| 摘要 |
1505756 High voltage direct current transmission systems ASEA AB 18 July 1975 [19 July 1974] 30189/75 Heading H2F A high voltage D.C. transmission system comprises a rectifier station 1 connected by a D.C. line 5 to an inverter station 2, the rectifier station being provided with a voltage sensor 7 and a current sensor 8 connected via a maximum voltage level indicator 9 and a minimum current level indicator 10 respectively to a signal generator 13, 14 for reducing the direct voltage of the rectifier station when a direct voltage above the maximum level and a direct current below the minimum level occur simultaneously. The system prevents overvoltages occurring on the line 5 and in the rectifier station on starting this station. The sensor 7 is a voltage divider which is connected to one input of a summation member 11 the other input of which receives the maximum voltage signal U krit . The sensor 8 is a current measuring transductor connected to a summation member 12 which also receives the minimum current signal I krit . In the event of the rectifier voltage exceeding the maximum level simultaneously with the current being less than the minimum level, the indictors 9, 10 provide signals to an AND gate 13 which, via a time delay 14, supplies a signal to the rectifier station to reduce the direct voltage supplied by the station. The voltage reduction may be achieved by controlling the firing angle of the rectifier valves, by blocking the rectifiers or by shunting one or more of the rectifiers in the station 1. In a modification, a circuit for simulating the current and voltage at the inverter station is connected to the outputs of the sensors 7, 8 to reduce the rectifier output voltage in the event of a fault at the inverter station. A circuit is also described for reducing the inverter output voltage in the event of a temporary decrease in the inverter current.
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