JPH06105263B2 - Current detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detecting device having an annular magnetic core for detecting a minute current such as a ground leakage current generated in a power transmission and distribution system by its circulating magnetic flux.

[Conventional technology]

When the insulation resistance of the distribution line or its load circuit decreases and the leakage current leaking to the ground side increases, electric heating occurs at the leakage current generating portion, which often causes a leakage fire. An earth leakage breaker is widely used in order to predict these risks and prevent disasters. In these devices, it is necessary to first detect leakage currents on the order of tens of mA or less, but since a large load current is flowing through the distribution line, a weak leakage current that overlaps with the load current is picked up. Therefore, there is known a current detection device having an annular magnetic core that detects a leakage current as an unbalanced current (zero-phase current) in a three-phase line or an unbalanced current in a single-phase reciprocating conductor.
A current magnetic field due to an unbalanced current is generated around the three-phase or single-phase electric line in a direction that goes around the electric line (referred to as an orbiting magnetic flux here), and an annular magnetic core with a large magnetic permeability should be placed. Thereby, the circulating magnetic flux can be focused in the magnetic core. As a method for detecting the orbiting magnetic flux in the annular magnetic core, a so-called zero-phase current transformer method in which a detection coil is wound around the annular magnetic core and the induced voltage due to the magnetic flux change is detected, and a magnetic path is formed in the circumferential direction of the annular magnetic core. There is known a method in which a gap is provided to divide and a magnetic field sensor such as a Hall element is arranged for the gap.

[Problems to be solved by the invention]

In the conventional zero-phase current transformer type current detection device, a high magnetic permeability material such as permalloy (Ni-Fe alloy) is installed to efficiently focus the circulating magnetic flux due to the weak unbalanced current on the annular magnetic core. In addition to increasing the cross-sectional area of the magnetic core to increase the amount of magnetic flux and increasing the number of turns of the detection coil to hundreds or thousands of turns, the size of the device is increased and the manufacturing cost is increased. There is a drawback that leads to. In addition, there is a problem in that versatility is lacking because the frequency of the unbalanced current waveform and the waveform distortion are easily affected, and measurement errors based on these are likely to occur. On the other hand, in the conventional sensor type device, since the Hall element has an unbalanced voltage due to its structure and emits an output signal even when the circulating magnetic flux is zero, it adversely affects the measurement accuracy of the weak ambient magnetic flux and There is a problem that the circuit configuration becomes complicated, including compensation of the balanced voltage and compensation of the temperature characteristic.

An object of the present invention is to obtain an economical current detection device that has excellent detection sensitivity for minute currents to be detected, is less susceptible to distortion of the current waveform to be detected and frequency, and has a simple structure.

[Means for solving problems]

In order to solve the above problems, according to the present invention, a pair of annular magnetic cores that form a magnetic path of a circulating magnetic flux generated by a detected current around an electromagnetic path, and a gap portion formed in the pair of annular magnetic cores are provided. A pair of orbiting magnetic flux sensors each of which has an inductance difference due to the orbiting magnetic flux, and a bridge circuit having the pair of orbiting magnetic flux sensors on two sides, each of which is composed of an amorphous thin wire and a high-frequency exciting coil disposed in parallel to the magnetic path. , An oscillator that supplies a high-frequency oscillating current through which the amorphous thin wire reaches a magnetic saturation region through this bridge circuit, and a detection of the unbalanced output of the bridge circuit that is based on the inductance difference is converted to a direct current and converted into the detected current. And a circuit.

[Action]

As described above, two circulating magnetic flux sensors in which a high-frequency exciting coil is wound around an amorphous thin wire are used, a bridge circuit having the high-frequency exciting coil on two sides is formed, and an electric line that generates an unbalanced current is collectively formed. The two surrounding magnetic flux sensors are arranged in parallel in the magnetic path direction of the circular magnetic flux of the circular magnetic core so that the high-frequency magnetic fields are opposite to each other in the voids of the two circular magnetic cores that surround and have a spatial gap in the circumferential direction. The oscillator was connected to the bridge circuit to supply high-frequency oscillating current. When the amorphous thin wires of the two orbiting magnetic flux sensors are high-frequency magnetized so as to reach the magnetic saturation region in such a state, the inductances of both high-frequency exciting coils are equal to each other and the bridge circuit is The output signal of the detection circuit arranged on the output side of the bridge circuit is zero while maintaining balance. When an unbalanced current is generated, the high-frequency magnetic flux in the pair of amorphous thin wires is added with the circulating magnetic flux on one side and negative on the other side, so that the respective magnetic saturation states change, the exciting inductance increases on the one side, and the exciting inductance on the other side increases. Decreases. Therefore, this inductance change is detected as an unbalanced output of the bridge circuit with high sensitivity, and is converted into a direct current by the detection circuit, whereby the influence of the waveform distortion can be eliminated and the detected current can be obtained.

〔Example〕

 Hereinafter, the present invention will be described based on examples.

FIG. 1 is a schematic configuration diagram showing an apparatus according to an embodiment of the present invention, and FIG.
FIG. 3 is a perspective view showing how the annular magnetic core is attached to the electric line in the embodiment apparatus, and FIG. 3 is an enlarged view of the orbiting magnetic flux sensor portion in the embodiment apparatus. In the figure, 10 is a single-phase electric line that guides the single-phase load current I, 20 is a three-phase electric line that guides the three-phase load current I, and a pair of annular magnetic cores 2A, 2B collectively enclose the electric line 10 or 20. However, it is supported by a support tool (not shown) so as to maintain a distance preventing mutual magnetic interference. Each of the pair of annular magnetic cores 2A, 2B has a gap portion 3 formed at one position in the circumferential direction, and each of the gap portions has an amorphous thin wire of 125 μm in diameter and several mm in length as shown in FIG. Circulating magnetic flux sensors 1A and 1B each having a plurality of bundles 11 as a magnetic core and a high frequency exciting coil 12 in which a plurality of turns of a copper wire having a diameter of about 0.1 mm are mounted are arranged parallel to the magnetic path direction of the annular magnetic core. ing. 5 is a bridge circuit, which is a high-frequency exciting coil
12A and 12B and two resistance sides 6 and 7, and a potentiometer type balancer 8 and a detection circuit 9 are provided on the side of the balanced detection circuit of the bridge circuit 5.
An oscillator 4 for supplying a high-frequency oscillating current indicated by IA in the figure is conductively connected to the power source side of. In addition, the high frequency exciting coil 12A, 1 which is conductively connected to the bridge circuit by the lead wires 13A, 13B.
By connecting the high frequency oscillating current IA to the bridge circuit so that the high frequency oscillating currents IA flow in opposite directions, the high frequency oscillating currents 2A can generate high frequency magnetic fluxes φA, φB in opposite directions in the pair of orbiting magnetic flux sensors 1A, 1B.

Next, the operation principle of the embodiment apparatus will be described. For example, the first
In the figure, when a leakage current (i.e., an unbalanced current) i is generated in the reciprocating electric line 10 passing through the load current I at the commercial frequency, a circulating magnetic flux φi corresponding to the unbalanced current i is generated. Therefore, by forming the annular magnetic core 2A, 2B using a magnetic material such as permalloy having a large initial magnetic permeability, an amplifying effect of converging the orbiting magnetic flux that tends to spread to the periphery into the annular magnetic core is obtained, and the annular magnetic core 1A, An orbiting magnetic flux φi that orbits in 1B in the same direction is generated. By the way, since the pair of orbiting magnetic flux sensors 1A and 1B generate high frequency (vibration) magnetic fluxes φA and φB which are opposite to each other,
On the side of the annular magnetic core 2A, φ1 and φA are in the same direction, and on the side of 2B, φ1 and φA are in the opposite directions. Assuming that the cycle of the circulating magnetic flux φ1 is significantly longer than the cycle of the high frequency magnetic flux, the high frequency magnetic fluxes φA and φB are biased in the opposite directions by the surrounding magnetic flux φ1.

4 to 6 show the magnetization characteristics of amorphous thin wires (B
(-H characteristic) diagram, which is simplified and shown by one curve ignoring hysteresis. FIG. 4 shows the circulating magnetic flux φi.
Shows the magnetization state of the amorphous thin wires 11A and 11B in the state of zero.
The pulsating current) indicated by the amorphous thin line is magnetized to hold the magnetic saturation region width Hs in + H side amplitude H _1.
FIG. 5 shows a state in which the magnetizing force Hi due to the orbiting magnetic flux φi is applied to the + H side, which is the same as H _1, and the magnetization curve is shifted to the + H side by Hi as shown by the solid line in the figure, and the magnetic saturation region width is Hs
Since it increases to + Hi, the amount of change in the high-frequency oscillating magnetic flux in the amorphous thin wire decreases, and as a result, the inductance of the high-frequency exciting coil decreases. FIG. 6 shows a state in which the magnetizing force Hi due to the orbiting magnetic flux φi is applied to the negative side in the opposite direction. Since the magnetization curve shifts to the negative side, the magnetic saturation region width narrows to Hs−Hi, and high frequency As the amount of change in the oscillating magnetic flux increases, the inductance of the high frequency exciting coil decreases as a result.

Therefore, if the orbiting magnetic flux sensors 1A and 1B are arranged in the gap portions of the annular magnetic cores 2A and 2B in directions opposite to each other, for example, when the amorphous thin wire 11A shows the magnetization state shown in FIG. Since the magnetization state shown in FIG. 6 is shown and this state is alternately replaced and repeated, the inductances of the high frequency exciting coils 12A and 12B increase on the one hand and decrease on the other hand. Therefore, the circulating magnetic flux φi
If the resistance values of the resistance sides 6 and 7 and the balancer 8 are adjusted so that the bridge circuit is balanced in the state of zero, the unbalanced current i
It is possible to detect the change in the inductance of the high-frequency exciting coil as a result of the unbalanced output of the bridge circuit.
The unbalanced output of the bridge circuit is rectified, amplified, and noise-removed by the detection circuit 9, and is converted and displayed as an unbalanced current value.

In the current detection device configured as described above, the Co-based amorphous thin wire has excellent frequency characteristics that maintain high magnetic permeability up to high frequency regions up to an ambient temperature of approximately 150 ° C, and has high rigidity and a diameter of approximately 125 μm. Diameter 1 for fine wire
It has the characteristic that a copper wire of about 00 μm can be easily wound. Therefore, the orbiting magnetic flux sensors 1A and 1B can be formed in an extremely small size, and the amorphous thin wire can be easily magnetized to a magnetic saturation amount region with a small amount of magnetization energy. Next, the amorphous thin wires that were high-frequency magnetized to one magnetic saturation region by the high-frequency vibration wave were arranged in the voids of the pair of annular magnetic cores in opposite directions. It is possible to detect by converting to the inductance difference of the magnetic flux sensor. further,
By converting this inductance change into an unbalanced output of a bridge circuit having a pair of orbiting magnetic flux sensors on two sides and outputting it, a minute inductance change, in other words, the generation of a current to be detected can be detected with high sensitivity. By converting the unbalanced output into a direct current in the circuit and converting the unbalanced output into a detected current, the detected current can be detected without being affected by the waveform distortion and frequency (including direct current).

〔The invention's effect〕

As described above, according to the present invention, a pair of revolving magnetic flux sensors, in which a high frequency exciting coil is wound around an amorphous thin wire, are arranged so that the high frequency magnetic fluxes are opposite to each other in a gap between a pair of annular magnetic cores which are magnetic paths of the revolving magnetic flux. A bridge circuit having the pair of orbiting magnetic flux sensors on two sides, an oscillator for supplying a high-frequency oscillating current to the amorphous thin wire via the bridge circuit, and a current value to be detected by converting the unbalanced output of the bridge circuit into a direct current. A detection circuit for detecting is determined. As a result, when magnetic flux is generated based on the current to be detected, the magnetic saturation state of the pair of amorphous thin wires changes in opposite directions, and this is converted into an increase / decrease in the inductance of the circular magnetic flux sensor, resulting in an unbalanced output of the bridge circuit. As it can be detected with high sensitivity, and the influence of the distortion and frequency of the detected current waveform can be eliminated by converting it to DC in the detection circuit, minute detected current such as unbalanced current in the electric line is affected by the waveform and frequency. Therefore, it is possible to provide a highly versatile current detection device that can be detected with high sensitivity without being concerned and can be applied to single-phase, three-phase AC power lines, DC power lines, and the like. Also,
Compared with the current detector of the zero-phase current transformer type, the orbiting magnetic flux sensor can be made small with a high-frequency exciting coil and an amorphous thin wire that have a small number of windings, which can significantly reduce the processing man-hours and reduce the number of elements in the Hall element. The effects of the equilibrium voltage and the ambient temperature are eliminated, and therefore there is an advantage that a compensating circuit is not required and the circuit configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an apparatus according to an embodiment of the present invention, and FIG.
FIG. 3 is a perspective view of a main part showing a state of attachment of the embodiment apparatus to an electric line, FIG. 3 is an enlarged view of a circulating magnetic flux sensor portion in the embodiment apparatus, and FIGS. 4 to 6 are amorphous thin wires in the embodiment apparatus. 3 is a magnetization characteristic diagram for explaining the magnetization state of FIG. 1A, 1B …… Orbiting magnetic flux sensor, 2A, 2B …… Annular magnetic core, 3,3A, 3
B: gap, 4: oscillator, 5: bridge circuit, 6,7
...... Resistance side, 8 …… Balancer, 9 …… Detection circuit, 11 …… Amorphous thin wire, 12 …… High frequency exciting coil, 10,20 ……
Electric line, i ... Leakage current (unbalanced current), φi ... Circulating magnetic flux, IA ... High frequency vibration current, φA, φB ... High frequency magnetic flux.

Claims (1)

[Claims] 1. A pair of annular magnetic cores that form a magnetic path of a circulating magnetic flux generated by a current to be detected around an electric line, and a pair of annular magnetic cores that are arranged in parallel with the magnetic path in a gap portion formed between the pair of annular magnetic cores. And a pair of orbiting magnetic flux sensors each of which has an inductance difference due to the orbiting magnetic flux, a bridge circuit having the pair of orbiting magnetic flux sensors on two sides, and the amorphous circuit via the bridge circuit. An oscillator for supplying a high-frequency oscillating current in which a thin wire reaches a magnetic saturation region, and a detection circuit for converting the unbalanced output of the bridge circuit based on the inductance difference into a direct current and converting the current into the detected current. Current detection device.