Abstract: An arrangement for changing current return path in a bipole direct current power transmission system includes a converter station having an active and a passive converter connected in series between an active and a passive pole line via a first neutral bus, a metallic return transfer switch in an electrode line, a ground return transfer switch in a current redirecting path between the passive pole line and the neutral bus and a control unit which in case of change to the passive pole line for providing a return current path is configured to, upon control of power related to the active converter from steady-state to zero, close the ground return transfer switch and thereafter open the metallic return transfer switch, whereupon power related to the active converter may be controlled back to steady state.

Abstract: An arrangement for changing current return path in a bipole direct current power transmission system includes a converter station having an active and a passive converter connected in series between an active and a passive pole line via a first neutral bus, a metallic return transfer switch in an electrode line, a ground return transfer switch in a current redirecting path between the passive pole line and the neutral bus and a control unit which in case of change to the passive pole line for providing a return current path is configured to, upon control of power related to the active converter from steady-state to zero, close the ground return transfer switch and thereafter open the metallic return transfer switch, whereupon power related to the active converter may be controlled back to steady state.

Abstract: An HVDC transmission including at least two converters. Each converter is adapted for connection between a three-phase alternating-voltage network. At least a first converter has ac leads for connection of the first converter to the alternating-voltage network without the use of a separate winding transformer. A dc link is common to the converters. A zero-sequence inductor connection is arranged in the ac leads of the first converter and designed such that the zero-sequence inductor connection exhibits a high impedance to zero-sequence currents and a low impedance to positive-sequence currents.

Abstract: An installation for transmission of electric power by means of high-voltage direct current has two converters (SRI, SRII), each of which is connected to an alternating-voltage network (NI, NII) and which are connected to each other through a dc connection (L). One converter (SRI) is controlled as a rectifier and another converter (SRII) is controlled as an inverter. One converter (SRI) is current-controlling and another converter (SRII) is voltage-controlling. The installation has means (VARC.sub.rect) adapted, at such a change of the control angle (.alpha..sub.rect) of the current-controlling converter (SRI) that the angle reaches a limit of a predetermined interval (.alpha..sub.max nom rect -.alpha..sub.min nom rect) to control, by means of the voltage-controlling converter (SRII), the direct voltage (Ud) of the transmission in such a way that said change is limited.

Abstract: Control equipment (CE1) generates an ordered value (AOL) of a control angle (.alpha.) in dependence on a limiting signal (AMINL, AMAXL), capable of being influenced, for a converter included in a series-compensated converter station. A calculating value (AFIRL) of a control angle is calculated continuously according to a predetermined relationship (H'1, H'2) which at least approximately imitates a relationship according to which, at a firing voltage (Ufir) for the valves of the converter equal to a preselected value (Uvref), said control angle is a function (G'0) of a current (Id1) and a voltage (Un1) in the converter station and the limiting signal is formed in dependence on the calculating value. (FIG.

Abstract: A series-compensated converter station in an installation for transmission of high-voltage direct current is connected to an alternating-voltage network (N) with three phases (A, B, C, respectively). The converter station comprises at least two direct-voltage series-connected six-pulse converter bridges (SR1, SR2, respectively), a three-phase transformer coupling with two secondary windings (SW1, SW2, respectively), and a star-connected primary winding (PW) with a neutral point (NP) connected to ground as well as a series capacitor unit (CN) for each one of the three phases. Each one of the converter bridges is connected to a respective secondary winding and the primary winding is connected to the alternating-voltage network via the series-capacitor units. The transformer coupling exhibits a high impedance to zero-sequence currents through the primary winding of the transformer coupling.

Abstract: Control equipment (CE2) generates an ordered value (AOL) of a control angle (.alpha.) in dependence on a limiting signal (AMAXL), capable of being influenced, for a converter included in a series-compensated converter station. A calculating value (AMARG) of a control angle is calculated continuously according to a predetermined relationship (M0, M1, M2, M3) which at least approximately resembles a relationship according to which, at a commutating margin (.gamma..sub.m) equal to a preselected value (.gamma..sub.p), said control angle is a function (F0) of a current (Id2) and a voltage (Un2) in the converter station and the limiting signal is formed in dependence on the calculating value.

Abstract: A series-compensated converter station included in an installation for transmission of high-voltage direct current comprises a converter (SR1, SR2) with at least one 6-pulse bridge (BR). Via series capacitors (SCR, SCS, SCT) the 6-pulse bridge is connected to a three-phase alternating-voltage network (N1, N2) with a fundamental frequency (f.sub.01, f.sub.02). Control equipment (CE1, CE2) generates an ordered value (AOL) of a control angle (.alpha.) for valves (V1-V6) included in the 6-pulse bridge in dependence on a limiting signal (AMAXL) capable of being influenced. An amplitude signal (AMPL) is formed which corresponds to the amplitude (C.sub.1) for a component (C.sub.1 cos(2.pi.f.sub.0 t+.phi..sub.1)) of the fundamental frequency in the direct voltage (Udb) of the 6-pulse bridge and a compensating signal (ACOMP) is continuously calculated in dependence on a sensed voltage (Un1, Un2) at the converter station and on the amplitude signal.

Abstract: An installation for transmission of high-voltage direct current comprises a first and a second converter (SR1, SR2, respectively), each one controlled by a separate piece of control equipment (CE1, CE2, respectively). Each one of the pieces of control equipment comprises a current controller (CC). The current controller of the second converter is supplied with a second current reference value (IOL2) and a current margin (IOM). The control equipment of the second converter comprises a function-forming member (11), which in dependence on an applied measured value (UD) of the direct voltage forms the current margin such that, when the direct voltage exceeds a first preselected voltage level (Udf), it assumes a first value (IOMf) and, when the direct voltage is lower than the first voltage level, it assumes a second value (IOMs), the magnitude of the second value being greater than the magnitude of the first value.

Abstract: A device in a system for power transmission by means of high voltage direct current wherein: a first current path and a second current path are interconnected at a branch point; a first semiconductor connection is connected into the first current path only and which is controllable between conducting and non-conducting states and vice versa; a second semiconductor connection having a diode function and which is connected into the second current path only; a capacitor branch comprising a capacitor and connected between a first connection point on the first current path and a second connection point on the second current path; the first connection point and the branch point are located on opposite sides of the first semiconductor connection; the second connection point and the branch point are located on opposite sides of the second semiconductor connection; and control members for controlling, in dependence on the voltage across the capacitor, the first semiconductor connection between a non-conducting and a c

Abstract: An HVDC transmission has two converters (SR1, SR2). Each converter is connected between an alternating-voltage network (N1, N2) and a d.c. link (L1, L2) common to the converters. At least one converter is connected to its alternating-voltage network without the use of any full transformer, for example directly, or via an inductor or an autotransformer, or via series capacitors. The transmission has a mutual inductor (IB) which is arranged on the d.c. side of the converter and which has two windings (IB1, IB2) which are each connected to a respective one of the d.c. supply lines of the converter and are magnetically coupled to each other, the inductor being designed and connected so as to exhibit a high impedance to ground mode currents.