JP2004228176A

JP2004228176A - Zero-phase current transformer

Info

Publication number: JP2004228176A
Application number: JP2003011763A
Authority: JP
Inventors: Takahiro Kudo; 高裕工藤
Original assignee: Fuji Electric Holdings Ltd
Current assignee: Fuji Electric Co Ltd
Priority date: 2003-01-21
Filing date: 2003-01-21
Publication date: 2004-08-12

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zero-phase current transformer of a structure that has small size and high sensitivity as a detection means of grounding current flowing in the case that a grounding accident occurs or an electric shock exists in a transmission and distribution line. <P>SOLUTION: The zero-phase current transformer is composed by providing a second annular iron core arranging a magnetic sensor on the outer shell of a first annular iron core surrounding the periphery of a conductor in which current flows. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、送配電線路において地絡電流を検出する零相変流器に関する。
【０００２】
【従来の技術】
従来の電流トランス型零相変流器の概略構成図を図５に示す。図５において、環状鉄芯１３は、全周にわたって二次導体の出力巻線１４が巻かれている。また、環状鉄芯１３の中空部を貫通するように、それぞれＲ相、Ｓ相、Ｔ相である一次導体１ａ、１ｂ、１ｃが配置されている。環状鉄芯１３の材料には、パーマロイなどの高透磁率材料が通常使用される。しかし、電流トランス型零相変流器は、出力巻線１４を数千ターン巻き回す必要があるために、小型化に限界があるという問題があった。
【０００３】
そこで、従来の電流トランス型に代わるものとして、図６に示すように、環状鉄芯４００中に設けた切欠部５に磁気センサ２として高感度な磁気インピーダンス素子を配置するものがある（例えば、特許文献１参照）。
【０００４】
【特許文献１】
特開平１０−２３２２５９号公報（第２−３頁、第１−２図）
【０００５】
【発明が解決しようとする課題】
このように、従来における零相変流器では、電流トランス型の場合に、出力巻線により環状鉄芯内の磁束を周回積分するので、導体の位置による出力変化が少ないといった利点を有している反面、出力巻線を巻回することによる小型化に難があった。
また、環状鉄芯中に磁気センサを配置する構成の場合は、小型化が可能な反面、磁束を周回積分できないので、導体の位置による出力変化が大きく、各導体からのアンペールの法則で発生する磁束の影響を受け易いために残留電流が増大することで検出感度が低いという問題があった。
【０００６】
この発明の目的は、送配電線路において、地絡事故が生じたり感電があった場合に流れる地絡電流の検出手段として、小型で高感度となる構造の零相変流器を提供することである。
【０００７】
【課題を解決するための手段】
上記課題を解決するために、環状コアと、磁気センサとを有する零相変流器において、
径が異なる少なくとも２つの環状コアが、中心位置をほぼ同一にして配置され、環状コアのうち最内郭に位置する第一環状コアの中空部に電流を導く導体が配置され、第一環状コアの外側であり最外郭に位置する第二環状コアに少なくとも１つの磁気センサを位置させることにする。
この際に、第二環状コアに少なくとも１箇所の切欠部を設け、切欠部に少なくとも１つの前記磁気センサを位置させることにする。
【０００８】
または、第二環状コアに少なくとも１箇所の切断部を設け、切断部に少なくとも１つの前記磁気センサを位置させることにする。
さらに、磁気センサは磁気インピーダンス素子とする。
また、第二環状コアと、前記磁気センサとをシールド材で覆うことにする。
【０００９】
【発明の実施の形態】
以下、本発明を実施例に基づき説明する。図１は、本発明の実施例に係る零相変流器の構成図である。本実施例における零相変流器は、２つの径が異なる環状鉄芯のうち、内側に第一環状鉄芯３を配置し、その外側には中心が一致するように径の大きい第二環状鉄芯４を配置する。第一環状鉄芯３の内側には、被測定電流を流すための３相の一次導体（Ｒ相、Ｓ相、Ｔ相）１ａ、１ｂ、１ｃを通しており、第二環状鉄芯４には切欠部５を設けて、切欠部５の中に磁気センサ２を配置する。
【００１０】
検出原理は、次の通りである。１次Ｒ相導体１ａ、１次Ｓ相導体１ｂ、１次Ｔ相導体１ｃに流れる電流をそれぞれＩｒ、Ｉｓ、Ｉｔとする。
地絡による漏洩電流が発生していない状態である三相平衡状態では、電流ＩｒとＩｓとＩｔの総和は常に零となり、第二環状鉄芯４内に発生する磁束は互いに打ち消し合うため、磁気センサ２には出力されない。
しかし、地絡により漏洩電流が発生した場合は、各相の電流ＩｒとＩｓとＩｔの総和は零ではなくなり、第二環状鉄芯４内には漏洩電流に応じた磁束が発生し、磁気センサ２に出力される。
【００１１】
次に、特許文献１に開示された一次導体と磁気センサを設けた鉄芯の間に環状鉄芯がない図６の従来構造と、本発明による図１に示した構造とを比較し、第一環状鉄芯３の効果について説明する。表１には、本発明による零相変流器（本発明方式）と従来の零相変流器（従来方式）とを、平衡状態における残留出力と、地絡時の漏洩電流出力とを比較した結果を示す。この比較において使用した解析モデルは、本発明方式に対するモデルを図２に、従来方式に対するモデルを図７に示した。
【００１２】
【表１】

図２と図７に示した記号は、表１と同一であり、Ｉ_Ａは一次Ｒ相導体１ａに流れる電流値、Ｒ_ｇ１は本発明のモデルにおけるＲ相導体１ａと第一環状鉄芯３との磁気抵抗、Ｒ_ｇ２は本発明のモデルにおける第一環状鉄芯３と第二環状鉄芯４との磁気抵抗、Ｒ_ｇ３は従来モデルにおけるＲとＲｇ２の間にある空気の磁気抵抗、Ｒｃは第二環状鉄芯４または環状鉄心４００の周回方向の磁気抵抗、Ｒｓは第一環状鉄芯３の周回方向の磁気抵抗、Ｓｃは第二環状鉄芯４の断面積である。また、残留出力は、平衡時に磁気センサ２から見た三つの導体の幾何学的な差より発生する磁束密度である。
【００１３】
漏洩電流発生時は、第一環状鉄芯３の有無に関わらず、図２の第二環状鉄芯４または図７環状鉄芯４００の磁束密度は式（１）で表される。

すなわち、漏洩電流発生時の出力は、第一環状鉄芯３の磁気抵抗に関係なく、第二環状鉄芯４の磁気抵抗で決まる。
次に、残留出力に注目すると、図２に示す第一環状鉄芯３の有る場合の残留出力を式（２）で表される。

また、図７に示す第一環状鉄芯が無い場合の出力を式（３）に示す。
【００１４】

さらに、第一環状鉄３による磁束密度の減少率は式（４）で表せる。

従って、残留出力を小さくするための条件は、式（５）となる。

すなわち、式（６）で表せる。

第一環状鉄芯３を挿入した場合、Ｒ_ｇ１，Ｒ_ｇ２が大きくなったために、残留出力が小さくなる。
比較結果は、表１に示すように、３０ｍＡの漏洩電流発生時に得られる磁気センサでの出力は、本発明方式と従来方式とで差異はない。しかし、平衡時に磁気センサ２から見た三つの導体の幾何学的な差より発生する残留出力が従来方式では約１５０倍大きくなるので、従来方式と比較して図１で示した本発明方式は、漏洩電流検出感度を約１５０倍向上することが可能となる。すなわち、従来方式では、残留出力の影響が無ければ計測が可能であるが、残留出力の影響が大きすぎて測定が困難である。これに対し、本発明では、磁気センサによる残留出力の影響を１／１５０に下げることが可能となったため、零相変流器としての検出感度が１５０倍に向上した。
【００１５】
図３は、本発明の別の実施例に係る零相変流器の構成図である。本実施例における図１との差異は、第二環状鉄芯４０を切断した切断部５０を設け、切断部５０に磁気センサ２を配置していることにある。
図４には、図１および図３における第二環状鉄芯４、４０にシールド６を用いた場合の構成例を示す。シールド６は、図４のように第二環状鉄芯４、４０の内側と外側配置しても良いし、また第二環状鉄芯４、４０の外側と、第一環状鉄芯３の外側とに配置しても良い。さらに、シールド６は、外部磁界の影響を遮蔽するために用いるため、使用環境に応じて用いても良いし、用いなくてもよい。
【００１６】
図１及び図３に示した通り、本発明による零相変流器においては、前記導体１ａ、１ｂ、１ｃに導かれた電流の漏洩電流を前記磁気センサ２で検出するが、磁気センサ２の検知磁界は数Ａ／ｍと微小であるので、ホール素子や磁気抵抗素子では検出が困難なため、高感度な磁気センサである磁気インピーダンス素子を使用することが望ましい。
【００１７】
【発明の効果】
この発明では、電流が通流する導体の周囲を取巻く第一の環状鉄芯の外郭に、磁気センサを配置した第二の環状鉄芯を備えることで零相変流器を構成したので、以下の効果が得られる。
従来の電流トランス型にように、出力巻線を数千ターン巻き回す必要がないので、小型・低コスト化が可能である。
また、センサを設けた環状鉄芯の中空部に導体を配置しただけの従来方式に比べ、３相平衡時の残留出力を大幅に低減することができるため、検出感度が向上し、実用環境下での支障となっていた測定が困難であることの問題を解決できるセンサを提供できる。
【００１８】
さらに、磁気センサに高感度な磁気インピーダンス素子を用いることで、検出感度が向上し、微弱な漏洩電流検出が可能となる。
【図面の簡単な説明】
【図１】本発明の実施例に係る零相変流器の構成図
【図２】本発明の零相変流器の解析モデル図
【図３】本発明の別の実施例に係る零相変流器の構成図
【図４】本発明の実施例に係る零相変流器のシールド構成図
【図５】従来の電流トランス型零相変流器の概略構成図
【図６】従来のセンサを設けた環状鉄芯を用いた零相変流器の構成図
【図７】従来の零相変流器の解析モデル図
【符号の説明】
１ａ：１次（Ｒ相）導体
１ｂ：１次（Ｓ相）導体
１ｃ：１次（Ｔ相）導体
２：磁気センサ
３：第一環状鉄心
４、４０：第二環状鉄心
５：切欠部
５０：切断部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a zero-phase current transformer for detecting a ground fault current in a transmission and distribution line.
[0002]
[Prior art]
FIG. 5 shows a schematic configuration diagram of a conventional current transformer type zero-phase current transformer. In FIG. 5, an annular core 13 has an output winding 14 of a secondary conductor wound all around. The primary conductors 1a, 1b, and 1c of the R phase, the S phase, and the T phase are arranged so as to penetrate the hollow portion of the annular iron core 13. As the material of the annular iron core 13, a high magnetic permeability material such as permalloy is usually used. However, the current transformer type zero-phase current transformer has a problem that there is a limit to miniaturization because the output winding 14 needs to be wound several thousand turns.
[0003]
Therefore, as an alternative to the conventional current transformer type, as shown in FIG. 6, there is a type in which a high-sensitivity magnetic impedance element is arranged as a magnetic sensor 2 in a notch 5 provided in an annular iron core 400 (for example, Patent Document 1).
[0004]
[Patent Document 1]
JP-A-10-232259 (page 2-3, FIG. 1-2)
[0005]
[Problems to be solved by the invention]
As described above, in the conventional zero-phase current transformer, in the case of a current transformer type, the output winding integrates the magnetic flux in the annular iron core in an orbital manner. On the other hand, it was difficult to reduce the size by winding the output winding.
In the case of a configuration in which a magnetic sensor is arranged in a ring-shaped iron core, the size can be reduced, but the magnetic flux cannot be circulated, so that the output varies greatly depending on the position of the conductor, which is generated by Ampere's law from each conductor. There is a problem that the detection sensitivity is low due to an increase in the residual current because of being easily affected by the magnetic flux.
[0006]
An object of the present invention is to provide a zero-phase current transformer having a small and highly sensitive structure as a means for detecting a ground fault current flowing when a ground fault occurs or an electric shock occurs in a transmission and distribution line. is there.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, in a zero-phase current transformer having an annular core and a magnetic sensor,
At least two annular cores having different diameters are arranged so that their center positions are substantially the same, and a conductor for conducting a current is arranged in a hollow portion of the first annular core located at the innermost position among the annular cores. And at least one magnetic sensor is located on the outermost second annular core.
At this time, at least one notch is provided in the second annular core, and at least one magnetic sensor is located in the notch.
[0008]
Alternatively, at least one cut portion is provided in the second annular core, and at least one magnetic sensor is located at the cut portion.
Further, the magnetic sensor is a magnetic impedance element.
Further, the second annular core and the magnetic sensor are covered with a shield material.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on examples. FIG. 1 is a configuration diagram of a zero-phase current transformer according to an embodiment of the present invention. The zero-phase current transformer in the present embodiment has a first annular iron core 3 disposed inside of two annular iron cores having different diameters, and a second annular iron core having a large diameter on the outer side so that the centers thereof coincide with each other. The iron core 4 is arranged. A three-phase primary conductor (R-phase, S-phase, T-phase) 1a, 1b, 1c for passing a current to be measured is passed through the inside of the first annular iron core 3, and the second annular iron core 4 is notched. The magnetic sensor 2 is disposed in the notch 5 by providing the portion 5.
[0010]
The detection principle is as follows. The currents flowing through the primary R-phase conductor 1a, the primary S-phase conductor 1b, and the primary T-phase conductor 1c are Ir, Is, and It, respectively.
In a three-phase equilibrium state in which no leakage current due to a ground fault occurs, the sum of the currents Ir, Is and It is always zero, and the magnetic fluxes generated in the second annular iron core 4 cancel each other out. No signal is output to the sensor 2.
However, when a leakage current occurs due to a ground fault, the sum of the currents Ir, Is, and It of each phase is not zero, and a magnetic flux corresponding to the leakage current is generated in the second annular iron core 4, and the magnetic sensor 2 is output.
[0011]
Next, a comparison was made between the conventional structure shown in FIG. 6 having no annular iron core between the primary conductor disclosed in Patent Document 1 and the iron core provided with the magnetic sensor, and the structure shown in FIG. 1 according to the present invention. The effect of the one-ring iron core 3 will be described. Table 1 compares the residual output in a balanced state and the leakage current output in the case of a ground fault between the zero-phase current transformer according to the present invention (the method of the present invention) and the conventional zero-phase current transformer (the conventional method). The results obtained are shown. The analysis model used in this comparison is shown in FIG. 2 for the model of the present invention, and FIG. 7 for the model of the conventional method.
[0012]
[Table 1]

Symbols shown in 2 and 7 are the same as in Table 1, I _A is the current value flowing through the primary R-phase conductor 1a, R _g1 is R phase conductor 1a and the first annular iron core 3 in a model of the present invention reluctance, R _g2 magnetoresistance, R _g3 magnetic resistance of the air which is between the R and Rg2 of the conventional model of the first annular iron core 3 in a model of the present invention and the second annular iron core 4, Rc and Is the magnetic resistance of the second annular iron core 4 or the annular iron core 400 in the circumferential direction, Rs is the magnetic resistance of the first annular iron core 3 in the circumferential direction, and Sc is the cross-sectional area of the second annular iron core 4. The residual output is a magnetic flux density generated due to a geometrical difference between three conductors viewed from the magnetic sensor 2 at the time of equilibrium.
[0013]
When a leakage current occurs, the magnetic flux density of the second annular iron core 4 of FIG. 2 or the annular iron core 400 of FIG. 7 is expressed by equation (1) regardless of the presence or absence of the first annular iron core 3.

That is, the output when the leakage current occurs is determined by the magnetic resistance of the second annular iron core 4 irrespective of the magnetic resistance of the first annular iron core 3.
Next, focusing on the residual output, the residual output when the first annular iron core 3 shown in FIG.

The output when the first annular iron core shown in FIG. 7 is not provided is shown in Expression (3).
[0014]

Further, the reduction rate of the magnetic flux density due to the first annular iron 3 can be expressed by equation (4).

Therefore, the condition for reducing the residual output is represented by the following equation (5).

That is, it can be expressed by equation (6).

When the first annular iron core 3 is inserted, the residual output decreases because R _g1 and R _g2 increase.
As shown in Table 1, as shown in Table 1, the output of the magnetic sensor obtained when a leakage current of 30 mA occurs is not different between the method of the present invention and the conventional method. However, the residual output generated due to the geometrical difference between the three conductors as viewed from the magnetic sensor 2 at the time of equilibrium is about 150 times larger in the conventional method, so the method of the present invention shown in FIG. Thus, the leakage current detection sensitivity can be improved about 150 times. That is, in the conventional method, measurement is possible if there is no influence of the residual output, but measurement is difficult because the influence of the residual output is too large. On the other hand, in the present invention, since the influence of the residual output by the magnetic sensor can be reduced to 1/150, the detection sensitivity as a zero-phase current transformer has been improved 150 times.
[0015]
FIG. 3 is a configuration diagram of a zero-phase current transformer according to another embodiment of the present invention. The difference from FIG. 1 in the present embodiment lies in that a cutting portion 50 is provided by cutting the second annular iron core 40, and the magnetic sensor 2 is arranged in the cutting portion 50.
FIG. 4 shows a configuration example in which the shield 6 is used for the second annular iron cores 4 and 40 in FIGS. 1 and 3. The shield 6 may be disposed inside and outside the second annular iron cores 4 and 40 as shown in FIG. 4, or may be disposed outside the second annular iron cores 4 and 40 and outside the first annular iron core 3. May be arranged. Furthermore, since the shield 6 is used to shield the influence of an external magnetic field, it may or may not be used depending on the use environment.
[0016]
As shown in FIGS. 1 and 3, in the zero-phase current transformer according to the present invention, the leakage current of the current guided to the conductors 1 a, 1 b, and 1 c is detected by the magnetic sensor 2. Since the detection magnetic field is as small as several A / m, it is difficult to detect with a Hall element or a magnetoresistive element. Therefore, it is desirable to use a magnetic impedance element which is a highly sensitive magnetic sensor.
[0017]
【The invention's effect】
In the present invention, a zero-phase current transformer is configured by providing a second annular iron core in which a magnetic sensor is arranged on an outer periphery of a first annular iron core surrounding a conductor through which a current flows. The effect of is obtained.
Unlike the conventional current transformer type, it is not necessary to wind the output winding several thousand turns, so that the size and cost can be reduced.
In addition, compared to the conventional method in which a conductor is simply placed in the hollow part of the annular iron core provided with the sensor, the residual output at the time of three-phase equilibrium can be greatly reduced, so that the detection sensitivity is improved and the practical environment is improved. A sensor that can solve the problem of difficulty in measurement, which has been an obstacle to the measurement, can be provided.
[0018]
Furthermore, by using a high-sensitivity magneto-impedance element for the magnetic sensor, the detection sensitivity is improved, and weak leakage current can be detected.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a zero-phase current transformer according to an embodiment of the present invention. FIG. 2 is an analysis model diagram of a zero-phase current transformer of the present invention. FIG. 3 is a zero-phase current according to another embodiment of the present invention. FIG. 4 is a block diagram of a zero-phase current transformer according to an embodiment of the present invention. FIG. 5 is a schematic diagram of a conventional current transformer type zero-phase current transformer. Configuration diagram of a zero-phase current transformer using an annular iron core provided with a sensor [FIG. 7] Analysis model diagram of a conventional zero-phase current transformer
1a: Primary (R phase) conductor 1b: Primary (S phase) conductor 1c: Primary (T phase) conductor 2: Magnetic sensor 3: First annular iron core 4, 40: Second annular iron core 5: Notch 50 : Cutting part

Claims

In a zero-phase current transformer having an annular core and a magnetic sensor,
At least two annular cores having different diameters are arranged so that their center positions are substantially the same, and a conductor that guides a current to a hollow portion of the first annular core located at the innermost position among the annular cores is arranged, A zero-phase current transformer, wherein at least one magnetic sensor is located on a second annular core located outside and outside the one annular core.

The zero-phase current transformer according to claim 1, wherein at least one notch is provided in the second annular core, and at least one magnetic sensor is located in the notch.

The zero-phase current transformer according to claim 1, wherein at least one cut portion is provided in the second annular core, and at least one of the magnetic sensors is located at the cut portion.

The zero-phase current transformer according to any one of claims 1 to 3, wherein the magnetic sensor is a magnetic impedance element.

The zero-phase current transformer according to any one of claims 1 to 3, wherein the second annular core and the magnetic sensor are covered with a shield material.