JP7623684B2

JP7623684B2 - Loop impedance tester and loop impedance measuring method

Info

Publication number: JP7623684B2
Application number: JP2021034044A
Authority: JP
Inventors: 篤和田
Original assignee: 共立電気計器株式会社
Priority date: 2021-03-04
Filing date: 2021-03-04
Publication date: 2025-01-29
Anticipated expiration: 2041-03-04
Also published as: JP2022134707A

Description

本発明は、ループインピーダンステスタ及びループインピーダンス測定方法に関する。 The present invention relates to a loop impedance tester and a loop impedance measurement method.

主電源（商用電源）の交流電圧を供給する配電設備において、活線Ｌ－接地線Ｅ間のループインピーダンスの値が、新規電気配線時や、配線変更時、定期点検時等において測定され、その値が安全上規定値内であることの確認が行われている。
活線Ｌ、中性線Ｎ及び接地線Ｅの３線を含む図１の電力線路において、活線Ｌ－接地線Ｅ間のループインピーダンスは、活線ＬのインピーダンスＺ_Ｌと接地線ＥのインピーダンスＺ_Ｅとの和（Ｚ_Ｌ＋Ｚ_Ｅ）である。 In power distribution equipment that supplies AC voltage from the main power source (commercial power source), the loop impedance between the live line L and the ground line E is measured when new electrical wiring is installed, when wiring is changed, during regular inspections, etc., and it is confirmed that the value is within safety specified values.
In the power line of FIG. 1 including three wires, a live wire L, a neutral wire N, and a ground wire E, the loop impedance between the live wire L and the ground wire E is the sum of the impedance ZL of the live wire _L and the impedance _ZE of the ground wire E ( _ZL + _ZE ).

通常、配電設備１４には漏電遮断器３が設置されている。活線Ｌと接地線Ｅとが短絡した場合、接地線Ｅに漏えい電流が流れ、漏電遮断器３が活線Ｌと中性線Ｎとの電流差を検出してトリップし、回路を遮断することで感電及び火災が防止される。しかし、活線Ｌ－接地線Ｅ間のループインピーダンスの値が高い場合は、漏電遮断器３が動作するだけの充分な漏えい電流が流れないため漏電遮断器３が動作しない。その場合、感電や火災等の事故につながることが考えられる。活線Ｌ－接地線Ｅ間のループインピーダンスの確認が必要なのはこのためである。 Normally, a ground fault circuit interrupter 3 is installed in the power distribution equipment 14. If the live line L and the ground wire E are short-circuited, a leakage current flows through the ground wire E, and the ground fault circuit interrupter 3 detects the current difference between the live line L and the neutral wire N and trips, interrupting the circuit to prevent electric shock and fire. However, if the loop impedance between the live line L and the ground wire E is high, the ground fault circuit interrupter 3 will not operate because there is not enough leakage current to operate it. In that case, it is possible that this could lead to accidents such as electric shock or fire. This is why it is necessary to check the loop impedance between the live line L and the ground wire E.

従来は、活線Ｌ－接地線Ｅ間に主電源２のエネルギーを用いて大きな電流を流し、その電圧降下を検出することで活線Ｌ－接地線Ｅ間のループインピーダンスを測定していた。活線Ｌ－接地線Ｅ間のループインピーダンスは小さいもので０．０１Ω単位の測定をする必要があるが、この方法で０．０１Ω単位の測定をするためには、活線Ｌ－接地線Ｅ間に６Ａ程度の大きな電流を流して電圧降下を検出する必要がある。この場合、配電設備１４に設置されている漏電遮断器３がトリップしてしまう。そこで、漏電遮断器３の電源側と負荷側とを電線でつないで漏電遮断器３をバイパスし、漏電遮断器３がトリップしないようにして測定を実施する必要があり、作業に時間を要していた。 Conventionally, the loop impedance between the live line L and the ground line E was measured by passing a large current between the live line L and the ground line E using the energy of the main power source 2 and detecting the voltage drop. The loop impedance between the live line L and the ground line E is small and needs to be measured in units of 0.01 Ω, but to measure in units of 0.01 Ω using this method, a large current of about 6 A needs to be passed between the live line L and the ground line E to detect the voltage drop. In this case, the earth leakage circuit breaker 3 installed in the distribution equipment 14 will trip. Therefore, it is necessary to bypass the earth leakage circuit breaker 3 by connecting the power supply side and the load side of the earth leakage circuit breaker 3 with an electric wire and perform the measurement without tripping the earth leakage circuit breaker 3, which takes time.

これを回避する手段として、特許文献１（特許第４２９７７７４号公報）では、高電流を活線Ｌ－接地線Ｅ間ではなく活線Ｌ－中性線Ｎ間に流したときの測定値と、中性線Ｎ－接地線Ｅ間に１５ｍＡ以下の漏電遮断器３が動作しない低い電流を流したときの測定値とを用いることで、活線Ｌ－接地線Ｅ間のループインピーダンスを算出する方法が開示されている。しかし、この方法であると、中性線Ｎ－接地線Ｅ間に１５ｍＡ以下の電流を流すためのエネルギー供給源（電流源）をループインピーダンステスタ内に設ける必要があり、電子部品の増加及びコストアップにつながっていた。また、エネルギー供給源として電池を用いることが考えられるが、配電設備１４の中性線Ｎ－接地線Ｅ間の信号には、多くの場合ノイズが重畳しており、例えばノイズが１０Ｖ存在した場合は、１０Ｖ以上の出力が可能な電流源を構成する必要がある。電圧１．５Ｖの乾電池等から高い出力電圧を発生させるにはループインピーダンステスタの小型化を考慮すると限界があることから、測定できない配電設備も存在した。 As a means to avoid this, Patent Document 1 (Patent Publication No. 4297774) discloses a method for calculating the loop impedance between the live line L and the ground line E by using a measurement value when a high current flows between the live line L and the neutral line N, not between the live line L and the ground line E, and a measurement value when a low current of 15 mA or less that does not activate the earth leakage circuit breaker 3 flows between the neutral line N and the ground line E. However, this method requires an energy supply source (current source) to be provided in the loop impedance tester to flow a current of 15 mA or less between the neutral line N and the ground line E, which leads to an increase in electronic components and an increase in costs. In addition, while it is possible to use a battery as an energy supply source, noise is often superimposed on the signal between the neutral line N and the ground line E of the power distribution equipment 14, and if there is noise of 10 V, for example, it is necessary to configure a current source capable of outputting 10 V or more. There is a limit to generating a high output voltage from a dry cell with a voltage of 1.5 V when considering the miniaturization of the loop impedance tester, and there were some power distribution equipment that could not be measured.

さらに、特許文献２（特許第６７８８２５９号公報）では、中性線Ｎを使用することなく、活線Ｌ－接地線Ｅ間に漏電遮断器３が動作しない１５ｍＡ以下の低い電流を流して測定を行う方法が開示されている。しかし、０．０１Ω単位でループインピーダンスを測定する場合、１５ｍＡ×０．０１Ω＝０．１５ｍＶの測定信号を主電源２の２３０Ｖ（欧州の場合）の電圧から分離する必要があり、Ｓ／Ｎ比が非常に小さい（信号に対するノイズの比が大きい）ことから、測定結果のバラツキが大きく信頼性に欠ける。その対策として多くのデータを取得し平均処理することで信頼性を高めることが考えられる。しかし、測定に１０秒以上の時間が必要となってしまい、点検業務の作業効率の低下につながり、また、最終的に得られた結果も特許文献１ほどの信頼性を得ることが困難であった。 Furthermore, Patent Document 2 (Patent Publication No. 6788259) discloses a method of measuring by passing a low current of 15 mA or less between the live line L and the ground line E, which does not operate the earth leakage circuit breaker 3, without using a neutral line N. However, when measuring loop impedance in units of 0.01 Ω, it is necessary to separate the measurement signal of 15 mA x 0.01 Ω = 0.15 mV from the voltage of the main power supply 2 of 230 V (in Europe), and since the S/N ratio is very small (the ratio of noise to signal is large), the measurement results vary greatly and are unreliable. As a countermeasure, it is possible to increase reliability by acquiring a large amount of data and averaging it. However, it takes more than 10 seconds to measure, which leads to a decrease in the efficiency of the inspection work, and it is difficult to obtain the final results with the same reliability as those of Patent Document 1.

特許第４２９７７７４号公報Patent No. 4297774 特許第６７８８２５９号公報Patent No. 6788259

そこで本発明は、コストを抑制しつつ、信頼性の高いループインピーダンステスタ及びループインピーダンス測定方法を提供することを目的とする。 The present invention aims to provide a highly reliable loop impedance tester and loop impedance measurement method while keeping costs down.

本発明の１つの観点に係るループインピーダンステスタ１は、第１の周波数ｆｍの周波数成分を含む交流電圧を供給する活線Ｌと、中性線Ｎと、接地線Ｅと、を含む電力線路における活線Ｌ及び接地線Ｅの間のループインピーダンスＺ_ＬＥを測定するために、活線Ｌ、中性線Ｎ、及び接地線Ｅに接続されるループインピーダンステスタであって、第１の計測回路１５と、電流生成部６と、第２の計測回路であるＶ_ＮＥ電圧取得回路９と、フィルター回路１０と、計測制御手段１２と、を含む。
第１の計測回路１５は、活線Ｌ及び中性線Ｎの間に負荷を接続しない状態での活線Ｌ及び接地線Ｅの間の第１の電圧値Ｖ_ＬＥ１と、活線Ｌ及び中性線Ｎの間に負荷抵抗Ｒを接続した状態での、活線Ｌ及び中性線Ｎの間の第２の電圧値Ｖ_ＬＮ２及び活線Ｌ及び接地線Ｅの間の第３の電圧値Ｖ_ＬＥ２と、を計測する。
電流生成部６は、活線Ｌ及び接地線Ｅの間に第１の周波数ｆｍより低い第２の周波数ｆｓの周波数成分を含む第１の交流電流Ｉ_ＬＥ１を流す。
Ｖ_ＮＥ電圧取得回路９は、活線Ｌ及び接地線Ｅの間に第１の交流電流Ｉ_ＬＥ１を流した状態での中性線Ｎ及び接地線Ｅの間の第１の交流電圧Ｖ_ＮＥ１を計測する。
フィルター回路１０は、第１の交流電圧Ｖ_ＮＥ１から第１の周波数ｆｍの周波数成分を低減した第２の交流電圧Ｖ_ＮＥ２を取り出す。
計測制御手段１２は、負荷抵抗Ｒの値と第１、第２及び第３の電圧値Ｖ_ＬＥ１、Ｖ_ＬＮ２及びＶ_ＬＥ２とから活線ＬのインピーダンスＺ_Ｌを算出し、第１の交流電流Ｉ_ＬＥ１の電流値及び第２の交流電圧Ｖ_ＮＥ２の電圧値から接地線ＥのインピーダンスＺ_Ｅを算出し、インピーダンスＺ_Ｌ及びＺ_ＥからループインピーダンスＺ_ＬＥを算出する。 A loop impedance tester 1 according to one aspect of the present invention is a loop impedance tester connected to a live line L, a neutral line N, and a ground line E in order to measure a loop impedance _ZLE between the live line L and the ground line E in a power line including the live line L supplying an AC voltage including a frequency component of a first frequency fm, the neutral line N, and the ground line E, and includes a first measurement circuit 15, a current generating unit 6, a _VNE voltage acquisition circuit 9 which is a second measurement circuit, a filter circuit 10, and measurement control means 12.
The first measurement circuit 15 measures a first voltage value _VLE1 between the live line L and the ground line E in a state where no load is connected between the live line L and the neutral line N, and a second voltage value _VLN2 between the live line L and the neutral line N and a third voltage value _VLE2 between the live line L and the ground line E in a state where a load resistance R is connected between the live line L and the neutral line N.
The current generating unit 6 causes a first AC current _ILE1 containing a frequency component of a second frequency fs lower than the first frequency fm to flow between the live line L and the ground line E.
The _VNE voltage acquisition circuit 9 measures a first AC voltage _VNE1 between the neutral line N and the ground line E in a state in which a first AC current _ILE1 is flowing between the live line L and the ground line E.
The filter circuit 10 extracts a second AC voltage _VNE2 by reducing the frequency component of the first frequency fm from the first AC voltage _VNE1 .
The measurement control means 12 calculates the impedance _ZL of the live line L from the value of the load resistance R and the first, second, and third voltage values _VLE1 , _VLN2 , and _VLE2 , calculates the impedance _ZE of the ground line E from the current value of the first AC current _ILE1 and the voltage value of the second AC voltage _VNE2 , and calculates the loop impedance _ZLE from the impedances _ZL and _ZE .

図１は、配電設備１４に接続された本発明の実施形態に係るループインピーダンステスタ１の概略構成を示す回路図である。FIG. 1 is a circuit diagram showing a schematic configuration of a loop impedance tester 1 according to an embodiment of the present invention that is connected to a power distribution facility 14. 図２は、本発明の実施形態における活線ＬのインピーダンスＺ_Ｌの測定について説明する回路図である。FIG. 2 is a circuit diagram for explaining measurement of the impedance _ZL of the live line L in the embodiment of the present invention. 図３は、本発明の実施形態における活線ＬのインピーダンスＺ_Ｌの測定について説明する回路図である。FIG. 3 is a circuit diagram for explaining measurement of the impedance _ZL of the live line L in the embodiment of the present invention. 図４は、本発明の実施形態における接地線ＥのインピーダンスＺ_Ｅの測定について説明する回路図である。FIG. 4 is a circuit diagram for explaining measurement of the impedance Z _E of the ground line E in the embodiment of the present invention. 図５（Ａ）～図５（Ｄ）は、本発明の実施形態における接地線ＥのインピーダンスＺ_Ｅの測定手順を説明する波形図である。5A to 5D are waveform diagrams illustrating a procedure for measuring the impedance Z _E of the ground line E in the embodiment of the present invention. 図６は、図１及び図４に示される電流生成部６の詳細を示す回路図である。FIG. 6 is a circuit diagram showing details of the current generating unit 6 shown in FIGS. 図７（Ａ）～図７（Ｈ）は、電流生成部６の動作を説明する波形図である。7A to 7H are waveform diagrams illustrating the operation of the current generating unit 6. In FIG.

以下、本発明の実施形態を、図面を参照しながら詳細に説明する。以下に説明される実施形態は、本発明の一例を示すものであって、本発明の内容を限定するものではない。また、実施形態で説明される構成及び動作の全てが本発明の構成及び動作として必須であるとは限らない。なお、同一の構成要素には同一の参照符号を付して、重複する説明を省略する。 The following describes in detail an embodiment of the present invention with reference to the drawings. The embodiment described below is merely an example of the present invention, and does not limit the content of the present invention. Furthermore, not all of the configurations and operations described in the embodiment are necessarily essential as the configurations and operations of the present invention. Note that the same components are given the same reference symbols, and duplicated explanations will be omitted.

＜１．ループインピーダンステスタ１の構成＞
図１は、配電設備１４に接続された本発明の実施形態に係るループインピーダンステスタ１の概略構成を示す回路図である。活線ＬはインピーダンスＺ_Ｌを有し、中性線ＮはインピーダンスＺ_Ｎを有し、接地線ＥはインピーダンスＺ_Ｅを有する。インピーダンスＺ_Ｌは第１のインピーダンスに相当し、インピーダンスＺ_Ｅは第２のインピーダンスに相当する。 1. Configuration of loop impedance tester 1
1 is a circuit diagram showing a schematic configuration of a loop impedance tester 1 according to an embodiment of the present invention, which is connected to a power distribution facility 14. A live line L has an impedance _ZL , a neutral line N has an impedance _ZN , and a ground line E has an impedance _ZE . The impedance _ZL corresponds to a first impedance, and the impedance _ZE corresponds to a second impedance.

ループインピーダンステスタ１は、活線Ｌに接続されるＬ端子４_Ｌと、中性線Ｎに接続されるＮ端子４_Ｎと、接地線Ｅに接続されるＥ端子４_Ｅと、を含む。ループインピーダンステスタ１は、さらに、スイッチＳＷ１と、負荷抵抗Ｒと、電流生成部６と、Ｖ_ＬＮ電圧取得回路７と、Ｖ_ＬＥ電圧取得回路８と、Ｖ_ＮＥ電圧取得回路９と、フィルター回路１０と、Ａ／Ｄ変換回路１１と、計測制御手段１２と、入出力手段１３と、を含む。Ｖ_ＬＮ電圧取得回路７及びＶ_ＬＥ電圧取得回路８は第１の計測回路１５を構成する。Ｖ_ＮＥ電圧取得回路９は第２の計測回路を構成する。 The loop impedance tester 1 includes an L terminal _4L connected to a live line L, an N terminal _4N connected to a neutral line N, and an E terminal _4E connected to a ground line E. The loop impedance tester 1 further includes a switch SW1, a load resistor R, a current generating unit 6, a _VLN voltage acquisition circuit 7, a _VLE voltage acquisition circuit 8, a _VNE voltage acquisition circuit 9, a filter circuit 10, an A/D conversion circuit 11, a measurement control means 12, and an input/output means 13. The _VLN voltage acquisition circuit 7 and the _VLE voltage acquisition circuit 8 constitute a first measurement circuit 15. The _VNE voltage acquisition circuit 9 constitutes a second measurement circuit.

スイッチＳＷ１及び負荷抵抗Ｒは、活線Ｌ－中性線Ｎ間に直列に接続されている。スイッチＳＷ１は通常オフであり通電を行わない。スイッチＳＷ１は活線ＬのインピーダンスＺ_Ｌを測定する際にオンにすることで主電源２を負荷抵抗Ｒに接続し、活線Ｌ－中性線Ｎ間に電流Ｉ_ＬＮ（図３）を流す。 The switch SW1 and the load resistance R are connected in series between the live line L and the neutral line N. The switch SW1 is normally off and does not conduct electricity. When measuring the impedance _ZL of the live line L, the switch SW1 is turned on to connect the main power supply 2 to the load resistance R and cause a current I _LN (FIG. 3) to flow between the live line L and the neutral line N.

Ｖ_ＬＮ電圧取得回路７は活線Ｌ－中性線Ｎ間に接続され、スイッチＳＷ１がオフ状態の時の活線Ｌ－中性線Ｎ間の電圧値Ｖ_ＬＮ１（図２）と、スイッチＳＷ１がオン状態の時の活線Ｌ－中性線Ｎ間の電圧値である第２の電圧値Ｖ_ＬＮ２（図３）とを取得する。 The V _LN voltage acquisition circuit 7 is connected between the live line L and the neutral line N, and acquires a voltage value V _LN1 (Figure 2) between the live line L and the neutral line N when the switch SW1 is in the off state, and a second voltage value V _LN2 (Figure 3), which is the voltage value between the live line L and the neutral line N when the switch SW1 is in the on state.

Ｖ_ＬＥ電圧取得回路８は活線Ｌ－接地線Ｅ間に接続され、スイッチＳＷ１がオフ状態の時の活線Ｌ－接地線Ｅ間の電圧値である第１の電圧値Ｖ_ＬＥ１（図２）と、スイッチＳＷ１がオン状態の時の活線Ｌ－接地線Ｅ間の電圧値である第３の電圧値Ｖ_ＬＥ２（図３）とを取得する。 The _VLE voltage acquisition circuit 8 is connected between the live line L and the ground line E, and acquires a first voltage value _VLE1 (Figure 2) which is the voltage value between the live line L and the ground line E when the switch SW1 is in the off state, and a third voltage value _VLE2 (Figure 3) which is the voltage value between the live line L and the ground line E when the switch SW1 is in the on state.

電流生成部６は活線Ｌ－接地線Ｅ間に接続されている。電流生成部６は通常オフであり通電を行わない。接地線ＥのインピーダンスＺ_Ｅの測定を行う際にオンにすることで、主電源２のエネルギーを利用し、活線Ｌ－接地線Ｅ間に第１の交流電流Ｉ_ＬＥ１（図４）を流す。第１の交流電流Ｉ_ＬＥ１の電流値は、漏電遮断器３を動作させる閾値よりも低い１５ｍＡ以下に制限される。 The current generating unit 6 is connected between the live line L and the ground line E. The current generating unit 6 is normally off and does not pass current. By turning it on when measuring the impedance Z _E of the ground line E, the energy of the main power supply 2 is used to flow a first AC current I _LE1 (FIG. 4) between the live line L and the ground line E. The current value of the first AC current I _LE1 is limited to 15 mA or less, which is lower than the threshold value that activates the earth leakage breaker 3.

Ｖ_ＮＥ電圧取得回路９は中性線Ｎ－接地線Ｅ間に接続され、電流生成部６がオン状態の時の中性線Ｎ－接地線Ｅ間の電圧である第１の交流電圧Ｖ_ＮＥ１（図４）を取得する。 The V _NE voltage acquisition circuit 9 is connected between the neutral line N and the ground line E, and acquires a first AC voltage V _NE1 (FIG. 4) which is the voltage between the neutral line N and the ground line E when the current generation unit 6 is in the on state.

フィルター回路１０は、Ｖ_ＮＥ電圧取得回路９で取得された第１の交流電圧Ｖ_ＮＥ１からノイズ成分を取り除くフィルターであり、第２の周波数ｆｓの電圧信号からなる第２の交流電圧Ｖ_ＮＥ２（図４）を出力する。 The filter circuit 10 is a filter that removes noise components from the first AC voltage V _NE1 acquired by the V _NE voltage acquisition circuit 9, and outputs a second AC voltage V _NE2 (FIG. 4) that is a voltage signal of a second frequency fs.

Ａ／Ｄ変換回路１１は、Ｖ_ＬＮ電圧取得回路７、Ｖ_ＬＥ電圧取得回路８及びフィルター回路１０の出力信号の振幅の大きさを測定しデジタル信号に変換する。 The A/D conversion circuit 11 measures the magnitude of the amplitude of the output signals of the _VLN voltage acquisition circuit 7, the _VLE voltage acquisition circuit 8 and the filter circuit 10, and converts them into digital signals.

計測制御手段１２は、スイッチＳＷ１及び電流生成部６を制御するほか、Ａ／Ｄ変換回路１１による測定値に基づいて、活線Ｌ－接地線Ｅ間のループインピーダンスＺ_ＬＥを算出する。 The measurement control means 12 controls the switch SW 1 and the current generating unit 6 , and also calculates the loop impedance Z _LE between the live line L and the ground line E based on the value measured by the A/D conversion circuit 11 .

入出力手段１３は、表示用ディスプレイ、表示ランプ、スピーカ、ボタン、操作パネルの全て又はいずれかを備える。入出力手段１３は、測定結果の表示による視覚報知、又は音声出力による聴覚報知を行い、さらに使用者の操作入力による各種試験モードの切り替えの指示を受け付ける。 The input/output means 13 includes all or any of the following: a display, an indicator lamp, a speaker, buttons, and an operation panel. The input/output means 13 provides a visual notification by displaying the measurement results, or an auditory notification by outputting a voice, and further receives an instruction to switch between various test modes by user input.

＜２．ループインピーダンステスタ１の動作＞
図２～図４は、本発明の実施形態における活線Ｌ－接地線Ｅ間のループインピーダンスＺ_ＬＥの測定方法を説明する回路図である。Ｚ_ＬＥの測定方法は、活線ＬのインピーダンスＺ_Ｌの測定（図２、図３）と、接地線ＥのインピーダンスＺ_Ｅの測定（図４）と、Ｚ_ＬとＺ_Ｅとの和の計算と、を含む。図２～図４の各々においては、図１と同じループインピーダンステスタ１が示されているが、各々の手順において使用されない構成要素などの一部の図示が省略されている。 2. Operation of the loop impedance tester 1
2 to 4 are circuit diagrams for explaining a method for measuring the loop impedance Z _LE between a live line L and a ground line E in an embodiment of the present invention. The method for measuring Z _LE includes measuring the impedance Z _L of the live line L (FIGS. 2 and 3), measuring the impedance Z _E of the ground line E (FIG. 4), and calculating the sum of Z _L and Z _E. Each of FIGS. 2 to 4 shows the same loop impedance tester 1 as in FIG. 1, but some of the components that are not used in each procedure are omitted.

＜２－１．活線ＬのインピーダンスＺ_Ｌの測定＞
＜２－１－１．電圧値Ｖ_ＬＮ１及び第１の電圧値Ｖ_ＬＥ１の測定＞
図２に示されるようにスイッチＳＷ１がオフである無負荷状態で、活線Ｌ－中性線Ｎ間の電圧値Ｖ_ＬＮ１をＶ_ＬＮ電圧取得回路７にて取得する。また、同様に無負荷状態で活線Ｌ－接地線Ｅ間の第１の電圧値Ｖ_ＬＥ１をＶ_ＬＥ電圧取得回路８にて取得する。電圧値Ｖ_ＬＮ１は主電源２の電圧値に相当し、第１の電圧値Ｖ_ＬＥ１は地電圧と主電源２の電圧との合計に相当する。ここで取得された電圧値Ｖ_ＬＮ１及び第１の電圧値Ｖ_ＬＥ１は、図１中のＡ／Ｄ変換回路１１にて測定が行われ、それぞれデジタル値に変換される。 <2-1. Measurement of impedance _ZL of live line L>
<2-1-1. Measurement of voltage value V _LN1 and first voltage value V _LE1 >
2, in a no-load state where switch SW1 is off, a voltage value _VLN1 between the live line L and neutral line N is acquired by a _VLN voltage acquisition circuit 7. Similarly, in a no-load state, a first voltage value _VLE1 between the live line L and ground line E is acquired by a _VLE voltage acquisition circuit 8. The voltage value _VLN1 corresponds to the voltage value of the main power supply 2, and the first voltage value _VLE1 corresponds to the sum of the ground voltage and the voltage of the main power supply 2. The voltage value _VLN1 and first voltage value _VLE1 acquired here are measured by an A/D conversion circuit 11 in FIG. 1 and are each converted into a digital value.

＜２－１－２．第２の電圧値Ｖ_ＬＮ２及び第３の電圧値Ｖ_ＬＥ２の測定＞
図３に示されるようにスイッチＳＷ１をオンにし、主電源２をＬ端子４_Ｌ及びＮ端子４_Ｎを経由して負荷抵抗Ｒに接続する。これにより活線Ｌ－中性線Ｎ間に電流Ｉ_ＬＮを流した状態で、活線Ｌ－中性線Ｎ間の第２の電圧値Ｖ_ＬＮ２をＶ_ＬＮ電圧取得回路７にて取得する。また、同様に電流Ｉ_ＬＮを流した状態で、活線Ｌ－接地線Ｅ間の第３の電圧値Ｖ_ＬＥ２をＶ_ＬＥ電圧取得回路８にて取得する。取得された第２の電圧値Ｖ_ＬＮ２及び第３の電圧値Ｖ_ＬＥ２は、Ａ／Ｄ変換回路１１にて測定が行われ、それぞれデジタル値に変換される。 <2-1-2. Measurement of the second voltage value V _LN2 and the third voltage value V _LE2 >
3, the switch SW1 is turned on, and the main power supply 2 is connected to the load resistance R via the L terminal _4L and the N terminal _4N . With this, a current _ILN flows between the live line L and the neutral line N, and a second voltage value _VLN2 between the live line L and the neutral line N is acquired by a _VLN voltage acquisition circuit 7. Similarly, with a current _ILN flowing, a third voltage value _VLE2 between the live line L and the ground line E is acquired by a _VLE voltage acquisition circuit 8. The acquired second voltage value _VLN2 and third voltage value _VLE2 are measured by an A/D conversion circuit 11 and converted into digital values, respectively.

＜２－１－３．Ｚ_Ｌの計算＞
第２の電圧値Ｖ_ＬＮ２は電流Ｉ_ＬＮを流した際の負荷抵抗Ｒにかかる電圧であるため、電流Ｉ_ＬＮは以下の式（１）で求められる。
Ｉ_ＬＮ＝Ｖ_ＬＮ２／Ｒ ... （１）
望ましい測定精度を確保するため、電流Ｉ_ＬＮの電流値が６Ａ以上の高い値となるように、負荷抵抗Ｒの値が設定される。但し、電流Ｉ_ＬＮは、活線Ｌ－中性線Ｎ間に流れ、接地線Ｅには流れないため、漏電遮断器３をトリップさせることはない。 <2-1-3. Calculation of _ZL >
Since the second voltage value V _LN2 is the voltage applied to the load resistance R when a current I _LN flows, the current I _LN can be calculated by the following equation (1).
I _LN = V _LN2 /R... (1)
In order to ensure a desired measurement accuracy, the value of the load resistor R is set so that the current I _LN is a high value of 6 A or more. However, since the current I _LN flows between the live line L and the neutral line N, and does not flow through the earth line E, it does not trip the earth leakage breaker 3.

第３の電圧値Ｖ_ＬＥ２は、地電圧と、電流Ｉ_ＬＮを流した際の負荷抵抗Ｒ及び中性線ＮのインピーダンスＺ_Ｎの両端にかかる電圧と、の合計であるから、地電圧と主電源２の電圧との合計である第１の電圧値Ｖ_ＬＥ１から第３の電圧値Ｖ_ＬＥ２を差し引けば、活線ＬのインピーダンスＺ_Ｌ両端の電圧になる。従って、Ｚ_Ｌは以下の式（２）で表される。
Ｚ_Ｌ＝（Ｖ_ＬＥ１－Ｖ_ＬＥ２）／Ｉ_ＬＮ ... （２） The third voltage value _VLE2 is the sum of the earth voltage and the voltage across the impedance _ZN of the load resistance R and the neutral line N when the current I _LN flows, so if the third voltage value _VLE2 is subtracted from the first voltage value _VLE1 , which is the sum of the earth voltage and the voltage of the main power supply 2, it becomes the voltage across the impedance _ZL of the live line L. Therefore, _ZL is expressed by the following equation (2).
Z _L = (V _LE1 - _{V LE2} )/I _LN ... (2)

式（１）及び式（２）より、Ｚ_Ｌは以下の式（３）で求められる。
Ｚ_Ｌ＝（Ｖ_ＬＥ１－Ｖ_ＬＥ２）／（Ｖ_ＬＮ２／Ｒ）
＝（Ｖ_ＬＥ１－Ｖ_ＬＥ２）Ｒ／Ｖ_ＬＮ２ ... （３） From the formulas (1) and (2), _ZL can be calculated by the following formula (3).
Z _L = (V _LE1 - V _LE2 )/(V _LN2 /R)
=(V _LE1 -V _LE2 )R/V _LN2 ... (3)

なお、主電源２の電圧値Ｖ_ＬＮ１から、電流Ｉ_ＬＮを流した際の負荷抵抗Ｒの両端の電圧値である第２の電圧値Ｖ_ＬＮ２を差し引けば、活線ＬのインピーダンスＺ_Ｌ及び中性線ＮのインピーダンスＺ_Ｎの両端の電圧が算出される。このため、活線Ｌ－中性線Ｎ間のループインピーダンスＺ_ＬＮは以下の式（４）で表される。
Ｚ_ＬＮ＝（Ｖ_ＬＮ１－Ｖ_ＬＮ２）／Ｉ_ＬＮ ... （４） In addition, the voltages across the impedance _ZL of the live line L and the impedance ZN of the neutral line N are calculated by subtracting a second voltage value _VLN2 , which is the voltage value across the load resistance _R when _a current _ILN flows, from the voltage value VLN1 of the main power supply 2. For this reason, the loop impedance _ZLN between the live line L and the neutral line N is expressed by the following equation (4).
Z _LN = (V _LN1 - _{V LN2} )/I _LN ... (4)

式（１）及び式（４）より、Ｚ_ＬＮは以下の式（５）で求められる。
Ｚ_ＬＮ＝（Ｖ_ＬＮ１－Ｖ_ＬＮ２）／（Ｖ_ＬＮ２／Ｒ）
＝（Ｖ_ＬＮ１－Ｖ_ＬＮ２）Ｒ／Ｖ_ＬＮ２ ... （５） From the formulas (1) and (4), Z _LN can be calculated by the following formula (5).
Z _LN = (V _LN1 - V _LN2 )/(V _LN2 /R)
=(V _LN1 -V _LN2 )R/V _LN2 ... (5)

Ｚ_ＬＮは、活線Ｌ－中性線Ｎ間が短絡した場合に流れる短絡電流を算出するために用いられるループインピーダンスである。このＺ_ＬＮは過電流保護装置の選定の際に使用されたり、過電流保護装置が正常にトリップすることの確認のために使用されたりする。本実施形態によれば、Ｚ_ＬＥの測定と併せて、式（５）によりＺ_ＬＮを測定することも可能である。 Z _LN is a loop impedance used to calculate a short-circuit current that flows when a short circuit occurs between the live line L and the neutral line N. This Z _LN is used when selecting an overcurrent protection device, and is used to confirm that the overcurrent protection device trips normally. According to this embodiment, it is also possible to measure Z _LN by equation (5) in addition to measuring Z _LE .

＜２－２．接地線ＥのインピーダンスＺ_Ｅの測定＞
＜２－２－１．第１の交流電流Ｉ_ＬＥ１の生成＞
図４に示されるように、主電源２から電流生成部６を介して活線Ｌ－接地線Ｅ間に既知の電流である第１の交流電流Ｉ_ＬＥ１を流す。第１の交流電流Ｉ_ＬＥ１は、主電源２の電圧が変動しても、その影響を受けず波高値が一定の交流定電流であり、主電源２の交流電圧に同期した半波整流波形を有し、且つ主電源２の周波数である第１の周波数ｆｍ（例えば５０Ｈｚ又は６０Ｈｚ）よりも低い第２の周波数ｆｓ（周期１／ｆｓ）で半波整流の極性を切り替えた電流である。
このような第１の交流電流Ｉ_ＬＥ１は、主電源２をエネルギー源として生成することが可能である。このため、ループインピーダンステスタ１の内部に特別な電流源を設ける必要が無くなる。 <2-2. Measuring the impedance Z _E of the ground wire E>
<2-2-1. Generation of first AC current _ILE1 >
4, a first AC current I _LE1, which is a known current, is caused to flow between the live line L and the ground line E from the main power supply 2 via the current generating unit 6. The first AC current I _LE1 is an AC constant current with a constant peak value that is not affected even if the voltage of the main power supply 2 fluctuates, has a half-wave rectified waveform synchronized with the AC voltage of the main power supply 2, and is a current in which the polarity of the half-wave rectification is switched at a second frequency fs (period 1/fs) that is lower than a first frequency fm (e.g., 50 Hz or 60 Hz) that is the frequency of the main power supply 2.
Such a first AC current I _LE1 can be generated using the main power supply 2 as an energy source. Therefore, it is not necessary to provide a special current source inside the loop impedance tester 1.

第１の交流電流Ｉ_ＬＥ１は活線Ｌ－接地線Ｅ間に流れる電流であることから、漏電遮断器３において漏電と検知される可能性がある。一般的な漏電遮断器としては定格感度電流が３０ｍＡであるものが多く使用されていることから、漏電遮断器３をトリップさせないためには、第１の交流電流Ｉ_ＬＥ１は定格感度電流の１／２の電流である１５ｍＡ以下にすることが望ましい。 Since the first AC current I _LE1 is a current flowing between the live line L and the ground line E, it may be detected as an electric leakage by the earth leakage circuit breaker 3. Since most of the earth leakage circuit breakers in use have a rated sensitivity current of 30 mA, in order to prevent the earth leakage circuit breaker 3 from tripping, it is desirable to set the first AC current I _LE1 to 15 mA or less, which is half the rated sensitivity current.

＜２－２－２．第１の交流電圧Ｖ_ＮＥ１の測定及びノイズの除去＞
次に、第１の交流電流Ｉ_ＬＥ１が流れている状態にて中性線Ｎ－接地線Ｅ間の第１の交流電圧Ｖ_ＮＥ１をＶ_ＮＥ電圧取得回路９にて取得する。第１の交流電圧Ｖ_ＮＥ１は、接地線ＥのインピーダンスＺ_Ｅに第１の交流電流Ｉ_ＬＥ１が流れることで発生した電圧信号を含む。 <2-2-2. Measurement of first AC voltage _VNE1 and elimination of noise>
Next, in a state in which the first AC current I _LE1 is flowing, a first AC voltage V _NE1 between the neutral line N and the ground line E is acquired by the V _NE voltage acquisition circuit 9. The first AC voltage V _NE1 includes a voltage signal generated by the first AC current I _LE1 flowing through the impedance Z _E of the ground line E.

しかし、配電設備１４の中性線Ｎ－接地線Ｅ間には、接地線Ｅに流れる漏れ電流や、電気機器から中性線Ｎに流れる負荷電流が存在していることが多い。このことから、第１の交流電圧Ｖ_ＮＥ１の波形は第１の交流電流Ｉ_ＬＥ１の波形と完全に比例するわけではなく、ノイズの混ざった波形となる。通常、ノイズ成分は、第１の周波数ｆｍの周波数成分を主成分とし、さらに第１の周波数ｆｍの高調波成分を含んだ信号で構成されている。 However, there are often leakage currents flowing through the ground wire E and load currents flowing from electrical equipment to the neutral wire N between the neutral wire N and the ground wire E of the power distribution equipment 14. For this reason, the waveform of the first AC voltage _VNE1 is not completely proportional to the waveform of the first AC current _ILE1 , and has a waveform that includes noise. Usually, the noise component is composed of a signal whose main component is the frequency component of the first frequency fm and further includes harmonic components of the first frequency fm.

図５（Ａ）～図５（Ｄ）は、本発明の実施形態における接地線ＥのインピーダンスＺ_Ｅの測定手順を説明する波形図である。図５（Ａ）に第１の交流電流Ｉ_ＬＥ１の波形が示されている。第１の交流電圧Ｖ_ＮＥ１に含まれるノイズの周波数が図５（Ｂ）に示されるように第１の周波数ｆｍと同じであった場合、第１の交流電流Ｉ_ＬＥ１に比例してＺ_Ｅの両端にかかる電圧信号にノイズが重畳した第１の交流電圧Ｖ_ＮＥ１の波形は、図５（Ｃ）に示されるようになる。この波形を図４のフィルター回路１０に通すことで、第１の交流電圧Ｖ_ＮＥ１から第２の周波数ｆｓより高い周波数成分を取り除き、図５（Ｄ）に示されるような第２の周波数ｆｓの電圧信号からなる第２の交流電圧Ｖ_ＮＥ２を取り出すことができる。第２の交流電圧Ｖ_ＮＥ２は接地線ＥのインピーダンスＺ_Ｅの大きさにほぼ比例する。なお、「取り除く」というのは完全に０にする場合に限られるものではなく、第１の周波数ｆｍの周波数成分を低減する場合を含む。
第２の交流電圧Ｖ_ＮＥ２は図１中のＡ／Ｄ変換回路１１にて測定が行われ、デジタル値に変換される。 5(A) to 5(D) are waveform diagrams for explaining the procedure for measuring the impedance Z _E of the ground line E in the embodiment of the present invention. FIG. 5(A) shows the waveform of the first AC current I _LE1 . When the frequency of the noise contained in the first AC voltage V _NE1 is the same as the first frequency fm as shown in FIG. 5(B), the waveform of the first AC voltage V _NE1 in which noise is superimposed on the voltage signal applied to both ends of Z _E in proportion to the first AC current _{I LE1} is as shown in FIG. 5(C). By passing this waveform through the filter circuit 10 of FIG. 4, frequency components higher than the second frequency fs are removed from the first AC voltage V _NE1 , and the second AC voltage V _NE2 consisting of a voltage signal of the second frequency fs as shown in FIG. 5(D) can be extracted. The second AC voltage V _NE2 is approximately proportional to the magnitude of the impedance Z _E of the ground line E. Note that "removing" is not limited to completely reducing it to zero, but also includes reducing the frequency component of the first frequency fm.
The second AC voltage _VNE2 is measured by the A/D conversion circuit 11 in FIG. 1 and converted into a digital value.

ここで、取り除くノイズは主に第１の周波数ｆｍの周波数成分であり、第１の周波数ｆｍは第２の周波数ｆｓより高いことから、フィルター回路１０としてはローパスフィルターを用いることができる。あるいは、中性線Ｎ－接地線Ｅ間には第１の周波数ｆｍ以外の周波数成分を含む様々なノイズ成分が重畳している場合もあるため、第２の周波数ｆｓの信号成分のみを取り出すバンドパスフィルターやロックインアンプを用いることでより信頼性を向上させることもできる。 The noise to be removed here is mainly frequency components of the first frequency fm, which is higher than the second frequency fs, so a low-pass filter can be used as the filter circuit 10. Alternatively, since various noise components including frequency components other than the first frequency fm may be superimposed between the neutral line N and the ground line E, reliability can be improved by using a band-pass filter or lock-in amplifier that extracts only the signal component of the second frequency fs.

主電源２をエネルギー源として活線Ｌ－接地線Ｅ間に交流電流を流す方法として、単純に抵抗などを介して電流を流す方法をとった場合は、その交流電流の周波数は第１の周波数ｆｍと同じ５０Ｈｚや６０Ｈｚとなってしまう。この場合だと、中性線Ｎ－接地線Ｅ間の電圧を測定した際に重畳しているノイズと必要な信号成分とを区別するのが難しくなり、測定結果の信頼性の低下につながってしまう。
そこで本実施形態では、第１の交流電流Ｉ_ＬＥ１の波形を、図５（Ａ）に示されるように主電源２の交流電圧に同期した半波整流波形で、且つ第１の周波数ｆｍよりも低い第２の周波数ｆｓで半波整流の極性を切り替えた波形としている。これにより、フィルター回路１０によって、第１の交流電圧Ｖ_ＮＥ１から第１の周波数ｆｍの周波数成分を主とするノイズ成分を容易に取り除くことができる。 If a method of simply passing an AC current between the live line L and the ground line E using the main power supply 2 as an energy source is used in which the current is passed through a resistor or the like, the frequency of the AC current will be 50 Hz or 60 Hz, the same as the first frequency fm. In this case, it will be difficult to distinguish between the superimposed noise and the necessary signal component when measuring the voltage between the neutral line N and the ground line E, leading to a decrease in the reliability of the measurement results.
Therefore, in this embodiment, the waveform of the first AC current _ILE1 is a half-wave rectified waveform synchronized with the AC voltage of the main power supply 2, as shown in Fig. 5A, and the polarity of the half-wave rectification is switched at a second frequency fs lower than the first frequency fm. This makes it possible to easily remove noise components mainly consisting of frequency components of the first frequency fm from the first AC voltage _VNE1 by the filter circuit 10.

また、主電源２の電圧には歪みやノイズが存在し、理想的な正弦波となっていない場合が多い。第１の交流電流Ｉ_ＬＥ１が主電源２の波形の歪みやノイズの影響を受け、主電源２の電圧と同様に歪みやノイズを含んでしまうと、測定結果の誤差も大きくなる。
そこで、第１の交流電流Ｉ_ＬＥ１は、主電源２の電圧が変動しても、その影響を受けず波高値が一定の交流定電流とされることが望ましい。 In addition, distortion and noise are present in the voltage of the main power supply 2, and it is often not an ideal sine wave. If the first AC current _ILE1 is affected by distortion and noise in the waveform of the main power supply 2 and contains distortion and noise like the voltage of the main power supply 2, the error in the measurement result will also be large.
Therefore, it is desirable that the first AC current _ILE1 be an AC constant current whose peak value is constant and which is not affected even if the voltage of the main power supply 2 fluctuates.

＜２－２－３．Ｚ_Ｅの計算＞
第２の交流電圧Ｖ_ＮＥ２は接地線ＥのインピーダンスＺ_Ｅに第１の交流電流Ｉ_ＬＥ１が流れることで発生した第１の交流電圧Ｖ_ＮＥ１からノイズ成分を取り除いたものであるから、Ｚ_Ｅは、第１の交流電流Ｉ_ＬＥ１の電流値及び第２の交流電圧Ｖ_ＮＥ２の電圧値を用いて以下の式（７）で表される。
Ｚ_Ｅ＝Ｖ_ＮＥ２／Ｉ_ＬＥ１ ... （７） <2-2-3. Calculation of Z _E >
The second AC voltage _VNE2 is obtained by removing noise components from the first AC voltage _VNE1 generated when the first AC current _ILE1 flows through the impedance _ZE of the ground line E. Therefore, _ZE is expressed by the following equation (7) using the current value of the first AC current _ILE1 and the voltage value of the second AC voltage _VNE2 .
Z _E = V _NE2 /I _LE1 ... (7)

中性線Ｎ－接地線Ｅ間には、先に記載したようにノイズが重畳しているが、このノイズは、ほとんどの場合大きくても２０Ｖ程度である。このノイズ成分の大きさに対し、接地線ＥのインピーダンスＺ_Ｅに第１の交流電流Ｉ_ＬＥ１が流れた際の信号の大きさは、Ｚ_Ｅが０．０１Ωの場合で０．０１Ω×１５ｍＡ＝０．１５ｍＶと微小である。しかし、主電源２の２３０Ｖが含まれた活線Ｌ－接地線Ｅ間の電圧を取得してＺ_Ｅを測定する場合と比較してＳ／Ｎ比は１０倍以上に改善され、より精度の高い測定を短時間で行える。 As described above, noise is superimposed between the neutral wire N and the ground wire E, but in most cases this noise is at most about 20 V. In comparison with the magnitude of this noise component, the magnitude of the signal when the first AC current I _LE1 flows through the impedance Z _E of the ground wire E is minute, at 0.01 Ω x 15 mA = 0.15 mV when Z _E is 0.01 Ω. However, compared to the case where Z _E is measured by acquiring the voltage between the live wire L, which includes the 230 V of the main power supply 2, and the ground wire E, the S/N ratio is improved by 10 times or more, and more accurate measurements can be performed in a shorter time.

＜２－３．Ｚ_ＬとＺ_Ｅとの和の計算＞
最後に、式（３）及び式（７）に基づいて活線Ｌ－接地線Ｅ間のループインピーダンスＺ_ＬＥを以下の式（８）にて算出する。
Ｚ_ＬＥ＝Ｚ_Ｌ＋Ｚ_Ｅ
＝（Ｖ_ＬＥ１－Ｖ_ＬＥ２）Ｒ／Ｖ_ＬＮ２＋Ｖ_ＮＥ２／Ｉ_ＬＥ１ ... （８） <2-3. Calculating the sum of _{Z L} and Z _E >
Finally, based on the equations (3) and (7), the loop impedance Z _LE between the live line L and the ground line E is calculated by the following equation (8).
Z _LE = Z _L + Z _E
= (V _LE1 -V _LE2 )R/V _LN2 +V _NE2 /I _LE1 ... (8)

＜３．電流生成部６の構成＞
図６は、図１及び図４に示される電流生成部６の詳細を示す回路図である。電流生成部６は、全波整流回路６１と、コンパレータ６２と、制御信号生成部６３と、Ｄ／Ａコンバータ６４と、定電流回路６５と、を含む。 3. Configuration of current generating unit 6
Fig. 6 is a circuit diagram showing details of the current generating unit 6 shown in Fig. 1 and Fig. 4. The current generating unit 6 includes a full-wave rectifier circuit 61, a comparator 62, a control signal generating unit 63, a D/A converter 64, and a constant current circuit 65.

全波整流回路６１はブリッジダイオードで構成されている。全波整流回路６１の交流入力端子６１ａ及び６１ｂが活線Ｌ－接地線Ｅ間に接続され、正極出力端子６１ｃは定電流回路６５に接続されている。全波整流回路６１は、活線Ｌ－接地線Ｅ間の交流電圧波形のうちの負極性の部分を反転することにより、正の脈動電圧を出力する。 The full-wave rectifier circuit 61 is composed of bridge diodes. The AC input terminals 61a and 61b of the full-wave rectifier circuit 61 are connected between the live line L and the ground line E, and the positive output terminal 61c is connected to the constant current circuit 65. The full-wave rectifier circuit 61 outputs a positive pulsating voltage by inverting the negative polarity portion of the AC voltage waveform between the live line L and the ground line E.

コンパレータ６２の非反転入力端子（＋）は活線Ｌに接続され、反転入力端子（－）は接地線Ｅに接続されている。コンパレータ６２の出力端子は制御信号生成部６３に接続されている。コンパレータ６２は活線Ｌ－接地線Ｅ間の電圧の極性に応じたｈｉｇｈ又はｌｏｗの出力電圧を含むゼロクロス信号を出力する。 The non-inverting input terminal (+) of the comparator 62 is connected to the live line L, and the inverting input terminal (-) is connected to the ground line E. The output terminal of the comparator 62 is connected to the control signal generating unit 63. The comparator 62 outputs a zero-cross signal that includes a high or low output voltage according to the polarity of the voltage between the live line L and the ground line E.

制御信号生成部６３は、マイクロコンピューターなどの処理装置で構成される。制御信号生成部６３は、メモリに格納されたプログラムに従い、ゼロクロス信号に同期して、定電流回路６５に流れる電流の電流波形を制御するためのデジタル信号をＤ／Ａコンバータ６４に出力する。
Ｄ／Ａコンバータ６４の出力端子は、定電流回路６５に接続されている。 The control signal generating unit 63 is composed of a processing device such as a microcomputer. The control signal generating unit 63 outputs a digital signal for controlling the current waveform of the current flowing through the constant current circuit 65 to the D/A converter 64 in synchronization with the zero cross signal according to a program stored in the memory.
The output terminal of the D/A converter 64 is connected to a constant current circuit 65 .

定電流回路６５は、オペアンプ６６と、ＦＥＴ６７と、検出抵抗Ｒ１と、を含む。Ｄ／Ａコンバータ６４の出力端子がオペアンプ６６の非反転入力端子（＋）に接続され、オペアンプ６６の出力端子がＦＥＴ６７のゲート端子に接続されている。ＦＥＴ６７のドレイン端子が全波整流回路６１の正極出力端子６１ｃに接続され、ソース端子が、片側を接地された検出抵抗Ｒ１とオペアンプ６６の反転入力端子（－）とに接続されている。ＦＥＴ６７の代わりにバイポーラ型のトランジスタが用いられてもよい。 The constant current circuit 65 includes an operational amplifier 66, a FET 67, and a detection resistor R1. The output terminal of the D/A converter 64 is connected to the non-inverting input terminal (+) of the operational amplifier 66, and the output terminal of the operational amplifier 66 is connected to the gate terminal of the FET 67. The drain terminal of the FET 67 is connected to the positive output terminal 61c of the full-wave rectifier circuit 61, and the source terminal is connected to the detection resistor R1, one side of which is grounded, and the inverting input terminal (-) of the operational amplifier 66. A bipolar transistor may be used instead of the FET 67.

＜４．電流生成部６の動作＞
図７（Ａ）～図７（Ｈ）は、電流生成部６の動作を説明する波形図である。図７（Ａ）に活線Ｌ－接地線Ｅ間の電圧の波形が示されている。 4. Operation of current generating unit 6
7A to 7H are waveform diagrams illustrating the operation of the current generating unit 6. A waveform of the voltage between the live line L and the ground line E is shown in FIG.

全波整流回路６１の出力電圧（図７（Ｂ））の波形は、活線Ｌ－接地線Ｅ間の電圧を全波整流した波形となる。但し、全波整流回路６１から出力される電流は、定電流回路６５によって規制される。 The waveform of the output voltage of the full-wave rectifier circuit 61 (Figure 7 (B)) is a waveform obtained by full-wave rectifying the voltage between the live line L and the ground line E. However, the current output from the full-wave rectifier circuit 61 is regulated by the constant current circuit 65.

コンパレータ６２は、活線Ｌ－接地線Ｅ間の電圧の極性が第１の周波数ｆｍで切り替わるタイミングに同期したゼロクロス信号（図７（Ｃ））を出力する。ゼロクロス信号は方形波で構成される。ゼロクロス信号は制御信号生成部６３に入力される。 The comparator 62 outputs a zero-cross signal (Figure 7(C)) synchronized with the timing at which the polarity of the voltage between the live line L and the ground line E switches at the first frequency fm. The zero-cross signal is composed of a square wave. The zero-cross signal is input to the control signal generator 63.

制御信号生成部６３は、ゼロクロス信号の極性が第１の周波数ｆｍで切り替わるタイミングを利用して、第１の交流電流Ｉ_ＬＥ１の電流波形を規定するためのデジタル信号を出力する。デジタル信号はＤ／Ａコンバータ６４に入力される。 The control signal generator 63 uses the timing at which the polarity of the zero-cross signal switches at the first frequency fm to output a digital signal for defining the current waveform of the first AC current _ILE1 . The digital signal is input to the D/A converter 64.

Ｄ／Ａコンバータ６４は、デジタル信号をアナログの電圧信号（図７（Ｄ））に変換する。この電圧信号の波形を拡大すると、図７（Ｅ）に示されるように階段状になっている。電圧信号はオペアンプ６６の非反転入力端子（＋）に入力される。 The D/A converter 64 converts the digital signal into an analog voltage signal (Figure 7(D)). When the waveform of this voltage signal is enlarged, it has a stepped shape as shown in Figure 7(E). The voltage signal is input to the non-inverting input terminal (+) of the operational amplifier 66.

定電流回路６５は、オペアンプ６６にて検出抵抗Ｒ１からのフィードバック信号をモニターすることで、Ｄ／Ａコンバータ６４から入力される電圧信号（図７（Ｄ））の電圧に比例した電流（図７（Ｆ））を流す。この電流は、活線Ｌ－接地線Ｅ間の電圧（図７（Ａ））の振幅が変動してもその影響を受けない定電流となる。 The constant current circuit 65 monitors the feedback signal from the detection resistor R1 with the operational amplifier 66, and passes a current (Fig. 7(F)) proportional to the voltage of the voltage signal (Fig. 7(D)) input from the D/A converter 64. This current is a constant current that is not affected by fluctuations in the amplitude of the voltage (Fig. 7(A)) between the live line L and the ground line E.

定電流回路６５に電流が流れることで、活線Ｌ－接地線Ｅ間に第１の交流電流Ｉ_ＬＥ１（図７（Ｇ））が流れる。図７（Ｇ）に示される期間ｔ_１～ｔ_７の各々の長さは主電源２の周期１／ｆｍの半分に相当する。
定電流回路６５に流れる電流（図７（Ｆ））は片極性の電流であるが、活線Ｌ－接地線Ｅ間に流れる第１の交流電流Ｉ_ＬＥ１（図７（Ｇ））は両極性の電流となる。但し、期間ｔ_１、ｔ_３及びｔ_６の各々においては、定電流回路６５に電流が流れないため、全波整流回路６１の出力電流が遮断され、第１の交流電流Ｉ_ＬＥ１も０となる。第１の交流電流Ｉ_ＬＥ１を０とするタイミングは、制御信号生成部６３で生成されるデジタル信号によって規定される。 When a current flows through the constant current circuit 65, a first AC current I _LE1 (FIG. 7(G)) flows between the live line L and the ground line E. The length of each of the periods t ₁ to t ₇ shown in FIG. 7(G) corresponds to half the period 1/fm of the main power supply 2.
The current flowing through the constant current circuit 65 (FIG. 7(F)) is a unipolar current, but the first AC current I _LE1 flowing between the live line L and the ground line E (FIG. 7(G)) is a bipolar current. However, during each of periods t ₁ , t ₃ and t ₆ , no current flows through the constant current circuit 65, so the output current of the full-wave rectifier circuit 61 is cut off and the first AC current I _LE1 also becomes zero. The timing at which the first AC current I _LE1 becomes zero is determined by a digital signal generated by the control signal generator 63.

第１の交流電流Ｉ_ＬＥ１を０とするタイミングを切り替えることで、第１の交流電流Ｉ_ＬＥ１の極性を切り替えることができる。例えば、期間ｔ_１～ｔ_７のうちのｔに付した添え字が奇数となるタイミング（例えば、ｔ_１及びｔ_３）、すなわち活線Ｌ－接地線Ｅ間の電圧が正極性となるタイミングで第１の交流電流Ｉ_ＬＥ１を０とし、それぞれの前後の各半周期の期間に第１の交流電流Ｉ_ＬＥ１を流すことで、第１の交流電流Ｉ_ＬＥ１は負極性となる。一方、ｔに付した添え字が偶数となるタイミング（例えば、ｔ_６）、すなわち活線Ｌ－接地線Ｅ間の電圧が負極性となるタイミングで第１の交流電流Ｉ_ＬＥ１を０とし、その前後の各半周期の期間に第１の交流電流Ｉ_ＬＥ１を流すことで、第１の交流電流Ｉ_ＬＥ１は正極性となる。第１の交流電流Ｉ_ＬＥ１の極性の切り替えは、主電源２の周期１／ｆｍよりも長い周期１／ｆｓで行われる。 The polarity of the first AC current I _LE1 can be switched by switching the timing at which the first AC current I _LE1 is set to 0. For example, the first AC current I LE1 is set to 0 at the timing when the subscript attached to t in the period t ₁ to t ₇ is an odd number (for example, t ₁ and t ₃ ), i.e., at the timing when the voltage between the live line L and the ground line E is positive, and the first AC current I _LE1 is made to flow during each half cycle period before and after each of the timings, so that the first AC current I _LE1 becomes negative. On the other hand, the first AC current I _LE1 is set to 0 at the timing when the subscript attached to t is an even number (for example, t ₆ ), i.e., at the timing when the voltage between the live line L and the ground line _{E is negative, and the first AC current I LE1 is made to flow during each half cycle period before and after each of the timings, so that the first AC current I LE1} _becomes _positive . The polarity of the first AC current _ILE1 is switched with a period 1/fs that is longer than the period 1/fm of the main power supply 2.

電流生成部６は、ループインピーダンステスタ１を漏電遮断器テスタとして機能させる場合にも使用することができる。漏電遮断器テスタは、活線Ｌ－接地線Ｅ間に疑似的な漏れ電流としての第２の交流電流Ｉ_ＬＥ２（図７（Ｈ））を流すことで、配電設備１４の漏電遮断器３をトリップさせて、漏電発生からトリップまでにかかる時間を測定する。 The current generating unit 6 can also be used when the loop impedance tester 1 functions as an earth leakage circuit breaker tester. The earth leakage circuit breaker tester trips the earth leakage circuit breaker 3 of the power distribution facility 14 by passing a second AC current I _LE2 (FIG. 7(H)) as a pseudo leakage current between the live line L and the ground line E, and measures the time required from the occurrence of the earth leakage to the tripping.

第２の交流電流Ｉ_ＬＥ２は、漏電遮断器３をトリップさせる閾値よりも大きい電流である点、及びｔ_１、ｔ_３及びｔ_６のような休止期間を含まない点で、第１の交流電流Ｉ_ＬＥ１と異なる。しかし、第２の交流電流Ｉ_ＬＥ２は、正確な測定を行うために、主電源２の波形の歪みやノイズの影響を受けず、波高値が一定の交流定電流とされることが望ましい点で、第１の交流電流Ｉ_ＬＥ１と同様である。本実施形態によれば、共通の電流生成部６を用いながら、制御信号生成部６３で生成されるデジタル信号によって、第１の交流電流Ｉ_ＬＥ１を流す第１のモードか、第２の交流電流Ｉ_ＬＥ２を流す第２のモードかを切り替えることができる。 The second AC current I _{LE2 differs from the first AC current I LE1} in that the second AC current I LE2 is a current greater than the threshold for tripping the earth leakage circuit breaker 3 and does not include pause periods such as t ₁ , t ₃ and t _6. However, the second AC current I _LE2 is similar to the first AC current I _LE1 in that, in order to perform accurate measurement, it is desirable that the second AC current I _LE2 be an AC constant current with a constant peak value without being affected by distortion or noise of the waveform of the main power supply 2. According to this embodiment, while using a common current generating unit 6, it is possible to switch between a first mode in which the first AC current I _LE1 flows and a second mode in which the second AC current I _LE2 flows, by a digital signal generated by the control signal generating unit 63.

＜５．実施形態による効果＞
（１）以上説明した本発明の実施形態によれば、電流生成部６は、活線Ｌ及び接地線Ｅの間に、主電源２の第１の周波数ｆｍより低い第２の周波数ｆｓの周波数成分を含む第１の交流電流Ｉ_ＬＥ１を流す。Ｖ_ＮＥ電圧取得回路９は、活線Ｌ及び接地線Ｅの間に第１の交流電流Ｉ_ＬＥ１を流した状態での中性線Ｎ及び接地線Ｅの間の第１の交流電圧Ｖ_ＮＥ１を計測する。フィルター回路１０は、第１の交流電圧Ｖ_ＮＥ１から第１の周波数ｆｍの周波数成分を低減した第２の交流電圧Ｖ_ＮＥ２を取り出す。計測制御手段１２は、第１の交流電流Ｉ_ＬＥ１の電流値及び第２の交流電圧Ｖ_ＮＥ２の電圧値から接地線ＥのインピーダンスＺ_Ｅを算出し、Ｚ_Ｅを用いてループインピーダンスＺ_ＬＥを算出する。
これによれば、第１の交流電圧Ｖ_ＮＥ１から第１の周波数ｆｍの周波数成分を低減した第２の交流電圧Ｖ_ＮＥ２を取り出すことで、正確で信頼性の高いループインピーダンスＺ_ＬＥの測定を短時間にて行うことができ、特別な電流源を設ける必要が無いため安価で小型なループインピーダンステスタ１を実現することができる。 5. Effects of the embodiment
(1) According to the embodiment of the present invention described above, the current generating unit 6 flows a first AC current I LE1 including a frequency component of a second frequency fs lower than the first frequency fm of the main power supply 2 between the live line L and the ground line E. The V _NE voltage acquiring circuit 9 measures a first AC voltage V _{NE1 between the neutral line N and the ground line E in a state in which the first AC current I LE1} _flows between the live line _{L and the ground line E. The filter circuit 10 extracts a second AC voltage V NE2} _{obtained by reducing the frequency component of the first frequency fm from the first AC voltage V NE1} _. The measurement control means 12 calculates an impedance Z _E of the ground line E from the current value of the first AC current I _LE1 and the voltage value of the second AC voltage V _NE2 , and calculates a loop impedance Z _LE using Z _E.
According to this, by extracting the second AC voltage _VNE2 obtained by reducing the frequency component of the first frequency fm from the first AC voltage _VNE1 , it is possible to perform accurate and reliable measurement of the loop impedance _ZLE in a short time, and since there is no need to provide a special current source, it is possible to realize an inexpensive and small loop impedance tester 1.

（２）本発明の実施形態によれば、電流生成部６の制御信号生成部６３は、活線Ｌ及び接地線Ｅの間の電圧の極性が第１の周波数ｆｍで切り替わるタイミングを利用して、第１の交流電流Ｉ_ＬＥ１の極性の第２の周波数ｆｓによる切り替えを制御する。
これによれば、活線Ｌ－接地線Ｅ間の電圧の極性が切り替わるタイミングを利用することで、このタイミングに同期した制御信号を生成し、第１の交流電流Ｉ_ＬＥ１の極性を切り替えることができる。 (2) According to an embodiment of the present invention, the control signal generating unit 63 of the current generating unit 6 controls the switching of the polarity of the first AC current _ILE1 at the second frequency fs, by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E switches at the first frequency fm.
According to this, by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E changes, a control signal synchronized with this timing can be generated to switch the polarity of the first AC current _ILE1 .

（３）本発明の実施形態によれば、電流生成部６は、活線Ｌ及び接地線Ｅの間に接続された全波整流回路６１と、この全波整流回路６１の出力電流を第１の周波数ｆｍで遮断するタイミングを切り替えることにより第１の交流電流Ｉ_ＬＥ１の極性を切り替える制御信号生成部６３と、を含む。
これによれば、活線Ｌ－接地線Ｅ間の電圧が正極性となるタイミングで全波整流回路６１の出力電流を遮断することで第１の交流電流Ｉ_ＬＥ１を負極性とし、活線Ｌ－接地線Ｅ間の電圧が負極性となるタイミングで全波整流回路６１の出力電流を遮断することで第１の交流電流Ｉ_ＬＥ１を正極性とすることができる。 (3) According to an embodiment of the present invention, the current generating unit 6 includes a full-wave rectifier circuit 61 connected between the live line L and the ground line E, and a control signal generating unit 63 that switches the polarity of the first AC current _ILE1 by switching the timing at which the output current of the full-wave rectifier circuit 61 is cut off at the first frequency fm.
According to this, the output current of the full-wave rectifier circuit 61 is cut off at the timing when the voltage between the live line L and the ground line E becomes positive, thereby making the first AC current I _LE1 negative, and the output current of the full-wave rectifier circuit 61 is cut off at the timing when the voltage between the live line L and the ground line E becomes negative, thereby making the first AC current I _LE1 positive.

（４）本発明の実施形態によれば、電流生成部６の制御信号生成部６３は、第１のモードと第２のモードとの切り替えが可能となっている。第１のモードは、第１の交流電流Ｉ_ＬＥ１の電流値を、活線Ｌと中性線Ｎとの間に接続された漏電遮断器３をトリップさせる閾値より小さい値にすることにより、ループインピーダンスＺ_ＬＥの測定を可能とするモードである。第２のモードは、活線Ｌ及び接地線Ｅの間に閾値より大きい電流値を有する第２の交流電流Ｉ_ＬＥ２を流すことにより、ループインピーダンステスタ１を漏電遮断器テスタとして機能させることを可能とするモードである。
これによれば、制御信号生成部６３の動作モードを切り替えることによりループインピーダンスＺ_ＬＥの測定機能と漏電遮断器テスタとしての機能とを切り替えることができ、電流生成部６の回路を共通化することもできる。 (4) According to the embodiment of the present invention, the control signal generating unit 63 of the current generating unit 6 can be switched between a first mode and a second mode. The first mode is a mode that enables measurement of the loop impedance ZLE by setting the current value of the first AC current _ILE1 to a value smaller than a threshold value that trips the earth leakage circuit breaker 3 connected between the live line L and the neutral line N. The second mode is a mode that enables the loop impedance tester ₁ to function as an earth leakage circuit breaker tester by passing a second AC current _ILE2 having a current value larger than a threshold value between the live line L and the ground line E.
According to this, by switching the operation mode of the control signal generating unit 63, it is possible to switch between the function of measuring the loop impedance _ZLE and the function as an earth leakage breaker tester, and it is also possible to share the circuit of the current generating unit 6.

１...ループインピーダンステスタ、２...主電源、３...漏電遮断器、４_Ｌ...Ｌ端子、４_Ｎ...Ｎ端子、４_Ｅ...Ｅ端子、６...電流生成部、７...Ｖ_ＬＮ電圧取得回路、８...Ｖ_ＬＥ電圧取得回路、９...Ｖ_ＮＥ電圧取得回路、１０...フィルター回路、１１...Ａ／Ｄ変換回路、１２...計測制御手段、１３...入出力手段、１４...配電設備、１５...第１の計測回路、６１...全波整流回路、６１ａ、６１ｂ...交流入力端子、６１ｃ...正極出力端子、６２...コンパレータ、６３...制御信号生成部、６４...Ｄ／Ａコンバータ、６５...定電流回路、６６...オペアンプ、６７...ＦＥＴ、Ｌ...活線、Ｎ...中性線、Ｅ...接地線、Ｒ...負荷抵抗、Ｒ１...検出抵抗、ＳＷ１...スイッチ REFERENCE SIGNS LIST 1...loop impedance tester, 2...main power supply, 3...earth leakage circuit breaker, 4 _L ...L terminal, 4 _N ...N terminal, 4 _E ...E terminal, 6...current generating unit, 7...V _LN voltage acquisition circuit, 8...V _LE voltage acquisition circuit, 9...V _NE voltage acquisition circuit, 10...filter circuit, 11...A/D conversion circuit, 12...measurement control means, 13...input/output means, 14...power distribution equipment, 15...first measurement circuit, 61...full-wave rectifier circuit, 61a, 61b...AC input terminal, 61c...positive output terminal, 62...comparator, 63...control signal generating unit, 64...D/A converter, 65...constant current circuit, 66...operational amplifier, 67...FET, L...live line, N...neutral line, E...ground line, R...load resistor, R1...detection resistor, SW1...switch

Claims

A loop impedance tester is connected to a live line L, a neutral line N, and a ground line E in order to measure a loop impedance _ZLE between the live line L and the ground line E in a power line including the live line L, the neutral line N, and the ground line E, the loop impedance tester comprising:
a first measurement circuit that measures a first voltage value _VLE1 between the live line L and the ground line E in a state where no load is connected between the live line L and the neutral line N, and a second voltage value _VLN2 between the live line L and the neutral line N and a third voltage value _VLE2 between the live line L and the ground line E in a state where a load resistor R is connected between the live line L and the neutral line N;
a current generating unit that flows a first AC current _ILE1 including a frequency component of a second frequency fs lower than the first frequency fm between the live line L and the ground line E;
a second measurement circuit that measures a first AC voltage _VNE1 between the neutral wire N and the ground wire E in a state in which the first AC current _ILE1 is flowing between the live wire L and the ground wire E;
a filter circuit that extracts a second AC voltage _VNE2 by reducing a frequency component of the first frequency fm from the first AC voltage _VNE1 ;
A measurement control means,
calculating a first impedance _ZL of the live line L from the value of the load resistance R and the first, second and third voltage values _VLE1 , _VLN2 and _VLE2 ;
calculating a second impedance Z _E of the ground wire E from the current value of the first AC current I _LE1 and the voltage value of the second AC voltage V _NE2 ;
Calculating the loop impedance _ZLE from the first and second impedances _ZL and _ZE ;
The measurement control means;
Including,
The current generating unit is
a full-wave rectifier circuit including a first AC input terminal connected to the live line L, a second AC input terminal connected to the ground line E, and an output terminal for outputting an output current of one polarity;
A control signal generating unit;
Including,
The control signal generating unit
a first process for cutting off the output current when a voltage between the live line L and the ground line E is positive, and for allowing the output current to flow when a voltage between the live line L and the ground line E is negative, thereby making the first AC current ILE1 flowing between the live line L and the ground line E via the first and second AC input terminals _negative ;
a second process of cutting off the output current when the voltage between the live line L and the ground line E is negative, and flowing the output current when the voltage between the live line L and the ground line E is positive, thereby making the first AC current ILE1 flowing between the live line L and the ground line E via the first and second AC input terminals _positive ;
by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E switches at the first frequency fm, thereby switching the polarity of the first AC current _ILE1 at the second frequency fs .

The current generating unit further includes a comparator that outputs an output signal according to the polarity of the voltage between the live line L and the ground line E,
The control signal generation unit switches between the first processing and the second processing based on the output signal .
2. The loop impedance tester of claim 1.

the current generating unit further includes a transistor connected to the output terminal and regulating the output current;
The control signal generating unit
In the first process, when the voltage between the live line L and the ground line E is positive, the transistor cuts off the output current, and when the voltage between the live line L and the ground line E is negative, the transistor passes the output current;
In the second process, when the voltage between the live line L and the ground line E is negative, the transistor cuts off the output current, and when the voltage between the live line L and the ground line E is positive, the transistor passes the output current.
The control signal is output so that
2. The loop impedance tester of claim 1.

A loop impedance tester is connected to a live line L, a neutral line N, and a ground line E in order to measure a loop impedance ZLE between the live line L and the ground line E in a power line including _the live line L, the neutral line N, and the ground line E, the loop impedance tester comprising:
a first measurement circuit that measures a first voltage value _VLE1 between the live line L and the ground line E in a state where no load is connected between the live line L and the neutral line N, and a second voltage value VLN2 between the live line L and the neutral line N and a third voltage value VLE2 between _the live line L and the ground line E in a state where a load resistor R is connected between the live line L and the _neutral line N;
a current generating unit that flows a first AC current _ILE1 including a frequency component of a second frequency fs lower than the first frequency fm between the live line L and the ground line E ;
a second measurement circuit that measures a first AC voltage _VNE1 between the neutral wire N and the ground wire E in a state in which the first AC current _ILE1 is caused to flow between the live wire L and the ground wire E ;
a filter circuit that extracts a second AC voltage _VNE2 by reducing a frequency component of the first frequency fm from the first AC voltage VNE1 _;
A measurement control means,
calculating a first impedance ZL of the live line L from _the value of the load resistance R and the first, second and third voltage values VLE1 _, VLN2 _and VLE2 _;
calculating a second impedance Z _E of the ground line E from the current value of the first AC current I _LE1 and the voltage value of the second AC voltage V _NE2 ;
Calculating the loop impedance ZLE from _the first and second impedances ZL _and ZE _;
The measurement control means;
Including,
The current generating unit is
a first mode in which the loop impedance _ZLE can be measured by setting the current value of the first AC current _ILE1 to a value smaller than a threshold value that trips an earth leakage breaker connected between the live conductor L and the neutral conductor N;
a second mode in which a second AC current _I having a current value greater than the threshold value flows between the live line L and the ground line E, thereby enabling the loop impedance tester to function as a ground fault circuit interrupter tester;
A control signal generating unit that can be switched to
Loop impedance tester.

A loop impedance measuring method for measuring a loop impedance _ZLE between a live line L supplying an AC voltage including a frequency component of a first frequency fm, a neutral line N, and a ground line E in a power line including the live line L and the ground line E, the method comprising the steps of:
measuring a first voltage value _VLE1 between the live line L and the ground line E in a state where no load is connected between the live line L and the neutral line N, and a second voltage value _VLN2 between the live line L and the neutral line N and a third voltage value VLE2 between the live line _L and the ground line E in a state where a load resistance R is connected between the live line L and the neutral line N;
A first AC current _ILE1 including a frequency component of a second frequency fs lower than the first frequency fm is caused to flow between the live line L and the ground line E;
measuring a first AC voltage _VNE1 between the neutral wire N and the ground wire E in a state where the first AC current _ILE1 is flowing between the live wire L and the ground wire E;
A second AC voltage _VNE2 is obtained by reducing the frequency component of the first frequency fm from the first AC voltage _VNE1 ;
calculating a first impedance _ZL of the live line L from the value of the load resistance R and the first, second and third voltage values _VLE1 , _VLN2 and _VLE2 ;
calculating a second impedance Z _E of the ground line E from the current value of the first AC current I _LE1 and the voltage value of the second AC voltage V _NE2 ;
calculating the loop impedance _ZLE from the first and second impedances _ZL and _ZE ;
The first AC current I _LE1 is
A full-wave rectifier circuit including a first AC input terminal connected to the live line L, a second AC input terminal connected to the ground line E, and an output terminal for outputting a unipolar output current,
a first process for cutting off the output current when a voltage between the live line L and the ground line E is positive, and for allowing the output current to flow when a voltage between the live line L and the ground line E is negative, thereby making the first AC current ILE1 flowing between the live line L and the ground line E via the first and second AC input terminals _negative ;
a second process of cutting off the output current when the voltage between the live line L and the ground line E is negative, and flowing the output current when the voltage between the live line L and the ground line E is positive, thereby making the first AC current ILE1 flowing between the live line L and the ground line E via the first and second AC input terminals _positive ;
The polarity of the first AC current ILE1 is switched at _the second frequency fs by utilizing the timing at which the polarity of the voltage between the live line L and the ground line E switches at the first frequency fm.
A method for measuring loop impedance by generating a loop impedance.