Abstract: Unique systems, methods, techniques and apparatuses of power transmission systems are disclosed herein. One exemplary embodiment is an AC power transmission system converted for transmission of high voltage direct current (HVDC) power, the converted system comprising an AC cable system, a first converter system, a second converter system, and a control system. The first converter system is structured to receive and convert AC power to DC power and output the DC power. The second power converter system is structured to receive the DC power, convert the DC power to a second AC power, and output the second AC power. The control system is structured to receive power demand information, determine a reduced DC voltage less than a rated HVDC voltage, control the first converter system such that the DC power is controlled to the reduced voltage, and control the second power converter system to operate in an active power control mode.

Abstract: Unique systems, methods, techniques and apparatuses of fault location in DC power distribution systems are disclosed. One exemplary embodiment is a DC power distribution system including a plurality of zones each including a DC power distribution line and a protective device. Each protective device structured to sense one or more electrical characteristics of a line and to controllably open a circuit including the line. At least one intelligent electronic device is structured to determine a line inductance based upon electrical characteristics sensed by one or more of the protective devices and to evaluate a location of the line fault based upon the determined line inductance.

Abstract: A DC connection system for renewable power generators includes a first monopole DC collection network, a second monopole DC collection network and a first bipole transmission system. The first monopole DC collection network aggregates positive-valued DC voltage outputs of a first cluster of renewable power generators onto a positive terminal of the first monopole DC collection network. The second monopole DC collection network aggregates negative-valued DC voltage outputs of a second cluster of renewable power generators onto a negative terminal of the second monopole DC collection network. The first bipole transmission system is coupled to the positive and negative terminals of the monopole DC collection networks, for transferring the aggregated power to a power grid substation.

Abstract: Technologies for detecting a fault location in a DC electrical distribution system include a bus protection unit that monitors a DC electrical bus. The bus protection unit includes at least one sensor to produce sensor data indicative of one or more characteristics of the DC electrical bus monitored by the bus protection unit. The bus protection unit monitors the sensor data, determines whether a fault has occurred based on the sensor data, and determines whether the fault occurred within a bus zone defined by the DC electrical bus in response to determining that the fault has occurred. Further, the bus detection unit trips isolation devices within the bus zone in response to a determination that the fault occurred within the bus zone or a communication from another bus protection unit indicating the fault has occurred within the bus zone. The bus protection unit transmits a bus fault indication signal to another bus protection unit in response to a determination that the fault has occurred.

Abstract: While transient current magnitudes at different locations within a DC distribution system themselves are not a reliable indicator of fault location, it is recognized herein that accumulating energy or pseudo energy values provides a reliable basis for tripping the protection element at a fault location. Thus, in one aspect of the teachings herein, pseudo energy values are accumulated independently during a fault condition, for each of one or more protected branch circuits and the protection element for each such branch circuit is tripped responsive to the accumulated pseudo energy values reaching a defined pseudo energy threshold. The pseudo energy thresholds are defined so that the protection element in the branch circuit where the fault is located will trip first.

Abstract: According to one aspect of the teachings herein, various feeder connection arrangements and architectures are disclosed, for collecting electricity from wind turbines in an offshore collection grid that operates at a fixed low frequency, e.g., at one third of the targeted utility grid frequency. Embodiments herein detail various feeder arrangements, such as the use of parallel feeder connections and cluster-based feeder arrangements where a centralized substation includes a common step-up transformer for outputting electricity at a stepped-up voltage, for low-frequency transmission to onshore equipment. Further aspects relate to advantageous generation arrangements, e.g., tower-based arrangements, for converting wind power into electrical power using, for example, medium-speed or high-speed gearboxes driving generators having a rated electrical frequency for full-power output in a range from about 50 Hz to about 150 Hz, with subsequent conversion to the fixed low frequency for off-shore collection.

Abstract: A method to facilitate fault detection in the protected unit after connection to the at least a portion of the power system. A current is sensed in the protected unit during a plurality of different time periods. Compliance of at least one of the sensed currents with a respective first current criteria is determined based on a first current threshold value. On a condition that there is determined that at least one of the sensed currents comply with the respective first current criteria, a fault in the protected unit is detected.

Abstract: A power distribution system for off-shore natural resource platforms includes an off-shore medium voltage direct current (MVDC) power bus. The MVDC power bus includes multiple power bus segments, each of which may be connected to one or more other power bus segments via a corresponding circuit breaker. Each power bus segment may also be electrically coupled to an off-shore renewable energy source, such as a wind farm, and/or an off-shore drilling platform. The off-shore drilling platforms may include local power distribution systems electrically connected to a corresponding power bus segment via a circuit breaker to receive power from the MVDC power bus and supply power to local equipment of the off-shore drilling platform.

Abstract: Methods and apparatus for protecting a direct-current (DC) electric power distribution system that includes one or more AC/DC converters and/or one more DC/DC converters, and one or more loads, connected by DC buses. An example method, which is carried out in response to the detection of a fault somewhere in the system, begins with limiting an output current of each of one or more of the converters so that each of the limited converters outputs a limited DC current at or about a corresponding predetermined current level. After the current limiting of the one or more converters has taken place, one or more protection devices in the system are activated, where the activating at least partly depends on the limited DC currents being at or about the predetermined fault current levels.

Abstract: A wind turbine is disclosed having a generator and rectifier and structured to provide direct current power that in one form is medium voltage direct current (MVDC). The wind turbine includes a crowbar circuit arranged to protect from a condition such as an overvoltage. The crowbar can be activated based on a voltage measurement or rate of change of voltage. A resistor can be coupled to the crowbar to absorb excess power provided by the generator during the overvoltage condition. Individual wind turbines in a wind farm can each have individual crow bars that can be activated based on local measurement of a voltage condition. In some forms the crowbar can be coupled with a transformer, for example coupled with a tertiary winding of a three winding transformer.

Abstract: Technologies for detecting a fault location in a DC electrical distribution system include a bus protection unit that monitors a DC electrical bus. The bus protection unit includes at least one sensor to produce sensor data indicative of one or more characteristics of the DC electrical bus monitored by the bus protection unit. The bus protection unit monitors the sensor data, determines whether a fault has occurred based on the sensor data, and determines whether the fault occurred within a bus zone defined by the DC electrical bus in response to determining that the fault has occurred. Further, the bus detection unit trips isolation devices within the bus zone in response to a determination that the fault occurred within the bus zone or a communication from another bus protection unit indicating the fault has occurred within the bus zone. The bus protection unit transmits a bus fault indication signal to another bus protection unit in response to a determination that the fault has occurred.

Abstract: Unique systems, methods, techniques and apparatuses of fault location in DC power distribution systems are disclosed. One exemplary embodiment is a DC power distribution system including a plurality of zones each including a DC power distribution line and a protective device. Each protective device structured to sense one or more electrical characteristics of a line and to controllably open a circuit including the line. At least one intelligent electronic device is structured to determine a line inductance based upon electrical characteristics sensed by one or more of the protective devices and to evaluate a location of the line fault based upon the determined line inductance.

Abstract: A protection device includes a diode having its forward direction in a normal power flow of a region of a DC collection system, a first switch in parallel with the diode, a second switch in series with the diode and a control unit for controlling the switches. The first switch can be opened so that current can flow through the diode in the forward direction without the first switch bypassing the diode, and closed if no current is flowing through the diode in the forward direction and power is needed upstream of the diode. The second switch can be closed so that current can flow through the diode in the forward direction to an AC grid interface of the DC collection system, and opened if no current is flowing through the diode in the forward direction due to a fault in a DC feeder to which the device is coupled.

Abstract: A power generation system includes at least one generator having at least two sets of stator windings, an active rectifier comprising power cell based modular converters associated with each set of generator windings. Each set of windings is connected to an AC voltage side of the associated active rectifier, with each active rectifier having a positive DC voltage output and a negative DC voltage output. The DC voltage outputs of active rectifiers are connected to each other in series. A medium voltage DC (MVDC) collection network comprises positive pole cables and negative pole cables, wherein each positive pole cable is connected to the positive DC voltage output of a first active rectifier and each negative pole cable is connected to the negative DC voltage output of a last active rectifier. A substation receives the negative and positive pole cables of the MVDC collection network for further transformation and transmission.

Abstract: An apparatus for use in an electrical power generation plant. The apparatus includes: at least two adjustable speed drives, each connected, on an alternating current side, to an associated auxiliary motor; at least one reactive power consuming auxiliary device connected to an alternating current bus; a controller; a converter for converting alternating current to direct current or vice versa between the alternating current bus and a direct current bus; and at least one electrical power source arranged to provide power to the direct current bus. Each of the at least two adjustable speed drive is connected, on a direct current side, to the direct current bus.

Abstract: Methods, systems, and computer readable media for adaptive out of step protection for power generators with load resynchronization capability are disclosed. According to one method, when a fault condition occurs in a load being supplied by a power generator, a number of pole slips expected to occur in the generator due to the fault before resynchronization is estimated. It is determined whether the estimated number of pole slips exceeds a threshold. An offline or online status of the generator is controlled based on the determination as to whether the estimated number of pole slips exceeds the threshold.

Abstract: A DC connection system for renewable power generators includes a first monopole DC collection network, a second monopole DC collection network and a first bipole transmission system. The first monopole DC collection network aggregates positive-valued DC voltage outputs of a first cluster of renewable power generators onto a positive terminal of the first monopole DC collection network. The second monopole DC collection network aggregates negative-valued DC voltage outputs of a second cluster of renewable power generators onto a negative terminal of the second monopole DC collection network. The first bipole transmission system is coupled to the positive and negative terminals of the monopole DC collection networks, for transferring the aggregated power to a power grid substation.

Abstract: A method to facilitate fault detection in the protected unit after connection to the at least a portion of the power system. A current is sensed in the protected unit during a plurality of different time periods. Compliance of at least one of the sensed currents with a respective first current criteria is determined based on a first current threshold value. On a condition that there is determined that at least one of the sensed currents comply with the respective first current criteria, a fault in the protected unit is detected.

Abstract: Multi-terminal HVDC systems and control methods therefore are disclosed. Methods for controlling multi-terminal HVDC systems having a plurality of converter stations may include receiving a plurality of measurements from a plurality of measurement units disposed on the HVDC system, identifying from the measurements a disruption within the HVDC system, monitoring the measurements to identify a steady-state disrupted condition for the HVDC system, calculating a new set point for at least one of the plurality of converter stations, which new set point may be based on the steady-state disrupted condition and the measurements, and transmitting the new set point to the at least one of the plurality of converter stations. In some examples, the HVDC systems may include an HVDC grid interconnecting the plurality of converter stations and a controller communicatively linked to the plurality of measurement units and the plurality of converter stations.

Abstract: A protection device includes a diode having its forward direction in a normal power flow of a region of a DC collection system, a first switch in parallel with the diode, a second switch in series with the diode and a control unit for controlling the switches. The first switch can be opened so that current can flow through the diode in the forward direction without the first switch bypassing the diode, and closed if no current is flowing through the diode in the forward direction and power is needed upstream of the diode. The second switch can be closed so that current can flow through the diode in the forward direction to an AC grid interface of the DC collection system, and opened if no current is flowing through the diode in the forward direction due to a fault in a DC feeder to which the device is coupled.