A direct-current circuit includes: a breaker that is inserted into the direct-current line and becomes a path for direct current when in a steady state; a resonance circuit connected in parallel with the breaker and superimposing resonance current on the direct current; and a first disconnector and a second disconnector connected to first and second connection points of the breaker and the resonance circuit, respectively, and forming a path for the direct current together with the breaker. The resonance circuit includes a series circuit that includes a capacitor and a reactor and generates the resonance current, a charging resistor for charging the capacitor with a direct-current potential of the direct-current line, a high-speed switch connected in series with the series circuit on the capacitor side and superimposing the resonance current on the direct current, and an arrester connected in parallel with the capacitor and the high-speed switch.

A direct-current circuit includes: a breaker that is inserted into the direct-current line and becomes a path for direct current when in a steady state; a resonance circuit connected in parallel with the breaker and superimposing resonance current on the direct current; and a first disconnector and a second disconnector connected to first and second connection points of the breaker and the resonance circuit, respectively, and forming a path for the direct current together with the breaker. The resonance circuit includes a series circuit that includes a capacitor and a reactor and generates the resonance current, a charging resistor for charging the capacitor with a direct-current potential of the direct-current line, a high-speed switch connected in series with the series circuit on the capacitor side and superimposing the resonance current on the direct current, and an arrester connected in parallel with the capacitor and the high-speed switch.

The current transformer system that is the present invention allows for surveillance of an electronic grid at electrical power generating stations, at individual operational substations and in electric power distribution for electric network and grid measurement, protection, and control ranging from very low currents to high current magnitudes. The reception and relay of information from the CT primary circuit is sensed and transmitted by a primary electronic circuitry, digitized, converted to a fiber optic mode, transmitted to a secondary electronic circuit, processed and converted to a digital output and transmitted to various monitoring and recording devices.

A current transformer includes first and second transformer assemblies that each respectively comprise first and second groups of stacked iron core components. A first interface and a second interface are defined at an end of the first transformer assembly. A third interface and a fourth interface are defined at an end of the second transformer assembly. At least one of the first interface and the second interface is detachably connected with at least one of the third interface and the fourth interface. When the first and second transformer assemblies are connected with each other, the first and second groups of iron core components are combined to form a plurality of closed ring-shaped iron cores, and coils are respectively wound on at least two closed ring-shaped iron cores. An enclosed area defined between the first and second transformer assemblies causes induced current to be generated in at least one coil.

A direct-current circuit includes: a breaker that is inserted into the direct-current line and becomes a path for direct current when in a steady state; a resonance circuit connected in parallel with the breaker and superimposing resonance current on the direct current; and a first disconnector and a second disconnector connected to first and second connection points of the breaker and the resonance circuit, respectively, and forming a path for the direct current together with the breaker. The resonance circuit includes a series circuit that includes a capacitor and a reactor and generates the resonance current, a charging resistor for charging the capacitor with a direct-current potential of the direct-current line, a high-speed switch connected in series with the series circuit on the capacitor side and superimposing the resonance current on the direct current, and an arrester connected in parallel with the capacitor and the high-speed switch.

A direct-current circuit includes: a breaker that is inserted into the direct-current line and becomes a path for direct current when in a steady state; a resonance circuit connected in parallel with the breaker and superimposing resonance current on the direct current; and a first disconnector and a second disconnector connected to first and second connection points of the breaker and the resonance circuit, respectively, and forming a path for the direct current together with the breaker. The resonance circuit includes a series circuit that includes a capacitor and a reactor and generates the resonance current, a charging resistor for charging the capacitor with a direct-current potential of the direct-current line, a high-speed switch connected in series with the series circuit on the capacitor side and superimposing the resonance current on the direct current, and an arrester connected in parallel with the capacitor and the high-speed switch.

The invention relates to a method (100) for detecting faults in a LVDC electric line (500) characterized in that it comprises the following steps: acquiring (101) a first detection signal (V.sub.LOW) indicative of low-frequency components of an unbalancing current (I.sub.G) between a plurality of conductors of said electric line, said first detection signal being obtained by means of a low-pass filtering of a corresponding measuring signal (V.sub.M1) indicative of said unbalancing current; acquiring (102) a second detection signal (V.sub.HIGH) indicative of high-frequency components of an unbalancing current (I.sub.G) between a plurality of conductors of said electric line, said second detection signal being obtained by means of a high-pass filtering of a corresponding measuring signal (V.sub.M2) indicative of said unbalancing current; obtaining (103) a third detection signal (RT) by calculating the ratio between said first and second detection signals (V.sub.LOW, V.sub.HIGH); checking (104) whether a DC current (I.sub.F) is present by comparing said third detection signal (RT) with a first threshold value (TH1). In a further aspect, the invention relates to an electronic device (1) including processing means for carrying out said method.

The invention relates to a method (100) for detecting faults in a LVDC electric line (500) characterized in that it comprises the following steps: acquiring (101) a first detection signal (V.sub.LOW) indicative of low-frequency components of an unbalancing current (I.sub.G) between a plurality of conductors of said electric line, said first detection signal being obtained by means of a low-pass filtering of a corresponding measuring signal (V.sub.M1) indicative of said unbalancing current; acquiring (102) a second detection signal (V.sub.HIGH) indicative of high-frequency components of an unbalancing current (I.sub.G) between a plurality of conductors of said electric line, said second detection signal being obtained by means of a high-pass filtering of a corresponding measuring signal (V.sub.M2) indicative of said unbalancing current; obtaining (103) a third detection signal (RT) by calculating the ratio between said first and second detection signals (V.sub.LOW, V.sub.HIGH); checking (104) whether a DC current (I.sub.F) is present by comparing said third detection signal (RT) with a first threshold value (TH1). In a further aspect, the invention relates to an electronic device (1) including processing means for carrying out said method.

A sensor of electric current including a fiber (1) from a soft magnetic material with a uniform cross-sectional area and uniform magnetic properties along its whole length, equipped with an excitation coil (2) wound on said fiber (1) with a uniform winding density along the substantially whole length and possibly equipped with a sensing coil (3) wound on said fiber (1) with uniform winding density along the substantially whole length, where said fiber (1) ends are mechanically joined to form a loop enclosing the measured current carrying conductor (4) by said fiber (1), wherein said excitation coil (2) is connected to the current output of a current source (5) through a current transducer (6) generating a current signal corresponding to the excitation current flowing through said excitation coil (2) wherein the sensor is equipped with a voltage transducer (7) generating a voltage signal corresponding to the voltage on the possibly present sensing coil (3) or on the excitation coil (2) wherein said voltage signal and said current signal are fed into a processor unit (8). The present disclosure also relates to a method for electric current measurement using said sensor.

A sensor of electric current including a fiber (1) from a soft magnetic material with a uniform cross-sectional area and uniform magnetic properties along its whole length, equipped with an excitation coil (2) wound on said fiber (1) with a uniform winding density along the substantially whole length and possibly equipped with a sensing coil (3) wound on said fiber (1) with uniform winding density along the substantially whole length, where said fiber (1) ends are mechanically joined to form a loop enclosing the measured current carrying conductor (4) by said fiber (1), wherein said excitation coil (2) is connected to the current output of a current source (5) through a current transducer (6) generating a current signal corresponding to the excitation current flowing through said excitation coil (2) wherein the sensor is equipped with a voltage transducer (7) generating a voltage signal corresponding to the voltage on the possibly present sensing coil (3) or on the excitation coil (2) wherein said voltage signal and said current signal are fed into a processor unit (8). The present disclosure also relates to a method for electric current measurement using said sensor.