| 摘要 |
<p>848,161. Rectifying. ALLMANNA SVENSKA ELEKTRISKA A.B. Aug. 26, 1958 [Aug. 31, 1957], No. 27300/58. Class 38 (2). In order to prevent commutation from starting, at very low loads, between anodes belonging to two different groups 2 and 3 of floating grid rectifiers, such as 1, with consequent voltage rise due to shifting into six-phase operation, the discharge paths of a group the current of which temporarily becomes zero, are blocked when the direct voltage exceeds the no-load value. The two commutating groups are fed by star-connected secondaries 4, 5 having their neutral points connected by an interphase transformer and the blocking is done by a self-excited transductor amplifier 17 which applies the blocking voltage to grid voltage device 15. The transductor 17 has a control winding 22 connected across the D.C. lines 10, 11 and an opposing winding 23 fed from the alternating voltage mains 8. When the load current falls sufficiently to reach the under-critical range, rise of the direct voltage causes winding 22 to predominate so that one commutating group is blocked. To prevent repeated blocking and unblocking a third winding 27 which assists winding 23 is fed from a bridge-circuit comprising two halves of resistor 30 and the windings of a measuring transductor 29, the output being dependent on the current from the rectifier 1 but only in a very narrow range close to zero. Metal rectifier 32 through which winding 27 is fed has an output voltage which remains substantially constant until the direct current through transductor 29 falls close to zero, when it decreases quickly. A number of rectifiers in parallel may be successively blocked or unblocked in dependence on the load. To avoid all the three-phase groups being blocked a basic load resistor 34 may be provided or the direct voltage windings in the transductors may serve this purpose. The transductor 17 may be unstably self-excited and have two voltage-sensitive windings so that a blocking voltage may be produced at a direct voltage somewhat above the critical voltage while the rectifiers are unblocked at a somewhat lower voltage.</p> |
