Basic Problems of Increasing the Density of Unit Power of Electric Machines

The scientific and technological progress forces a continual intensification of parameters in all fields. Every new solution is expected to be cheaper, lighter, faster, more efficient, etc. The progress in the field of electric machines development should consist, among others, in designing new generations of machines that exhibit higher efficiencies and higher densities of unit power. The operation of electric machines utilises the unique properties of magnetic flux whose field energy is able to bind the electrical energy in the stator winding Eel and the mechanical energy of the rotor E_mech into the E_el hArr E_mech conversion process. A basic difficulty in increasing the density of unit power of electric machines is the poor choice of materials that could be used for constructing the magnetic circuit, and especially the lack of a material fully insulating for magnetic flux -a super-diamagnetic of mu_r rarr 0. Adopting a dissipationless loop of magnetic flux for shaping the reactive structures of electric machines makes it possible to evade the constructional limitations connected with the lack of an insulator for magnetic flux, by the assistance of magnetomotive forces (MMFs) connected with the kinetic system of the rotor according to the adopted slot cutting conception. Thus it is possible to construct low-speed (for 50Hz) electric machines of a large number of pole pairs and full ability to develop torques. The distinguishing feature of these machines -the low diameter -in high-speed applications creates new types of high-frequency machines with so far unknown high densities of unit power in relation to conventional machines. Presented in the paper are the basic principles that need to be observed while shaping the reactive structures of electric machines, that lead to the slot cutting conception.