GB485128A - Means for controlling the regenerative operation of series motors over current converters - Google Patents

Abstract

485,128. Controlling D.C. motors ; converting. ALLMANNA SVENSKA ELEKTRISKA AKTIEBOLAGET. March 18, 1937, No. 7993. Convention date, Sept. 10, 1936. [Class 38 (iii)] [Also in Group XXXV] The regenerative operation of a series motor connected to an A.C. network through a converter is controlled by a member responsive to the machine voltage and acting on control grids or equivalent members in the converter, the said member acting to raise the ratio between the absorbed D.C. voltage and the A.C. voltage when the machine voltage rises above a certain limit. This rise in the D.C. voltage reduces the voltage drop in the converter and thereby reduces the current which acts in turn on the machine voltage to prevent the latter from rising above a dangerous value. In the arrangement shown, the motor 1 with series field 2 is operated over a valve 4 having anodes 5 and control grids 6 from a singlephase supply 3 through a transformer having a network winding 8, valve winding 9 and an auxiliary winding 10 for supplying the grids. A current transformer 12 and equalizing inductance 11 are connected between the winding 9 and the machine. A change-over switch 13 is provided for facilitating the alternative operation as a motor or generator. The voltage on the machine terminals acts on an inductance 15 which permits the passage of an alternating current proportional to the machine voltage. This current is rectified over a polygon 17 of dry rectifiers and is subtracted from a standard current obtained over a corresponding D.C. saturated inductance 18 and rectifier polygon 19. The difference current is conducted over a rectifier 20 to a saturating winding on an inductance 21 which is connected in series with a resistance 22 to the secondary winding of a transformer 23. The primary winding of the grid transformer 24 is connected as shown, and its secondary winding is connected to the grids through resistances 25, the mid-point of the winding being connected to the cathode 7 through a resistance. 26 of a higher order of magnitude than the resistances 25. The grid control circuit may include a current responsive device 28 which normally keeps the load current within given limits. When the terminal voltage of the machine rises above a certain value, the direct current from the polygon 17 rises and approaches the value of the standard current from the polygon 19 ; the difference current through the saturating winding of the inductance 21 simultaneously falls, so that the value of the inductance rises from an initial low value, in which it has no appreciable influence on the phase of the grid voltage, to a higher value at which the phase is retarded. This causes the inverter to deliver a higher counter-voltage, whereby the current is decreased and the original rise of voltage on the machine terminals is counteracted. The standard voltage delivered by the polygon 19 may be made dependent on the line voltage ; in this case, the line voltage may be connected directly to the polygon 19 and the intermediate device 18 may be omitted. When the regulation is used both for motor and generator operation, it may be arranged to operate at different voltages in the two cases by connecting a rectifier 29 in shunt with part of a resistance 14 between the machine and the inductance 15.