpendicular to both. Now, with forefinger alligned with vector l and middle finger alligned with B, thumb determines the direction of force. Alternatively, direction of any vector product can be determined by an imaginary experiment, where the first vector of the product (l in (2.2)) is rotated toward the second vector (B). Envisaging a screw that is turned by such rotation, the screw would advance along the axis perpendicular to l − B plane. The direction of the vector product is determined by the advance of the (right) screw.
- 2.
Flux is a scalar quantity having no direction. Flux through surface S is equal to the surface integral of the vector of magnetic induction B, also called flux density. Surface S is encircled by contour C; thus, the said surface integral is called flux through the contour. Flux through a flat surface S placed in a homogeneous external magnetic field depends on its position relative to the field. With the positive normal on S aligned with the direction of the vector B, the flux through S is equal to Φ = BS. Although the flux Φ is a scalar, it is inherently related to spatial orientation of the surface S and/or the vector B. The flux vector is obtained by associating the spatial orientation (i.e., direction) to the scalar Φ. In the given example, the spatial orientation is defined by the positive normal on S. Direction of the positive normal is determined by applying the right-hand rule to the reference circling direction for the contour C. The external magnetic field is the one which is not created by the electrical currents in the contour C.
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© 2013 Springer Science+Business Media New York
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Vukosavic, S.N. (2013). Electromechanical Energy Conversion. In: Electrical Machines. Power Electronics and Power Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-0400-2_2
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DOI: https://doi.org/10.1007/978-1-4614-0400-2_2
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