GB728473A - Improvements relating to alternating current frequency converters - Google Patents

Abstract

728,473. Frequency converters. KRAUSS, K. Jan. 26, 1953 [Jan. 24, 1952], No. 2238/53. Class 35. The rotor of a frequency converter is driven through a continuously variable gear from a shaft rotating at constant or substantially constant speed. The principle of the invention is shown in Fig. 1 in which phase-splitting machine a which runs from single phase supply t and generates three-phase current of the same frequency f1, drives the rotor of a converter c through variable speed gearing b. The stator of the converter is fed with three-phase current at mains frequency, the output frequency f2 depending on the slip-speed of the rotor. If three-phase supply is available the phase converter a may be dispensed with. In a particular embodiment, Fig. 2, the motor and converter are in the same machine 1, the rotors b and c being concentric in the same three-phase energized stator a and coupled together through fixed gearing 2 and variable gearing 3. The outer rotor b is caused to rotate by the interaction of a squirrel cage or D.C. energized winding on its outer surfaces and the rotating field of the stator. The inner surface of the rotor b is polarized by direct current through slip-rings b1 to form a rotating field at synchronous or near-synchronous speed. The inner rotor c carries a polyphase winding supplying current through slip-rings c1, the frequency generated being dependent on the speed of this rotor. Rotor c is fixed to the same shaft as sun wheel K, the outer annular gear g is fixed to rotor b, and the planet wheel cage m is driven through variable-speed gearing o through gears i, q, p1, p2, at a speed producing the required frequency output. Specifications 524,598, 671,561 and 676,245, [all in Group XXIV], are referred to.