Abstract: It is presented a converter arm for power conversion. The converter arm comprises: a plurality of converter cells, wherein each converter cell comprises a plurality of semiconductor switches, an energy storage element and at least three control signal connections arranged to control the conducting state of the plurality of semiconductor switches. Each converter cell is connected to receive a control signal from at least three entities via said control signal connections, wherein at least two of the three entities are neighboring converter cells, and each converter cell is arranged to forward a control signal to all connected neighboring converter cells via said control signal connections. A corresponding converter device is also presented.

Abstract: It is presented a converter arm for power conversion. The converter arm comprises: a plurality of converter cells, wherein each converter cell comprises a plurality of semiconductor switches, an energy storage element and at least three control signal connections arranged to control the conducting state of the plurality of semiconductor switches. Each converter cell is connected to receive a control signal from at least three entities via said control signal connections, wherein at least two of the three entities are neighbouring converter cells, and each converter cell is arranged to forward a control signal to all connected neighbouring converter cells via said control signal connections. A corresponding converter device is also presented.

Abstract: A device for sensing a binary signal includes a device configured to measure a signal level of the signal, a device configured to determine whether the measured signal level is “low” or “high”, a device configured to provide a variable input impedance, and a device configured to control the input impedance in response to the measured signal level. The variable input impedance may be provided by way of a transistor and a resistor, and by controlling the duty ratio of the transistor using pulse width modulation. Preferably, the input impedance is controlled to be low for low signal levels and to be high for high signal levels, which results in a more reliable sensing of binary signals. The device may be used for detecting the state of contact transducers suffering from parasitic resistances caused by moist and/or polluted environments. Further, a method of sensing a binary signal is provided.

Abstract: A control arrangement for a circuit breaker station includes a central control system and, for each of the circuit breakers, a circuit breaker operating unit connected to the central control system to obtain switching instructions and to the respective circuit breaker to control the operation thereof. The central control system and the circuit breaker operating units each have a local clock that are synchronized with one another. The central control system is, during use, arranged to calculate a point of time for switching each of the circuit breakers based on measured voltages, currents, and circuit breaker positions, and to send the point of time in a switching instruction to the circuit breaker operating unit. Each of the circuit breaker operating units is arranged to switch the circuit breaker, to which it is connected, at the point of time which is received in the switching instruction from the central control system.

Abstract: A method, device and computer program product for providing increased reliability in the processing of digital signals. The device includes a module for performing analog measurement of a received signal intended to occupy two logical states at various instances in time, a module for determining if there is a change in the analog signal level, a module for determining if the change fulfills at least one logical state change condition, wherein a first logical state change condition is based on the speed of change of the analog signal level, and a module for determining that there is a change from one logical state to the other if at least one logical state change condition is fulfilled. The invention provides secure detection of unreliable digital signals that may be generated in harsh environments that are polluted or moist.

Abstract: The present invention relates to an apparatus for connection between power transmission system field equipment and control and protection equipment and comprising at least one input/output module (24). The module (24) comprises a box (34) enclosing a circuit board with at least one signal handling unit, at least one bus connector (36, 38) that stretches through a first side of the box, and a set of terminal blocks (40) for connection of field wires to the field equipment, where the terminal blocks are placed on a second side of the box. The at least one signal handling unit includes at least one unit for conversion of input and output signals to and from the field equipment and bus communication according to a bus communication protocol.

Abstract: A method and apparatus for determining the time of arrival of a fault wave at a measurement point of a power transmission system includes a measurement unit measuring a power quantity of the system at the measurement point (P1) for obtaining a measurement quantity being a potential fault wave, a time keeping unit, a storage unit storing the measurement quantity, a comparing unit comparing the measurement quantity with a threshold (T1) for detecting the presence of a fault wave (W1) and an analyzing unit. The analyzing unit analyzes measurements made before the fault wave presence was detected, determines the starting point (SP) of the fault wave based on the analysis and sets the time of the starting point to be the fault wave arrival time (T1).

Abstract: A method for sending signals from an active computer in a high-voltage power transmission system including active protection computers and active and standby control computers in a hierarchical structure having at least two hierarchical levels. A high-voltage power transmission system and a control station for at least a part of such a transmission system. In the system all computers on the various hierarchical levels are connected to at least two separate computer communication networks. An active computer sends signals that are to be received by at least one other computer at the same or another hierarchical level simultaneously on the two separate computer communication networks to which it is connected.

Abstract: A control arrangement for a circuit breaker station includes a central control system and, for each of the circuit breakers, a circuit breaker operating unit connected to the central control system to obtain switching instructions and to the respective circuit breaker to control the operation thereof. The central control system and the circuit breaker operating units each have a local clock that are synchronized with one another. The central control system is, during use, arranged to calculate a point of time for switching each of the circuit breakers based on measured voltages, currents, and circuit breaker positions, and to send the point of time in a switching instruction to the circuit breaker operating unit. Each of the circuit breaker operating units is arranged to switch the circuit breaker, to which it is connected, at the point of time which is received in the switching instruction from the central control system.

Abstract: A method for sending signals from an active computer in a high-voltage power transmission system including active protection computers and active and standby control computers in a hierarchical structure having at least two hierarchical levels. A high-voltage power transmission system and a control station for at least a part of such a transmission system. In the system all computers on the various hierarchical levels are connected to at least two separate computer communication networks. An active computer sends signals that are to be received by at least one other computer at the same or another hierarchical level simultaneously on the two separate computer communication networks to which it is connected.

Abstract: A device for sensing a binary signal includes a device configured to measure a signal level of the signal, a device configured to determine whether the measured signal level is “low” or “high”, a device configured to provide a variable input impedance, and a device configured to control the input impedance in response to the measured signal level. The variable input impedance may be provided by way of a transistor and a resistor, and by controlling the duty ratio of the transistor using pulse width modulation. Preferably, the input impedance is controlled to be low for low signal levels and to be high for high signal levels, which results in a more reliable sensing of binary signals. The device may be used for detecting the state of contact transducers suffering from parasitic resistances caused by moist and/or polluted environments. Further, a method of sensing a binary signal is provided.

Abstract: A distribution and power transformer has its primary connected to the high voltage bus of the network and its secondary connected to a switching device. Upon the occurrence of a condition known to cause a dynamic overvoltage (DOV) and the occurrence of the DOV, a control system causes the switching device to change from a nonconductive mode to a conductive mode in less than the time for one cycle of the operating frequency of the AC network. This change in switching device conduction places a short circuit across the transformer secondary and thus mitigates the DOV.

Abstract: A method and apparatus for determining the time of arrival of a fault wave at a measurement point of a power transmission system includes a measurement unit measuring a power quantity of the system at the measurement point (P1) for obtaining a measurement quantity being a potential fault wave, a time keeping unit, a storage unit storing the measurement quantity, a comparing unit comparing the measurement quantity with a threshold (T1) for detecting the presence of a fault wave (W1) and an analyzing unit. The analyzing unit analyzes measurements made before the fault wave presence was detected, determines the starting point (SP) of the fault wave based on the analysis and sets the time of the starting point to be the fault wave arrival time (T1).

Abstract: A method and device for providing redundant control of a controllable current valve in a converter of a power transmission system. A first converter control unit sends a first valve control signal. A first active/standby indicator is associated with the first converter. A second converter control unit sends a second valve control signal. A second active/standby indicator is associated with the second converter control unit. The device also includes a valve control unit. An active/standby indicator indicates if a corresponding converter control unit is active or standby. Only one indicator indicates an active unit at a given point in time. The valve control unit receives the active/standby indicators and valve control signals, selects a valve control signal to be applied if the corresponding active/standby indicator indicates an active converter control unit and controls the current valve using the selected valve control signal.

Abstract: A voltage measurement device for connection to a primary voltage dividing element provided between ground and an electrically conducting element in a system for controlling an electrical process and such a system. The device includes at least one first branch of secondary voltage dividing elements, where the branch is adapted to be connected in parallel with the primary voltage dividing element, and a first measuring unit connected to one of the secondary voltage dividing elements of the first branch and arranged to measure the voltage across this secondary voltage dividing element and provide a first voltage signal corresponding to a voltage of the electrically conducting element.

Abstract: An HVDC transmission system including a rectifier station and an inverter station each having a series connection of at least two converters. A by-pass DC breaker is connected in parallel with each converter. A control device is adapted to deblock a blocked converter by starting to control the converter at high delay angle and gradually decreasing the delay angle until substantially all DC current flows through the converter and to then control the by-pass breaker to open at substantially zero current, and to stop the operation of a converter by controlling the converter at gradually increasing delay angle until the voltage across the converter is substantially zero and to then control the converter to be blocked by firing a by-pass pair thereof and to then control the by-pass breaker to close for taking over all the DC current when the voltage between a neutral bus and a pole of a transmission line between the stations is to be increased and reduced, respectively.

Abstract: The present invention relates to an apparatus for connection between power transmission system field equipment and control and protection equipment and comprising at least one input/output module (24). The module (24) comprises a box (34) enclosing a circuit board with at least one signal handling unit, at least one bus connector (36, 38) that stretches through a first side of the box, and a set of terminal blocks (40) for connection of field wires to the field equipment, where the terminal blocks are placed on a second side of the box. The at least one signal handling unit includes at least one unit for conversion of input and output signals to and from the field equipment and bus communication according to a bus communication protocol.

Abstract: A method, device and computer program product for providing increased reliability in the processing of digital signals. The device includes a module for performing analog measurement of a received signal intended to occupy two logical states at various instances in time, a module for determining if there is a change in the analog signal level, a module for determining if the change fulfills at least one logical state change condition, wherein a first logical state change condition is based on the speed of change of the analog signal level, and a module for determining that there is a change from one logical state to the other if at least one logical state change condition is fulfilled. The invention provides secure detection of unreliable digital signals that may be generated in harsh environments that are polluted or moist.

Abstract: A voltage measurement device for connection to a primary voltage dividing element provided between ground and an electrically conducting element in a system for controlling an electrical process and such a system. The device includes at least one first branch of secondary voltage dividing elements, where the branch is adapted to be connected in parallel with the primary voltage dividing element, and a first measuring unit connected to one of the secondary voltage dividing elements of the first branch and arranged to measure the voltage across this secondary voltage dividing element and provide a first voltage signal corresponding to a voltage of the electrically conducting element.

Abstract: A method and device for providing redundant control of a controllable current valve in a converter of a power transmission system. A first converter control unit sends a first valve control signal. A first active/standby indicator is associated with the first converter. A second converter control unit sends a second valve control signal. A second active/standby indicator is associated with the second converter control unit. The device also includes a valve control unit. An active/standby indicator indicates if a corresponding converter control unit is active or standby. Only one indicator indicates an active unit at a given point in time. The valve control unit receives the active/standby indicators and valve control signals, selects a valve control signal to be applied if the corresponding active/standby indicator indicates an active converter control unit and controls the current valve using the selected valve control signal.