Abstract: A device for damping of high frequency currents is provided. The device includes a conductor extending along a main axis, a first damping path including a first damping element extending along a first axis and a second damping path including a second damping element extending along a second axis. The first and second damping elements are arranged on opposite sides of the conductor. The main axis, the first axis and the second axis are different and separate from each other. The first damping element and the second damping element are spaced apart from the conductor and electrically connected in parallel with the conductor between a first position and a second position along the conductor. Further, from the first position to the second position, a resistance of the conductor is lower than a resistance of either one of the first and second damping paths.

Abstract: A device for damping of high frequency currents is provided. The device includes a conductor extending along a main axis, a first damping path including a first damping element extending along a first axis and a second damping path including a second damping element extending along a second axis. The first and second damping elements are arranged on opposite sides of the conductor. The main axis, the first axis and the second axis are different and separate from each other. The first damping element and the second damping element are spaced apart from the conductor and electrically connected in parallel with the conductor between a first position and a second position along the conductor. Further, from the first position to the second position, a resistance of the conductor is lower than a resistance of either one of the first and second damping paths.

Abstract: A DC grid (100) comprising a plurality of AC/DC converters (105) which are interconnected via DC lines (115) is provided, wherein, in order to limit the effects of a fault in the DC grid, the DC grid is divided into at least two zones (200) by means of at least one current limiter (205) in a manner so that a current limiter is connected in each of the DC line(s) (115z) by which two zones are interconnected. A method of limiting the effects of a fault in a DC grid by dividing the DC grid into at least two zones is also provided.

Abstract: A voltage balancing unit for a symmetric monopole high voltage direct current (HVDC) transmission line interconnecting two voltage source converters (VSCs), the transmission line including first arresters having a first switching impulse protective level (SIPL) is provided. The voltage balancing unit includes a pair of second arresters having a second SIPL which is less than the first SIPL, and a switching device being arranged for temporarily connecting, in the event of a voltage unbalance on the transmission line, the first arresters between either pole and ground. A voltage unbalance on the transmission line may be removed by temporarily connecting second arresters, with a significantly lower SIPL than the first arresters, for limiting the pole voltage to a level close to the normal voltage. Further, a method of voltage balancing is provided. Voltage unbalances may arise as a consequence of lightning induced earth faults.

Abstract: A high voltage direct current (HVDC) switchyard is provided. The switchyard is arranged for interconnecting three or more sections of an HVDC power network, such as transmission lines, converters, or any other type of HVDC equipment. The switchyard comprises at least one main circuit breaker and at least four transfer switches. The at least one main circuit breaker and the at least four transfer switches are arranged so as to enable to individually disconnect any one of the at least three sections of the HVDC power distribution network. In an embodiment of the invention, the transfer switches which usually are comprised in direct current (DC) hybrid circuit breakers are used as selector switches, thereby reducing the number of main breakers in the switchyard.

Abstract: The present invention relates to a fault detection system for detection of line faults on an electrode line in an HVDC system wherein the electrode line comprises a first and second branch connected in parallel. The fault detection system comprises a first and second pulse generation circuit arranged to generate electrical pulses onto the first and second branches, respectively, as well as first and second current measurement devices arranged to generate signals indicative of electrical signals occurring in first and second injection lines, respectively. The possibility of independent generation of electrical pulses onto the first and second branches, respectively, as well as the independent registration of first and second signal patterns representing electrical signals on the first and second injection lines, respectively, increases the information content in the collected data, thereby facilitating for a more reliable analysis of whether or not a fault is present on the electrode line.

Abstract: A method is provided for controlling power flow within a wind park system for power transmission to a main power grid, the wind park system including two or more parallel-connected island wind park grids. The method includes the steps of: controlling a first voltage source converter as a swing bus in frequency control, the frequency control including controlling frequency to a steady state reference operating point for operating points within a power dead band and by frequency droop control when exceeding an end point of the power dead band, and controlling at least a second voltage source converter in power control, the power control including controlling power flow to a steady state reference operating point for operating points within a frequency dead band and by power droop control when exceeding an end point of the frequency dead band. A controller and computer program product are also provided.

Abstract: A breaker failure detection device for a direct current (DC) circuit breaker (200) is provided. The circuit breaker comprises a circuit breaking element (204) and a non-linear resistor, e.g., a surge arrester (205), connected in parallel. The breaker failure detection device comprises a current sensor (212, 213, 214, 215), for measuring a current commutating from the circuit breaking element (204), and a breaker failure detection unit (211). The breaker failure detection unit (211) is arranged for comparing the measured current to desired values and deciding that an internal commutation process of the circuit breaker (200) does not proceed as desired if the measured current deviates from the desired values. The present invention makes use of an understanding that an improved detection of breaker failures may be achieved by monitoring the internal commutation process of the circuit breaker. Further, a method of breaker failure detection is provided.

Abstract: The invention relates to an HVDC breaker (300) comprising at least two individually controllable HVDC breaker sections (305) connected in series, wherein the HVDC breaker is arranged in a manner so that the number of HVDC breaker sections tripped upon tripping of the HVDC breaker depends on the operational event in response to which the tripping occurs. The invention further relates to a control apparatus (400) for controlling the HVDC breaker, as well as to a method of breaking an HVDC line. The method comprises receiving (500) a system status signal indicative of an operational event requiring the breaking of the HVDC line, and determining (505) the number of HVDC breaker sections required for the breaking.

Abstract: A high voltage direct current (HVDC) switchyard is provided. The switchyard is arranged for interconnecting three or more sections of an HVDC power network, such as transmission lines, converters, or any other type of HVDC equipment. The switchyard comprises at least one main circuit breaker and at least four transfer switches. The at least one main circuit breaker and the at least four transfer switches are arranged so as to enable to individually disconnect any one of the at least three sections of the HVDC power distribution network. In an embodiment of the invention, the transfer switches which usually are comprised in direct current (DC) hybrid circuit breakers are used as selector switches, thereby reducing the number of main breakers in the switchyard.

Abstract: A meshed HVDC power transmission network comprises at least three HVDC converter stations interconnected in a first closed path by at least three transmission lines. A first DC power flow control device is series connected to a first of the at least three transmission lines. That first DC power flow control device takes its power from the first transmission line and balances the DC current distribution in the first closed path.

Abstract: A current-limitation system for limiting a current through an DC connection in case of a fault occurring in a DC grid of which the DC connection forms a part is provided, as well as a method of operating a current-limitation system for limiting a current through an DC connection in case of a fault occurring in a DC grid of which the DC connection forms a part.

Abstract: The invention relates to a method for controlling power flow within a wind park system (100) for power transmission to a main power grid (90), the wind park system (100) comprising two or more parallel-connected island wind park grids. The method comprises the steps of: controlling a first voltage source converter (10) as a swing bus in frequency control, the frequency control comprising controlling frequency to a steady state reference operating point for operating points within a power dead band and by means of frequency droop control when exceeding an end point of the power dead band, and controlling at least a second voltage source converter (20), (30), (40) in power control, the power control comprising controlling power flow to a steady state reference operating point for operating points within a frequency dead band and by means of power droop control when exceeding an end point of the frequency dead band. The invention also relates to controllers, computer programs and computer program products.

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 breaker failure detection device for a direct current (DC) circuit breaker (200) is provided. The circuit breaker comprises a circuit breaking element (204) and a non-linear resistor, e.g., a surge arrester (205), connected in parallel. The breaker failure detection device comprises a current sensor (212, 213, 214, 215), for measuring a current commutating from the circuit breaking element (204), and a breaker failure detection unit (211). The breaker failure detection unit (211) is arranged for comparing the measured current to desired values and deciding that an internal commutation process of the circuit breaker (200) does not proceed as desired if the measured current deviates from the desired values. The present invention makes use of an understanding that an improved detection of breaker failures may be achieved by monitoring the internal commutation process of the circuit breaker. Further, a method of breaker failure detection is provided.

Abstract: A current-limitation system for limiting a current through an DC connection in case of a fault occurring in a DC grid of which the DC connection forms a part is provided, as well as a method of operating a current-limitation system for limiting a current through an DC connection in case of a fault occurring in a DC grid of which the DC connection forms a part.

Abstract: A DC grid (100) comprising a plurality of AC/DC converters (105) which are interconnected via DC lines (115) is provided, wherein, in order to limit the effects of a fault in the DC grid, the DC grid is divided into at least two zones (200) by means of at least one current limiter (205) in a manner so that a current limiter is connected in each of the DC line(s) (115z) by which two zones are interconnected. A method of limiting the effects of a fault in a DC grid by dividing the DC grid into at least two zones is also provided.

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: In a multi-terminal HVDC power transmission network comprising at least three HVDC converter stations interconnected by at least two transmission lines, where at least one of the transmission lines is a long line, an active voltage source device is series connected to one of the transmission lines, which maintains the DC voltage of the transmission lines of the network to be within a predefined voltage range by injecting an additional DC voltage in series with the one transmission line.

Abstract: A voltage balancing unit for a symmetric monopole high voltage direct current (HVDC) transmission line interconnecting two voltage source converters (VSCs), the transmission line including first arresters having a first switching impulse protective level (SIPL) is provided. The voltage balancing unit includes a pair of second arresters having a second SIPL which is less than the first SIPL, and a switching device being arranged for temporarily connecting, in the event of a voltage unbalance on the transmission line, the first arresters between either pole and ground. A voltage unbalance on the transmission line may be removed by temporarily connecting second arresters, with a significantly lower SIPL than the first arresters, for limiting the pole voltage to a level close to the normal voltage. Further, a method of voltage balancing is provided. Voltage unbalances may arise as a consequence of lightning induced earth faults.