The detection of an insulation fault on a network furnished with tappings by a first monitor can be followed by the location and identification of the fault by way of a locator to be placed on the tappings. To satisfy the level-two security, or SIL-2, in which the risk of occurrence of a hazard is decreased by a factor of greater than 100, second means for detecting the insulation fault are installed, to obtain a redundant item of information as regards the insulation resistance of the network, independently of the monitor but associated with a locator.

The detection of an insulation fault on a network furnished with tappings by a first monitor can be followed by the location and identification of the fault by way of a locator to be placed on the tappings. To satisfy the level-two security, or SIL-2, in which the risk of occurrence of a hazard is decreased by a factor of greater than 100, second means for detecting the insulation fault are installed, to obtain a redundant item of information as regards the insulation resistance of the network, independently of the monitor but associated with a locator.

A new approach to Ground Fault Detection and Interruption. The entire DC port is driven with a small-amplitude oscillation or modulation, and the power converter's controller tests for the presence of some version of that signal. If the detected oscillations are too small, either as a result of the GFDI fuse being blown, OR as a result of the DC port having too low of an impedance to ground (ground fault), the circuit detects that and causes the power converter to shut down.

The device comprises at least a first part intended to detect an electrical fault occurring in a network and a second part comprising at least one switch connecting the network to a power supply source, the first part comprising at least one reflectometry detection system capable of being coupled with the network, the system detecting and analyzing the impedance changes occurring in the network, a signal being sent by the system to trigger the opening of the switch when a detected impedance change is considered by the system to be an electrical fault.

The device comprises at least a first part intended to detect an electrical fault occurring in a network and a second part comprising at least one switch connecting the network to a power supply source, the first part comprising at least one reflectometry detection system capable of being coupled with the network, the system detecting and analyzing the impedance changes occurring in the network, a signal being sent by the system to trigger the opening of the switch when a detected impedance change is considered by the system to be an electrical fault.

A method monitors an energy transmission device, in particular an energy transmission line or an energy distribution network, via which electric current is transmitted at a predefined network frequency. An electrical measurement signal having at least one non-network frequency, i.e. a frequency which differs from the network frequency, or a non-network frequency band, is fed into the energy transmission device at a predefined position thereon. An electrical measured quantity related to the non-network frequency or the non-network frequency band is measured at the predefined position or a different position on the energy transmission device with the formation of at least one measured value or frequency-band-related measured value characteristic. A fault signal is generated if the measured value, the frequency-band-related measured value characteristic, a comparative value or comparative value characteristic formed with the measured value or the measured value characteristic indicates a fault in the energy transmission device.

A method monitors an energy transmission device, in particular an energy transmission line or an energy distribution network, via which electric current is transmitted at a predefined network frequency. An electrical measurement signal having at least one non-network frequency, i.e. a frequency which differs from the network frequency, or a non-network frequency band, is fed into the energy transmission device at a predefined position thereon. An electrical measured quantity related to the non-network frequency or the non-network frequency band is measured at the predefined position or a different position on the energy transmission device with the formation of at least one measured value or frequency-band-related measured value characteristic. A fault signal is generated if the measured value, the frequency-band-related measured value characteristic, a comparative value or comparative value characteristic formed with the measured value or the measured value characteristic indicates a fault in the energy transmission device.

An electrical protective device (20) and method are for selective disconnection of a subsystem (6a, 6b) in the event of a second fault in an ungrounded power supply system (2) with a main system (4) and at least one subsystem (6a, 6b), the subsystem (6a, 6b) having a differential current measuring device (12a, 12b) and a switching device (14a, 14b) for separating the subsystem (6a, 6b). The invention is based on generating and applying a measuring signal voltage (U.sub.m) between one or more phase(s) of the main system (4) or from a neutral point of the main system (4) against ground (9) using a resonant coupling circuit (22) that has a measuring signal generator (24) and a series resonant circuit (26) connected in series to the measuring signal generator (24), a resonant frequency (f.sub.0AK) of the series resonant circuit (26) being set to correspond to the measuring signal frequency.

An electrical protective device (20) and method are for selective disconnection of a subsystem (6a, 6b) in the event of a second fault in an ungrounded power supply system (2) with a main system (4) and at least one subsystem (6a, 6b), the subsystem (6a, 6b) having a differential current measuring device (12a, 12b) and a switching device (14a, 14b) for separating the subsystem (6a, 6b). The invention is based on generating and applying a measuring signal voltage (U.sub.m) between one or more phase(s) of the main system (4) or from a neutral point of the main system (4) against ground (9) using a resonant coupling circuit (22) that has a measuring signal generator (24) and a series resonant circuit (26) connected in series to the measuring signal generator (24), a resonant frequency (f.sub.0AK) of the series resonant circuit (26) being set to correspond to the measuring signal frequency.

A first voltage output unit generates a cyclic voltage that changes cyclically, and applies the cyclic voltage to the other end of a coupling capacitor via a first resistance. A second resistance and a third resistance are connected in series between a node and a second voltage output unit, the node being between the coupling capacitor and the first resistance. A voltage measurement unit measures a voltage at a voltage dividing point between the second resistance and the third resistance. In a period in which two types of fixed voltages are applied to the voltage dividing point in order, a diagnosing unit determines whether the leakage detecting device is in a normal state, based on the voltage measured by the voltage measurement unit.