Multi-phase electrical converter stations

摘要

1,078,336. Converting. ALLM NNA SVENSKA ELEKTRISKA A.B. Oct. 28, 1964 [Oct. 31, 1963], No. 43919/64. Heading H2F. In a polyphase converter station in which the constituent converters are operated in mutually phase-displaced groups, the total power output is regulated so as to be approximately the same for each group in order to reduce the number of harmonics in the A.C. side of the converter. Fig. 3 shows a chain of converters 1-6 between D.C. lines 7 and 8. The converter transformers have their inputs connected in parallel to an A.C. network as at 9 and their outputs provide star and delta phase groups Y, D. Under normal conditions, all the converters 1-6 provide equal voltages and carry equal currents. If a converter in one group is by-passed under fault conditions, the power balance between the groups may be restored by tap-changing on the converter transformers so as to increase the output voltage of the converters in the affected group and reduce the output voltage of the converters in the other group. Alternatively, the balance may be restored by drawing currents from D.C. lines 10 and 11 (which may connect with an adjacent converter station) and a centre-tapped earth line (Fig. 2, not shown), such that the 'total current carried by the converters of the affected group is increased with respect to the total current of the other group. Tap-changing may also be used to compensate for any current unbalance caused by an adjacent converter station. In a further embodiment (Fig. 4, not shown), two or more chains of converters may be connected in parallel. If a converter in one chain becomes by-passed, the voltage in a parallel chain may be lowered to restore the power balance either by disconnecting a converter in the parallel chain or by grid control of the converters in the parallel chain. Fig. 5 (not shown), illustrates an arrangement for co-ordinating the control of the current and voltage of a converter station having two groups of constituent converters, in which each converter is provided with a grid control system (2) which determines the control angle of the converter valve group (1), a tap selector (4) and a watt-meter (5). The total power for the two groups of converters is determined by summation units (7 and 8) and compared by a device (9). The output from device (9) is fed as an error signal to the grid control system (2) and the tap selector (4). In the embodiments described, A.C. machines or generators may be connected to Y-D pairs of converters.