JP2004138493A

JP2004138493A - Electronic watthour meter

Info

Publication number: JP2004138493A
Application number: JP2002303188A
Authority: JP
Inventors: Yasumasa Hayashi; 林　泰正; Tetsuya Nakamura; 中村　哲也
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2002-10-17
Filing date: 2002-10-17
Publication date: 2004-05-13

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic watthour meter which can measure accurately an AC current containing a distortion waveform and DC component, with a simple circuit. <P>SOLUTION: The watthour meter is equipped with first and second power-pulse transducing units 9 and 11, first and second optical coupling sections 12 and 13, and a pulse composition/integration metering section 14. The first section 9 detects a voltage and a current supplied from a power source to a load through first pathways 16, 17, setting an electric potential of a first line 16 constituting the first pathway as a reference potential, calculates power, and outputs it as a first power signal setting the potential of the first line 16 as the reference potential. A second section 11 detects a voltage and a current supplied from the power source to the load through second pathways 17, 18, setting an electric potential of a third line 18 constituting the second pathway as a reference potential, calculates power and outputs it as a second power signal setting an electric potential of the third line 18 as a reference potential. The first and second optical coupling sections 12 and 13 convert the second power signal from the second section 11 to a third power signal. A pulse compound/integration metering part 14 combines the first power signal with the third power signal and obtains energy. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は電子式電力量計に関し、特に電気使用量を正確に計量する技術に関する。
【０００２】
【従来の技術】
従来、ユーザによる電気使用量を計量するために電子式電力量計が使用されている。図３はこのような電子式電力量計の１つである低圧用の単相３線式の電子式電力量計の構成を示すブロック図である（特許文献１）。この電子式電力量計は、電源側端子２、負荷側端子３、第１電流検出部（ＣＴ１）３２、第３電流検出部（ＣＴ３）３３、第１電圧検出部４、第３電圧検出部５、電源回路３４、電力−パルス変換部３５、積算計量部３６及び表示部１５から構成されている。
【０００３】
電源側端子２は、電源の第１相が接続される端子１Ｓ、ニュートラル相（Ｎ相）が接続される端子２Ｓ、及び第３相が接続される端子３Ｓから構成されている。なお、単相３線式の場合は、第１相の電力と第３相の電力とは位相が異なる訳ではない（単相である）が、本明細書では便宜上、「第１相」及び「第３相」と呼ぶ。同様に、負荷側端子３は、負荷の第１相に接続される端子１Ｌ、ニュートラル相（Ｎ相）に接続される端子２Ｌ、及び第３相に接続される端子３Ｌから構成されている。
【０００４】
電源側からの電力は、電子式電力量計の電源側端子２から負荷側端子３を経由して負荷側へ供給される。以下では、電源側端子２の端子１Ｓから負荷側端子３の端子１Ｌまでを第１線路１６、電源側端子２の端子２Ｓから負荷側端子３の端子２Ｌまでを第２線路１７、電源側端子２の端子３Ｓから負荷側端子３の端子３Ｌまで第３線路１８と呼ぶ。
【０００５】
第１電流検出部３２は、第１線路１６を貫通させるように配置された電流トランスから構成されている。第１電流検出部３２は、第１線路１６を流れる電流を非接触で検出し、第１電流信号Ｉ１として電力−パルス変換部３５に送る。第１電流信号Ｉ１の電位は、第１線路１６の電位とは分離（絶縁）されている。
【０００６】
第１電圧検出部４は、第２線路１７の電位に対する第１線路１６の電位、つまりＮ相を基準とする第１相の電圧を検出する。第１電圧検出部４は、一端が第２線路１７に接続された抵抗Ｒ１１と、この抵抗Ｒ１１の他端に一端が接続されると共に他端が第１線路１６に接続された抵抗Ｒ１２とから構成されている。第１電圧検出部４は、抵抗Ｒ１１とＲ１２との接続点の電圧を第１電圧信号Ｖ１として電力−パルス変換部３５に送る。この場合、抵抗Ｒ１１及びＲ１２の各抵抗値は、第１電圧信号Ｖ１が数ボルト程度といったロジックレベルの信号になるように選択されている。
【０００７】
第３電流検出部３３は、第３線路１８を貫通させるように配置された電流トランスから構成されている。第３電流検出部３３は、第３線路１８を流れる電流を非接触で検出し、第３電流信号Ｉ３として電力−パルス変換部３５に送る。第３電流信号Ｉ３の電位は、第３線路１８の電位とは分離（絶縁）されている。
【０００８】
第３電圧検出部５は、第２線路１７の電位に対する第３線路１８の電位、つまりＮ相を基準とする第３相の電圧を検出する。第３電圧検出部５は、一端が第２線路１７に接続された抵抗Ｒ２１と、この抵抗Ｒ２１の他端に一端が接続されると共に他端が第３線路１８に接続された抵抗Ｒ２２とから構成されている。第３電圧検出部５は、抵抗Ｒ２１とＲ２２との接続点の電圧を第３電圧信号Ｖ３として電力−パルス変換部３５に送る。この場合、抵抗Ｒ２１及び抵抗Ｒ２２の各抵抗値は、第３電圧信号Ｖ３がロジックレベルの信号になるように選択されている。
【０００９】
電源回路３４は、Ｎ相と第１相との相間電圧（単相３線式では１００Ｖ）からロジックレベルの電圧を有する直流電力を生成する。この場合、第２線路１７の電位が基準電位、つまりグランドＧとして使用されている。この電源回路３４で生成された直流電力は、電力−パルス変換部３５、積算計量部３６及び表示部１５に供給される。
【００１０】
電力−パルス変換部３５は、第１電流検出部３２からの第１電流信号Ｉ１と第１電圧検出部４からの第１電圧信号Ｖ１とを乗算して第１相の電力を算出し、また、第３電流検出部３３からの第３電流信号Ｉ３と第３電圧検出部５からの第３電圧信号Ｖ３とを乗算して第３相の電力を算出し、これら算出された２つの電力を合成して合成電力を求める。そして、求められた合成電力に比例する周波数のパルスを有するパルス信号Ｐを生成して積算計量部３６に送る。
【００１１】
積算計量部３６は、電力−パルス変換部３５から送られてくるパルス信号Ｐに含まれるパルスを積算（累積加算）して記憶すると共に、記憶されている積算されたパルス数を使用電力量として表示部１５に送る。これにより、使用電力量が表示部１５に表示される。
【００１２】
【特許文献１】
特許第３１１２６１１号（第３頁−６頁、第５図）
【００１３】
【発明が解決しようとする課題】
上述したように、従来の電子式電力量計においては、電源側から負荷側に流れる交流電流を検出するために電流トランスが使用されている。この電流トランスは、交流電流が正弦波形を有する場合は問題ないが、正弦波形が歪んだり、交流電流が直流成分を含む場合は正確な計測ができなくなる。特に、最近は負荷の多様化が著しく、交流電流の正弦波形に歪みが発生したり、交流電流に直流成分が含まれる可能性がある。従って、このような悪条件でも正しい電力量を計量できる電力量計が求められている。
【００１４】
ところで、歪んだ波形を有する電流や直流成分を含んだ電流を計測するためには、シャント抵抗を用いて電源側から負荷側に流れる電流を直接計測することが考えられる。シャント抵抗は、電流の流れを阻害しないで低レベルの電流信号を検出するための抵抗である。しかしながら、従来の電流トランスをシャント抵抗に置き換えようとすると、単相３線式等といった電力量の計算のために２つ以上の乗算が必要な電子式電力量計では、第１線路１６と第３線路１８との基準電位が異なるため、シャント抵抗からの信号を電力−パルス変換部に入力することができない。
【００１５】
本発明は、簡単な回路で歪み波形や直流成分を含んだ交流電流でも正確に計量できる電子式電力量計を提供することにある。
【００１６】
【課題を解決するための手段】
上記課題を達成するために、請求項１の発明は、電源から第１経路を介して負荷に供給される電圧及び電流を該第１経路を構成する第１線路の電位を基準電位として検出して電力を計算し、第１線路の電位を基準電位とする第１電力信号として出力する第１電力計算部と、電源から第２経路を介して負荷に供給される電圧及び電流を該第２経路を構成する第３線路の電位を基準電位として検出して電力を計算し、第３線路の電位を基準電位とする第２電力信号として出力する第２電力計算部と、第２電力計算部からの第２電力信号を第１線路の電位を基準電位とする第３電力信号に変換する変換部と、第１電力計算部からの第１電力信号と変換部からの第３電力信号とを合成して電力量を求める計量部とを備えることを特徴とする。
【００１７】
請求項１の発明によれば、第１経路の電力を表す第１電力信号と第２経路の電力を表す第２電力信号とは基準電位が異なる信号であるが、第２電力信号の基準電位を第１電力信号の基準電位と同じになるように変換し、この変換により得られた第３電力信号と第１電力信号とを合成し、電力量を求めるようにしている。従って、例えば従来の電子式電力量計で使用されている電流トランスの代わりに例えばシャント抵抗を用いることが可能になり、その結果、簡単な回路で歪み波形や直流成分を含んだ交流電流でも正確に計量できる。
【００１８】
請求項２の発明において、第１電力計算部は、第１電力信号として、計算された電力に含まれる正方向の電力に比例した周波数の正パルス信号と負方向の電力に比例した周波数の負パルス信号とを出力し、第２電力計算部は、第２電力信号として、計算された電力に含まれる正方向の電力に比例した周波数の正パルス信号と負方向の電力に比例した周波数の負パルス信号とを出力し、計量部は、第１電力計算部からの第１電力信号に含まれる正パルス信号及び負パルス信号と、変換部からの第３電力信号に含まれる正パルス信号及び負パルス信号とを符号を考慮して積算することにより電力量を求めるように構成できる。
【００１９】
請求項２の発明によれば、電力量が正パルス信号及び負パルス信号で得られるので、電子式電力量計で一般に採用されているプロセッサを流用したデジタル処理によって積算処理を行うことができる。
【００２０】
請求項３の発明において、第１電力計算部は、第１電力信号として、計算された電力に比例した周波数のパルス信号と該パルス信号が正方向の電力であるか負方向の電力であるかを表す符号信号とを出力し、第２電力計算部は、第２電力信号として、計算された電力に比例した周波数のパルス信号と該パルス信号が正方向の電力であるか負方向の電力であるかを表す符号信号とを出力し、計量部は、第１電力計算部からの第１電力信号に含まれるパルス信号を符号信号に応じて累積的に加算又は減算して第１電力量を算出し、第２電力計算部から変換部を経由して送られてくる第３電力信号に含まれるパルス信号を符号信号に応じて累積的に加算又は減算して第３電力量を算出し、第１電力量と第３電力量とを加算することにより電力量を求めるように構成できる。
【００２１】
請求項３の発明によれば、電力量がパルス信号及び符号信号で得られるので、電子式電力量計で一般に採用されているプロセッサを流用したデジタル処理によって電力量を求めることができる。
【００２２】
請求項４の発明において、第１電力計算部は、第１線路に挿入されたシャント抵抗を用いて第１経路を流れる電流を検出し、第２電力計算部は、第３線路に挿入されたシャント抵抗を用いて第２経路を流れる電流を検出するように構成できる。請求項５の発明において、変換部は、フォトカプラから構成できる。
【００２３】
【発明の実施の形態】
以下、本発明の実施の形態に係る電子式電力量計を図面を参照しながら詳細に説明する。なお、以下では、従来の技術の欄で説明した部分と同一又は相当部分には同じ符号を付して説明する。
【００２４】
（第１の実施の形態）
図１は本発明の第１の実施の形態に係る低圧用の単相３線式の電子式電力量計の構成を示すブロック図である。この電子式電力量計は、電源側端子２、負荷側端子３、第１電圧検出部４、第３電圧検出部５、第１電流検出部６、第３電流検出部７、第１電源回路８、第１電力−パルス変換部９、第３電源回路１０、第３電力−パルス変換部１１、第１光結合部１２、第２光結合部１３、パルス合成・積算計量部１４及び表示部１５から構成されている。
【００２５】
電源側端子２は、電源の第１相が接続される端子１Ｓ、ニュートラル相（Ｎ相）が接続される端子２Ｓ、及び第３相が接続される端子３Ｓから構成されている。同様に、負荷側端子３は、負荷の第１相に接続される端子１Ｌ、ニュートラル相（Ｎ相）に接続される端子２Ｌ、及び第２相に接続される端子３Ｌから構成されている。
【００２６】
電源側からの電力は、電子式電力量計の電源側端子２から負荷側端子３を経由して負荷側へ供給される。以下では、電源側端子２の端子１Ｓから負荷側端子３の端子１Ｌまでを第１線路１６、電源側端子２の端子２Ｓから負荷側端子３の端子２Ｌまでを第２線路１７、電源側端子２の端子３Ｓから負荷側端子３の端子３Ｌまでを第３線路１８と呼ぶ。本発明の第１経路は、第１線路１６と第２線路１７とから構成され、本発明の第２経路は、第３線路１８と第２線路１７とから構成されている。
【００２７】
第１電圧検出部４は、第１線路１６の電位に対する第２線路１７の電位、つまり第１相を基準とするＮ相の電圧を検出する。第１電圧検出部４は、一端が第１線路１６に接続された抵抗Ｒ１１と、この抵抗Ｒ１１の他端に一端が接続されると共に他端が第２線路１７に接続された抵抗Ｒ１２とから構成されている。第１電圧検出部４は、抵抗Ｒ１１とＲ１２との接続点の電圧を第１電圧信号Ｖ１として第１電力−パルス変換部９に送る。この場合、抵抗Ｒ１１及びＲ１２の各抵抗値は、第１電圧信号Ｖ１が数ボルト程度といったロジックレベルの信号になるように選択される。
【００２８】
第１電流検出部６は、第１線路１６に挿入されたシャント抵抗から構成されており、第１線路１６を流れる電流を第１線路１６の電位を基準として検出する。第１電流検出部６で検出された第１電流信号Ｉ１は、第１電力−パルス変換部９に送られる。
【００２９】
第１電源回路８は、第１相とＮ相との相間電圧（単相３線式では１００Ｖ）からロジックレベルの電圧を有する直流電力を生成する。この場合、第１線路１６の電位が基準電位、つまりグランドＧ１として使用される。第１電源回路８で生成された直流電力は、第１電力−パルス変換部９、パルス合成・積算計量部１４及び表示部１５に供給される。
【００３０】
第１電力−パルス変換部９は、本発明の第１電力計算部に対応する。第１電力−パルス変換部９は、第１電圧検出部４からの第１電圧信号Ｖ１と第１電流検出部６からの第１電流信号Ｉ１とを乗算して第１相（本発明の第１経路に対応する）の電力を算出し、算出された電力に含まれる正方向の電力に比例した周波数の正パルス信号＋Ｐ１と負方向の電力に比例した周波数の負パルス信号−Ｐ１とから成る第１電力信号を生成する。従って、この第１電力信号は、第１線路１６の電位を基準とする信号である。第１電力−パルス変換部９で生成された正パルス信号＋Ｐ１及び負パルス信号−Ｐ１は、パルス合成・積算計量部１４に送られる。
【００３１】
第３電圧検出部５は、第３線路１８の電位に対する第２線路１７の電位、つまり第３相を基準とするＮ相の電圧を検出する。第３電圧検出部５は、一端が第３線路１８に接続された抵抗Ｒ２１と、この抵抗Ｒ２１の他端に一端が接続されると共に他端が第２線路１７に接続された抵抗Ｒ２２とから構成されている。第３電圧検出部５は、抵抗Ｒ２１とＲ２２との接続点の電圧を第３電圧信号Ｖ３として第２電力−パルス変換部１１に送る。この場合、抵抗Ｒ２１及びＲ２２の各抵抗値は、第３電圧信号Ｖ３がロジックレベルの信号になるように選択される。
【００３２】
第３電流検出部７は、第３線路１８に挿入されたシャント抵抗から構成されており、第３線路１８を流れる電流を第３線路１８の電位を基準として検出する。第３電流検出部７で検出された第３電流信号Ｉ３は、第３電力−パルス変換部１１に送られる。
【００３３】
第３電源回路１０は、第３相とＮ相との相間電圧（単相３線式では１００Ｖ）からロジックレベルの電圧を有する直流電力を生成する。この場合、第３線路１８の電位が基準電位、グランドＧ３として使用される。第３電源回路１０で生成された直流電力は、第３電力−パルス変換部１１に供給される。
【００３４】
第３電力−パルス変換部１１は、本発明の第２の電力計算部に対応する。第３電力−パルス変換部１１は、第３電圧検出部５からの第３電圧信号Ｖ３と第３電流検出部７からの第３電流信号Ｉ３とを乗算して第３相（本発明の第２経路に対応する）の電力を算出し、算出された電力に含まれる正方向の電力に比例した周波数の正パルス信号＋Ｐ３と負方向の電力に比例した周波数の負パルス信号−Ｐ３とから成る第２電力信号を生成する。従って、この第２電力信号は、第３線路１８の電位を基準とする信号である。第３電力−パルス変換部１１で生成された正パルス信号＋Ｐ３及び負パルス信号−Ｐ３は、それぞれ、第１光結合部１２及び第２光結合部１３に送られる。
【００３５】
第１光結合部１２は、本発明の変換部の一部に対応し、例えばフォトカプラから構成されている。第１光結合部１２は、第３電力−パルス変換部１１からの正パルス信号＋Ｐ３を入力し、入力された正パルス信号＋Ｐ３と電気的に絶縁された正パルス信号＋Ｐ３をパルス合成・積算計量部１４に送る。第１光結合部１２の出力側のトランジスタは、第１電源回路８からの電力で動作するようにパルス合成・積算計量部１４に接続される。従って、第３電力−パルス変換部１１から第１光結合部１２を経由して送られている正パルス信号＋Ｐ３は、第１線路１６の電位を基準とする信号に変換される。
【００３６】
第２光結合部１３は、本発明の変換部の他の一部に対応し、例えばフォトカプラから構成されている。第２光結合部１３は、第３電力−パルス変換部１１からの負パルス信号−Ｐ３を入力し、負パルス信号−Ｐ３と電気的に絶縁された負パルス信号−Ｐ３をパルス合成・積算計量部１４に送られる。第２光結合部１３の出力側のトランジスタは、第１電源回路８からの電力で動作するようにパルス合成・積算計量部１４に接続される。従って、第３電力−パルス変換部１１から第２光結合部１３を経由して送られている負パルス信号−Ｐ３は、第１線路１６の電位を基準とする信号に変換される。
【００３７】
パルス合成・積算計量部１４は、第１電力−パルス変換部９から送られてくる正パルス信号＋Ｐ１に含まれるパルス及び負パルス信号−Ｐ１に含まれるパルス、並びに第３電力−パルス変換部１１から第１光結合部１２を経由して送られてくる正パルス信号＋Ｐ３に含まれるパルス及び第２光結合部１３を経由して送られてくる負パルス信号−Ｐ３に含まれるパルスをそれぞれ計数する。そして、パルス合成・積算計量部１４は、計数されたパルスを符号を考慮して積算（累積加算）することにより合成して記憶すると共に、使用電力量として表示部１５に送る。これにより、使用電力量が表示部１５に表示される。
【００３８】
以上説明したように、１００Ｖの交流単相３線式の場合、第１線路１６の電位と第３線路の電位との差は交流２００Ｖであるが、第３電力−パルス変換部１１からの正パルス信号＋Ｐ３及び負パルス信号−Ｐ３は、第１光結合部１２及び第２光結合部１３で絶縁されて、第１線路１６の基準電位を有する信号に変換されるので、第１電力−パルス変換部９からの正パルス信号＋Ｐ１及び負パルス信号−Ｐ１と同じ基準電位を有することになる。
【００３９】
従って、第１電流検出部６及び第３電流検出部７としてシャント抵抗を用いることができる。その結果、簡単な回路で歪み波形や直流成分を含んだ交流電流でも正確に計量できる電子式電力量計を実現することができる。
【００４０】
（第２の実施の形態）
本発明の第２の実施の形態に係る電子式電力量計は、電力に比例した周波数のパルス信号の生成方法が第１の実施の形態のそれと異なる。以下では、第１の実施の形態の構成部分と同一部分には第１の実施の形態で用いた符号と同じ符号を用いて説明を省略する。
【００４１】
図２は本発明の第２の実施の形態に係る低圧用の単相３線式の電子式電力量計の構成を示すブロック図である。電子式電力量計は、電源側端子２、負荷側端子３、第１電圧検出部４、第３電圧検出部５、第１電流検出部６、第３電流検出部７、第１電源回路８、第１電力−パルス変換部２２、第３電源回路１０、第３電力−パルス変換部２３、第１光結合部１２、第２光結合部１３、パルス合成・積算計量部２４及び表示部１５から構成されている。
【００４２】
第１電力−パルス変換部２２は、第１電圧検出部４からの第１電圧信号Ｖ１と第１電流検出部６からの第１電流信号Ｉ１とを乗算して第１相（本発明の第１経路に対応する）の電力を算出し、算出された電力に比例した周波数のパルス信号Ｐ１と該パルス信号Ｐ１が正方向の電力であるか負方向の電力であるかを表す符号信号（＋／−）とから成る第１電力信号を生成する。この第１電力信号は、第１線路１６の電位を基準とする信号である。第１電力−パルス変換部２２で生成されたパルス信号Ｐ１及び符号信号（＋／−）は、パルス合成・積算計量部２４に送られる。
【００４３】
第３電力−パルス変換部２３は、第３電圧検出部５からの第３電圧信号Ｖ３と第３電流検出部７からの第３電流信号Ｉ３とを乗算して第３相（本発明の第２経路に対応する）の電力を算出し、算出された電力に比例した周波数のパルス信号Ｐ３と該パルス信号Ｐ３が正方向の電力であるか負方向の電力であるかを表す符号信号（＋／−）とから成る第２電力信号を生成する。この第２電力信号は、第３線路１８の電位を基準とする信号である。第３電力−パルス変換部２３で生成されたパルス信号Ｐ３及び符号信号（＋／−）は、それぞれ、第１光結合部１２及び第２光結合部１３に送られる。
【００４４】
第１光結合部１２は、第３電力−パルス変換部２３からのパルス信号Ｐ３を入力し、入力されたパルス信号Ｐ３と電気的に絶縁されたパルス信号Ｐ３をパルス合成・積算計量部２４に送る。これにより、第３電力−パルス変換部２３から第１光結合部１２を経由して送られているパルス信号Ｐ３は、第１線路１６の電位を基準とする信号に変換される。
【００４５】
第２光結合部１３は、第３電力−パルス変換部２３からの符号信号（＋／−）を入力し、入力された符号信号（＋／−）と電気的に絶縁された符号信号（＋／−）をパルス合成・積算計量部２４に送る。これにより、第３電力−パルス変換部２３から第２光結合部１３を経由して送られている符号信号（＋／−）は、第１線路１６の電位を基準とする信号に変換される。
【００４６】
パルス合成・積算計量部２４は、第１電力−パルス変換部２２から送られてくるパルス信号Ｐ１を符号信号（＋／−）に応じて累積的に加算又は減算することにより第１電力量を算出する。同様に、第２電力−パルス変換部２３から第１光結合部１２及び第２光結合部１３を経由して送られてくるパルス信号Ｐ３を符号信号（＋／−）に応じて累積的に加算又は減算することにより第２電力量計を算出する。そして、パルス合成・積算計量部２４は、第１電力量と第３電力量とを符号を考慮して加算することにより合成して記憶すると共に、使用電力量として表示部１５に送る。これにより、使用電力量が表示部１５に表示される。
【００４７】
第２の実施の形態に係る電子式電力量計によれば、パルス合成・積算計量部２４は、パルス信号Ｐ１を計数するカウンタとパルス信号Ｐ３を計数するカウンタといった２つのカウンタを備えればよい。従って、正パルス信号＋Ｐ１、負パルス信号−Ｐ１、正パルス信号＋Ｐ３、負パルス信号−Ｐ３を計数するための４つのカウンタを必要とする第１の実施の形態に係る電子式電力量計に比べ、パルス合成・積算計量部２４の構成を簡単にすることができる。
【００４８】
なお、上述した第１及び第２の実施の形態では、単相３線式に使用される電子式電力量計を例に挙げて説明したが、本発明は、例えば三相３線式といった２種類以上の電力を計算して合成する電子式電力量計にも適用可能であるのは勿論である。
【００４９】
【発明の効果】
以上説明したように、本発明によれば、簡単な回路で歪み波形や直流成分を含んだ交流電流でも正確に計量できる電子式電力量計を提供できる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態に係る電子式電力量計の構成を示すブロック図である。
【図２】本発明の第２の実施の形態に係る電子式電力量計の構成を示すブロック図である。
【図３】従来の電子式電力量計の構成を示すブロック図である。
【符号の説明】
２　電源側端子
３　負荷側端子
４　第１電圧検出部
５　第３電圧検出部
６　第１電流検出部
７　第３電流検出部
８　第１電源回路
９，２２　第１電力−パルス変換部
１０　第２電源回路
１１，２３　第３電力−パルス変換部
１２　第１光結合部
１３　第２光結合部
１４，２４　パルス合成・積算計量部
１５　表示部
１６　第１線路
１７　第２線路
１８　第３線路[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic watt-hour meter, and more particularly to a technique for accurately measuring the amount of electricity used.
[0002]
[Prior art]
Conventionally, an electronic watt-hour meter has been used to measure the amount of electricity used by a user. FIG. 3 is a block diagram showing a configuration of a single-phase three-wire electronic wattmeter for low voltage, which is one of such electronic wattmeters (Patent Document 1). This electronic watt-hour meter includes a power supply terminal 2, a load terminal 3, a first current detector (CT1) 32, a third current detector (CT3) 33, a first voltage detector 4, a third voltage detector. 5, a power supply circuit 34, a power-pulse converter 35, an integrating meter 36, and a display unit 15.
[0003]
The power supply terminal 2 includes a terminal 1S to which a first phase of the power supply is connected, a terminal 2S to which a neutral phase (N phase) is connected, and a terminal 3S to which a third phase is connected. In the case of the single-phase three-wire system, the power of the first phase and the power of the third phase are not necessarily different in phase (they are single-phase). Called "phase 3". Similarly, the load side terminal 3 includes a terminal 1L connected to the first phase of the load, a terminal 2L connected to the neutral phase (N phase), and a terminal 3L connected to the third phase.
[0004]
Power from the power supply side is supplied from the power supply side terminal 2 of the electronic wattmeter to the load side via the load side terminal 3. Hereinafter, the first line 16 extends from the terminal 1S of the power supply side terminal 2 to the terminal 1L of the load side terminal 3, and the second line 17 extends from the terminal 2S of the power supply side terminal 2 to the terminal 2L of the load side terminal 3. The third line 18 from the second terminal 3S to the terminal 3L of the load-side terminal 3 is referred to as a third line 18.
[0005]
The first current detection section 32 is configured by a current transformer arranged to penetrate the first line 16. The first current detector 32 detects a current flowing through the first line 16 in a non-contact manner, and sends the current to the power-pulse converter 35 as a first current signal I1. The potential of the first current signal I1 is separated (insulated) from the potential of the first line 16.
[0006]
The first voltage detector 4 detects a potential of the first line 16 with respect to a potential of the second line 17, that is, a first-phase voltage based on the N-phase. The first voltage detecting unit 4 includes a resistor R11 having one end connected to the second line 17 and a resistor R12 having one end connected to the other end of the resistor R11 and the other end connected to the first line 16. It is configured. The first voltage detector 4 sends the voltage at the connection point between the resistors R11 and R12 to the power-pulse converter 35 as a first voltage signal V1. In this case, the resistance values of the resistors R11 and R12 are selected such that the first voltage signal V1 is a signal of a logic level such as about several volts.
[0007]
The third current detector 33 is configured by a current transformer arranged to penetrate the third line 18. The third current detector 33 detects the current flowing through the third line 18 in a non-contact manner, and sends the current to the power-pulse converter 35 as a third current signal I3. The potential of the third current signal I3 is separated (insulated) from the potential of the third line 18.
[0008]
The third voltage detector 5 detects a potential of the third line 18 with respect to a potential of the second line 17, that is, a voltage of a third phase based on the N phase. The third voltage detecting unit 5 includes a resistor R21 having one end connected to the second line 17 and a resistor R22 having one end connected to the other end of the resistor R21 and the other end connected to the third line 18. It is configured. The third voltage detector 5 sends the voltage at the connection point between the resistors R21 and R22 to the power-pulse converter 35 as a third voltage signal V3. In this case, the resistance values of the resistors R21 and R22 are selected such that the third voltage signal V3 becomes a logic level signal.
[0009]
The power supply circuit 34 generates DC power having a logic level voltage from an inter-phase voltage between the N-phase and the first phase (100 V in a single-phase three-wire system). In this case, the potential of the second line 17 is used as the reference potential, that is, the ground G. The DC power generated by the power supply circuit 34 is supplied to the power-to-pulse converter 35, the integrating meter 36, and the display 15.
[0010]
The power-to-pulse converter 35 multiplies the first current signal I1 from the first current detector 32 by the first voltage signal V1 from the first voltage detector 4 to calculate a first-phase power, , Multiplying the third current signal I3 from the third current detector 33 by the third voltage signal V3 from the third voltage detector 5 to calculate the power of the third phase, and dividing the calculated two powers The combined power is obtained. Then, a pulse signal P having a pulse having a frequency proportional to the calculated combined power is generated and sent to the integrating and measuring unit 36.
[0011]
The integrating and weighing unit 36 integrates (accumulates and adds) the pulses included in the pulse signal P sent from the power-to-pulse converting unit 35, and stores the accumulated number of pulses as the power consumption. Send it to the display unit 15. As a result, the power consumption is displayed on the display unit 15.
[0012]
[Patent Document 1]
Patent No. 3112611 (pages 3-6, FIG. 5)
[0013]
[Problems to be solved by the invention]
As described above, in a conventional electronic watt-hour meter, a current transformer is used to detect an alternating current flowing from a power supply side to a load side. This current transformer has no problem when the AC current has a sine waveform, but cannot perform accurate measurement when the sine waveform is distorted or when the AC current includes a DC component. In particular, load diversification has been remarkable recently, and there is a possibility that a sine waveform of an AC current may be distorted or a DC component may be included in the AC current. Therefore, there is a need for a watt hour meter capable of measuring the correct amount of power even under such bad conditions.
[0014]
By the way, in order to measure a current having a distorted waveform or a current including a DC component, it is conceivable to directly measure a current flowing from the power supply side to the load side using a shunt resistor. The shunt resistor is a resistor for detecting a low-level current signal without obstructing a current flow. However, if an attempt is made to replace the conventional current transformer with a shunt resistor, in an electronic watt-hour meter requiring two or more multiplications for calculating the amount of power, such as a single-phase three-wire system, the first line 16 and the Since the reference potential differs from that of the three lines 18, a signal from the shunt resistor cannot be input to the power-to-pulse converter.
[0015]
An object of the present invention is to provide an electronic watt-hour meter that can accurately measure even an alternating current including a distortion waveform and a DC component with a simple circuit.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, a first aspect of the present invention is to detect a voltage and a current supplied from a power supply to a load via a first path using a potential of a first line constituting the first path as a reference potential. A first power calculation unit that calculates power by using the potential of the first line as a reference potential, and outputs a voltage and a current supplied from a power supply to a load via a second path. A second power calculator that detects the potential of the third line constituting the path as a reference potential, calculates power, and outputs the calculated power as a second power signal that uses the potential of the third line as a reference potential; Converting the second power signal from the first power signal into a third power signal using the potential of the first line as a reference potential; and converting the first power signal from the first power calculation unit and the third power signal from the conversion unit. And a measuring unit for obtaining the electric energy by combining.
[0017]
According to the first aspect of the present invention, the first power signal representing the power of the first path and the second power signal representing the power of the second path are signals having different reference potentials, but the reference potential of the second power signal is different. Is converted to be the same as the reference potential of the first power signal, and the third power signal and the first power signal obtained by the conversion are combined to obtain the power amount. Therefore, it is possible to use, for example, a shunt resistor instead of the current transformer used in the conventional electronic watt-hour meter. As a result, even a simple circuit can accurately output an AC current including a distortion waveform and a DC component. Can be weighed.
[0018]
In the invention according to claim 2, the first power calculation unit includes, as the first power signal, a positive pulse signal having a frequency proportional to the positive power included in the calculated power and a negative pulse signal having a frequency proportional to the negative power included in the calculated power. The second power calculation unit outputs a positive pulse signal having a frequency proportional to the positive power included in the calculated power and a negative pulse having a frequency proportional to the negative power as the second power signal. A pulse signal, and the weighing unit outputs a positive pulse signal and a negative pulse signal included in the first power signal from the first power calculation unit, and a positive pulse signal and a negative pulse signal included in the third power signal from the conversion unit. The power amount can be obtained by integrating the pulse signal with the sign in consideration.
[0019]
According to the invention of claim 2, since the electric energy is obtained by the positive pulse signal and the negative pulse signal, the integration processing can be performed by digital processing using a processor generally used in an electronic watt-hour meter.
[0020]
In the invention according to claim 3, the first power calculation unit determines whether the first power signal is a pulse signal having a frequency proportional to the calculated power and whether the pulse signal has a positive power or a negative power. And a second power calculation unit outputs, as the second power signal, a pulse signal having a frequency proportional to the calculated power and the pulse signal having a positive power or a negative power. And outputting a code signal indicating whether the pulse signal is present. The metering unit accumulatively adds or subtracts a pulse signal included in the first power signal from the first power calculation unit according to the code signal to calculate the first power amount. Calculating a third power amount by cumulatively adding or subtracting a pulse signal included in the third power signal transmitted from the second power calculation unit via the conversion unit in accordance with the code signal, The electric energy is obtained by adding the first electric energy and the third electric energy. It can be configured to so that.
[0021]
According to the third aspect of the present invention, since the electric energy is obtained by the pulse signal and the code signal, the electric energy can be obtained by digital processing using a processor generally employed in an electronic watt-hour meter.
[0022]
In the invention according to claim 4, the first power calculator detects a current flowing through the first path by using a shunt resistor inserted in the first line, and the second power calculator is inserted in the third line. It can be configured to detect a current flowing through the second path using a shunt resistor. In the invention according to claim 5, the conversion unit can be constituted by a photocoupler.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an electronic watt-hour meter according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following, the same or corresponding parts as those described in the section of the related art will be denoted by the same reference numerals.
[0024]
(First Embodiment)
FIG. 1 is a block diagram showing the configuration of a low-voltage single-phase three-wire electronic wattmeter according to a first embodiment of the present invention. This electronic watt-hour meter includes a power supply terminal 2, a load terminal 3, a first voltage detector 4, a third voltage detector 5, a first current detector 6, a third current detector 7, a first power circuit. 8, first power-to-pulse converter 9, third power supply circuit 10, third power-to-pulse converter 11, first optical coupler 12, second optical coupler 13, pulse synthesis / integration meter 14, and display 15 is comprised.
[0025]
The power supply terminal 2 includes a terminal 1S to which a first phase of the power supply is connected, a terminal 2S to which a neutral phase (N phase) is connected, and a terminal 3S to which a third phase is connected. Similarly, the load side terminal 3 includes a terminal 1L connected to the first phase of the load, a terminal 2L connected to the neutral phase (N phase), and a terminal 3L connected to the second phase.
[0026]
Power from the power supply side is supplied from the power supply side terminal 2 of the electronic wattmeter to the load side via the load side terminal 3. Hereinafter, the first line 16 extends from the terminal 1S of the power supply side terminal 2 to the terminal 1L of the load side terminal 3, and the second line 17 extends from the terminal 2S of the power supply side terminal 2 to the terminal 2L of the load side terminal 3. The third line 18 extends from the second terminal 3S to the terminal 3L of the load-side terminal 3. The first route according to the present invention includes a first line 16 and a second line 17, and the second route according to the present invention includes a third line 18 and a second line 17.
[0027]
The first voltage detector 4 detects a potential of the second line 17 with respect to a potential of the first line 16, that is, an N-phase voltage based on the first phase. The first voltage detector 4 includes a resistor R11 having one end connected to the first line 16 and a resistor R12 having one end connected to the other end of the resistor R11 and the other end connected to the second line 17. It is configured. The first voltage detector 4 sends the voltage at the connection point between the resistors R11 and R12 to the first power-to-pulse converter 9 as a first voltage signal V1. In this case, the resistance values of the resistors R11 and R12 are selected such that the first voltage signal V1 is a signal of a logic level such as about several volts.
[0028]
The first current detector 6 is configured by a shunt resistor inserted into the first line 16 and detects a current flowing through the first line 16 with reference to the potential of the first line 16. The first current signal I1 detected by the first current detector 6 is sent to the first power-to-pulse converter 9.
[0029]
The first power supply circuit 8 generates DC power having a logic level voltage from an interphase voltage between the first phase and the N phase (100 V in a single-phase three-wire system). In this case, the potential of the first line 16 is used as a reference potential, that is, the ground G1. The DC power generated by the first power supply circuit 8 is supplied to the first power-to-pulse converter 9, the pulse synthesizer / integrated meter 14, and the display 15.
[0030]
The first power-pulse converter 9 corresponds to the first power calculator of the present invention. The first power-to-pulse converter 9 multiplies the first voltage signal V1 from the first voltage detector 4 by the first current signal I1 from the first current detector 6 to obtain a first phase (the second phase of the present invention). (Corresponding to one path), and is composed of a positive pulse signal + P1 having a frequency proportional to the positive power included in the calculated power and a negative pulse signal -P1 having a frequency proportional to the negative power. Generate a first power signal. Therefore, the first power signal is a signal based on the potential of the first line 16. The positive pulse signal + P1 and the negative pulse signal -P1 generated by the first power-to-pulse converter 9 are sent to the pulse synthesizer / integration meter 14.
[0031]
The third voltage detection unit 5 detects a potential of the second line 17 with respect to a potential of the third line 18, that is, an N-phase voltage based on the third phase. The third voltage detecting unit 5 includes a resistor R21 having one end connected to the third line 18 and a resistor R22 having one end connected to the other end of the resistor R21 and the other end connected to the second line 17. It is configured. The third voltage detector 5 sends the voltage at the connection point between the resistors R21 and R22 to the second power-to-pulse converter 11 as a third voltage signal V3. In this case, the resistance values of the resistors R21 and R22 are selected so that the third voltage signal V3 becomes a logic level signal.
[0032]
The third current detector 7 is configured by a shunt resistor inserted into the third line 18 and detects a current flowing through the third line 18 with reference to the potential of the third line 18. The third current signal I3 detected by the third current detector 7 is sent to the third power-to-pulse converter 11.
[0033]
The third power supply circuit 10 generates DC power having a logic level voltage from an inter-phase voltage between the third phase and the N-phase (100 V in a single-phase three-wire system). In this case, the potential of the third line 18 is used as the reference potential and the ground G3. The DC power generated by the third power supply circuit 10 is supplied to the third power-to-pulse converter 11.
[0034]
The third power-to-pulse converter 11 corresponds to the second power calculator of the present invention. The third power-to-pulse converter 11 multiplies the third voltage signal V3 from the third voltage detector 5 by the third current signal I3 from the third current detector 7 to obtain a third phase (the third phase of the present invention). (Corresponding to two paths), and includes a positive pulse signal + P3 having a frequency proportional to the positive power included in the calculated power and a negative pulse signal -P3 having a frequency proportional to the negative power. A second power signal is generated. Therefore, the second power signal is a signal based on the potential of the third line 18. The positive pulse signal + P3 and the negative pulse signal -P3 generated by the third power-pulse converter 11 are sent to the first optical coupler 12 and the second optical coupler 13, respectively.
[0035]
The first optical coupling unit 12 corresponds to a part of the conversion unit according to the present invention, and includes, for example, a photocoupler. The first optical coupling unit 12 receives the positive pulse signal + P3 from the third power-to-pulse conversion unit 11 and performs pulse synthesis / integration measurement of the positive pulse signal + P3 electrically isolated from the input positive pulse signal + P3. Send to section 14. The transistor on the output side of the first optical coupling unit 12 is connected to the pulse synthesizing / integrating weighing unit 14 so as to operate with the power from the first power supply circuit 8. Therefore, the positive pulse signal + P3 sent from the third power-pulse converter 11 via the first optical coupler 12 is converted into a signal based on the potential of the first line 16.
[0036]
The second optical coupling unit 13 corresponds to another part of the conversion unit of the present invention, and is configured by, for example, a photocoupler. The second optical coupler 13 receives the negative pulse signal -P3 from the third power-to-pulse converter 11 and performs pulse synthesis and integration measurement of the negative pulse signal -P3 which is electrically insulated from the negative pulse signal -P3. It is sent to the unit 14. The transistor on the output side of the second optical coupling unit 13 is connected to the pulse synthesizing / accumulating unit 14 so as to operate with the power from the first power supply circuit 8. Therefore, the negative pulse signal -P3 sent from the third power-pulse converter 11 via the second optical coupler 13 is converted into a signal based on the potential of the first line 16.
[0037]
The pulse synthesizing / accumulating unit 14 includes a pulse included in the positive pulse signal + P1 and a pulse included in the negative pulse signal -P1 sent from the first power-pulse converter 9, and the third power-pulse converter 11 From the positive pulse signal + P3 transmitted through the first optical coupling unit 12 and the pulse included in the negative pulse signal -P3 transmitted through the second optical coupling unit 13, respectively. I do. Then, the pulse synthesizing / accumulating weighing unit 14 accumulates (accumulates and adds) the counted pulses in consideration of the sign, synthesizes and stores the same, and sends the same to the display unit 15 as the power consumption. As a result, the power consumption is displayed on the display unit 15.
[0038]
As described above, in the case of the AC single-phase three-wire system of 100 V, the difference between the potential of the first line 16 and the potential of the third line is 200 V AC. Since the pulse signal + P3 and the negative pulse signal -P3 are insulated by the first optical coupling unit 12 and the second optical coupling unit 13 and are converted into a signal having the reference potential of the first line 16, the first power-pulse The positive pulse signal + P1 and the negative pulse signal -P1 from the converter 9 have the same reference potential.
[0039]
Therefore, a shunt resistor can be used as the first current detector 6 and the third current detector 7. As a result, it is possible to realize an electronic watt-hour meter that can accurately measure even an AC current including a distortion waveform and a DC component with a simple circuit.
[0040]
(Second embodiment)
The electronic watt-hour meter according to the second embodiment of the present invention differs from that of the first embodiment in the method of generating a pulse signal having a frequency proportional to the power. In the following, the same components as those of the first embodiment are denoted by the same reference numerals as those used in the first embodiment, and description thereof is omitted.
[0041]
FIG. 2 is a block diagram showing the configuration of a low-voltage single-phase three-wire electronic wattmeter according to a second embodiment of the present invention. The electronic wattmeter includes a power supply side terminal 2, a load side terminal 3, a first voltage detection unit 4, a third voltage detection unit 5, a first current detection unit 6, a third current detection unit 7, and a first power supply circuit 8. , A first power-to-pulse converter 22, a third power supply circuit 10, a third power-to-pulse converter 23, a first optical coupling unit 12, a second optical coupling unit 13, a pulse synthesis / integration metering unit 24, and a display unit 15. It is composed of
[0042]
The first power-to-pulse converter 22 multiplies the first voltage signal V1 from the first voltage detector 4 by the first current signal I1 from the first current detector 6 to obtain a first phase (the second phase of the present invention). (Corresponding to one path) and calculates a pulse signal P1 having a frequency proportional to the calculated power and a code signal (+) indicating whether the pulse signal P1 is power in the positive direction or power in the negative direction. /-). This first power signal is a signal based on the potential of the first line 16. The pulse signal P <b> 1 and the sign signal (+/−) generated by the first power-to-pulse converter 22 are sent to the pulse synthesizer / integration meter 24.
[0043]
The third power-to-pulse converter 23 multiplies the third voltage signal V3 from the third voltage detector 5 by the third current signal I3 from the third current detector 7 to obtain a third phase (the third phase of the present invention). (Corresponding to two paths), and calculates a pulse signal P3 having a frequency proportional to the calculated power and a sign signal (+) indicating whether the pulse signal P3 is power in the positive or negative direction. /-). This second power signal is a signal based on the potential of the third line 18. The pulse signal P3 and the code signal (+/−) generated by the third power-pulse converter 23 are sent to the first optical coupler 12 and the second optical coupler 13, respectively.
[0044]
The first optical coupling unit 12 receives the pulse signal P3 from the third power-to-pulse conversion unit 23, and outputs the pulse signal P3 electrically isolated from the input pulse signal P3 to the pulse synthesis / integration measurement unit 24. send. As a result, the pulse signal P3 sent from the third power-pulse converter 23 via the first optical coupler 12 is converted into a signal based on the potential of the first line 16.
[0045]
The second optical coupling unit 13 receives the code signal (+/−) from the third power-to-pulse converter 23 and receives a code signal (+/−) that is electrically insulated from the input code signal (+/−). //) are sent to the pulse synthesizing / accumulating / measuring unit 24. As a result, the code signal (+/−) sent from the third power-pulse converter 23 via the second optical coupler 13 is converted into a signal based on the potential of the first line 16. .
[0046]
The pulse synthesis / integration metering unit 24 accumulatively adds or subtracts the pulse signal P1 sent from the first power-pulse conversion unit 22 in accordance with the sign signal (+/−), thereby calculating the first power amount. calculate. Similarly, the pulse signal P3 sent from the second power-pulse converter 23 via the first optical coupler 12 and the second optical coupler 13 is accumulated in accordance with the code signal (+/−). The second watt hour meter is calculated by adding or subtracting. Then, the pulse synthesizing / integrating and weighing unit 24 synthesizes and stores the first electric energy and the third electric energy by adding them in consideration of the sign, and sends the combined electric energy to the display unit 15 as the electric energy used. As a result, the power consumption is displayed on the display unit 15.
[0047]
According to the electronic watt-hour meter according to the second embodiment, the pulse synthesizing / accumulating weighing unit 24 may include two counters such as a counter that counts the pulse signal P1 and a counter that counts the pulse signal P3. . Therefore, as compared with the electronic watt-hour meter according to the first embodiment, which requires four counters for counting the positive pulse signal + P1, the negative pulse signal -P1, the positive pulse signal + P3, and the negative pulse signal -P3. In addition, the configuration of the pulse synthesizing / accumulating / measuring unit 24 can be simplified.
[0048]
In the above-described first and second embodiments, the electronic watt-hour meter used for a single-phase three-wire system has been described as an example. It is needless to say that the present invention can be applied to an electronic watt-hour meter that calculates and synthesizes more than kinds of electric power.
[0049]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an electronic watt-hour meter that can accurately measure even an AC current including a distortion waveform and a DC component with a simple circuit.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an electronic watt-hour meter according to a first embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an electronic watt-hour meter according to a second embodiment of the present invention.
FIG. 3 is a block diagram showing a configuration of a conventional electronic watt-hour meter.
[Explanation of symbols]
2 power supply side terminal 3 load side terminal 4 first voltage detection unit 5 third voltage detection unit 6 first current detection unit 7 third current detection unit 8 first power supply circuit 9,22 first power-pulse conversion unit 10 second Power supply circuits 11 and 23 Third power-to-pulse converter 12 First optical coupler 13 Second optical coupler 14 and 24 Pulse synthesizer / integrator 15 Display 16 First line 17 Second line 18 Third line

Claims

A voltage and a current supplied from a power supply to a load via a first path are detected by using the potential of a first line constituting the first path as a reference potential to calculate power, and the potential of the first line is set to a reference potential. A first power calculator that outputs the first power signal as
A voltage and a current supplied from the power supply to the load via the second path are detected by using the potential of the third line constituting the second path as a reference potential to calculate the power, and the potential of the third line is calculated. A second power calculation unit that outputs a second power signal as a reference potential,
A conversion unit that converts the second power signal from the second power calculation unit into a third power signal that uses the potential of the first line as a reference potential;
A weighing unit that combines the first power signal from the first power calculation unit and the third power signal from the conversion unit to obtain a power amount;
An electronic watt-hour meter comprising:

The first power calculator, as the first power signal, a positive pulse signal having a frequency proportional to the positive power included in the calculated power and a negative pulse signal having a frequency proportional to the negative power included in the calculated power Output,
The second power calculation unit includes, as the second power signal, a positive pulse signal having a frequency proportional to the positive power included in the calculated power and a negative pulse signal having a frequency proportional to the negative power included in the calculated power. Output,
The weighing unit includes a positive pulse signal and a negative pulse signal included in the first power signal from the first power calculation unit, and a positive pulse signal and a negative pulse signal included in the third power signal from the conversion unit. 2. The electronic watt-hour meter according to claim 1, wherein the electric energy is obtained by integrating the values in consideration of the sign.

The first power calculation unit may include, as the first power signal, a pulse signal having a frequency proportional to the calculated power and a code signal indicating whether the pulse signal is power in a positive direction or power in a negative direction. And output
The second power calculation unit may include, as the second power signal, a pulse signal having a frequency proportional to the calculated power and a code signal indicating whether the pulse signal is power in a positive direction or power in a negative direction. And output
The metering section calculates a first power amount by cumulatively adding or subtracting a pulse signal included in the first power signal from the first power calculating section in accordance with a code signal, and calculating the second power amount. A third power amount is calculated by cumulatively adding or subtracting a pulse signal included in the third power signal transmitted from the unit via the conversion unit in accordance with a code signal, and calculating the first power amount. The electronic watt-hour meter according to claim 1, wherein an electric energy is obtained by adding the third electric energy and the third electric energy.

The first power calculator detects a current flowing through the first path using a shunt resistor inserted into the first line,
The said 2nd power calculation part detects the electric current which flows through the said 2nd path | route using the shunt resistance inserted in the said 3rd line, The Claims 1 thru | or 3 characterized by the above-mentioned. Electronic watt-hour meter.

The electronic watt-hour meter according to any one of claims 1 to 4, wherein the conversion unit includes a photocoupler.