Abstract:
A converter station (STN1, STN2) having a voltage source converter (CON1, CON2) is coupled between a direct current link (W1, W2) and an alternating current network (N1, N2) in a high voltage direct current transmission system. A control system (CTRL1, CTRL2) for the converter station has means for control of active power flow (P) between the direct current link and the alternating current network by influencing the phase displacement (null) between a bus voltage (UL1, UL2, UL) in the alternating current network and a bridge voltage (UV1, UV2, UV) of the voltage source converter. The control system comprises detection means (48) for generation of a phase change order signal (PCO) in response to an indication of an abnormal voltage condition at the direct current link, and means (49) for influencing the phase position of the bridge voltage in response to said phase change order signal, so as to ensure that the phase displacement between the bridge voltage and the bus voltage will result in an active power flow from the direct current link to the alternating current network.
Abstract:
A multilevel converter cell includes a first section with a first group of series connected switching units in parallel with a first energy storage element, where a junction between a first and second switching units of the first group of series connected switching units forms one cell connection terminal, a second section with a second group of series connected switching units in parallel with a second energy storage element, where a junction between a third and fourth switching units of the second group of series connected switching units forms another cell connection terminal, and an interconnecting section with a third group of series-connected switching units comprising a fifth, sixth and seventh switching unit, with the fifth and sixth switching units connected in parallel with the first energy storage element and the sixth and seventh switching units connected in parallel with the second energy storage element.
Abstract:
A system for transient over voltage protection of a three-phase transformer. Two surge arresters are series connected across each winding of the transformer and the center point connection of the two surge arresters is electrically connected to a middle location of the winding. Three additional surge arresters are electrically connected from each phase to ground in the case of either a delta or Y connected transformer; and/or connected from a neutral point to ground in the case of a Y connected transformer. The system allows for all of the surge arresters to be packaged as an integrated surge arrester system to minimize induced transient over voltages and high stresses on the transformer winding due to internal resonances.
Abstract:
A multilevel converter cell includes a first section with a first group of series connected switching units in parallel with a first energy storage element, where a junction between a first and a second switching unit forms one cell connection terminal, a second section with a second group of series connected switching units in parallel with a second energy storage element, where a junction between a third and a fourth switching unit forms another cell connection terminal, and an interconnecting section with a third group of series-connected switching units comprising a fifth, sixth and seventh switching unit, with the fifth and sixth switching units connected in parallel with the first energy storage element and the sixth and seventh switching units connected in parallel with the second energy storage element.
Abstract:
The invention relates to a system and a method for assembly and maintenance of connection modules (3) in high-voltage switchgear (1). According to the invention assembly and maintenance are performed in a service bay (6) in the vicinity of the switchgear. Modules (3a) to be assembled, replaced or repaired are transported between the service bay (6) and its site (2a) in the switchgear area by a service vehicle (4). The vehicle (4), connection modules (3) and the positions for their base plates (2) are thus so adapted to each other that the service vehicle (4) can move about in the switchgear area while the switchgear is in operation. A special aspect of the invention is the custom-design of the service vehicle (4) specifically for its purpose.