Abstract: This invention relates to an apparatus for controlling a D.C. power transmission system having a line-commutated converter which is connected between a first A.C. system and D.C. power transmission lines and which performs power conversion between A.C. power and D.C. power, and a forced-commutated converter which is connected between the D.C. power transmission lines and having a second A.C. system and which performs power conversion between A.C. power and D.C. power. In order to control transmission power in the two-terminal D.C. power transmission system wherein the two A.C. systems are associated by direct current, a control apparatus for a D.C. power transmission system according to this invention includes a voltage detector which detects a D.C. voltage of the D.C.

Abstract: A power converter adapted for use in a high-voltage circuit and equipped with a plurality of arms each comprising a plurality of thyristor elements connected in series, wherein an overvoltage limiter having an overvoltage limiting element and means for short-circuiting the ends of the overvoltage limiting element in response to flow of a load current therein are connected between the anode and the cathode of each thyristor element. The short-circuiting means has a gap between the two electrodes connected respectively to the anode and the cathode of each thyristor element, and also a metal layer of a low melting point which is molten by heat generated due to the flow of a load current in the overvoltage limiting element to fill the gap.

Abstract: A transmission line interconnecting system including an AC-DC converter connected to a first transmission line; and a forced-commutated type inverter connected to a second transmission line. DC terminals of the AC-DC converters and the forced commutated type inverter are connected and the output voltage of the forced commutated type inverter is varied by controlling DC voltage to feed a reactive power to the second transmission line in a normal state and to feed an active power from the first transmission line through the AC-DC converter and the forced excited type inverter to the second transmission line in an emergency state.