Patent GB-635026-A (GB)
Title: Improvements in control systems for electric motors
IPC: B60L15/04
Filed: 1947-08-27
Abstract: 635,026. Control of D.C. motors; controllers. FORGES ET ATELIERS DE CONSTRUCTIONS ELECTRIQUES DE JEUMONT. Aug. 27, 1947, No. 23655. Convention date, March 13, 1942. [Class 38 (iii)] A control system providing rheostatic starting of a plurality of electric motor groups which may be connected in series, series-parallel, or parallel, comprises a plurality of rheostats of unequal resistance-valves divided into sections, so that, when said rheostats are inserted into the parallel motor circuits, a progressive cyclical step-by-step elimination of said sections takes place in the various motor circuits, the arrangement of the rheostat sections and the cyclical order in which the said sections are shortcircuited being such that the starting operation can always be carried out by the same contacts operating in the same order irrespective of the manner in which the motor-groups are connected. The rheostats and their sections may be given suitable values so that substantially the same increment of torque is obtained at each starting-step, and excessive unbalancing of currents in the various parallel circuits is avoided. Initially, switches are actuated to connect motors M1-M6, resistors R1, R2, R3, R<SP>11</SP>4, and a part of resistor R<SP>1</SP>4, in series between the supply-line L and earth. Switches C20 and C15 are respectively opened and closed to remove the resistor R<SP>11</SP>4 and insert the whole of the resistor R<SP>1</SP>4. Thereafter a switch C21 is closed to connect resistor R"4 in parallel with a portion of resistor R<SP>1</SP>4. Acceleration is afforded by the movement of a controller successively to operate a number of contacts short-circuiting sections of the various resistors in sequence. When the switches are operated to afford another combination, the motors are connected in two parallel-branches of three in series, the motors M1, M2, and M3 being connected in series with resistors R3 and R4, and motors M4, M5 and M6 being likewise connected to resistors Rl and R2. The contacts short-circuiting resistors R1-R4 are actuated in the same order as that obtaining during series-connection of the motors, the controller being moved through the same steps. The parallel-branches have unequal resistance-values, and the arrangement is such that a section of a resistor in the branch of higher resistance is short-circuited by movement of the controller, so reducing the resistance of that branch to a value below the other, the resistance of the latter branch is then reduced and the operation continues in alternate sequence. Sudden variations of the motortorque are thereby prevented, and, for a given maximum value of torque during the starting period, the average value of torque is increased. A third grouping of the motors provides seriesconnection of two motors in three parallelbranches. Motors M1 and M6 are connected in series with resistors R2 and R3, motors M2, M3, and resistor R1 are connected in another branch, and motors M4, M5, and resistor R4 are comprised in the third. The contacts which short-circuit the sections of the resistors R1- R4 are again operated in the same sequence, the resistances of the parallel-branches being, likewise, of unequal value. The reduction of the resistances in the parallel-branches is effected in a manner similar to that described, the branch of highest resistance being always the first to be reduced. The contactors controlling the removal of the starting resistance may be regulated by an acceleration relay, the coil of which is shunted by a resistance having a value dependent upon the number of parallel circuits in operation. Resistors R1 and R4 may be of equal value, resistors R2 and R3 being approximately one-half and two-thirds of this value respectively.