JPH11135346A - Current transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a loss generated in a shield winding, size and weight of current transformer and its cost. SOLUTION: A shield winding 3 is divided into shield winding pieces 3a to 3d. The divided parts are arranged at A part near the outermost outer conductor 5 in the shield winding 3. The shield windings 3a and 3d nearest the outer conductor 5 become farther from the outer conductor 5 than heretofore and their directions are changed, so that the magnetic combination to the outer conductor 5 becomes weak and the induced current becomes small, thereby reducing a loss.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current transformer for transforming a measured current into a current value suitable for measurement and the like.

[0002]

2. Description of the Related Art FIG.
FIG. 9 is an explanatory diagram of a conventional current transformer shown in No. 8. In the figure, 1 is a conductor through which a current to be measured flows, 2 is an iron core forming a magnetic path interlinking with the conductor 1, and 3 is a shield winding wound on the iron core 2, and four shield windings having the same number of turns are provided. Wire piece 3a ~
It is divided into 3d. Although a secondary winding is also wound on the iron core 2, its illustration is omitted. 4a, 4
b is a connection line connecting the same polarity sides of the shield winding pieces 3a to 3d, 5 is an outer conductor arranged near and parallel to the conductor 1, and the central portion of the nearest shield winding piece 3a is Facing the outer conductor 5.

[0003] In this configuration, a current proportional to the current to be measured flowing through the conductor 1 flows through the secondary winding. Since the shield winding pieces 3a to 3d have the same number of turns and are connected on the same polarity side, the induced current does not circulate due to the magnetic flux generated by the measured current. On the other hand, the outer conductor 5
A magnetic flux Φ generated by a current flowing through the iron core 2 penetrates the iron core 2. However, a current flows through the shield winding pieces 3a to 3d so as to reduce the infiltration magnetic flux, thereby preventing magnetic saturation of the iron core 2 due to the current of the outer conductor 5 and preventing an increase in the measurement error of the current transformer.

[0004]

Since the conventional current transformer is configured as described above, if there is an external conductor near which a large current flows, the shield winding piece closest to the external conductor (FIG. 4) In this case, a large current flows through 3a), and a relatively small current flows through distant shield winding pieces (3b to 3d). As a result, the generated loss of the shield winding piece closest to the outer conductor may increase and cause overheating, and as a countermeasure, an insulating material with good heat resistance and a winding material with a large cross-sectional area must be used. Therefore, there is a problem that the size, weight and cost are high.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has a small size, light weight, and low power consumption that suppresses a loss generated in a shield winding even when there is an external conductor near which a large current flows. The aim is to provide a costly current transformer.

[0006]

A current transformer according to the present invention divides a shield winding into four shield winding pieces and has a shield winding in a plane connecting a conductor through which a current to be measured flows and an outer conductor. This is the arrangement of the divided parts of the line. In the above, the shield winding pieces on both sides of the divided portion of the shield winding in the plane connecting the conductor and the outer conductor are separated from each other. In addition, a central portion of one shield winding piece is arranged in a plane connecting the conductor and the external conductor, and a series inductance is connected to the one shield winding piece.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows Embodiment 1 of the present invention.
FIG. 1 is an explanatory diagram showing a current transformer in FIG. 1, in which 1 is a conductor through which a current to be measured flows, 2 is an iron core provided in a ring shape so as to surround the conductor 1 and forms a magnetic path interlinking with the conductor 1; Reference numeral 3 denotes a shield winding wound substantially uniformly on the iron core 2 over the entire circumference, and is divided into four shield winding pieces 3a to 3d having the same number of turns. Although a secondary winding is also wound on the iron core 2, its illustration is omitted.

Reference numerals 4a and 4b denote connecting wires connecting the same polarity sides of the shield winding pieces 3a to 3d. Reference numeral 5 denotes an outer conductor arranged near and parallel to the conductor 1, for example, in pairs with the conductor 1. To form a reciprocating bus, or a combination of another conductor (not shown) to form a three-phase bus. The shield winding 3 is arranged so that the divided portion comes to a portion A closest to the outer conductor 5. That is,
The divided part of the shield winding 3 is arranged in a plane connecting the conductor 1 and the external conductor 5.

Next, the operation will be described. A current proportional to the measured current flowing through the conductor 1 flows through the secondary winding.
Using this current, current measurement, protection of the device, and the like are performed using an instrument and a protection relay (not shown). Since the shield winding pieces 3a to 3d have the same number of turns and are connected on the same polarity side, the induced current does not circulate due to the magnetic flux generated by the measured current.

On the other hand, the magnetic flux Φ generated by the current flowing through the outer conductor 5 enters the iron core 2. This magnetic flux enters from one part of the core 2 and escapes from the other part.
The direction of the magnetic flux and the magnetic flux density are different. Therefore, the induced voltages generated in the shield winding pieces 3a to 3d do not become the same,
A current flows through the shield winding pieces 3a to 3d so as to reduce the invasion magnetic flux. As a result, magnetic saturation of the iron core 2 due to the current of the outer conductor 5 is prevented, and the measurement error of the current transformer is prevented from increasing.

The shield winding pieces 3a and 3d of the shield winding 3 shown in FIG. 1 that are closest to the outer conductor 5 have a greater distance from the outer conductor 5 than the shield winding pieces 3a that are closest to FIG. As the orientation changes, the magnetic coupling with the external conductor 5 is weakened, and the induced current is suppressed.
In the experimental results, the distance between phases (distance between conductor 1 and outer conductor 5)
1100 mm, the diameter of the current transformer is 860 mm, the bus current (current of the conductor 1 and the outer conductor 5) is 30 kA, the number of turns of the shield winding 3 is 1500, and the cross-sectional diameter of the winding material of the shield winding 3 is 2.4 mm. In the winding arrangement of FIG.
The loss of W was reduced to 52 W when the winding arrangement shown in FIG. 1 was used.

Embodiment 2 FIG. FIG. 2 is an explanatory view showing a current transformer according to Embodiment 2 of the present invention. Reference numerals 5a and 5b denote external conductors disposed near and parallel to both ends of the conductor 1; , 5b constitute a three-phase bus. The outermost conductors 5a, 5a of the shield winding 3
The portions A and B close to b are divided portions.
That is, the divided portions of the shield winding 3 are arranged in a plane connecting the conductor 1 and the external conductors 5a and 5b. Then, the shield winding pieces 3a and 3d on both sides of the portion A are separated from each other, and a space where the shield winding 3 is not wound is formed therebetween. Shield winding pieces 3 on both sides of part B
The same applies to b and 3c. Part A, B
The shield winding 3 is wound substantially uniformly on the iron core 2 except for the portion where no shield winding is provided. 5c, 5d, 5
“e” is another external conductor constituting a three-phase bus, which is arranged in a plane parallel to the plane formed by the conductor 1 and the external conductors 5a and 5b. The rest is the same as in the first embodiment, and a description thereof will not be repeated.

In this configuration, the magnetic coupling between the outer conductor 5a and the shield winding pieces 3a and 3d and the magnetic coupling between the outer conductor 5b and the shield winding pieces 3b and 3c are different from those in the first embodiment. Further weakened, the induced current is suppressed,
The loss generated in the shield winding is reduced. Furthermore, since the closest portion C of the shield winding 3 is a divided portion of the shield winding 3 with respect to the penetration of magnetic flux generated by the current of the external conductor 5d of another three-phase bus, the shield winding piece 3
a, 3b, the shield winding pieces 3a, 3d of FIG.
Has the same effect as described above.

Embodiment 3 FIG. 3 is an explanatory view showing a current transformer according to Embodiment 3 of the present invention, in which a central portion of a shield winding piece 3 a closest to the external conductor 5 faces the external conductor 5. That is, the central portion of the shield winding piece 3a is arranged in a plane connecting the conductor 1 and the external conductor 5. 6 is a coil having an inductance,
It is connected to the shield winding piece 3a. The shield winding piece 3a is connected to the other shield windings 3b, 3c and 3d via the coil 6 by a connection wire 4b. The other parts are the same as those in the first embodiment, and a description thereof will be omitted.

In this configuration, since an inductance is added to the shield winding piece 3a closest to the outer conductor 5 and having strong magnetic coupling, the induced current of the shield winding piece 3a through which the induced current flows most is suppressed. In this embodiment, the shield winding 3 is divided into four, but may be divided into other plural parts such as six.

[0016]

Since the current transformer according to the present invention is constructed as described above, the induced current flowing through the shield winding is suppressed and the generated loss is reduced. Since a small winding material can be used, a current transformer having a small size, light weight, and low cost can be obtained. In the current transformer according to the present invention, the current flowing through the shield winding is reduced, and the shielding effect of the shield winding is reduced.
That is, the effect of preventing the core from being saturated by the intrusion of the magnetic flux generated by the current of the outer conductor and the error of the current transformer increasing is reduced. However, in the case where the shielding effect is already sufficient and the countermeasure for overheating of the shield winding is an important problem as a practical problem, the adoption of the current transformer according to the present invention has a great effect as a countermeasure. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a current transformer according to Embodiment 1 of the present invention.

FIG. 2 is an explanatory diagram showing a current transformer according to Embodiment 2 of the present invention.

FIG. 3 is an explanatory diagram showing a current transformer according to Embodiment 3 of the present invention.

FIG. 4 is an explanatory view showing a conventional current transformer.

[Explanation of symbols]

1 conductor, 2 iron core, 3 shield winding, 3a-3d
Shield winding piece, 4a, 4b connection wire, 5.5a-5d
Outer conductor, 6 coils.

Claims (3)

[Claims] An iron core surrounding a conductor through which a current to be measured flows, a secondary winding and a shield winding wound on the iron core, wherein the shield winding is formed by a plurality of shield winding pieces having the same number of turns In the current transformer in which the same polarity sides of the shield winding pieces are connected to each other, the shield winding is divided into four shield winding pieces, and the conductor and the conductor are arranged in parallel with each other. A current transformer, wherein a divided portion of the shield winding is arranged in a plane connecting an external conductor. 2. The current transformer according to claim 1, wherein shield winding pieces on both sides of a portion where the shield winding is divided in a plane connecting the conductor and the outer conductor are spaced apart from each other. 3. An iron core surrounding a conductor through which a current to be measured flows, a secondary winding and a shield winding wound on the iron core, and the shield winding is formed by a plurality of shield winding pieces having the same number of turns. In the current transformer in which the same polarity sides of the shield winding pieces are connected to each other, one shield winding piece is placed on a plane connecting the conductor and an external conductor arranged in parallel with the conductor. A current transformer having a central portion disposed therein, an inductance connected in series to the one shield winding piece, and connected to another shield winding piece via the inductance.