A system for ground fault detection includes an alternating current (AC) excitation source configured to provide an AC test signal to a circuit under test; a current transformer configured to detect a current of the AC test signal; a capacitive pickup configured to detect a voltage of the AC test signal; and a receiver which includes a display; and a processor configured to receive the voltage from the capacitive pickup; receive the current from the current transformer; and display on the display one or more components of the current.

Systems and method for automated self-testing of a protective device for a transformer are disclosed. One system includes a protection circuit electrically connected to a transformer neutral, the transformer electrically connected to a power grid, the protection circuit may include a DC blocking component, a switch assembly, and a spark gap assembly each positioned in parallel between the transformer neutral and ground, a switch assembly. The system may further include various testing circuits configured within the protection circuit and switches which when actuated inject a signal to test various components in the protective device.

A main electrical cabling is subject to variations in ambient temperature over its length. A detection system for detecting fault in the main electrical cabling able to cause a serial arc, or heating within a connection, includes a monitor electrical cabling placed as a return loop alongside the main electrical cabling, a monitoring device, and a return cable bringing back electrical potential at the output of the main electrical cabling to the monitoring device. The monitoring device includes a controllable current generator injecting, into the monitor electrical cable, a current dependent on current flowing through the main electrical cabling. Electronic circuitry determines a difference in voltages at inputs and outputs of the main electrical cabling and of the monitor electrical cabling, to detect a potential fault in the main electrical cabling leading to a serial arc or increase in temperature. A fault in the main electrical cabling is detected despite variations in temperature.

A main electrical cabling is subject to variations in ambient temperature over its length. A detection system for detecting a fault in the main electrical cabling able to cause a serial arc, or heating within a connection, includes a monitor electrical cabling placed alongside the main electrical cabling and a controllable current generator injecting, at the input of the monitor electrical cable, a current proportional to the current flowing through the main electrical cabling. The main and monitor sets of electrical cabling being joined at the output, an electronic circuitry measures the difference between the electrical potential at the input of the main electrical cabling and that at the input of the monitor electrical cabling and detects a fault in the main electrical cabling when the difference of the electrical potentials exceeds a predefined threshold. A fault in the main electrical cabling is detected despite the variations in temperature.

A combined monitoring device for insulation-resistance monitoring and protective-conductor-resistance monitoring in a power supply system includes a grounded power supply system and an ungrounded power supply system, the combined monitoring device having a coupling circuit for being coupled to one or several active conductors of the grounded power supply system via coupling points, the combined monitoring device including an active monitoring device with a first operating mode for monitoring an insulation resistance in an ungrounded network state of the power supply system and a second operating mode for monitoring a protective-conductor resistance in a grounded network state of the power supply system, the combined monitoring device having an evaluation unit switchable between the first and second operating modes as a function of the ungrounded or grounded network state and configured for testing the insulation resistance in the first operating mode and the protective-conductor resistance in the second operating mode.

The invention relates to an electric circuit arrangement and a method for coupling an insulation monitoring device to an ungrounded power supply system via a coupling impedance, which is realized to be operant for each active conductor of the power supply system and which is formed as an ohmic resistance circuit, the ohmic resistance circuit having a settable resistance value which is changeable and a switching-off function for decoupling the insulation monitoring device from the network and being realized as a bidirectional cascade comprising a series circuit of two transistors provided in a mirror-inverted manner, each having a diode connected in parallel, a controlled change in resistance of the transistors for setting the changeable resistance value being effected by a control circuit and the switching-off function for decoupling from the grid being realized by setting a maximum resistance value.

In a multi-phase power grid fed by a power source, earth fault (460) is located by means of a power supply source synchronized with the power grid, which is connected between a zero point of the grid and earth. In a fault current compensation mode (420), a control unit controls the alternating voltage source to compensate for any ground fault current in the power grid to a value below a threshold level. In a fault detecting mode (430), the control unit gradually adjusts the output voltage of the alternating voltage source with respect to amplitude and/or phase angle (440). A change of zero-sequence current and zero-sequence admittance between the alternating voltage source and a fault location is measured (450) by means of at least one detector. The at least one detector is communicatively connected to the control unit and reports recorded measured values representing zero-sequence current and/or zero-sequence admittance to the control unit. In the fault detecting mode, the control unit localizes a ground fault (460) based on at least one of said measurement values representing changes of the zero-sequence current and/or zero-sequence admittance, upon which an affected branch is disconnected (470) or the system switches to the fault compensation mode (420).

Systems and method for automated self-testing of a protective device for a transformer are disclosed. One system includes a protection circuit electrically connected to a transformer neutral, the transformer electrically connected to a power grid, the protection circuit may include a DC blocking component, a switch assembly, and a spark gap assembly each positioned in parallel between the transformer neutral and ground, a switch assembly. The system may further include various testing circuits configured within the protection circuit and switches which when actuated inject a signal to test various components in the protective device.

A combined monitoring device for insulation-resistance monitoring and protective-conductor-resistance monitoring in a power supply system includes a grounded power supply system and an ungrounded power supply system, the combined monitoring device having a coupling circuit for being coupled to one or several active conductors of the grounded power supply system via coupling points, the combined monitoring device including an active monitoring device with a first operating mode for monitoring an insulation resistance in an ungrounded network state of the power supply system and a second operating mode for monitoring a protective-conductor resistance in a grounded network state of the power supply system, the combined monitoring device having an evaluation unit switchable between the first and second operating modes as a function of the ungrounded or grounded network state and configured for testing the insulation resistance in the first operating mode and the protective-conductor resistance in the second operating mode.

An electrical link (8) between a DC high-voltage power source (2) and a user apparatus (5) including: an electrical conductor (4) surrounded by an insulating cover (4a), and an electrical protection device (3) that includes a conductive sleeve (7) arranged around the insulating cover (4a), a current generator (10) connected to a current injection point (30) of the conductive sleeve (7), a circuit breaker (9) arranged on the conductor and configured to cut off a current transiting through the conductor (4), and a detection module (11) connected to a current tap-off point (31) of the conductive sleeve (7) and to the circuit breaker (9) and configured to detect a current leak out of the conductor (4) and command the circuit breaker (9).