Abstract: A substation has a converter comprising a first set (S1) of series connected converter valve elements provided between a first (V1) and a second (V2) potential, where the absolute value of the second potential is higher than the absolute value of the first potential, and a second set (S2) of converter valve elements, comprising at least one converter valve element, provided between the second and a third potential (V3), where the absolute value of the third potential is higher than the absolute value of the second potential and all converter valve elements of the second set are placed inside one or more casings (28) placed on elongated post-like insulation (24), where the potential of the end of the post-like insulation on which the casings are placed is in a range between the second and the third potential, while the other end of the post like insulation is at ground potential.

Abstract: A method for controlling power flow within a multi-terminal DC power transmission system including two or more converter stations and the corresponding multi-terminal DC power transmission system are provided. The method includes the steps of: controlling the power flow to a steady state reference operating point for operating points within a control dead band defined for each respective converter station, and controlling the power flow by means of droop control in at least one of the converter stations upon detection of exceeding of an end point of one or more of the control dead bands.

Abstract: A method for controlling power flow within a multi-terminal DC power transmission system including two or more converter stations and the corresponding multi-terminal DC power transmission system are provided. The method includes the steps of: controlling the power flow to a steady state reference operating point for operating points within a control dead band defined for each respective converter station, and controlling the power flow by means of droop control in at least one of the converter stations upon detection of exceeding of an end point of one or more of the control dead bands.

Abstract: A substation has a converter comprising a first set (S1) of series connected converter valve elements provided between a first (V1) and a second (V2) potential, where the absolute value of the second potential is higher than the absolute value of the first potential, and a second set (S2) of converter valve elements, comprising at least one converter valve element, provided between the second and a third potential (V3), where the absolute value of the third potential is higher than the absolute value of the second potential and all converter valve elements of the second set are placed inside one or more casings (28) placed on elongated post-like insulation (24), where the potential of the end of the post-like insulation on which the casings are placed is in a range between the second and the third potential, while the other end of the post like insulation is at ground potential.

Abstract: A land electrode for a high voltage direct current transmission system including a converter station with a grounding point. The land electrode is connected to the grounding point and includes a plurality of electrode sections. A line electrode includes a part interconnecting two electrode sections. The part of the line electrode exhibits a line resistance. Each electrode section includes at least one electrode element.

Abstract: A land electrode for a high voltage direct current transmission system including a converter station with a grounding point. The land electrode is connected to the grounding point and includes a plurality of electrode sections. Each electrode section includes at least one electrode element.

Abstract: Improved apparatus for discharging power from a high-voltage direct current line. A direct voltage convertor is connected in series with a smoothing filter and a DC high voltage line on one side and a second smoothing filter and a power discharge inverter on the other side. The rated voltage of the discharge inverter is substantially lower than the line voltage and the direct voltage convertor applies the lower voltage to the discharge inverter.