A method involves a circuit interrupter installation having a circuit interrupter with a plurality of poles and an ETU electrically connected with a neutral current sensor situated in proximity to a neutral conductor. The method includes determining that a plurality of fundamental frequency phase current vectors, when summed, are substantially equal to a fundamental frequency neutral current vector, and/or that a plurality of triplen odd-numbered harmonic phase current vectors, when summed, are substantially equal to a triplen odd-numbered harmonic neutral current vector. Responsive to the determining, the method includes outputting a notification which represents a possibility that a neutral current detection apparatus is mis-wired, and/or employing with the ETU a reverse vector that is an opposite of the fundamental frequency neutral current vector in the ongoing monitoring for an event that would trigger the movement of the circuit interrupter from the ON condition to the OFF or TRIPPED condition.

An embodiment of the invention relates to a method for ground fault detection for low-voltage three-phase AC circuits having a neutral conductor, in which first to fourth analog current signals of the first to third phase conductors and of the neutral conductor of the three-phase AC circuit are ascertained that each contain the level or an equivalent of the level of the current. The analog current signals are time-division multiplexed, subjected to a/d conversion, and a sequence of time-division-multiplexed first to fourth digital current values present in first to fourth successive time frames form first to fourth current signals. Three of the four digital current signals are interpolated to ascertain interpolated current values. The current value of the time frame of the uninterpolated current signal and the interpolated current values for the time frame of the uninterpolated current signal are used for discovering the ground fault.

A safety arrangement of an elevator and a method for monitoring electrical safety in an elevator system is disclosed. The safety arrangement of an elevator includes a motor drive of the elevator, which motor drive includes a main circuit, an accessible conducting part, which is earthed, an insulator, which is adapted to electrically insulate the aforementioned conducting part from the aforementioned main circuit and also a monitoring circuit, which is configured to determine an earth fault of the aforementioned main circuit occurring via the aforementioned conducting part. The monitoring circuit is configured to form a signal indicating the danger of electric shock in the motor drive of the elevator, if the aforementioned earth fault is diagnosed.

A method and an apparatus for use in an earth-fault protection in a three-phase electric network, the apparatus configured to detect a phase-to-earth fault in the three-phase electric network, to determine for each of the three phases of the three-phase electric network a phase current during the detected phase-to-earth fault or a change in the phase current due to the detected phase-to-earth fault, to determine an estimate of an earth-fault current on the basis of the determined phase currents or on the basis of the determined changes in the phase currents, to determine, if the estimate of the earth-fault current represents an actual earth-fault current or an apparent earth-fault current, and to determine, in response to determining that the estimate of the earth-fault current represents the actual earth-fault current, that the estimate of the earth-fault current is valid.

A method and an apparatus for use in an earth-fault protection in a three-phase electric network, the apparatus is configured to detect a phase-to-earth fault in the network, to determine for each of the phases of the network a phase current during the fault or a change in the phase current due to the fault, to detect a faulted phase of the network, to determine an estimate of an earth-fault current on the basis of the faulted phase and the phase currents or the changes in the phase currents, to determine a zero-sequence voltage of the electric network or a change in the zero-sequence voltage, and to determine a direction of the phase-to-earth fault from the measuring point on the basis of the estimate of the earth-fault current and the zero-sequence voltage or the change in the zero-sequence voltage.

A fault switch configuration and clearing method in a flexible DC converter station, the flexible DC converter station is configured with a grid side switch and a valve side phase-split switch in the converter station. When a fault occurs, a faulty phase and a non-faulty phase are detected and identified by means of differential protection or low voltage overcurrent. An alternating current zero crossing condition is created by means of firstly turn off the non-faulty phase valve side phase-split switch and the grid side switch, thereby cutting off the faulty phase, disconnecting the connection between a power supply and a fault point, and achieving the clearing for faults. The described fault-clearing method is simple and practical, highly reliable, and connection between the fault point and the power supply is quickly and effectively cut; converter station equipment is effectively protected, and further expansion of the fault is avoided.

A method for determining direction of an earth fault (EF) in a feeder of a high impedance grounded power system can be performed by an Intelligent Electronic Device (IED). The method includes obtaining a measure of a first order harmonic active current component derived from residual voltage and current of the feeder when the EF occurred in the feeder, obtaining a measure of a higher order harmonic reactive current component derived from the residual voltage and current of the feeder when the EF occurred in the feeder, and determining the direction of the EF in the feeder based on a combination of the first order harmonic active current component and the higher order harmonic reactive current component.

A protection circuit is disclosed. The protection circuit includes a direct current (DC) blocking component electrically connected between a neutral of the transformer and a ground, and an overvoltage protection device electrically connected in parallel with the DC blocking component. The overvoltage protection device is constructed to repeatably and reliably provide overvoltage protection in response to a voltage at the transformer neutral above a threshold. The DC blocking component has an impedance below a predetermined value, thereby effectively grounding the neutral of the transformer. The DC blocking component is persistently maintained in connection to the transformer neutral.

An example method of operating a solidly grounded, multi-source, multi-phase power distribution system having coupled neutral conductors is disclosed. The power distribution system includes a bus, a plurality of source protection devices coupled to the bus, and a plurality of feeder protection devices coupled to the bus. The method includes receiving, for each source protection device of the plurality of source protection devices, data indicative of detected source phase currents associated with the source protection device. Data indicative of detected feeder neutral currents and detected feeder phase currents associated with the feeder protection device are received for each feeder protection device of the plurality of feeder protection devices. A net source ground fault current associated with the plurality of source protection devices is determined based on the received data indicative of source phase currents and the received data indicative of feeder neutral currents and feeder phase currents.

A ground fault current interrupter circuit includes a plurality of comparators, threshold generation circuitry, and a plurality of timer circuits. Each of the comparators is configured to compare a threshold voltage to a signal representative of a difference of current flow to a load and current flow from the load. The threshold generation circuitry is configured to generate a plurality of different threshold voltages. Each of the different threshold voltages is provided as the threshold voltage for one of the comparators. Each of the comparators is coupled to one of the timer circuits, and the one of the timer circuits is configured to activate a fault signal responsive to activation of an output of the comparator for a time that is related to the threshold voltage provided to the comparator. The time increases with lower values of the threshold voltage.