GB492887A - Improvements in and relating to moving contact electric current converters - Google Patents

Abstract

492,887. Converting. SIEMENSSCHUCKERTWERKE AKT.-GES. Jan. 25, 1937, Nos. 2189 and 2190. Convention dates, Jan. 24, 1936 and March 13, 1936. Addition to 492,369. [Class 38 (ii)] Commutator switching arrangements.-A moving contact electric current converter as described in the parent Specification is provided with means for regulating the current and voltage by which the ratio of the period for which the contacts are closed to the period for which the contacts are open can be varied. When the converter is provided with sliding contacts, the instant of closure of these contacts can be varied by varying the length of the sliding contact or the fixed contacts or both. If the converter is provided with camoperated lifting contacts, each contact may be operated by two cam discs which can be relatively angularly adjusted or which are mounted on separate shafts driven by separate synchronous motors so that the period of contact closure is variable. Alternatively, the contacts may be closed by a cam by which the instants of closing of the contacts can be varied, the contacts being prevented from opening by an electromagnetic holding device until the current has fallen to a value permitting sparkless opening of the contacts. The Figure shows a converter in the instants at which the contacts 84, 85, shunted by impedances 80, are closed and opened, can be varied, the contacts being operated by wedge-shaped cams 87 carried on a shaft 86 driven by a synchronous motor 90 supplied through a phase shifting device 91. The shaft 86 is arranged to be movable in an axial direction by an electromagnetic device 97 acting against a spring 98, the device 97 being energized in accordance with circuit conditions such as the power transmitted or the voltage. The arrangements described above may be provided with means for variably premagnetizing the saturable impedances in series with the contacts. These means may comprise biassing windings energized through a regulating resistance. Alternatively, the cross-sections of the magnetic cores of the saturable impedances may be variable. In rectifier arrangements, the variation of the instants of opening of the contacts may be made dependent on the value of the back electromotive force in the load circuit or on the difference between this voltage and the D.C. voltage supplied by the rectifier or on the degree of smoothing of the direct current or on the amount and phase position of the harmonics present.