| 摘要 |
1434557 Control of two D.C. motors JEUMONT-SCHNEIDER 24 July 1973 [31 July 1972] 35279/73 Heading H2J D.C. machines having armatures M1, M2 and field windings N1, N2 are operated in the following four modes by actuation of contactors C1 ... C4 and the moving contacts I1 ... I4 of a four-pole changeover switch I between positions 1 and 2:- Mode 1.-The machines operate as serieswound motors connected in series by movement of switch I to its position 1, opening of contactors C1, C3 and closing of contactors C2, C4, rheostats R1, R2 being adjusted to give the required speed. Mode 2.-This is produced by changing from mode 1 by opening contactor C4 and closing contactors C1, C3, whereby the machines operate as parallel-connected series motors with smooth changeover and subsequent speed control by adjustment of the rheostats R1, R2. Mode 3.-Switch I is moved to position 2, contactors C1 ... C4 are opened and rheostats R1, R2 are set to a predetermined value, whereby the machines operate as separately-excited parallel-connected generators returning power to the supply E, the excitation of their seriesconnected field windings N1, N2 being varied by a controlled rectifier bridge P to vary the braking torque. Mode 4.-When the machine speeds have fallen to a value corresponding to a voltage below that of supply E, mode 3 is altered by closing contactor C4 and adjusting members P, R1, R2 whereby the machines operate as separately-excited series-connected generators returning power to the supply E, members P, R1, R2 again varying the braking torque. The diodes D1 ... D4 prevent reversal of the braking current if the voltage of supply E exceeds the system voltage produced by the machines when generating. There may be a direct transition from mode 2 to mode 4, if the machine speeds at the end of mode 2 are too low for the machine output voltage to be in excess of the supply E. |
