GB745826A - Improvements in or relating to rotary electrical apparatus in which a permanent magnet is included in the magnetic circuit - Google Patents

Abstract

745,826. Magnetic structures; dynamoelectric machines. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Nov. 25, 1952 [Nov. 28, 1951], No. 29792/52. Classes 35 and 38 (2) Electrical apparatus such as a dynamoelectric machine comprises a winding in a gap between two parts including or consisting of permanent magnetic material having a specific resistance of at least 1000 ohm-cm., and of such nature that it is not easily demagnetized. Suitable materials are the polyoxides of iron and at least one of the metals Ba, Sr, Pb and, if required, Ca, such as from the subject-matter of Specification 708,127. The material may be magnetized at higher than air temperatures as described and claimed in Specification 719,004. The machine of Fig. 1 comprises a polarized part 1 of this material which has relative rotation to a polarized part 2 of the material in which part is embedded a coil 3 in which an E.M.F. is induced by the change of flux produced by the alternate assisting and opposing action of the poles. In a modification, a coil moves relative to the magnetic parts in a circular air-gap between those parts. The gap not occupied by the coil may be filled with magnetically soft material which may be of the kind known as Ferroxcube, having a high specific resistance, Fig. 3 (not shown). Fig. 4 shows a machine in which two coils 11, 12 rotate about an axis 13 in an axial field between polarized permanent magnet segments 14, 15, 16, 17, magnetically soft discs 21, 22 completing the magnetic circuit. The use of magnetic material of high specific resistance makes the machines useful for high frequencies.