JP2005043231A - Wattmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a small-sized and inexpensive wattmeter capable of measuring single-phase three-wire electric power and three-phase three-wire electric power at the same time, to detect a phase connected with single-phase three wires when measuring the electric power, to enhance working efficiency, and to reduce an expense by dispensing with a dedicated apparatus. <P>SOLUTION: This wattmeter is a wattmeter for measuring the electric power of a different capacity three-phase four-wire type electric power source for supplying the electric power from a prescribed phase of three-phase alternating current to a single-phase three-wire load. The wattmeter has a voltage detecting means for detecting grounding-to-grounding voltages to transmission lines for the three-phase alternating current using a grounding potential as a reference, a current detecting means for detecting line currents in the transmission lines of the first phase and the third phase in the three-phase alternating current, and a current flowing in the single-phase three-wire load, and a computing means for conducting at least either of calculation for the single-phase three-wire electric power based on a voltage impressed to the single-phase three-wire load out of the grounding-to-grounding voltages, and a current flowing in the load, or calculation for the three-phase electric power based on the grounding-to-grounding voltages and line currents. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a wattmeter that measures a power value of a three-phase alternating current, and in particular, when a single-phase three-wire load is connected to a predetermined three-phase phase, the three-phase power and the single-phase power can be measured simultaneously. Regarding possible wattmeters.

Equipment installed in factories, etc. is supplied with 200V three-phase power as a power source, and Scott connection is made to a predetermined phase among them to create a 100V system power supply, and a single phase is used for loads such as electric lights. Power is being supplied. Such a connection method is said to be a different capacity three-phase four-wire system, and in the power measurement, two potential wattmeters for single-phase three-wires and three-phase three-wires are used because the potentials for measurement are different. It was measured using one multi-channel isolated input type wattmeter.
Prior art documents related to a power meter for measuring three-phase power include the following.

JP-A-6-34678 Japanese Patent Laid-Open No. 11-344514

FIG. 9 is an explanatory diagram showing conventional single-phase three-wire and three-phase three-wire power measurements.
FIG. 9A is an explanatory diagram showing power measurement using a single-phase three-wire wattmeter and a three-phase three-wire wattmeter.
In FIG. 9A, a three-phase power source 1 is configured by three-phase three-wires, and supplies three-phase power to loads RL1, RL2, and RL3 connected to each phase. The R-S phase of the three-phase power source 1 is grounded at an intermediate position N, and single-phase power is supplied to loads RL4 and RL5 connected between R-N and S-N.

In the three-phase power meter 2, the input terminal Nin connected to the common potential point in the power meter has a voltage applied to a transmission line (hereinafter referred to as an S-phase line) connecting the S phase and the load of the three-phase power source 1. The input terminal Vin1 is connected to a transmission line connecting the R phase and the load (hereinafter referred to as an R phase line), and Vin3 is connected to a transmission line connecting the T phase and the load (hereinafter referred to as a T phase line). The voltage Vrs between S and the voltage Vts between TS are measured. Further, the current clamp CL1 is connected to the input terminal CH1 of the three-phase wattmeter 2, and the current clamp CL2 is connected to the input terminal CH2. The current clamp CL1 clamps the R-phase line and measures the current Ir flowing through the line, and the current clamp CL2 clamps the T-phase line and measures the current It flowing through the line.
The electric power P1 is obtained by multiplying the measured Vrs and Ir, and the electric power P3 is obtained by multiplying Vts and It. Based on the two-watt meter method, P1 and P3 are added to calculate the total power of the three-phase power.

  On the other hand, in the single-phase wattmeter 3, the input terminal Nin connected to the common potential point in the wattmeter is grounded, the voltage input terminal Vin1 is connected to the R-phase line, and the voltage input terminal Vin2 is connected to the S-phase line. Then, the RN voltage Vrn applied to the single-phase load RL4 and the S-N voltage Vsn applied to the single-phase load RL5 are measured. The current clamp CL3 is connected to the input terminal CH1 of the single-phase wattmeter 3, and the current clamp CL4 is connected to the input terminal CH2. The current Ira flowing through the load RL4 is measured by the current clamp CL3, and the current Is flowing through the load RL5 is measured by the current clamp CL4.

  Multiply Vrn and Ira to obtain power P4 supplied to RL4, multiply Vsn and Is to obtain power P5 supplied to RL5, and add P4 and P5 to calculate single-phase power To do.

FIG. 9B is an explanatory diagram showing power measurement using a multi-channel isolated input type power meter.
In FIG. 9B, the connection relationship between the three-phase power source 1 and the load and the method of measuring the power are the same as in FIG. The difference from FIG. 9A is that the wattmeter 4 is a multi-channel isolated input type, so even if the voltage reference point is different as in the power measurement of single-phase three-wire and three-phase three-wire. Both powers can be measured with one unit divided into the three-phase measuring unit 5 and the single-phase measuring unit 6.

FIG. 10 is a block diagram showing an example of a conventional multi-channel isolated input type wattmeter.
FIG. 10 shows a wattmeter having four voltage measurement channels and four current measurement channels with clamps. Each voltage input channel is isolated. The amplifiers 1 to 4 normalize the voltages applied to the voltage input terminals Vin1 to Vin4 with reference to the potentials of the voltage input terminals Nin1 to Nin4. The A / D converters 9 to 12 A / D convert the normalized voltage.

Current clamps CL1 to CL4 are connected to the input terminals CH1 to CH4 of each current measurement channel, and a current flowing through the power supply line is detected and converted into a voltage. The amplifiers 5 to 8 normalize the converted voltages, and the A / D converters 13 to 16 sequentially switch the outputs of the amplifiers, and A / D convert the normalized output voltages of each amplifier.

The zero cross detectors 17 to 20 detect points where each voltage input waveform crosses the zero level, output waveform cycle data, and send the waveform data to the MPU 22 which is a processor via the insulation circuits 21a to 21h.
The insulating circuits 21a to 21h are composed of photocouplers, transformers or insulating elements that replace them, and A / D converted measurement data and period data are insulated and transmitted to the MPU 22, and control signals output from the MPU 22 are sent to amplifiers and A / Send to D converter. The MPU 22 controls the entire wattmeter, and calculates power based on the received voltage digital data, current digital data, and period data.

The display 23 is composed of a CRT, LCD, or the like, and displays the measurement result calculated by the MPU 22 under the control of the MPU 22.
In addition, an operation means including a keyboard (not shown) is provided, and an operator operates the power meter via the operation means.

Also, in the power measurement with different capacity three-phase four-wire system, even if there is no wiring diagram, even if there is no wiring, the reliability is low and it is unknown where the single-phase three-wire is connected from which phase of the three-phase three-wire power supply There is a need to check the wiring.
Conventional wattmeters do not have a function to check the connected phase of a single-phase three-wire load. As a dedicated device to check the wiring, the signal is superimposed on each phase line of the power supply and the signal on the single-phase load side The method of detecting is used.

This will be described with reference to the drawings.
FIG. 11 is an explanatory diagram showing detection of a single-phase three-wire connected phase in the prior art.
In FIG. 11, a three-phase power source 1 is constituted by three-phase three-wires, and supplies three-phase power to loads RL1, RL2, and RL3 connected to each phase. The R-S phase of the three-phase power supply 1 is grounded at an intermediate position N, so that single-phase power is supplied to loads RL4, RL5 connected between R-N and S-N.

The signal superimposing unit 30 applies a minute signal having a frequency sufficiently higher than a commercial frequency such as 4 kHz and 50 mV between the phases of the three-phase power supply and superimposes the signal on each phase line. The signal detector 31 has a function of detecting a superimposed signal from a line in which a single-phase three-wire load is wired to a three-phase power source and notifying an operator. That is, when the signal detector 31 detects the superimposed signal, the phase in which the single-phase three-wire load is wired is known depending on which phase the signal is superimposed on.

  In the conventional example shown in FIG. 9, since the potential as a measurement reference is different, two wattmeters for single-phase three-wire and three-phase three-wire are used, or one wattmeter of a multi-channel insulated input type is used. Must be measured. For this reason, when using two power meters, cost and installation man-hours are required. In addition, the multi-channel insulated input type power meter has a problem that it is large and expensive.

  Further, in the conventional example shown in FIG. 11, a dedicated device for wiring confirmation is required and the power source side and the load side are separated. For example, when the positions of the power source and the load are separated, two people are in contact with each other. Work efficiency is poor. In addition, since the signal detector handles a minute signal, it may be weak to noise and cannot be detected correctly.

  Therefore, the problem to be solved by the present invention is to realize a small and inexpensive power meter that can measure single-phase three-wire and three-phase three-wire at the same time, and to measure the phase in which single-phase three-wire is connected when measuring power. It is possible to detect, improve work efficiency and reduce costs by not using dedicated equipment.

(1) In a wattmeter that measures the power of a different-capacity three-phase four-wire power source that supplies power from a predetermined phase of three-phase AC to a single-phase three-wire load,
Voltage detection means for detecting a ground-to-ground voltage between the three-phase AC transmission line with reference to the ground potential;
Current detection means for detecting the line currents of the three-phase alternating current first and third phase transmission lines and the current flowing through the single-phase three-wire load;
Calculation of single-phase three-wire power based on the voltage applied to the single-phase three-wire load in the voltage between the grounds and current flowing through the load, and calculation of three-phase power based on the voltage between the grounds and the line current Computing means for performing at least one of the following;
A wattmeter characterized by the provision of

(2) The computing means obtains voltages between the first and second phase transmission lines of the three-phase alternating current and between the second and third phase transmission lines by performing a vector operation on the voltage between the grounds, The three-phase power is calculated based on the line voltage and the first-phase and third-phase line currents. The power meter according to (1),

(3) The calculation means obtains a second-phase line current by performing a vector operation on the first-phase and third-phase line currents, and calculates three-phase power based on the line current and the voltage between the grounds. The wattmeter as described in (1) characterized by the above-mentioned.

(4) The phase of three-phase alternating current to which a single-phase three-wire load is connected is detected based on the result of vector calculation by combining two of the voltages between the grounds. (1) to (3) The wattmeter as described in any one.

(5) The power meter according to any one of (1) to (4), wherein the current measuring unit detects a current to be measured using a clamp-type current sensor.

  According to the first to third aspects of the present invention, the voltage between the ground between the three-phase AC transmission line, the three-phase AC line current, and the current flowing through the single-phase three-wire load with reference to the ground potential are determined. Since it is possible to measure and calculate single-phase three-wire power and three-phase power, a small and inexpensive watt-hour meter can be provided.

  According to the invention described in claim 4, since it is possible to detect in advance information on which phase of the three-phase three-wire the phase to which the single-phase three-wire load is connected using the measured voltage, There is no need to add a circuit to the wattmeter or use a dedicated device to check, and it is possible to prevent an increase in expenses and deterioration in work efficiency.

  According to the fifth aspect of the present invention, the current can be detected in a non-contact manner by using the current clamp.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a first explanatory diagram showing power measurement using a power meter according to the present invention.

  In FIG. 1, a three-phase power source 1 is composed of three-phase three-wires and supplies three-phase power to loads RL1, RL2, and RL3 connected to each phase. The R-S phase of the three-phase power source 1 is grounded at a predetermined intermediate position N, and supplies single-phase power to loads RL4 and RL5 connected to the RN phase and the S-N phase.

  In the wattmeter 40 to which the present invention is applied, the input terminal Nin connected to the common potential point in the wattmeter is grounded, the voltage input terminal Vin1 is an R-phase line, Vin2 is an S-phase line, and Vin3 is The RN phase voltage Vrn, the SN phase voltage Vsn, and the TN phase voltage Vtn are measured. These voltages correspond to the voltage between the grounds.

The output terminals of the current clamps CL1, CL2, CL3, and CL4 are connected to the input terminals CH1, CH2, CH3, and CH4, respectively. The current clamp CL1 clamps the line connecting the R-phase line and the load RL4 and measures the current Ira flowing through this line, and the current clamp CL2 clamps the line connecting the S-phase line and the load RL5. The current Is flowing through is measured. The current clamp CL3 clamps the line connecting the R phase and the loads RL1 and RL3 and measures the current Irb flowing through the line, and the current clamp CL4 clamps the line connecting the T phase and the loads RL2 and RL3. Is measured.

FIG. 2 is a configuration diagram showing an embodiment of a power meter according to the present invention.
In each of the amplifiers 51 to 53, one of the input terminals is connected to the terminal Nin of the wattmeter, and this terminal Nin is grounded outside the wattmeter and connected to a common potential point in the wattmeter.

The other input terminals of the amplifiers 51, 52, 53 are connected to the terminals Vin1, Vin2, Vin3 of the wattmeter, respectively. The aforementioned voltages Vrn, Vsn, Vtn are respectively applied to the terminals Vin1, Vin2, Vin3, and each amplifier normalizes these voltages and outputs them.

The A / D converter 59 simultaneously holds the output voltages of the amplifiers 51, 52, and 53 by the sample hold function, and sequentially performs A / D conversion by switching the held voltages. The converted digital data is taken into the MPU 62 which is a processor through an insulating circuit 61 including a photocoupler, a transformer, or an insulating element instead. The portion so far corresponds to voltage detection means.

Current clamps CL1, CL2, CL3, and CL4 are connected to the input terminals CH1, CH2, CH3, and CH4 of each current measurement channel, respectively, and the currents Ira, Irb, Is, and It described above are detected and converted to voltages. This voltage is input to amplifiers 54, 55, 56, and 57, respectively. The amplifiers 54, 55, 56 and 57 normalize and output the converted voltage.

The A / D converter 60 simultaneously holds the voltages normalized by the amplifiers 54, 55, 56, and 57 by the sample hold function, and sequentially performs A / D conversion by switching the held voltages. The converted digital data is taken into the MPU 62. The portion so far corresponds to current detection means.

  The zero-cross detector 58 detects one cycle from the zero-cross point of the output voltage of the amplifiers 51, 52, 53, and the detected cycle data is taken into the MPU 62 via the insulation circuit 61.

  The MPU 62 controls the entire power meter such as the range control of each amplifier and the control of the display 7. The MPU 62 performs an effective value calculation process from the acquired voltage value, current value, and period data, and a voltage Vrn applied to the single-phase load. , Vsn and the currents Ira, Is flowing through the single-phase load, the single-phase three-wire power P13 is calculated as shown below.

Further, vector addition is performed using the voltages Vrn, Vsn, and Vtn to obtain an interphase voltage between the RT phase and the TS phase, and the total power P33 of the three phases is calculated, or the R-phase line and the T-phase are calculated. The current flowing in the S-line is vector-added to obtain the current flowing in the S-phase line, and the three-phase total power P33 can be calculated from the voltages Vrn, Vsn, Vtn and the three line currents. This MPU 62 corresponds to a calculation means. The calculation of the three-phase power is based on the two wattmeter method.

Vector addition / subtraction can be performed by performing addition / subtraction using sampling data obtained by simultaneously measuring the measurement signals of the respective voltages and currents and calculating the effective value of those results.
As shown in the above equation, P33 calculation may be performed by adding vectors of voltages Vrn, Vsn, and Vtn, or by using vector addition of line currents Irb and It.

The display unit 63 displays the power value calculated by the MPU 62 or displays the setting state of the power meter.
In addition, operation means (not shown) including a keyboard or the like is provided, and the user operates the wattmeter via the operation means.

FIG. 3 is a diagram in which the voltage and current input to the power meter in the power measurement of FIG. 1 are displayed as vectors.
In FIG. 3, the input unit 64 of the wattmeter is the same as the input unit comprising the amplifiers 51, 52, 53 of FIG. 2, and the output voltages Vrn, Vsn, Vtn of the amplifiers are RN phase, S based on the ground potential. -N-phase and TN-phase voltages are shown. Since Vrn and Ira, and Vsn and Is are in phase, the single-phase three-wire power is obtained by multiplying Vrn and Ira and Vsn and Is. It can be obtained by adding.

  Further, when obtaining the total power of three phases, the voltage of RS phase is obtained by vector subtraction of Vsn from Vrn, and the voltage of TS phase is obtained by vector subtraction of Vsn from Vtn. Based on these phase voltages and line currents Irb and It separately measured, the total power can be calculated using a two-watt meter method.

FIG. 4 is a second explanatory diagram showing power measurement using the power meter according to the present invention.
In FIG. 4, the difference from FIG. 1 is that the current measurement point for measuring the single-phase three-wire power is changed in accordance with the connection of the single-phase three-wire load to the ST phase. It is.
The wattmeter 40 measures the RN phase voltage Vrn, the SN phase voltage Vsn, and the TN phase voltage Vtn with reference to the ground potential, and the single-phase three-wire load currents Is, Ita, and R phase. The line current Ir and the T-phase line current Itb are measured.

FIG. 5 is a vector display of the voltage and current input to the power meter in the power measurement of FIG.
Similarly to the description in FIG. 3, since Vsn and Is, and Vtn and Ita are in the same phase, the single-phase three-wire power P13 is obtained by adding the multiplication result of Vsn and Is and the multiplication result of Vtn and Ita. It is done.
Further, by performing vector calculation using the voltages Vrn, Vsn, and Vtn, the interphase voltages of the RT phase and the TS phase can be obtained, and the three-phase total power P33 can be calculated by the two-watt meter method.

ベクトルの加減算は、各電圧、電流の測定信号を同時に測定したサンプリングデータを用いて加減算を行いそれらの結果を実効値演算すればよい。 Specifically, the calculation is performed using the following equation. In addition, the thing similar to the above voltage and electric current is shown with the same symbol.

Vector addition and subtraction may be performed by adding and subtracting using sampling data obtained by simultaneously measuring each voltage and current measurement signal and calculating the effective value of those results.

FIG. 6 is a third explanatory view showing power measurement using the power meter according to the present invention.
In FIG. 6, the difference from FIG. 1 and FIG. 4 is that the current measurement point for measuring the single-phase three-wire power is changed in accordance with the connection of the single-phase three-wire load to the TR phase. It is a point.
The wattmeter 40 measures the RN phase voltage Vrn, the SN phase voltage Vsn, and the TS phase voltage Vtn with reference to the ground potential, and the single-phase three-wire load currents Ira, Ita, R The phase line current Irb and the T-phase line current Itb are measured.

FIG. 7 is a vector representation of the voltage and current input to the wattmeter in FIG.
3 and 5, Vrn and Ira, and Vtn and Ita are in the same phase, so the single-phase three-wire power P13 adds the multiplication result of Vrn and Ira and the multiplication result of Vtn and Ita. If you do.

Further, the interphase voltages of the RT and TS phases are obtained by performing a vector operation using the voltages Vrn, Vsn, and Vtn, and are calculated using the R-phase line current value Irb and the T-phase line current value Itb. The three-phase total power P33 can be calculated by the wattmeter method.

Specifically, the calculation is performed using the following equation. In addition, the thing similar to the above voltage and electric current is shown with the same symbol.

Vector addition / subtraction can be performed by performing addition / subtraction using sampling data obtained by simultaneously measuring the measurement signals of the respective voltages and currents and calculating the effective value of those results.

ここで、ｖｒｎ，ｖｓｎ，ｖｔｎ，ｉｒａ，ｉｓ，ｉｒｂ，ｉｔ，ｉｔｂは時刻ｔにおける測定電圧および測定電流のサンプリングデータであり、Ｔは１周期である。 Calculation of the voltage and current used in the above equations is performed by the following equations.

Here, vrn, vsn, vtn, ira, is, irb, it, and itb are sampling data of the measurement voltage and measurement current at time t, and T is one cycle.

As described above, in the single-phase three-wire power measurement, the calculation formula differs depending on which phase of the three phases the load is connected to, but in the three-phase three-wire power measurement, there is no need to change the connection and the same is always the same. Since it can be calculated by an arithmetic expression, measurement with good work efficiency can be performed.
In addition, the amount of electric power can be measured by integrating the electric power measurement values obtained according to the present invention, and a small and inexpensive electric energy meter can be provided.

  On the other hand, in the single-phase three-wire power measurement of the above-described embodiment, the calculation formula differs depending on which of the three phases the single-phase three-wire load is connected. Therefore, the wattmeter must have in advance information on which phase of the three-phase three-wire the phase to which the single-phase three-wire load is connected is. For this reason, if the operator sets the power meter based on the wiring diagram, or if there is no wiring diagram or the reliability thereof is low, it is necessary to investigate using a dedicated device separately. For this reason, problems such as an increase in expenses and deterioration in work efficiency occur.

In order to cope with this, the voltage values Vrn, Vsn, and Vtn obtained in the above-described embodiment are vector-calculated to detect a phase in which single-phase three-wires are connected. This will be described with reference to the drawings.
FIG. 8 is an explanatory diagram showing detection of a phase in which single-phase three-wires are connected.
In FIG. 8, the three-phase power source 1 shows a case where each phase is grounded at an intermediate position. When the phase is between the R and S phases, it is N1, when it is between the S and T phases, it is N2, and when it is between the T and R phases. Is grounded at N3. The input unit 2 of the wattmeter is the same as the input unit including the amplifiers 1, 2, and 3 in FIG. 2, and the output voltages Vrn, Vsn, and Vtn of the amplifier are RN phase and SN phase based on the ground potential. , TN phase voltages are respectively shown, and when the voltages of the single-phase three-wires are balanced, the vector calculation of these voltages is as follows.

Ｓ−Ｔ相間に単相３線の負荷が接続されている場合。

Ｔ−Ｒ相間に単相３線の負荷が接続されている場合。

When a single-phase three-wire load is connected between the RS phases.

When a single-phase three-wire load is connected between the ST phases.

When a single-phase three-wire load is connected between the TR phases.

Even in the case of unbalance, the result of the above equation can be expected to be a sufficiently low value with respect to the rated voltage (for example, 100V), so if the right side of the above equation is not 0, for example 10% or less of the rated voltage. Judgment is possible.
Thereby, it is possible to detect in advance information on which phase of the three-phase three-wire the phase to which the single-phase three-wire load is connected using the measured voltage. When calculating the power of the single-phase three-wire load, the power meter determines a calculation formula to be used using this connection information. Furthermore, the detection result is displayed on the display unit to notify the operator.
Therefore, there is no need to add a circuit to the power meter or use a dedicated device to check, and it is possible to prevent an increase in expenses and a deterioration in work efficiency.

It is the 1st explanatory view showing power measurement using the power meter concerning the present invention. It is the block diagram which showed one Example of the wattmeter which concerns on this invention. It is the figure which displayed the voltage and current input into a wattmeter in the vector measurement by the electric power measurement of FIG. It is the 2nd explanatory view showing power measurement using the power meter concerning the present invention. FIG. 5 is a diagram in which the voltage and current input to the wattmeter in the power measurement of FIG. 4 are displayed as vectors. It is the 3rd explanatory view showing power measurement using the power meter concerning the present invention. It is the figure which carried out vector display of the voltage and electric current which are input into a power meter in FIG. It is explanatory drawing which showed the detection of the phase by which the single phase 3 wire was connected. It is explanatory drawing which showed the electric power measurement of the conventional single phase 3 wire and three phase 3 wire. It is a block diagram which shows an example of the conventional multichannel insulation input type wattmeter. It is explanatory drawing which showed the detection of the phase by which the conventional single phase 3 line was connected.

Explanation of symbols

51, 52, 53, 54, 55, 56, 57 Amplifier 58 Zero cross detector 59, 60 A / D converter 61 Insulation circuit 62 MPU
63 Display

Claims (5)

In a wattmeter that measures the power of a different-capacity three-phase four-wire power source that supplies power to a single-phase three-wire load from a predetermined phase of three-phase alternating current,
Voltage detection means for detecting a ground-to-ground voltage between the three-phase AC transmission line with reference to the ground potential;
Current detection means for detecting the line currents of the three-phase alternating current first and third phase transmission lines and the current flowing through the single-phase three-wire load;
Calculation of single-phase three-wire power based on the voltage applied to the single-phase three-wire load in the voltage between the grounds and current flowing through the load, and calculation of three-phase power based on the voltage between the grounds and the line current Computing means for performing at least one of the following;
A wattmeter characterized by comprising:   The computing means calculates the voltage between the grounds to obtain a voltage between the first-phase and second-phase transmission lines of the three-phase AC and between the second-phase and third-phase transmission lines, and the voltage between these lines. The wattmeter according to claim 1, wherein three-phase power is calculated based on the line currents of the first phase and the third phase.   The computing means calculates the phase current of the first phase and the phase of the third phase to obtain a second phase of the line current, and calculates three-phase power based on the line current and the voltage between the grounds. The wattmeter according to claim 1.   The phase of a three-phase alternating current to which a single-phase three-wire load is connected is detected based on a result of a vector operation combining the two voltages between the grounds. The wattmeter described. The wattmeter according to any one of claims 1 to 4, wherein the current measuring means detects a measured current using a clamp type current sensor.

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