Aspects of the disclosure provide for a circuit. In some examples, the circuit includes a first current source having a terminal coupled to a first node and a second terminal, a first switch coupled between the second terminal of the first current source and a second node, a first resistor coupled between the second node and a ground terminal, a second current source having a terminal coupled to the first node and a second terminal, a second switch coupled between the second terminal of the second current source and a third node, a second resistor coupled between the third node and the ground terminal, a third current source having a terminal coupled to the first node and a second terminal, a third switch coupled between the second terminal of the third current source and a fourth node, and a third resistor coupled between the fourth node and the ground terminal.

Ground fault circuit interrupter is provided, including a transformer, a protection switch, a residual current protection control unit, a residual current simulation unit and a self-test unit, wherein the self-test unit is coupled with the line where the protection switch is located; in a self-test state, the self-test unit is configured to control the residual current simulation unit to generate a simulated residual current, detect a level change on the line where the protection switch is located, and control the protection switch to be disconnected from the residual current protection control unit or to make the line where the protection switch is located be conducted after a preset protection time period of receiving the residual current signal higher than a preset operating threshold. Improper actions of the ground fault circuit interrupter caused by a large electromotive force generated when a simulated residual current disappears are avoided.

Real-time detection of high-impedance faults in a distribution circuit is described. The real-time detection of high-impedance faults includes two steps. First, adaptive soft denoising is employed to perform a filtering process on a healthy dataset, and to determine a threshold. This reduces the rate of false alarms. Second, faulty datasets are prefiltered via adaptive soft denoising, then the denoised signals are processed via discrete wavelet transform to perform high-impedance fault detection using the threshold.

An intelligent leakage current detection and interruption device for a power cord, including a switch module for controlling electrical connection of two power lines between input and output ends; a leakage current detection module, including two leakage current detection lines and a signal feedback line, one end of the parallelly coupled two leakage current detection lines being coupled via the signal feedback line to a point between the two power lines, for respectively detecting a leakage current on the two power lines; a detection monitoring module, coupled to the leakage current detection module, for detecting open circuit conditions in the two leakage current detection lines; and a drive module, coupled to the switch module, the leakage current detection module and the detection monitoring module, for driving the switch module to disconnect power to the output end in response to any detected leakage current or open circuit condition.

An intelligent leakage current detection and interruption device for a power cord, including a switch module for controlling electrical connection of two power lines between input and output ends; a leakage current detection module, including two leakage current detection lines and a signal feedback line, one end of the parallelly coupled two leakage current detection lines being coupled via the signal feedback line to a point between the two power lines, for respectively detecting a leakage current on the two power lines; a detection monitoring module, coupled to the leakage current detection module, for detecting open circuit conditions in the two leakage current detection lines; and a drive module, coupled to the switch module, the leakage current detection module and the detection monitoring module, for driving the switch module to disconnect power to the output end in response to any detected leakage current or open circuit condition.

One embodiment provides an electric leakage detecting device for shutting off an AC electric circuit. A digital comparator generates a detection signal by comparing an output signal corresponding to output signals of a zero-phase current transformer with positive and negative thresholds, a control signal generator generates a control signal based on the detection signal, and a judging device generates a judgment signal if an electric leakage state is judged. In addition, a delay counter generates a final control signal if the judgment signal has been received continuously more than a first prescribed time, a reset counter resets every time the control signal is received, and resets the judging device and the delay counter if the control signal is not received in a second prescribed time, and a switch driving circuit shuts off the AC electric circuit based on the final control signal.

The present invention increases noise immunity of an electrical leakage detection circuit. A first comparator COMP1 generates a first comparison signal indicating a comparison result between a voltage corresponding to a detected signal from a zero-phase-sequence current transformer and a predetermined first threshold voltage V.sub.TH1. A judgment circuit outputs a judgment signal indicating if there is electrical leakage based on the first comparison signal and outputs a mask signal corresponding to the first comparison signal. A mask circuit generates a latch input signal based on the judgment signal and the mask signal. An output stage comprises a latch circuit which latches a state of the latch input signal when the latch input signal is asserted. The output stage generates a drive signal corresponding to the state of the latch circuit.

A direct current (DC) power combiner operable to interconnect multiple interconnected photovoltaic strings is disclosed. The DC power combiner may include a device adapted for disconnecting at least one photovoltaic string from the multiple interconnected photovoltaic strings, each photovoltaic string connectible by a first and second DC power line. The device may include a differential current sensor adapted to measure differential current by comparing respective currents in the first and second DC power lines. A first switch is connected in series with the first DC power line. A control module is operatively attached to the differential current sensor and the first switch. The control module may be operable to open the first switch when the differential current sensor measures the differential current to be greater than a maximum allowed current differential, thereby disconnecting the photovoltaic string from the interconnected photovoltaic strings.

A method for distinguishing an arc from a luminous gas at least containing metal vapor includes sensing light in a monitoring region and determining a first intensity I.sub.λ1 of the sensed light at a first wavelength λ1 and a second intensity I.sub.λ2 of the sensed light at a second, greater wavelength λ2. The ratio I.sub.λ1/I.sub.λ2 between the first intensity I.sub.λ1 and the second intensity I.sub.λ2 is determined. The sensed light is associated with an arc if said ratio I.sub.λ1/I.sub.λ2 is greater than a specifiable first threshold value and/or with a luminous gas at least containing metal vapor if said ratio I.sub.λ1/I.sub.λ2 is less than a specifiable second threshold value.

A method for distinguishing an arc from a luminous gas at least containing metal vapor includes sensing light in a monitoring region and determining a first intensity I.sub.λ1 of the sensed light at a first wavelength λ1 and a second intensity I.sub.λ2 of the sensed light at a second, greater wavelength λ2. The ratio I.sub.λ1/I.sub.λ2 between the first intensity I.sub.λ1 and the second intensity I.sub.λ2 is determined. The sensed light is associated with an arc if said ratio I.sub.λ1/I.sub.λ2 is greater than a specifiable first threshold value and/or with a luminous gas at least containing metal vapor if said ratio I.sub.λ1/I.sub.λ2 is less than a specifiable second threshold value.