Implementations of ground fault circuit interrupter (GFCI) self-test circuits may include: a current transformer coupled to a controller, a silicon controlled rectifier (SCR) test loop coupled to the controller, a ground fault test loop coupled to the controller, and a solenoid coupled to the controller. The SCR test loop may be configured to conduct an SCR self-test during a first half wave portion of a phase and the ground fault test loop may be configured to conduct a ground fault self-test during a second half wave portion of a phase. An SCR may be configured to activate the solenoid to deny power to a load upon one of the SCR self-test or the ground fault self-test being identified as failing.

In monitoring an isolation of an ungrounded power grid an AC voltage source is connected to the power grid via at least one test resistor. A test signal with a periodic continuous voltage course with regard to ground and with a frequency is applied to the power grid by means of the AC voltage source. A leakage current flowing due to the test signal is measured; and an ohmic isolation resistance is determined from the leakage current. The frequency of the test signal is varied such that an active current part of the leakage current keeps a predetermined recommended value at varying leakage capacitances of the power grid. This provides for a desired level of accuracy at maximum speed of isolation or ground fault detection.

In monitoring an isolation of an ungrounded power grid an AC voltage source is connected to the power grid via at least one test resistor. A test signal with a periodic continuous voltage course with regard to ground and with a frequency is applied to the power grid by means of the AC voltage source. A leakage current flowing due to the test signal is measured; and an ohmic isolation resistance is determined from the leakage current. The frequency of the test signal is varied such that an active current part of the leakage current keeps a predetermined recommended value at varying leakage capacitances of the power grid. This provides for a desired level of accuracy at maximum speed of isolation or ground fault detection.

An insulation impedance detection method includes: An inverter injects a first common-mode voltage into an alternating current side, where the first common-mode voltage is divided by an alternating current grounding insulation impedance of an alternating current cable and a direct current grounding insulation impedance of a photovoltaic unit. The inverter can obtain an impedance value of the alternating current grounding insulation impedance based on the first common-mode voltage, a voltage divided by the alternating current grounding insulation impedance for the first common-mode voltage (a second common-mode voltage on the alternating current grounding insulation impedance), and an impedance value of the direct current grounding insulation impedance. The alternating current grounding insulation impedance is detected by using a necessary device, namely, the inverter in a photovoltaic power generation system. In this way, an additional detection device is not mounted, which reduces costs and complexity of alternating current grounding insulation impedance detection.

An insulation impedance detection method includes: An inverter injects a first common-mode voltage into an alternating current side, where the first common-mode voltage is divided by an alternating current grounding insulation impedance of an alternating current cable and a direct current grounding insulation impedance of a photovoltaic unit. The inverter can obtain an impedance value of the alternating current grounding insulation impedance based on the first common-mode voltage, a voltage divided by the alternating current grounding insulation impedance for the first common-mode voltage (a second common-mode voltage on the alternating current grounding insulation impedance), and an impedance value of the direct current grounding insulation impedance. The alternating current grounding insulation impedance is detected by using a necessary device, namely, the inverter in a photovoltaic power generation system. In this way, an additional detection device is not mounted, which reduces costs and complexity of alternating current grounding insulation impedance detection.

It is described a switching device comprising a semiconductor switching unit; a contactor electrically coupled in series with the semiconductor switching unit; and a controller being configured for activating an electrically isolating state of the switching device and/or activating an electrically conducting state of the switching device based on a command signal or based on a comparison of a measured value and predetermined activation condition.

It is described a switching device comprising a semiconductor switching unit; a contactor electrically coupled in series with the semiconductor switching unit; and a controller being configured for activating an electrically isolating state of the switching device and/or activating an electrically conducting state of the switching device based on a command signal or based on a comparison of a measured value and predetermined activation condition.

The present disclosure relates to the determination of impedances in an electrical network. Methods and apparatuses for determining one or more impedances within a root and branch network are disclosed. The impedance of a common root part and the impedance of a branch of the electrical network may be determined based on the current in the common root part, the current in a branch of the electrical network and the voltage across the common root part and the branch. By determining the impedance of different parts of the electrical network in this way, the network may be monitored over time and the location of any faults or impending faults in the network may be identified more exactly without requiring invasive network probing and testing.

The present disclosure relates to the determination of impedances in an electrical network. Methods and apparatuses for determining one or more impedances within a root and branch network are disclosed. The impedance of a common root part and the impedance of a branch of the electrical network may be determined based on the current in the common root part, the current in a branch of the electrical network and the voltage across the common root part and the branch. By determining the impedance of different parts of the electrical network in this way, the network may be monitored over time and the location of any faults or impending faults in the network may be identified more exactly without requiring invasive network probing and testing.

A circuit arrangement (20) having an active measuring voltage (U.sub.G) for determining an insulation resistance (R.sub.F) or a complex-valued insulation impedance (Z.sub.F) of an ungrounded power supply system (12) against ground potential (PE), the circuit arrangement (20) having a measuring path (24) which runs between an active conductor (L1, L2) of the power supply system (12) and the ground potential (PE) and includes a measuring-voltage generator (V.sub.G) for generating the measuring voltage (U.sub.G), a measuring resistance (R.sub.M) for capturing a measured voltage (U.sub.M) and a coupling resistance (R.sub.A), the circuit arrangement (20) having a signal evaluation circuit (26) which includes a signal input for evaluating the measured voltage (U.sub.M) and a ground connection (GND). The ground connection (GND) is connected to a ground potential (PE).