Abstract: A high voltage direct current transmission includes a rectifier station and an inverter station connected by a DC line. The rectifier station has uncontrolled valves and an arrangement enabling current control to be effective at over-current conditions for controlling the alternating voltage connected to the valves. There are first and second control circuits, the first of which is controlled in dependence on the line voltage and the second in dependence on the line current. A circuit for selecting either the first or the second control circuit is provided between the control circuits and the voltage control arrangement. The valves of the rectifier station may be arranged in two six-pulse groups mutually offset in phase, so reactively connected that they have the commutating reactance partly in common.

Abstract: In a static convertor which comprises at least one rectifier bridge with valves or rectifiers arranged in commutating groups and a control pulse emitter connected to the valves by individual control circuits, in order to ensure that during operation one valve in each group always receives an ignition signal, a holding circuit is provided for each valve and its control circuit and a signal output for indicating valve ignition. The holding circuit is connected on its input side to the signal outputs for the valves in the proper commutating group in such a way that the holding circuit is switched on by the signal outputs of its own valves and switched off by the signals from the signal outputs of the other valves.

Abstract: A high voltage direct current transmission includes a rectifier station and an inverter station each connected to an AC network and connected together by a DC line. In order to limit over-voltages on the line and in the rectifier station on starting the station towards an open line, this station is provided with an arrangement which senses the voltage and the current of the station and is connected by level indicators for maximum voltage and minimum current to a signal emitter which reduces the direct voltage of the station in response to a direct voltage above a certain level and a direct current below a certain level.

Abstract: In the operation of a bipolar direct-current transmission system having bipolar convertor stations with earthed center taps and transmission lines connecting the stations, one for each polarity, in which system in the event of disconnection of one pole of the stations the corresponding pole of the transmission line is connected as a return conductor for the remaining pole, in order to load the return connector with current and discharge the ground connections between the stations, the current of the corresponding pole in one of the stations is increased to the same value as the pole in operation, and thereafter the ground connection of such corresponding pole is interrupted.

Abstract: A direct current transmission system includes two separate parallel transmission circuits each including convertors. The transmission circuits are bipolar. One pole of one of the circuits is provided with pole reversing switches for the convertors of that pole. The poles of each of the circuits are connected in parallel by transmission lines. Switches are provided by which one of the transmission lines of one circuit can be disconnected from that circuit and connected across a faulty transmission line of the other circuit, which meanwhile is disconnected therefrom, so as to substitute for the disconnected transmission line of the second circuit.