JP2004309182A - Instrument and method for measuring ground resistance - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、電気設備技術基準で定められているＢ種接地極と、低圧機器の筐体を接地するための機器用接地極との直列合成接地抵抗値を測定する接地抵抗測定器及び接地抵抗測定方法に関する。
【０００２】
【従来の技術】
従来、高低圧変圧器の低圧側端子の一つもしくは中性線を接地するためのＢ種接地極や、高低圧変圧器の低圧側電路に接続される低圧機器の筐体等を接地するためのＤ種接地極やＣ種接地極の接地抵抗値を接地抵抗計２０で測定する場合、図２に示すような電位降下法に基づいて行なわれる。この電位降下法とは、大地に埋設された測定対象接地極２１と電流補助極２２の間に交流電源２３から出力された交流電圧を計測用標準電圧として印加することにより、測定対象接地極２１と電流補助極２２の間に流れる電流Ｉを電流計２４で測定すると同時に、測定対象接地極２１と電流補助極２２の間の設置した電位補助極２５と測定対象接地極２１の間の電圧Ｖを電圧計２６で測定したうえ、電圧Ｖ／電流Ｉの計算をすることによって測定対象接地極２１の接地抵抗値を求める方法である。（例えば、非特許文献１参照。）
【０００３】
【非特許文献１】
高橋健彦著「接地技術入門」株式会社オーム社出版、昭和６３年２月１０日 ｐ１５０−１５３
【０００４】
【発明が解決しようとする課題】
上記従来の接地抵抗計２０で測定対象接地極２１、例えばＢ種接地極の接地抵抗値を測定する場合、高低圧変圧器等の電気設備の竣工時、あるいは年次点検時に需要家構内を停電にし、測定対象接地極２１を高低圧変圧器から電気的に切り離して測定しなければならない。そのため、測定対象接地極２１の接地抵抗値を随時、測定することは現実的に困難である。また、計測用標準電圧を出力するための交流電源２３を必要とする。
尚、一般に接地極の接地抵抗値は、気温や大地の水分量により季節的に変動するため、年間を通して一定値にはならないことが知られている。このため、高低圧変圧器の竣工時、あるいは年次点検時にのみ、接地極の接地抵抗値を測定するだけでは、接地極の接地抵抗値が電気設備技術基準で定められている許容値以下に常に保たれていることを保証することができない。
【０００５】
そこで本発明では、計測用標準電圧が不要で、且つ、１次側が特別高圧もしくは高圧の高低圧変圧器が稼動中であっても、Ｂ種接地極と低圧機器を接地するための機器用接地極との直列合成接地抵抗値を測定することができる接地抵抗測定器及び接地抵抗測定方法を提供するとともに、測定した直列合成接地抵抗値に基づいて計算した季節変動率を、高低圧変圧器の竣工時に予め測定されているＢ種接地極及び機器用接地極それぞれの接地抵抗値に乗じることによって、それぞれの接地極の接地抵抗値が電気設備技術基準で定められている許容値以下に保たれているか否かを判断することができる接地抵抗測定方法を提供することを解決すべき課題とするものである。
【０００６】
【課題を解決するための手段】
上記課題は、特許請求の範囲の欄に記載した接地抵抗測定器及び接地抵抗測定方法により解決することができる。
【０００７】
請求項１記載の接地抵抗測定器によれば、高低圧変圧器の低圧側電路から低圧機器の筐体に漏洩電流が流れた場合、電流検出手段により、低圧機器の筐体から機器用接地極、大地、及びＢ種接地極を介して低圧側電路に戻る第１の通電路を流れる漏洩電流と、低圧機器の筐体から可変電気抵抗を介して当該高低圧変圧器の低圧側電路に戻るように接続された第２の通電路を流れる漏洩電流とが反対の通電方向で同時に検出されると、調整手段は、電流検出手段から出力される電流検出信号がゼロになるように可変電気抵抗の抵抗値を自動的に調整するため、出力手段は、その抵抗値を出力する。このように、電流検出手段の電流検出値がゼロになるように可変電気抵抗の抵抗値が自動的に調整された場合に出力手段から出力された可変電気抵抗の抵抗値を、Ｂ種接地極と機器用接地極の直列合成接地抵抗値として測定する。
これにより、計測用標準電圧が不要で、且つ高低圧変圧器が稼動中であっても、Ｂ種接地極と低圧機器を接地するための機器用接地極の直列合成接地抵抗を測定することができる。
【０００８】
請求項２記載の接地抵抗測定方法によれば、高低圧変圧器の低圧側電路から低圧機器の筐体に漏洩電流が流れた場合、低圧機器の筐体から機器用接地極、大地、及びＢ種接地極を介して低圧側電路に戻る第１の通電路を流れる漏洩電流と、低圧機器の筐体から可変電気抵抗を介して当該高低圧変圧器の低圧側電路に戻るように接続された第２の通電路を流れる漏洩電流とが検出されると、第１、第２の二つの通電路を流れる漏洩電流が等しくなるように第２の通電路の可変電気抵抗の抵抗値が調整されるため、当該可変電気抵抗の抵抗値に基づいてＢ種接地極と機器用接地極の直列合成接地抵抗値を測定することができる。
これにより、計測用標準電圧が不要で、且つ高低圧変圧器が稼動中であっても、Ｂ種接地極と低圧機器を接地するための機器用接地極の直列合成接地抵抗を測定することができる。
【０００９】
請求項３記載の接地抵抗測定方法によれば、高低圧変圧器の低圧側電路から低圧機器の筐体に漏洩電流が流れた場合、低圧機器の筐体から前記機器用接地極、大地、及び前記Ｂ種接地極を介して低圧側電路に戻る第１の通電路を流れる漏洩電流と、Ｂ種接地極と前記機器用接地極の想定される直列合成接地抵抗値より大きい抵抗値の固定電気抵抗を有する第２の通電路を流れる漏洩電流とを、それぞれの漏洩電流の通電方向が反対になるように変流器により検出した状態で、第２の通電路の変流器への巻数を、第１、第２の二つの通電路を流れる漏洩電流の変流器による検出電流がゼロになるように調整する。この状態での第２の通電路の変流器への巻数と当該固定電気抵抗の抵抗値に基づいてＢ種接地極と機器用接地極の直列合成接地抵抗値を求めることができる。
これにより、計測用標準電圧が不要で、且つ高低圧変圧器が稼動中であっても、Ｂ種接地極と低圧機器を接地するための機器用接地極の直列合成接地抵抗を求めることができる。
【００１０】
請求項４記載の接地抵抗測定方法によれば、Ｂ種接地極と機器用接地極の直列合成接地抵抗値が定期的に測定されると、直列合成接地抵抗値の季節変動率が計算されるため、Ｂ種接地極及び機器用接地極それぞれの予め測定されている接地抵抗値に上記季節変動率を乗じることによってＢ種接地極及び機器用接地極それぞれの接地極の接地抵抗値を計算することができる。
これにより、Ｂ種接地極及び機器用接地極それぞれの接地抵抗値を簡易的に求めることができるため、Ｂ種接地極及び機器用接地極それぞれの接地抵抗値が電気設備技術基準に定められている許容値以下に保たれているか否かを判断することができる。
【００１１】
【発明の実施の形態】
次に、本発明の実施の形態について説明する。
図１は、電気設備技術基準で定められているＢ種接地極ＥＢと、１次側が特別高圧もしくは高圧の高低圧変圧器Ｔｒ１の低圧側電路ＬＬに接続される低圧機器ＬＭの筐体を接地するための機器用接地極（Ｄ種接地極、もしくは４００ボルト回路が存在すればＣ種接地極）ＥＤとの直列合成接地抵抗値を測定するための接地抵抗測定器１の構成を説明するための系統図である。
尚、上記低圧機器ＬＭは、電動機、電熱機器、照明機器等の電気機器や、電子機器、事務機器等の弱電機器、及び金属製電線管や金属製配線ダクト等を総称したものである。
【００１２】
Ｂ種接地極ＥＢは、高低圧変圧器Ｔｒ１の低圧側端子の一つもしくは中性線を接地するための接地極であり、Ｂ種接地極ＥＢと高低圧変圧器Ｔｒ１の低圧側端子の一つもしくは中性線とは接地線ＥＢＬで接続されている。また、低圧機器ＬＭの筐体と機器用接地極ＥＤとは接地線ＥＤＬで接続されている。
尚、接地線ＥＤＬは、一般的に良好な接地特性を有する建物の基礎Ｇに接続されることが多い。
【００１３】
図１に示すように、接地線ＥＢＬは電流検出手段である変流器ＺＣＴを貫通するようにセットされる。また、接地線ＥＢＬと接地線ＥＤＬの間に通電路２が接続されており、通電路２の中間部には可変抵抗器Ｒが直列に接続されている。尚、可変抵抗器Ｒに対して接地線ＥＢＬ側の配線２Ｌは、接地線ＥＢＬを流れる電流と反対の方向に流れる電流が検出されるように変流器ＺＣＴをセットされる。
【００１４】
変流器ＺＣＴにより検出される電流は、前記低圧側電路ＬＬから低圧機器ＬＭの筐体に漏洩した漏洩電流であり、その漏洩電流の一部Ｉ１は、接地線ＥＤＬから、通電路２の配線２Ｒ、可変抵抗器Ｒ、配線２Ｌ、接地線ＥＢＬを流れ、低圧側電路ＬＬに戻る回路を流れ、残りの漏洩電流Ｉ２は、接地線ＥＤＬから、機器用接地極ＥＤ、大地、Ｂ種接地極ＥＢ、接地線ＥＢＬを流れ、低圧側電路ＬＬに戻る回路を流れる。この場合、漏洩電流Ｉ１と漏洩電流Ｉ２は流れる方向が反対の状態で変流器ＺＣＴにより同時に検出される。
【００１５】
変流器ＺＣＴは調整手段である制御回路３に接続されており、漏洩電流Ｉ１と漏洩電流Ｉ２の電流検出信号が変流器ＺＣＴから制御回路３に入力される。制御回路３は、変流器ＺＣＴから出力された電流検出信号がゼロとなるように前述の可変抵抗器Ｒの抵抗値を調整する。制御回路３が可変抵抗器Ｒの抵抗値を調整する手段としては、フィードバック制御により可変抵抗器Ｒをサーボモータで駆動する手段や、リレースイッチ等を利用して、いくつかの抵抗素子を直並列に接続替えを行い、抵抗値を変化させる手段などがある。
【００１６】
上記のように、制御回路３が変流器ＺＣＴから出力される電流検出信号をゼロにするように前述の可変抵抗器Ｒの抵抗値を調整した場合、この状態での可変抵抗器Ｒの抵抗値がＢ種接地極ＥＢと機器用接地極ＥＤの直列合成接地抵抗値となる。この可変抵抗器Ｒの抵抗値は、制御回路３から表示装置等の出力手段４に出力される。尚、図１に示すように機器用接地極ＥＤと建物基礎Ｇが並列的に接続されている場合、可変抵抗器Ｒの抵抗値は、機器用接地極ＥＤの接地抵抗値ＲＤと建物基礎Ｇの接地抵抗値ＲＸとを並列合成した接地抵抗値とＢ種接地極ＥＢの接地抵抗値ＲＢを直列に合成した直列合成接地抵抗値と等しくなる。
Ｒ＝｛ＲＤ・ＲＸ／（ＲＤ＋ＲＸ）｝＋ＲＢ・・・・・式（１）
尚、前述の接地線ＥＤＬが建物基礎Ｇに接続されていない場合、当然、可変抵抗器Ｒの抵抗値は、機器用接地極ＥＤの接地抵抗値ＲＤとＢ種接地極ＥＢの接地抵抗値ＲＢとを直列に合成した直列合成接地抵抗値と等しくなる。
Ｒ＝ＲＤ＋ＲＢ・・・・・・・・・・・・・・・・・・式（２）
【００１７】
以上のように、変流器ＺＣＴで前述の漏洩電流Ｉ１と漏洩電流Ｉ２が同時に検出されて変流器ＺＣＴから出力される電流検出信号がゼロとなるように可変抵抗器Ｒが調整された場合、制御回路３は、式（１）で示される抵抗値を、Ｂ種接地極ＥＢと機器用接地極ＥＤと建物基礎Ｇの合成接地抵抗値として測定する。
また、前述の接地線ＥＤＬが建物基礎Ｇに接続されていない場合、制御回路３は、式（２）で示される抵抗値を、Ｂ種接地極ＥＢと機器用接地極ＥＤの直列合成接地抵抗値として測定する。
【００１８】
接地抵抗測定担当者は、接地抵抗測定器１を用いることにより、上記式（１）、式（２）で示される直列合成接地抵抗値を高低圧変圧器Ｔｒ１の竣工時から定期的に測定することによって、その直列合成接地抵抗値の季節的変動幅と季節的変動率を計算する。
【００１９】
Ｂ種接地極ＥＢ、及び、機器用接地極ＥＤは、それぞれの接地極の竣工時に、高低圧変圧器Ｔｒ１に関する電気設備と接続されていない状態でそれぞれの接地極の接地抵抗値が従来の接地抵抗計により測定されている。
Ｂ種接地極ＥＢ、及び、機器用接地極ＥＤそれぞれの接地抵抗値が、上記直列合成接地抵抗値と同様に季節的に変動するものと仮定すれば、既に測定されているＢ種接地極ＥＢ、及び、機器用接地極ＥＤそれぞれの竣工時の接地抵抗値に上記直列合成接地抵抗値の季節的変動率を乗算することによって、それぞれの接地極の接地抵抗値が電気設備技術基準で定められている許容値以下となっているか否かを判断することが可能である。
【００２０】
以上の説明した接地抵抗測定器１では、制御回路３により自動的に直列合成接地抵抗値を求めるものであるが、制御回路３を無くすとともに、変流器ＺＣＴの代わりに漏れ電流計測用の表示付き携帯型クランプセンサを用い、その表示値がゼロとなるように、即ち、前述の漏洩電流Ｉ１と漏洩電流Ｉ２が等しくなるように可変抵抗器Ｒを調整し、表示値がゼロとなったときの可変抵抗Ｒの抵抗値を機器用接地極ＥＤとＢ種接地極ＥＢの直列合成接地抵抗値としてもよい。
【００２１】
また、図１における可変抵抗器Ｒを、測定対象となるＢ種接地極ＥＢと機器用接地極ＥＤの想定される直列合成接地抵抗値の１０倍程度の固定抵抗器に代えるとともに、変流器ＺＣＴを、漏れ電流計測用の表示付き携帯型クランプセンサに代えた状態で、その表示値がゼロとなるように、表示付き携帯型クランプセンサに巻きつける配線（図１に示した配線２Ｌに相当する）の巻数Ｎを増やす。そして、その固定抵抗の抵抗値を上記配線の巻数Ｎで除した値を、機器用接地極ＥＤとＢ種接地極ＥＢの直列合成接地抵抗値としてもよい。尚、この場合、固定抵抗の抵抗値は、測定対象となるＢ種接地極ＥＢと機器用接地極ＥＤの想定される直列合成接地抵抗値より大きいほど、直列合成接地抵抗値の測定精度が高くなる。その理由は、表示付き携帯型クランプセンサに巻きつける配線の巻数Ｎが増えて検出電流の分解能が高くなるためである。
【００２２】
【発明の効果】
本発明によれば、計測用標準電圧が不要で、且つ高低圧変圧器が稼動中であってもＢ種接地極と機器用接地極の直列合成接地抵抗値を測定することができる。また、定期的に測定した直列合成接地抵抗値に基づいて計算した直列合成接地抵抗値の季節変動率を、Ｂ種接地極及び機器用接地極それぞれの竣工時に既に測定されている接地抵抗値に乗じることによって、それぞれの接地極の接地抵抗値が電気設備技術基準で定められている許容値以下に保たれているか否かを判断することができる。
【図面の簡単な説明】
【図１】接地抵抗測定器の全体的な構成と接地抵抗値を測定するための方法を説明するための系統図である。
【図２】接地抵抗値を測定するための従来の手段を説明した説明図である。
【符号の説明】
１ 接地抵抗測定器
２ 通電路
３ 制御回路
４ 出力手段
Ｔｒ１ 高低圧変圧器
ＥＢ Ｂ種接地極
ＥＤ 機器用接地極
ＥＢＬ Ｂ種接地線
ＥＤＬ 接地線
Ｒ 可変抵抗器
ＬＬ 低圧側電路
ＬＭ 低圧機器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a grounding resistance measuring instrument and a grounding resistance measuring series combined grounding resistance of a class B grounding electrode defined by the technical standards of electrical equipment and a grounding electrode for equipment for grounding a housing of a low-voltage equipment. Related to the measurement method.
[0002]
[Prior art]
Conventionally, to ground one of the low-voltage terminals of a high-low voltage transformer or a B-type grounding electrode for grounding the neutral conductor, or to ground the housing of a low-voltage device connected to the low-voltage circuit of the high-low voltage transformer When the ground resistance of the D-class ground electrode or the C-class ground electrode is measured by the ground resistance meter 20, the measurement is performed based on the potential drop method as shown in FIG. The potential drop method is to apply an AC voltage output from an
[0003]
[Non-patent document 1]
Takehiko Takahashi, Introduction to Grounding Technology, Ohmsha Publishing Co., Ltd., February 10, 1988, p150-153
[0004]
[Problems to be solved by the invention]
When measuring the grounding resistance of the grounding electrode 21 to be measured, for example, the class B grounding electrode, with the above-mentioned conventional grounding resistance meter 20, when the electrical equipment such as a high-low voltage transformer or the like is completed, or when the annual inspection is performed, the power in the customer premises is interrupted. The measurement must be performed by electrically disconnecting the ground electrode 21 to be measured from the high / low voltage transformer. Therefore, it is practically difficult to measure the ground resistance value of the measurement target ground electrode 21 at any time. Further, an
In general, it is known that the grounding resistance value of the grounding electrode does not become constant throughout the year because it varies seasonally depending on the temperature and the water content of the ground. Therefore, simply measuring the grounding resistance of the grounding electrode only at the time of completion of the high-low voltage transformer or at the time of annual inspection, the grounding resistance of the grounding electrode falls below the allowable value specified by the Electrical Equipment Technical Standards. We cannot guarantee that it is always kept.
[0005]
Therefore, in the present invention, even if a standard voltage for measurement is not required and the primary side is operating a special high voltage or high voltage low / high voltage transformer, the class B grounding electrode and the equipment ground for grounding the low voltage equipment are used. A ground resistance measuring instrument and a ground resistance measuring method capable of measuring a series combined ground resistance value with a pole are provided, and a seasonal variation rate calculated based on the measured series combined ground resistance value is calculated for a high-low voltage transformer. By multiplying the ground resistance values of the class B ground electrode and the equipment ground electrode measured in advance at the time of completion, the ground resistance value of each ground electrode is kept below the allowable value specified in the Electrical Equipment Technical Standards. It is an object of the present invention to provide a ground resistance measuring method capable of judging whether or not the ground resistance is measured.
[0006]
[Means for Solving the Problems]
The above object can be solved by a ground resistance measuring instrument and a ground resistance measuring method described in the claims.
[0007]
According to the grounding resistance measuring device of the present invention, when a leakage current flows from the low-voltage side electric circuit of the high-low voltage transformer to the housing of the low-voltage device, the current detecting means moves the grounding electrode for the device from the housing of the low-voltage device. , Ground, and leakage current flowing through the first current path returning to the low-voltage side electric circuit via the B-type grounding electrode, and returning to the low-voltage side electric circuit of the high-low-voltage transformer via the variable electric resistance from the housing of the low-voltage device. When the leakage current flowing through the second current path connected as described above is detected simultaneously in the opposite direction of current flow, the adjustment means adjusts the variable electric resistance so that the current detection signal output from the current detection means becomes zero. In order to automatically adjust the resistance value, the output means outputs the resistance value. As described above, when the resistance value of the variable electric resistance is automatically adjusted so that the current detection value of the current detection means becomes zero, the resistance value of the variable electric resistance output from the output means is changed to the class B ground electrode. It is measured as the series combined ground resistance value of the device and the ground electrode for the device.
This makes it possible to measure the series combined ground resistance of the class B ground electrode and the equipment ground electrode for grounding the low-voltage equipment even when the standard voltage for measurement is unnecessary and the high-low voltage transformer is operating. it can.
[0008]
According to the grounding resistance measuring method of claim 2, when a leakage current flows from the low-voltage side electric circuit of the high-low voltage transformer to the housing of the low-voltage device, the equipment grounding pole, the ground, and the B from the low-voltage device housing. A leakage current flowing through the first current path returning to the low-voltage side electric circuit via the seed grounding electrode, and a connection is made to return to the low-voltage side electric circuit of the high / low-voltage transformer via a variable electric resistance from the housing of the low-voltage device. When the leakage current flowing through the second current path is detected, the resistance value of the variable electric resistance of the second current path is adjusted so that the leakage current flowing through the first and second current paths becomes equal. Therefore, based on the resistance value of the variable electric resistance, the series combined ground resistance value of the class B ground electrode and the equipment ground electrode can be measured.
This makes it possible to measure the series combined ground resistance of the class B ground electrode and the equipment ground electrode for grounding the low-voltage equipment even when the standard voltage for measurement is unnecessary and the high-low voltage transformer is operating. it can.
[0009]
According to the grounding resistance measuring method of claim 3, when a leakage current flows from the low-voltage side electric circuit of the high-low voltage transformer to the housing of the low-voltage device, the device grounding pole, the ground, and the low-voltage device housing. A leakage current flowing through the first current path returning to the low-voltage side electric circuit via the class-B ground electrode, and a fixed electricity having a resistance value larger than an assumed series combined ground resistance value of the class-B ground electrode and the equipment ground electrode. The number of turns of the second current path to the current transformer is determined in a state where the current flowing through the second current path having resistance is detected by the current transformer so that the current directions of the respective leakage currents are opposite to each other. , The leakage current flowing through the first and second current paths is adjusted so that the current detected by the current transformer becomes zero. In this state, the series combined ground resistance value of the class B ground electrode and the equipment ground electrode can be obtained based on the number of turns of the second current path to the current transformer and the resistance value of the fixed electric resistance.
Thus, even when the standard voltage for measurement is unnecessary and the high-low voltage transformer is in operation, the series combined ground resistance of the class B ground electrode and the equipment ground electrode for grounding the low-voltage equipment can be obtained. .
[0010]
According to the ground resistance measuring method of the fourth aspect, when the series combined ground resistance value of the class B ground electrode and the equipment ground electrode is periodically measured, the seasonal variation rate of the series combined ground resistance value is calculated. Therefore, the ground resistance value of each of the class B ground electrode and the equipment ground electrode is calculated by multiplying the previously measured ground resistance value of each of the class B ground electrode and the equipment ground electrode by the seasonal variation rate. be able to.
This makes it possible to easily determine the ground resistance value of each of the Class B ground electrode and the equipment ground electrode. Therefore, the ground resistance value of each of the Class B ground electrode and the equipment ground electrode is determined by the technical standards for electrical equipment. It can be determined whether or not the value is kept below the allowable value.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described.
FIG. 1 illustrates the grounding of the type-B grounding electrode EB defined in the technical standards for electrical equipment and the housing of the low-voltage device LM whose primary side is connected to the low-voltage side electric circuit LL of the high-low-voltage transformer Tr1 of extra high voltage or high voltage. The grounding resistance measuring device 1 for measuring a series combined grounding resistance value with a device grounding pole (D-class grounding pole or a C-class grounding pole if a 400 volt circuit is present) ED to perform the measurement is described. FIG.
The low-voltage device LM is a general term for electric devices such as electric motors, electric heating devices, and lighting devices, weak electric devices such as electronic devices and office devices, and metal conduits and metal wiring ducts.
[0012]
The class B ground electrode EB is a ground electrode for grounding one of the low-voltage terminals of the high / low voltage transformer Tr1 or the neutral wire, and is one of the low voltage terminals of the class B ground electrode EB and the high / low voltage transformer Tr1. Or the neutral line is connected to a ground line EBL. Further, the housing of the low-voltage device LM and the device ground electrode ED are connected by a ground line EDL.
The ground line EDL is often connected to the foundation G of a building having generally good grounding characteristics.
[0013]
As shown in FIG. 1, the ground line EBL is set so as to pass through a current transformer ZCT which is a current detecting means. A current path 2 is connected between the ground line EBL and the ground line EDL, and a variable resistor R is connected in series to an intermediate portion of the current path 2. The current transformer ZCT is set on the
[0014]
The current detected by the current transformer ZCT is a leakage current leaking from the low-voltage side electric circuit LL to the housing of the low-voltage device LM, and a part I1 of the leakage current is transmitted from the ground line EDL to the wiring of the current path 2. 2R, the variable resistor R, the
[0015]
The current transformer ZCT is connected to the control circuit 3 as adjusting means, and current detection signals of the leakage current I1 and the leakage current I2 are input to the control circuit 3 from the current transformer ZCT. The control circuit 3 adjusts the resistance value of the variable resistor R so that the current detection signal output from the current transformer ZCT becomes zero. As means for the control circuit 3 to adjust the resistance value of the variable resistor R, means for driving the variable resistor R with a servomotor by feedback control, or using a relay switch or the like to connect several resistance elements in series and parallel. There is a method of changing the connection and changing the resistance value.
[0016]
As described above, when the control circuit 3 adjusts the resistance value of the variable resistor R so that the current detection signal output from the current transformer ZCT becomes zero, the resistance of the variable resistor R in this state is adjusted. The value is a series combined ground resistance value of the class B ground electrode EB and the equipment ground electrode ED. The resistance value of the variable resistor R is output from the control circuit 3 to output means 4 such as a display device. When the equipment ground electrode ED and the building foundation G are connected in parallel as shown in FIG. 1, the resistance value of the variable resistor R is equal to the ground resistance value RD of the equipment ground electrode ED and the building foundation G. And the ground resistance value RX obtained by combining the ground resistance value RX of the B-type ground electrode EB in series with the ground resistance value obtained by combining the ground resistance values RX in parallel with each other.
R = {RD.RX / (RD + RX)} + RB... Formula (1)
When the above-mentioned ground line EDL is not connected to the building foundation G, the resistance value of the variable resistor R is naturally the ground resistance value RD of the equipment ground electrode ED and the ground resistance value RB of the class B ground electrode EB. Are combined in series to be equal to a series combined ground resistance value.
R = RD + RB (2)
[0017]
As described above, when the above-described leakage current I1 and leakage current I2 are simultaneously detected by the current transformer ZCT and the variable resistor R is adjusted so that the current detection signal output from the current transformer ZCT becomes zero. The control circuit 3 measures the resistance value represented by the equation (1) as a combined ground resistance value of the class B ground electrode EB, the equipment ground electrode ED, and the building foundation G.
When the above-mentioned ground line EDL is not connected to the building foundation G, the control circuit 3 sets the resistance value represented by the equation (2) to a series combined ground resistance of the class B ground electrode EB and the equipment ground electrode ED. Measure as a value.
[0018]
The person in charge of measuring the ground resistance uses the ground resistance measuring device 1 to periodically measure the series combined ground resistance value represented by the above formulas (1) and (2) from the time of completion of the high / low voltage transformer Tr1. Thus, the seasonal fluctuation range and the seasonal fluctuation rate of the series combined ground resistance value are calculated.
[0019]
The class B ground pole EB and the equipment ground pole ED have the ground resistance of each ground pole at the time of completion of each ground pole in a state where the ground resistance value of each ground pole is not connected to the electrical equipment related to the high / low voltage transformer Tr1. It is measured by a resistance meter.
Assuming that the ground resistance values of the class B ground electrode EB and the device ground electrode ED fluctuate seasonally similarly to the series combined ground resistance value, the class B ground electrode EB already measured is assumed. , And by multiplying the ground resistance at the time of completion of each of the equipment ground poles ED by the seasonal variation rate of the series combined ground resistance, the ground resistance of each ground pole is determined by the electrical equipment technical standards. It is possible to determine whether or not it is equal to or less than the allowable value.
[0020]
In the grounding resistance measuring device 1 described above, the series combined grounding resistance is automatically obtained by the control circuit 3. However, the control circuit 3 is eliminated, and a display for measuring a leakage current is provided instead of the current transformer ZCT. When the variable resistor R is adjusted so that the display value becomes zero, that is, the above-described leakage current I1 and the leakage current I2 are equalized using the portable clamp sensor with May be used as a series combined ground resistance value of the equipment ground electrode ED and the class B ground electrode EB.
[0021]
Further, the variable resistor R in FIG. 1 is replaced with a fixed resistor having a value of about 10 times the assumed series combined ground resistance value of the type B ground electrode EB and the equipment ground electrode ED to be measured, and a current transformer. Wiring (equivalent to the
[0022]
【The invention's effect】
According to the present invention, a series combined ground resistance value of the class B ground electrode and the equipment ground electrode can be measured even when the standard voltage for measurement is unnecessary and the high / low voltage transformer is operating. In addition, the seasonal variation rate of the series combined ground resistance calculated based on the series combined ground resistance measured periodically is changed to the ground resistance already measured at the completion of each of the Class B ground pole and the equipment ground pole. By multiplying, it is possible to determine whether or not the ground resistance value of each ground electrode is maintained at or below an allowable value defined by the electrical equipment technical standards.
[Brief description of the drawings]
FIG. 1 is a system diagram for explaining an overall configuration of a ground resistance measuring device and a method for measuring a ground resistance value.
FIG. 2 is an explanatory view illustrating a conventional means for measuring a ground resistance value.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ground resistance measuring device 2 Current path 3 Control circuit 4 Output means Tr1 High / low voltage transformer EB Class B ground pole ED Equipment ground pole EBL Class B ground wire EDL Ground wire R Variable resistor LL Low voltage side circuit LM Low voltage device
Claims (4)
前記高低圧変圧器の低圧側電路から前記低圧機器の筐体に漏洩電流が流れた場合、前記低圧機器の筐体から前記機器用接地極、大地、及び前記Ｂ種接地極を介して前記低圧側電路に戻る第１の通電路を流れる漏洩電流と、前記低圧機器の筐体から可変電気抵抗を介して当該高低圧変圧器の低圧側電路に戻るように接続された第２の通電路を流れる漏洩電流とを、前記第１の通電路を流れる漏洩電流の通電方向と反対の通電方向で同時に検出する電流検出手段と、前記電流検出手段から出力される電流検出信号がゼロになるように前記可変電気抵抗の抵抗値を自動的に調整する調整手段と、前記調整手段で調整された可変電気抵抗の抵抗値を外部に出力する出力手段とを備え、前記電流検出手段の電流検出値がゼロになるように前記可変電気抵抗の抵抗値が自動的に調整された場合の当該可変電気抵抗の抵抗値に基づいて前記Ｂ種接地極と前記機器用接地極の直列合成接地抵抗値を測定することを特徴とする接地抵抗測定器。A device for grounding one of the low-voltage terminals of the high-low voltage transformer or a class B ground electrode for grounding the neutral conductor, and a low-voltage device housing used in the low-voltage circuit of the high-low voltage transformer A ground resistance measuring device for measuring a series combined ground resistance value with a ground electrode for
When a leakage current flows from the low-voltage side electric circuit of the high-low voltage transformer to the housing of the low-voltage equipment, the low-voltage equipment is connected to the low-voltage equipment via the equipment grounding pole, the ground, and the B-type grounding pole. A leakage current flowing through the first current path returning to the side power path and a second current path connected to return to the low voltage side power path of the high / low voltage transformer via a variable electric resistance from the housing of the low voltage device. Current detection means for simultaneously detecting the flowing leakage current in the direction of current flow opposite to the direction of current flow of the leakage current flowing through the first current path, and a current detection signal output from the current detection means being zero. Adjustment means for automatically adjusting the resistance value of the variable electric resistance, and output means for outputting the resistance value of the variable electric resistance adjusted by the adjustment means to the outside, wherein the current detection value of the current detection means is The variable electrical resistor is set to zero. Measuring the series combined ground resistance value of the class B ground electrode and the device ground electrode based on the resistance value of the variable electric resistance when the resistance value of the device is automatically adjusted. vessel.
前記高低圧変圧器の低圧側電路から前記低圧機器の筐体に漏洩電流が流れた場合、前記低圧機器の筐体から前記機器用接地極、大地、及び前記Ｂ種接地極を介して前記低圧側電路に戻る第１の通電路を流れる漏洩電流と、前記低圧機器の筐体から可変電気抵抗を介して当該高低圧変圧器の低圧側電路に戻るように接続された第２の通電路を流れる漏洩電流とを検出する行程と、前記第１、第２の二つの通電路を流れる漏洩電流が等しくなるように前記第２の通電路の可変電気抵抗の抵抗値を調整する行程と、前記第１、第２の二つの通電路を流れる漏洩電流が等しくなるように前記第２の通電路の可変電気抵抗の抵抗値が調整された場合の当該抵抗値に基づいて前記Ｂ種接地極と前記機器用接地極の直列合成接地抵抗値を測定する行程とを有することを特徴とする接地抵抗測定方法。A device for grounding one of the low-voltage terminals of the high-low voltage transformer or a class B ground electrode for grounding the neutral conductor, and a low-voltage device housing used in the low-voltage circuit of the high-low voltage transformer A ground resistance measuring method for measuring a series combined ground resistance value with a ground electrode for
When a leakage current flows from the low-voltage side electric circuit of the high-low voltage transformer to the housing of the low-voltage equipment, the low-voltage equipment is connected to the low-voltage equipment via the equipment grounding pole, the ground, and the B-type grounding pole. A leakage current flowing through the first current path returning to the side power path and a second current path connected to return to the low voltage side power path of the high / low voltage transformer via a variable electric resistance from the housing of the low voltage device. A step of detecting a flowing leakage current, a step of adjusting a resistance value of a variable electric resistance of the second current path so that the leakage current flowing through the first and second current paths becomes equal, When the resistance value of the variable electric resistance of the second current path is adjusted so that the leakage currents flowing through the first and second two current paths become equal, the B-type ground electrode is Measuring a series combined earth resistance value of the equipment earth electrode. Ground resistance measurement method according to claim Rukoto.
前記高低圧変圧器の低圧側電路から前記低圧機器の筐体に漏洩電流が流れた場合、前記低圧機器の筐体から前記機器用接地極、大地、及び前記Ｂ種接地極を介して前記低圧側電路に戻る第１の通電路を流れる漏洩電流と、前記低圧機器の筐体から前記Ｂ種接地極と前記機器用接地極の想定直列合成接地抵抗値より大きい抵抗値の固定電気抵抗を介して前記高低圧変圧器の低圧側電路に戻るように接続された第２の通電路を流れる漏洩電流とを、それぞれの漏洩電流の通電方向が反対になるように変流器により検出する行程と、前記第２の通電路の変流器への巻数を調整して前記第１、第２の二つの通電路を流れる漏洩電流の検出電流がゼロになるように調整する行程と、変流器の検出電流がゼロになるように前記第２の通電路の変流器への巻数が調整された場合の巻数と前記固定電気抵抗の抵抗値に基づいて前記Ｂ種接地極と前記機器用接地極の直列合成接地抵抗値を求める行程とを有することを特徴とする接地抵抗測定方法。A device for grounding one of the low-voltage terminals of the high-low voltage transformer or a class B ground electrode for grounding the neutral conductor, and a low-voltage device housing used in the low-voltage circuit of the high-low voltage transformer A ground resistance measuring method for measuring a series combined ground resistance value with a ground electrode for
When a leakage current flows from the low-voltage side electric circuit of the high-low voltage transformer to the housing of the low-voltage equipment, the low-voltage equipment is connected to the low-voltage equipment via the equipment grounding pole, the ground, and the B-type grounding pole. A leakage current flowing through a first current path returning to the side electric circuit, and a fixed electric resistance having a resistance value larger than an assumed series combined ground resistance value of the class B ground electrode and the equipment ground electrode from the housing of the low voltage device. Detecting the leakage current flowing through the second current path connected back to the low-voltage side electric circuit of the high-low voltage transformer with a current transformer so that the direction of current flow of each leakage current is opposite. Adjusting the number of turns of the second current path to the current transformer so as to adjust the detection current of the leakage current flowing through the first and second two current paths to zero; and So that the detected current of the second current path becomes zero. Determining a series combined ground resistance value of the class B ground electrode and the equipment ground electrode based on the number of turns when the resistance is adjusted and the resistance value of the fixed electrical resistance. .
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