A monitoring system is applied to an electrical system, which includes a DC power source and an electrical apparatus that is connected to the DC power source by a pair of electric power leads incorporating respective switches. To detect leakage current from the DC power source, a low-frequency AC signal is applied via a large-capacitance capacitor to a specific connection position, between a first terminal of the DC power source and the corresponding switch, and the resultant voltage of that signal is measured. To detect a short-circuit failure of one or both of the switches, a high-frequency AC signal is applied via a low-capacitance capacitor to the specific connection position, and the resultant signal voltage is measured. Judgement as to occurrence of leakage current and/or short-circuit failure is based on the measured signal voltage values.

A subsea electrical unit is provided. The subsea electrical unit includes a first electric power connection for receiving electric power for operating the subsea electrical unit and a second electric power connection towards a further subsea electrical unit. A line insulation monitor is coupled to the second electric power connection. A control unit is adapted to determine whether electric power is present on the second electric power connection, and is further adapted to disconnect the line insulation monitor form the second electric power connection if it determines that power is present on the second electric power connection.

An apparatus for monitoring ground current includes a signal generation module that generates a plurality of AC components of different frequencies. An injection module injects the plurality of AC components on one or more phases of a set of power cables connecting a power source to a load. The set of power cables includes an equipment grounding conductor. The AC components are injected in the equipment grounding conductor. An AC detection module that determines an AC current corresponding to each frequency of the AC components present in current in the equipment grounding conductor, an AC threshold module determines if one or more of the AC currents is below an AC threshold, and a trip module opens a contact if the AC threshold module determines that at least one of the AC currents is below an AC threshold. The contact disconnects the power source from the power cables.

An apparatus for monitoring ground current includes a signal generation module that generates a plurality of AC components of different frequencies. An injection module injects the plurality of AC components on one or more phases of a set of power cables connecting a power source to a load. The set of power cables includes an equipment grounding conductor. The AC components are injected in the equipment grounding conductor. An AC detection module that determines an AC current corresponding to each frequency of the AC components present in current in the equipment grounding conductor, an AC threshold module determines if one or more of the AC currents is below an AC threshold, and a trip module opens a contact if the AC threshold module determines that at least one of the AC currents is below an AC threshold. The contact disconnects the power source from the power cables.

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).

An electrical link (290) configured to link a DC high-voltage power source (270) to a user apparatus (250), and includes an electrical conductor (240) surrounded by an insulating cover and an electrical protection device (200) including: a conductive sleeve (280) arranged around the insulating cover, a biasing module (245) configured to voltage-bias the conductive sleeve (280), a circuit breaker (210) arranged on the conductor (240) and configured to cut off a current transiting through the conductor (240), and a detection module (220) connected to the conductive sleeve (280) and configured to detect a current leak out of the conductor (240) and to command the circuit breaker (210) on the basis of the detection. The invention also relates to a method for the secure supply of electric power.

An abnormality detection device includes: a coupling-capacitor having a first-end and a second-end coupled with a high-voltage circuit; a signal output unit; a signal extraction unit; and a signal input unit. The signal output unit is coupled with the first-end of the coupling-capacitor via a detection-resistor, and outputs an alternating-current inspection-signal. The signal extraction unit extracts the inspection-signal, as an extraction-signal, output between the detection-resistor and the coupling-capacitor. The signal input unit detects abnormality of insulation resistance of the high-voltage circuit based on a level of the inputted extraction-signal. The signal extraction unit includes a signal removing filter and a subtraction circuit. The filter removes a signal equal in frequency to the inspection-signal and passes low-frequency noises lower in frequency than the inspection-signal. The subtraction circuit outputs a differential signal, as the extraction-signal, between a signal having passed through the filter and a signal not having passed through the filter.

The invention relates to a method and to devices for extended insulation-fault search in an IT power supply system using a multifunctional test current, wherein, selectively and depending on the application, the test current functions as a voltage compensation current so as to compensate a voltage increase in an active conductor of the IT power supply system, as a tripping current so as to trip a residual current protection device arranged in a subsystem of the IT power supply system and/or as a leakage-capacitance compensation current so as to compensate a capacitive leakage current. The test current can fulfil more than one of the cited functions simultaneously.

In one example, a ground fault circuit interrupter is provided. It may include a current imbalance detection circuit configured to provide a leakage signal and a main processing circuit including a processor. The leakage signal may correspond to a current imbalance between a supply path and a return path. The processor may be configured to receive the leakage signal, analyze a time pattern of the leakage signal, determine whether a ground fault exists based on analysis of the time pattern, and generate a first trigger signal if the ground fault is determined to exist. The ground fault circuit interrupter may further include a back-EMF detection circuit configured to provide a back-EMF detection signal. Methods for detecting and responding to a ground fault are also provided.

In one example, a ground fault circuit interrupter is provided. It may include a current imbalance detection circuit configured to provide a leakage signal and a main processing circuit including a processor. The leakage signal may correspond to a current imbalance between a supply path and a return path. The processor may be configured to receive the leakage signal, analyze a time pattern of the leakage signal, determine whether a ground fault exists based on analysis of the time pattern, and generate a first trigger signal if the ground fault is determined to exist. The ground fault circuit interrupter may further include a back-EMF detection circuit configured to provide a back-EMF detection signal. Methods for detecting and responding to a ground fault are also provided.