A DC electrical network comprising DC terminals operatively connectable to a converter; and DC transmission paths arranged to interconnect the DC terminals, and including a DC power transmission medium and a switching apparatus. The DC network further including: an active power electronic device connected in at the DC transmission paths, the active power electronic device; a detector configured to detect faults in the DC transmission paths; and a control unit programmed to operate the active power electronic device to vary an apparent impedance of a faulty DC transmission path to force a current flowing in the faulty DC transmission path to reduce to a target current level, and operate the switching apparatus to block current from flowing in the faulty DC transmission path when the current flowing in the faulty corresponding DC transmission path is reduced to the target current level.

A method and a device for disconnection of faults in an electric network comprising a plurality of stations connected in a loop, comprising feeding the loop from at least two feeding points from a power source, earthing a neutral point of the electric network through an impedance, detecting earth faults in a directional earth fault protection in at least one first secondary substation provided with directional earth fault protection, disconnecting a detected earth fault by a load switching device in said at least one first secondary substation provided with directional earth fault protection, detecting fault currents arising from short circuits between two or more phases in an over-current protection of a second secondary substation, and opening said loop with a circuit breaker of said second secondary substation.

The invention provides a method for overcoming the influence of out-flowing current on bus differential protection. The method comprises the following steps: acquiring and processing branch current signals; selecting a fault bus, and determining the branch current with maximum amplitude from branches connected with the fault bus; calculating differential current and restraint current of a large differential element, and determining whether the large differential element acts. The method for overcoming the influence of out-flowing current on bus differential protection does not need to reduce the braking coefficient during splitting operation in a two-bus connecting mode, can adaptively improve the sensitivity of bus differential protection under an internal fault in the presence of out-flowing current, and simultaneously ensures the reliability under an external fault.

An autonomous breaker can apply a current through a high impedance source to a bus coupled to either end of a breaker in order to measure an impedance of the bus. The status of the bus can be determined from the measurement. Based on the determined status, a fault detection procedure can be selected and implemented to determine if a fault exists on the bus. When the fault detection procedure has been implemented and no fault has been detected, the breaker can close, and thus couple the bus to another bus.

An autonomous breaker can apply a current through a high impedance source to a bus coupled to either end of a breaker in order to measure an impedance of the bus. The status of the bus can be determined from the measurement. Based on the determined status, a fault detection procedure can be selected and implemented to determine if a fault exists on the bus. When the fault detection procedure has been implemented and no fault has been detected, the breaker can close, and thus couple the bus to another bus.

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.

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.

A method for detecting faults (4) in a three-phase electrical distribution network comprising determining a zero sequence current (21 C), a first phase current (21A) and a second phase current (21 B) at a location of the three-phase electrical distribution network, determining first filtered currents (22) by removing a frequency component from the determined currents corresponding to a fundamental frequency of the electrical distribution network through filtering out said frequency component, determining directions of the first filtered currents during a first time period (23), and comparing said directions (24) relatively to each other, and, if at least one of the determined directions is opposite with respect to at least one of the other two determined directions, signaling a detection of a fault (25).

A method and system restores power in a power distribution network. The network includes a plurality of power sources, a plurality of loading zones, a plurality of switching devices interconnected between the plurality of power sources and the plurality of loading zones, and an intelligent electronic device associated with each of the plurality of switching devices to control the switching devices. A base network state is defined and a power restoration logic is created for the base network state. A simulation is run for the power restoration logic and then the power restoration logic is transmitted to a power restoration controller which thereafter monitors and controls the intelligent electronic devices.

A method and system restores power in a power distribution network. The network includes a plurality of power sources, a plurality of loading zones, a plurality of switching devices interconnected between the plurality of power sources and the plurality of loading zones, and an intelligent electronic device associated with each of the plurality of switching devices to control the switching devices. A base network state is defined and a power restoration logic is created for the base network state. A simulation is run for the power restoration logic and then the power restoration logic is transmitted to a power restoration controller which thereafter monitors and controls the intelligent electronic devices.