JP4532034B2 - Zero phase current transformer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a zero-phase current transformer that detects a zero-phase current that flows when a ground fault occurs in a transmission / distribution line or when there is an electric shock.
[0002]
[Prior art]
FIG. 7 is a cross-sectional view of a zero-phase current transformer disclosed in Japanese Patent Laid-Open No. 2000-68139.
The zero-phase current transformer includes conductors 1a, 1b, and 1c made of rectangular copper wires corresponding to three-phase U phase, V phase, and W phase, and a rectangular core 2 that surrounds the conductors 1a, 1b, and 1c, A coil 3 wound around the core 2, a first magnetic shield 4 covering the core 2 and the coil 3, and a second magnetic shield 5 covering the coil 3 provided inside the first magnetic shield 4 And.
The core 2 is configured by sequentially joining thin strip-shaped magnetic plates 2a, 2b, 2c, and 2d having the same dimensions made of permalloy, silicon steel, iron-based, cobalt-based amorphous alloy, or the like at the ends.
The coil 3 is a secondary conductor wound through a resin bobbin at an intermediate portion of the magnetic plate 2c.
The first magnetic shield 4 includes an inner peripheral shield part 4a, an outer peripheral shield part 4b, and a pair of side shield parts that close the space between the inner peripheral shield part 4a and the outer peripheral shield part 4b. And the back side).
The second magnetic shield 5 is made of permalloy, nickel-based or cobalt-based amorphous alloy. The second magnetic shield 5 having a U-shaped cross section is arranged with its opening facing the outer shield part 4 b and covers the three surfaces of the coil 3.
[0003]
In the zero-phase current transformer having the above configuration, when a load current flows through the conductors 1a, 1b, and 1c, magnetic fluxes generated in the core 2 by these currents cancel each other, and the coil 3 that is an output winding No voltage is induced.
However, for example, when a ground fault occurs and a difference occurs in the currents of the conductors 1a, 1b, and 1c, that is, when a zero-phase current flows, a voltage is induced in the coil 3. An earth leakage circuit breaker equipped with a zero-phase current transformer uses this principle. When a ground fault occurs or an electric shock occurs, power supply is immediately stopped by the output signal from the coil 3, and the circuit is protected. .
[0004]
[Problems to be solved by the invention]
In the conventional zero-phase current transformer, the core 2 is configured by sequentially joining thin strip-shaped magnetic plates 2a, 2b, 2c, and 2d having the same dimensions at the end portions. Even when only a balanced load current flows because the magnetic characteristics change at the corners and the winding of the conductors varies at the corners, a voltage is induced (residual) in the coil 3 that is the output winding. If an unbalanced signal is output from the coil 3 and this residual voltage is larger than the output for the zero-phase current, there is a problem that, for example, the leakage breaker malfunctions.
The core 2 is formed with a plurality of layers of coils 3 formed by winding a conductive wire. Since the conductive wire is wound in the same direction in each layer in the circumferential direction of the core 2, the outer periphery of the entire core 2 is wound. A multi-layered coil structure along the plane is also formed, and a residual voltage is induced in this coil structure by an external magnetic field outside the core 2, and an unbalanced signal is output from the coil 3 in the same manner as described above. There was a problem that it was.
[0005]
An object of the present invention is to eliminate the above-mentioned problems, and an object of the present invention is to obtain a zero-phase current transformer that can reduce the generation of an unbalanced signal and has improved output sensitivity to zero-phase current. Yes.
[0006]
[Means for Solving the Problems]
A zero-phase current transformer according to the present invention includes a current line through which a load current flows, an annular core that surrounds the current line, and an output coil configured by winding a conductive wire around the core at a predetermined pitch. A zero-phase current transformer comprising a magnetic shield with a slit surrounding the core and a conductor shield with a slit surrounding the core, wherein the output coil is at least one layer of the conductor. The coil portion is composed of a coil portion in which the winding direction with respect to the circumferential direction of the core is one direction, and a coil portion having the same number of layers as that of the coil portion and in the reverse direction of the winding direction . A magnetic shield case, and a second magnetic shield case surrounding the first magnetic shield case.
The conductor shield is a conductive film formed on the wall surface of the first magnetic shield case or the second magnetic shield case .
[0007]
In the zero-phase current transformer according to the present invention, the second magnetic shield case is configured by laminating thin magnetic plates.
[0008]
In the zero-phase current transformer according to the present invention, the winding start end portion of the output coil is connected to the core wire of the coaxial cable, and the winding end end portion of the output coil is connected to the shield wire and the conductor shield of the coaxial cable.
[0009]
In the zero-phase current transformer according to the present invention, the winding start end portion of the output coil is inside the conductor shield.
[0010]
In the zero-phase current transformer according to the present invention, the output coil formed by winding the conducting wire at a uniform pitch in the same layer is wound in the odd-numbered layer and the even-numbered layer in the circumferential direction of the core of the conducting wire. The direction is reversed.
[0011]
In the zero-phase current transformer according to the present invention, the output coil includes a coil portion in which the conducting wire is wound at a uniform pitch in the same layer and the winding direction with respect to the circumferential direction of the core is one direction, and the coil portion The return coil portion is wound along the outer peripheral side of the core in the circumferential direction opposite to the winding direction by the same number of layers.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Reference Example 1
The zero-phase current transformer of Reference Example 1 of the present invention will be described below. FIG. 1 is a plan sectional view of the zero-phase current transformer of Reference Example 1 , and FIG. 2 is a sectional view taken along the line II-II of the zero-phase current transformer of FIG.
This zero-phase current transformer is constituted by current lines 26a and 26b through which a load current flows, an annular core 20 surrounding the current lines 26a and 26b, and a conductive wire wound around the core 20 at a predetermined pitch. An output coil 21, a first magnetic shield case 22 that is a magnetic shield that surrounds the core 20, and a second magnetic shield case 23 that is a magnetic shield that surrounds the first magnetic shield case 22. A conductor shield case 24 is provided between the first magnetic shield case 22 and the second magnetic shield case 23 and is a conductor shield surrounding the first magnetic shield case 22. In addition, a slit is formed in each of the first magnetic shield case 22, the second magnetic shield case 23, and the conductor shield 24 so as not to form an electrical closed circuit.
[0013]
As shown in FIG. 3, the winding start end portion 21 a of the output coil 21 is connected to the core wire 25 a of the coaxial cable 25 inside the conductor shield 24. The winding end 21 b of the output coil 21 is connected to the shield wire 25 b and the conductor shield 24 of the coaxial cable 25.
In the output coil 21, as shown by a dotted line in FIG. 1, the conductive wire is wound around the core 20 from the winding start end portion 21 a in the clockwise direction at a predetermined pitch, and in the circumferential direction of the core 20, the clockwise direction (the direction of arrow B) It is wound around. Thereafter, the conducting wire is reversed at the position (a) in the vicinity of the winding start end portion 21a, and this time, as shown by the solid line in FIG. 1, is wound at a predetermined pitch in the clockwise direction, and in the circumferential direction of the core 20 It is wound counterclockwise (in the direction of arrow C). Finally, the winding end 21 b is connected to the shield wire 25 b and the conductor shield 24 of the coaxial cable 25.
[0014]
In the zero-phase current transformer configured as described above, when only balanced load currents having opposite directions and equal magnitudes flow through the pair of current lines 26a and 26b, the magnetic flux generated by these currents cancels each other, and the output coil No voltage is induced at 21.
However, for example, when a ground fault occurs and a difference occurs between the current lines 26a and 26b, that is, when a zero-phase current flows, a voltage is induced in the output coil 21, and the power supply is immediately stopped by this output signal. And the circuit is protected.
[0015]
By the way, in the zero-phase current transformer of this reference example , the first layer coil portion of the output coil 21 detects the magnetic flux φi generated in the core 20, but at the same time, the entire first layer coil portion of the core 20 is detected. A one-turn coil wound in a clockwise direction in the circumferential direction is formed, and this one-turn coil detects an external magnetic field φo outside the core 20.
On the other hand, the coil portion of the second layer of the output coil 21 is formed with a one-turn coil wound counterclockwise in the circumferential direction of the core 20 with respect to the coil portion of the first layer. The second layer coil portion operates differentially with respect to φo, and no induced voltage is generated in the output coil 21 due to an external magnetic field.
On the other hand, for the first layer coil portion and the second layer coil portion of the output coil 21, the conducting wire is wound around the core 20 in the same direction. On the other hand, a summing operation is performed, and a large induced voltage is obtained in the output coil 21.
Therefore, in the zero-phase current transformer of this reference example 1 , the output of the unbalanced signal due to the external magnetic field is reduced, and a zero-phase current transformer with high output sensitivity to the zero-phase current can be obtained.
[0016]
The inventor of the present application is a zero-phase current transformer of Reference Example 1 , a conventional zero-phase current transformer in which a core and a shield are rectangular, a conductive wire is wound around the core, and the core is wound around the core. An experiment was conducted to investigate the difference in the magnitude of the unbalanced current. According to the experimental result, when a single-phase current of 100 A was passed through the current line, the zero-phase current transformer of Reference Example 1 flowed an unbalanced current of 15.69 μA, whereas the conventional zero-phase current It was found that an unbalanced current of 173.83 μA flows in the generator, and the zero-phase current transformer of Reference Example 1 has a significantly reduced unbalanced current compared to the conventional zero-phase current transformer.
[0017]
The inventor of the present application examined the influence of the load current flowing outside the zero-phase current transformer of the zero-phase current transformer of Reference Example 1 and the conventional zero-phase current transformer by experiments. When a single-phase current of 100 A is passed along the axis of the zero-phase current transformer 70 mm on one side with respect to the center line of the zero-phase current transformer, the zero-phase current transformer of Reference Example 1 has a non-current of 30.2 μA. While the balanced current flows, the conventional zero-phase current transformer has an unbalanced current of 382.6 μA, and the zero-phase current transformer of Reference Example 1 is compared with the conventional zero-phase current transformer. It was found that the influence of the load current flowing outside the zero-phase current transformer on the unbalanced current is small.
[0018]
Since the output coil 21 is surrounded by the first magnetic shield case 22 and the second magnetic shield case 23, the influence of the external magnetic field is reduced, the output of the unbalanced signal is reduced, and the zero-phase current is reduced. It can be detected more reliably.
Further, the core 20 is surrounded by a conductor shield case 24, the winding start end portion 21a of the output coil 21 is connected to the core wire 25a of the coaxial cable 25, and the winding end end portion 21b of the output coil 21 is connected to the coaxial cable 25. Since the output coil 21 is connected to the shield wire 25b and the conductor shield 24, the influence of the external electric field is reduced, the output of the unbalanced signal is reduced, and the zero-phase current can be detected more reliably. .
Further, since the winding start end portion 21a of the output coil 21 is inside the conductor shield case 24, the output coil 21 can further reduce the influence of the external electric field and more reliably detect the zero-phase current. .
Furthermore, since the core 20 has an annular shape, the conducting wire can be wound at a uniform pitch, and generation of an unbalanced signal due to variations in the winding of the conducting wire in the output coil 21 can be prevented.
[0019]
In the above reference example , the output coil 21 has been described with respect to the case where the total number of layers is two. However, the total number of layers may be an even number of four or more layers. In this case, in the output coil, the winding direction with respect to the circumferential direction of the core of the conductive wire may be reversed in the odd-numbered layer and the even-numbered layer, and half of the total number of layers and the remaining half of the layers You may reverse the winding direction with respect to the circumferential direction of the core of a conducting wire between the outer peripheral side layers.
Moreover, you may use the twisted pair wire with an electric field shield as a coaxial cable.
[0020]
Embodiment 1 FIG .
FIG. 4 is a sectional side view of the main part of the zero-phase current transformer according to Embodiment 1 of the present invention.
In addition, the same code | symbol is attached | subjected and demonstrated about the same member as the reference example 1, and an equivalent member.
In this embodiment, a copper-plated conductive film 30 is formed on the outer wall surface of the first magnetic shield case 22 as a conductor shield. Other configurations are the same as those in Reference Example 1 .
Since the conductive film 30 is formed on the first magnetic shield case 22, compared with the zero-phase current transformer of Reference Example 1 using the conductor shield case 24, the cost can be reduced and the size can be reduced by reducing the number of assembly steps. Can be achieved.
The conductive film 30 may be formed on the inner wall surface of the first magnetic shield case 22, or may be formed on the inner wall surface and the outer wall surface of the second magnetic shield case 23.
[0021]
Embodiment 2 FIG .
FIG. 5 is a side sectional view of a principal part of a zero-phase current transformer according to Embodiment 2 of the present invention.
In this embodiment, the second magnetic shield case 40 is configured by laminating thin magnetic plates. For example, a high magnetic permeability silicon steel plate, permalloy, or amorphous is used as the magnetic plate.
The second magnetic shield case 40 includes a cylindrical inner peripheral portion 40a positioned on the current line 26 side, a cylindrical outer peripheral portion 40b positioned on the outermost peripheral side, and an inner peripheral portion 40a and an outer peripheral portion 40b. It consists of a donut-shaped top surface portion 40c and a bottom surface portion 40d provided therebetween.
Other configurations are the same as those in the first embodiment .
According to this embodiment, the second magnetic shield case 40 is formed by laminating magnetic plates having a high magnetic permeability and a thin plate thickness. Therefore, the second magnetic shield case 40 is thicker than a case where a normal iron plate is used. The same shield effect can be obtained at half the length, and the dimensional change of the second magnetic shield case 40 can be accommodated by the number of laminated magnetic plates, which makes it easy to assemble and process, and further reduces eddy current loss. Although it is conceivable to use ferrite as a material having a high magnetic permeability, since it is a powder alloy, it is necessary to perform mold processing, and the size cannot be easily changed, and a large second magnetic shield is manufactured. It is difficult and the manufacturing cost is high.
[0022]
Embodiment 3 FIG .
FIG. 6 is a front view of the output coil of the zero-phase current transformer according to Embodiment 3 of the present invention.
In this embodiment, the output coil 50 includes a coil portion 51 in which the conductive wires are wound counterclockwise at a uniform pitch, and the winding direction with respect to the circumferential direction of the core 20 is counterclockwise. The winding direction is composed of a return coil portion 52 wound along the outer peripheral side of the core 20 in the clockwise direction opposite to the winding direction.
In this embodiment, the first coil portion 51 of the output coil 50 and the return coil portion 52 of the output coil 50 are wound in opposite directions in the circumferential direction of the core 20, so that the external magnetic field φo The return coil section 52 operates differentially with respect to the coil section 51, and no induced voltage is generated in the output coil 50 due to an external magnetic field.
In the zero-phase current transformer of this embodiment, the length of the lead wire of the return coil portion 52 is shorter than that of the lead wire of the coil portion 51, and the cost of the output coil 50 can be reduced.
[0023]
In the reference example and each of the above embodiments, the zero-phase current transformer in the case of a single phase has been described. However, the present invention can be applied to, for example, a zero-phase current transformer in the case of a three-phase. .
[0024]
【The invention's effect】
As described above, according to the zero-phase current transformer according to the present invention, a current line through which a load current flows, an annular core that surrounds the current line, and a conductive wire wound around the core at a predetermined pitch. A zero-phase current transformer comprising an output coil configured as described above, a magnetic shield with a slit surrounding the core, and a conductor shield with a slit surrounding the core. Since at least one layer is composed of a coil portion in which the winding direction with respect to the circumferential direction of the core of the conductive wire is unidirectional, and a coil portion having the same number of layers as the coil portion and the winding direction being opposite, A conducting wire can be wound around the core at a uniform pitch, and an induced voltage due to an external magnetic field can be canceled out in the output coil, and a zero-phase current transformer with high output sensitivity to zero-phase current can be obtained.
In addition, generation of an unbalanced signal from the output coil due to a load current flowing outside the zero-phase current transformer can be reduced.
[0025]
Further, according to the zero-phase current transformer according to the present invention, the magnetic shield is composed of the first magnetic shield case and the second magnetic shield case surrounding the first magnetic shield case. Therefore, the influence of the external magnetic field is reduced, and the zero-phase current can be detected more reliably.
[0026]
Further, according to the zero-phase current transformer according to the present invention, since the conductor shield is a conductive film formed on the wall surface of the first magnetic shield case or the second magnetic shield case, the assembly man-hour is reduced. Cost reduction and downsizing can be achieved.
[0027]
Further, according to the zero-phase current transformer according to the present invention, the second magnetic shield case is configured by laminating thin magnetic plates, so that the dimensional change of the second magnetic shield case is magnetic. It can be handled by the number of stacked plates, is easy to assemble and process, and has low eddy current loss.
[0028]
Further, according to the zero-phase current transformer according to the present invention, the winding start end portion of the output coil is connected to the core wire of the coaxial cable, and the winding end end portion of the output coil is connected to the shield wire and the conductor shield of the coaxial cable. As a result, the output coil is less affected by the external electric field and can detect the zero-phase current more reliably.
[0029]
In addition, according to the zero-phase current transformer according to the present invention, since the winding coil end portion of the output coil is inside the conductor shield, the output coil is further reduced in the influence of the external electric field, and the zero-phase current is further increased. It can be detected reliably.
[0030]
Further, according to the zero-phase current transformer according to the present invention, the output coil formed by winding the conducting wires at a uniform pitch in the same layer has the odd-numbered and even-numbered layers around the core of the conducting wire. Since the winding direction with respect to the direction is opposite, a zero-phase current transformer with high output sensitivity to the zero-phase current can be obtained.
In addition, generation of an unbalanced signal from the output coil due to variations in the installation position of the current line can be reduced.
[0031]
Further, according to the zero-phase current transformer according to the present invention, the output coil includes a coil portion in which the conductive wire is wound at a uniform pitch in the same layer, and the winding direction with respect to the circumferential direction of the core is one direction, Since this coil portion is composed of a return coil portion wound along the outer peripheral side of the core in the circumferential direction opposite to the winding direction by the same number of layers, the length of the lead wire of the return coil portion is coiled. Compared with the lead wire of the part, it becomes shorter, and the cost of the output coil can be reduced.
[Brief description of the drawings]
FIG. 1 is a plan sectional view of a zero-phase current transformer of Reference Example 1 of the present invention.
FIG. 2 is a cross-sectional view taken along the line II-II in FIG.
FIG. 3 is a diagram showing a connection state between a coaxial cable and a conductor of an output coil.
FIG. 4 is a cross-sectional view of a main part of the zero-phase current transformer according to Embodiment 1 of the present invention.
FIG. 5 is a cross-sectional view of a main part of a zero-phase current transformer according to Embodiment 2 of the present invention.
FIG. 6 is a cross-sectional view of a main part of a zero-phase current transformer according to Embodiment 3 of the present invention.
FIG. 7 is a cross-sectional view of a conventional zero-phase current transformer.
[Explanation of symbols]
20 cores, 21 and 50 output coils, 21a winding start end, 21b winding end end, 22 first magnetic shield case, 23 second magnetic shield case, 24 conductor shield case, 25 coaxial cable, 25a core wire, 25b Shield wire, 26 Current wire, 30 Conductive film, 40 Second magnetic shield case, 51 parts, 52 Return coil part.

Claims (6)

A current line through which the load current flows;
An annular core surrounding this current line;
An output coil configured by winding a conductive wire around the core at a predetermined pitch;
A magnetic shield with a slit surrounding the core;
A conductor shield with a slit surrounding the core;
A zero-phase current transformer with
The output coil is composed of at least one coil portion in which the winding direction of the conducting wire with respect to the circumferential direction of the core is one direction, and a coil portion having the same number of layers as the coil portion and the winding direction in the reverse direction. and,
The magnetic shield is composed of a first magnetic shield case and a second magnetic shield case surrounding the first magnetic shield case,
The conductor shield is a zero-phase current transformer which is a conductive film formed on the wall surface of the first magnetic shield case or the second magnetic shield case . The zero-phase current transformer according to claim 1, wherein the second magnetic shield case is configured by laminating thin magnetic plates. The zero phase according to claim 1 or 2, wherein a winding start end portion of the output coil is connected to a core wire of the coaxial cable, and a winding end end portion of the output coil is connected to a shield wire and a conductor shield of the coaxial cable. Current transformer. The zero-phase current transformer according to claim 3 , wherein the winding start end portion of the output coil is inside the conductor shield. The output coil formed by winding the conducting wires at a uniform pitch in the same layer has opposite winding directions with respect to the circumferential direction of the core of the conducting wires in the odd and even layers. zero-phase current transformer according to any one of 4. The output coil has a coil portion in which the conductive wire is wound at a uniform pitch in the same layer and the winding direction with respect to the circumferential direction of the core is one direction, and is opposite to the winding direction by the same number of layers as the coil portion. zero-phase current transformer according to any one of claims 1 to 4 in the circumferential direction along the outer peripheral side of the core is composed of a wound on the return coil unit.

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