JP2011013032A - Current measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce measurement error of current flowing through a distribution line.

SOLUTION: A phase error Δϕ caused by an impedance of a clamp-type ammeter 10 and a resistance 15 connected in parallel to an output terminal of the clamp-type ammeter 10, a phase error 2πΔt caused by a difference of times to input data of voltage and current to be input at a same time, and a phase error α due to non-proportionality of a magnetic flux density within iron cores 11a, 11b of clamp-type ammeters 10a, 10b to a magnetic field applied to the iron cores 11a, 11b are previously memorized. Then, phases of current I_U, I_W, measured by the clamp-type ammeter 10 in which a coil 12 is wrapped onto the iron cores 11a, 11b to distribute approximately over all circumferences of the iron cores 11a, 11b, are corrected based on a phase error η added with these phase errors Δϕ, 2πΔt and α.

COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a current measuring device, and is particularly suitable for use in non-contact measurement of a current flowing through a distribution line.

The ideal way to measure the power of a distribution line is to directly measure the voltage drop in the distribution line and the current flowing through the distribution line, and measure the power based on the measured voltage drop and current (this method Is called the voltage drop method). However, since the distribution line is long and complicated, it is difficult to directly measure the voltage drop in the distribution line. In addition, since the substation in the facility is always in operation, it is not practical to stop the operation of the substation and connect a large number of ammeters and shunt resistors for current monitoring to the distribution line.
Therefore, as a method of measuring the power of the distribution line, there is a method of directly measuring the voltage of the distribution line and measuring the current flowing through the distribution line in a non-contact manner using a clamp-type ammeter (see Patent Document 1). reference).

JP-A-8-101237

However, when a clamp-type ammeter is used, the current flowing through the distribution line is not directly measured. Nevertheless, the technique described in Patent Document 1 does not consider measurement errors due to the configuration of the clamp-type ammeter. For this reason, there is a concern that the measurement error of the current flowing through the distribution line becomes large and the measurement error of the power becomes large.
The present invention has been made in view of such a problem, and an object thereof is to reduce a measurement error of a current flowing through a distribution line.

  The current measuring device of the present invention has a pair of iron cores that can be separated and a coil wound around the iron core, and when the pair of iron cores are combined, the pair of iron cores are closed magnetically. A clamp-type ammeter that measures the current flowing through the distribution line that passes through the space inside the closed magnetic circuit, and the current that flows through the distribution line is calculated using the current measured by the clamp-type ammeter. A current calculation device comprising: a current calculation device comprising: a current calculation device comprising: a phase of a current actually supplied to the distribution line and a current obtained based on a measurement by the clamp-type ammeter; When storing the current data based on the measurement with the clamp type ammeter for the calculation of the power of the distribution line and the storage means for storing the phase error which is the difference with the phase in advance, the phase of the current is Said And correcting means for correcting, based on the phase error stored in 憶 means, characterized by having a.

  According to the present invention, the phase error, which is the difference between the phase of the current actually passed through the distribution line and the phase of the current obtained based on the measurement with the clamp type ammeter, is measured and stored in advance. Using the phase error, the phase of the current based on the measurement with the clamp-type ammeter was corrected, and the power of the distribution line was calculated using the current whose phase was corrected. Therefore, the measurement error of the current flowing through the distribution line can be reduced, and the measurement error of the power of the distribution line can be reduced.

The figure which shows an example of a structure of the distribution line used as the object which measures electric power with the electric power measurement apparatus of this embodiment, the clamp type ammeter in the state which pinched | interposed the distribution line, and the voltage measurement apparatus which measures the voltage of a distribution line directly It is. It is a figure which shows an example of a structure of the electric power calculation apparatus which measures and displays electric power. It is a figure which shows an example of the outline of the coil | winding structure of the clamp type ammeter of this embodiment. It is a figure explaining the principle which measures the electric current which flows into a distribution line by the clamp type ammeter of this embodiment. It is a figure explaining an example of the method of measuring the electric current which flows into shunt resistance. It is a figure which shows an example of the measurement result of the time difference with respect to the frequency of a simulation signal. It is a figure which shows an example of the relationship between the phase error and energization current by the magnetic flux density in the iron core of a clamp type ammeter being not proportional to the magnetic field applied to an iron core. A state in which the coil is wound around only one portion of the straight portion of the closed magnetic circuit formed by the iron core, and a clamp-type ammeter casing the iron core around which the coil is wound in this way, is a U-phase distribution line. It is a figure which shows a mode that is inserted | pinched. The relationship between the phase error obtained by subtracting the phase of the current obtained based on the measurement with the conventional clamp-type ammeter from the phase of the current actually energized in the distribution line, and the rotation angle of the conventional clamp-type ammeter It is a figure which shows an example. The phase error obtained by subtracting the phase of the current obtained based on the measurement with the clamp-type ammeter of the present embodiment from the phase of the current actually passed through the distribution line, and the rotation angle of the clamp-type ammeter of the present embodiment FIG. It is a figure which shows an example of the relationship between the current amplitude accuracy obtained with the electric power measurement apparatus of this embodiment, and an energization current. It is a figure which shows the measurement result of the electric power (transmission end electric power) of the power transmission end of a distribution line, and the electric power (power reception end electric power) of a receiving end. It is a figure which shows an example of the result of having performed calculation of the line loss by the voltage drop method, and calculation of the line loss by the method of this embodiment 60 times on the same conditions. It is a figure which shows an example of the result of having performed the calculation of the line loss by the voltage drop method, and the calculation of the line loss by the method of this embodiment, changing the energization current.

Hereinafter, an embodiment of the present invention will be described.
<Schematic configuration of power measuring device>
FIG. 1 shows a distribution line (FIG. 1 (a)) to be measured by the power measuring device of the present embodiment, a clamp-type ammeter (FIG. 1 (b)) with the distribution line interposed therebetween, It is a figure which shows an example of the voltage measuring apparatus (FIG.1 (c)) which measures the voltage of a distribution line directly. FIG. 2 is a diagram illustrating an example of the configuration of a power calculation apparatus that measures and displays power.
In the present embodiment, as shown in FIG. 1 (a), transmission of a distribution line using a three-phase AC power source 1 (symmetric three-phase AC) as a power source and a three-phase load 2 (symmetric three-phase load) as a load. A case where the power loss P _loss of the distribution line is calculated by subtracting the power P _r (W) of the power receiving end 4 from the power P _s (W) of the end 3 will be described as an example.
Since the clamp-type ammeters 10a and 10b shown in FIG. 1B are the same, in the following description, the clamp-type ammeters 10a and 10b are collectively referred to as the clamp-type ammeter 10 as necessary. . Similarly, since the voltage measuring devices 20a and 20b shown in FIG. 1C are the same, in the following description, the voltage measuring devices 20a and 20b are collectively referred to as the voltage measuring device 20 as necessary.

<Clamp ammeter>
FIG. 3 is a diagram illustrating an example of a schematic winding structure of the clamp-type ammeter 10. Specifically, FIG. 3A is a front view showing an iron core and a coil (a part thereof) in a state where the clamp-type ammeter 10 is closed, and FIG. 3B is a view of A in FIG. It is sectional drawing seen from -A 'direction, FIG.3 (c) is sectional drawing seen from the BB' direction of Fig.3 (a).
3, the clamp-type ammeter 10 has a first clamp portion located on the lower side and a second clamp portion located on the upper side as viewed in FIG. The 1st clamp part has iron core 11a, coils 12a-12d, insulating tapes 13a-13d, and insulating tapes 14a-14d. The 2nd clamp part has iron core 11b, coils 12e-12h, insulating tapes 13e-13h, and insulating tapes 14e-14h. Here, the same reference numerals (numeric characters) are the same.

The iron cores 11a and 11b constitute a half circumference of a circumferential closed magnetic circuit formed when the clamp-type ammeter 10 is closed (when the iron cores 11a and 11b are combined). Thus, the clamp-type ammeter 10 uses a pair of split-type iron cores 11a and 11b that can be separated.
The coils 12a to 12h are wound around the iron cores 11a and 11b the same number of times in the same winding direction.
The coils 12a to 12d in the first clamp part are connected in series. For example, except for the winding start portion of the coil 12a and the winding end portion of the coil 12d, each of the coils 12a to 12d has a winding start portion whose winding start portion is adjacent to the winding start portion. It is electrically connected to the end part.

Similarly, the coils 12e to 12h in the second clamp portion are also connected in series. For example, except for the winding start portion of the coil 12e and the winding end portion of the coil 12h, each of the coils 12e to 12h has a winding start portion whose winding start portion is adjacent to the winding start portion. It is electrically connected to the end part.
The coils 12a to 12h are configured to be connected in series when the clamp-type ammeter 10 is closed. In the example described above, for example, when the clamp-type ammeter 10 is closed, the winding end portion of the coil 12d and the winding start portion of the coil 12e are electrically connected to each other. .

In this embodiment, each coil 12a-12h is comprised by winding a copper wire 80 micrometers in diameter 100 times, and when the coils 12a-12h are connected in series, the whole number of turns will be 800 times. In this embodiment, the total resistance of the copper wires constituting the coils 12a to 12h connected in series (in this specification, “resistance” means “DC resistance”) is 78.3Ω. The inductance is 4.3H.
In the present embodiment, the number of turns of the coils 12a to 12h is the same, but the number of turns of the coils 12a to 12h may be different. In this embodiment, two coils are arranged in a straight line portion of the closed magnetic circuit formed when the clamp-type ammeter 10 is closed, but the number of coils arranged in the iron core is It can be determined appropriately according to the shape of the material. For example, a plurality of coils are arranged in at least one straight line portion of the closed magnetic circuit formed when the clamp-type ammeter 10 is closed, and 1 is set in the other straight line portion where the plurality of coils are not arranged. Two coils may be arranged.

The insulating tapes 13a to 13h are, for example, insulating double-sided tapes. In addition to insulating the iron cores 11a and 11b and the coils 12a to 12h, the role of fixing the coils 12a to 12h to the iron cores 11a and 11b is here. Fulfill.
The insulating tapes 13a to 13h are, for example, Kapton tapes, fix the coils 12a to 12h, and the first case (second clamp part) is an insulating molded product (first case) 2), it serves to protect the coils 12a to 12h. Since the first case and the second case can be realized by a known technique, a detailed description thereof is omitted here.
In the following description, the entire coils 12a to 12h connected in series when the clamp-type ammeters 10a and 10b are closed will be referred to as a coil 12 as necessary.

FIG. 4 is a diagram for explaining the principle of measuring the current flowing through the distribution line with the clamp-type ammeter 10. As shown in FIG. 3, the coils 12 are distributed (preferably uniformly) around substantially the entire circumference of the iron cores 11a and 11b. However, in FIG. It is indicated that the coil 12 is wound around only a part of the direction of the closed magnetic path to be formed.
As shown in FIG. 4, a resistor 15 is connected in parallel to the output end of the clamp-type ammeter 10 (in the example described above, the winding start portion of the coil 12a and the winding end portion of the coil 12h).
In the clamp type ammeters 10a and 10b, a clamp type is used as a physical quantity representing the currents I _U and I _W flowing through the distribution line (U phase, W phase) passing through the space inside the closed magnetic circuit formed by the iron cores 11a and 11b. The induced voltage induced at the output terminals of the ammeters 10a and 10b is output.

When this induced voltage is E ₀ (V), the resistance 15 is R (Ω), and the number of turns of the coil 12 is N (times), the current I _CT obtained by the clamp-type ammeter 10 is expressed by the following equation (1). expressed.
I _CT = (N × E ₀ ) / (R × K _ave ) (1)
Here, K _ave is an average value of the coupling coefficient K expressed by the following equation (2), and is a constant in this embodiment. This _Kave is obtained in advance by performing a calibration experiment described later.
K = (N × E ₀ ) / (R × I _shunt ) (2)
In the equation (2), I _shunt is a current obtained from the voltage applied to both ends of the shunt resistor arranged (inserted) in series with the load in the laboratory level calibration experiment and the resistance value of the shunt resistor.
FIG. 5 is a diagram for explaining an example of a method for measuring the current I _shunt flowing through the shunt resistor during a calibration experiment performed in advance to obtain K _ave . In this calibration experiment, a shunt resistor is inserted into an actual distribution line, and the experiment is not performed, but a distribution line that is simulated at the laboratory level is used.
As shown in FIG. 5, the voltage applied to both ends of the shunt resistor 41 arranged in the middle of the simulated distribution line is input through the insulation amplifier 42, and the voltage is divided by the resistance value of the shunt resistor 41, thereby The current I _shunt flowing through the resistor 41 can be obtained. Here, the voltage applied to both ends of the shunt resistor 41 arranged in the U phase is measured, but the voltage applied to both ends of the shunt resistor 41 is measured by arranging the shunt resistor 41 in the V phase or the W phase. You may make it do. Further, an ammeter may be arranged in place of the shunt resistor 41, and the indicated value of the ammeter may be used as the value of the current I _shunt .

<Voltage measuring device>
Returning to the description of FIG. 1, in FIG. 1C, the voltage measuring devices 20a and 20b have resistance voltage dividers 21a and 21b and insulation amplifiers 22a and 22b. The resistor voltage dividers 21 a and 21 b are for stepping down the voltages V _UV and V _WV to voltages that can be taken into the power calculation device 30. The insulation amplifiers 22a and 22b are for electrically insulating the distribution line side and the power calculation device 30. In the present embodiment, the voltages V _UV and V _WV are directly measured by the voltage measuring devices 20a and 20b having such a configuration.
<Power calculation device>
In FIG. 2, the power calculation device 30 includes input terminals 31 a and 31 b, A / D converters 32 a and 32 b, processing devices 33 a and 33 b, a loss calculation device 34, and a display device 35. The configurations of the input terminals 31a and 31b, the A / D converters 32a and 32b, and the processing devices 33a and 33b are the same. Therefore, in the following description, these will be referred to as the input terminals 31 and A as necessary. Collectively referred to as / D converter 32 and processing device 33.
In this embodiment, since the distribution line to be measured is a balanced three-phase circuit, the input terminal 31 has 4ch terminals. When the distribution line to be measured is an unbalanced three-phase circuit, the input terminal 31 is a 6ch terminal. The induced voltage E ₀ output from the clamp-type ammeters 10a and 10b for measuring the currents I _U and I _W flowing through the U-phase and W-phase distribution lines at the 1ch and 2ch terminals of the input terminal 31, respectively. Is entered. Here, the induced voltage E ₀ output from the clamp-type ammeters 10 a and 10 b attached to the power transmission terminal 3 is input to the 1ch and 2ch terminals of the input terminal 31 a, respectively, and is clamped to the power reception terminal 4. ammeter 10a, the induced voltage E ₀ which is output from 10b, 1ch each input terminal 31b, and shall be entered into the terminal of 2ch.
The voltages V _UV and V _WV output from the voltage measuring devices 20a and 20b are input to the 3ch and 4ch terminals of the input terminal 31, respectively. Here, the voltages V _UV and V _WV output from the voltage measuring devices 20 a and 20 b attached to the power transmission end 3 are respectively input to the 3 ch and 4 ch terminals of the input terminal 31 a and the voltages attached to the power receiving end 4. Assume that the voltages V _UV and V _WV output from the measuring devices 20a and 20b are respectively input to the 3ch and 4ch terminals of the input terminal 31b.
In the present embodiment, the input terminal 31 has a channel switch, and the channel output to the A / D converter 32 is sequentially switched by this channel switch.

The A / D converters 32a and 32b convert the induced voltage E ₀ , the voltages V _UV and V _WV output from the input terminals 31a and 31b, respectively, into digital signals.
The processing devices 33a and 33b _receive the digital signals of the induced voltages E ₀ , voltages V _UV and V _WV of the clamp-type ammeters 10a and 10b from the A / D converters 32a and 32b, respectively, and transmit the power transmission ends of the distribution lines. 3 of calculated power P _r of the power P _s and the receiving end 4.
Loss calculation device 34, the power P _s of the sending end 3, by subtracting the power P _r of the receiving end 4, is displayed on the display device 35 calculates the power loss P _loss of the power distribution line. The processing device 33 and the loss calculation device 34 can be realized by using, for example, a microcomputer including a CPU, ROM (for example, mask ROM and EEPROM), RAM, and VRAM. However, the hardware configuration of the processing device 33 and the loss calculation device 34 is not limited to this.

The processing devices 33a and 33b include, as their functions, current capturing units 36a and 36b, storage units 37a and 37b, current correcting units 38a and 38b, voltage capturing units 39a and 39b, and power calculating units 40a and 40b. And have. The current capturing units 36a and 36b, the storage units 37a and 37b, the current correcting units 38a and 38b, the voltage capturing units 39a and 39b, and the power calculating units 40a and 40b have the same configuration. In the description, these are collectively referred to as a current acquisition unit 36, a storage unit 37, a current correction unit 38, a voltage acquisition unit 39, and a power calculation unit 40 as necessary.
The processing in the processing device 33 is started after the user operates the user interface included in the power calculation device 30 and makes a predetermined input before starting measurement. For example, after the user performs an input operation of predetermined information, the process in the processing device 33 is started by giving an instruction to start measurement.
The current capturing unit 36 captures the digital signal of the induced voltage E ₀ of the clamp type ammeters 10 a and 10 b into the processing device 33.
The storage unit 37 previously calculates a phase error η (rad) obtained by subtracting the phase of the current obtained based on the measurement with the clamp-type ammeters 10a and 10b from the phase of the current actually supplied to the distribution line. Remember). This phase error η is stored in the storage unit 37, for example, based on an operation by a user of a user interface provided in the power calculation device 30.
Here, the phase error η is expressed by the following equation (3).
η = Δφ + 2 × π × f × Δt + α (3)

In the equation (3), Δφ is a phase error (rad) caused by the impedance of the clamp-type ammeter 10 and the resistor 15 connected in parallel to the output terminal of the clamp-type ammeter 10, and the following (4) It is expressed by an expression.
Δφ = tan ⁻¹ ((2 × π × f × L _a ) / (R _a + R)) (4)
f is the frequency (Hz), L _a is a clamping ammeter 10 inductance (H), R _a is the resistance of the coil 12 of the clamp type ammeter 10 (Omega), R is The resistance value (Ω) of the resistor 15. In this embodiment, this phase error Δφ is a constant (a constant value), and this phase error Δφ is stored in advance in the storage unit 37 based on an operation by the user. Here, the user inputs the phase error Δφ itself, but it is not always necessary to do so. For example, the value of R _a, L _a is because it is unique to the clamping ammeter 10, processor 33 may store only those values, the frequency in the distribution line (Hz) and the resistor 15 The resistance value R (Ω) may be input by a user operation.

In Expression (3), Δt is a difference in time taken for data to be taken in at the same time (in this embodiment, a time difference that occurs until the data is actually taken into the processing device 33, including a channel switching time in the input terminal 31). (Sec)).
The time difference Δt is obtained by simultaneously inputting simulated signals (voltages) output from one signal source to the two channels of the input terminal 31 and sequentially switching the channels of the input terminal 31 to transfer the simulated signal data from the two channels. It is obtained by taking in the processing device 33. That is, the time difference Δt is the difference in time when the processing device 33 fetches the data of the simulation signal. FIG. 6 is a diagram illustrating an example of a measurement result of the time difference Δt with respect to the frequency f of the simulation signal. In the results shown in FIG. 6, the time difference Δt is 30 ± 0.04 μsec, which is approximately 30 μsec, regardless of the frequency f of the simulation signal. Therefore, in the present embodiment, the time difference Δt is a constant (a constant value), and this time difference Δt is stored in advance in the storage unit 37 based on an operation by the user. In the present embodiment, the time difference Δt is a value obtained by subtracting the time when the voltage acquisition unit 39 has acquired the voltage data corresponding to the current from the time when the current acquisition unit 36 has acquired the current data of the simulated distribution line. Yes.

  In Expression (3), α is a phase error (rad) due to the fact that the magnetic flux density in the iron cores 11a and 11b of the clamp-type ammeters 10a and 10b is not proportional to the magnetic field applied to the iron cores 11a and 11b. Since it is difficult to theoretically obtain the phase error α, in the present embodiment, the phase error α is obtained experimentally. The obtained phase error α is stored in advance in the storage unit 37 based on an operation by the user.

Here, an example of a method for obtaining the phase error α will be described.
The shunt resistor 41 and the insulation amplifier 42 shown in FIG. 5 are arranged not only for the U phase of the simulated distribution line but also for the W phase, and the voltage applied to both ends of the shunt resistor 41 arranged in the U phase and the W phase is expressed as follows: The currents I _U and I _W flowing through the U-phase and W-phase simulated distribution lines are obtained by inputting the data of these voltages to the 1ch and 2ch of the input terminal 31 and dividing the data of the voltages by the resistance value of the shunt resistor 41 (hereinafter referred to as the “I”). in the description, the current I _U, the I _W, optionally, referred to as current I _U, I _W measured by the shunt resistor).
On the other hand, the induced voltage E ₀ output from the clamp-type ammeters 10a and 10b with the U-phase simulated distribution line and the W-phase simulated distribution line interposed therebetween is input to the 1ch and 2ch of the input terminal 31, By substituting the data of the induced voltage E _{0 into} the equation (1), currents I _U and I _W flowing through the U-phase and W-phase simulated distribution lines are obtained (in the following explanation, these currents I _U and I _W are (If necessary, the currents I _U and I _W measured with a clamp-type ammeter are referred to.)
Further, the phase error Δφ and the time difference Δt are obtained in advance as described above.

Then, the phases of the currents I _U and I _W measured by the clamp type ammeter are subtracted from the phases of the currents I _U and I _W measured by the shunt resistance. The subtraction value obtained in this way is equal to the phase error η. Therefore, the phase error α can be obtained by substituting the phase error η (subtraction value), the phase error Δφ, and the time difference Δt into the equation (3).
The calculation of the phase error α as described above is performed by changing the value of the current flowing through the simulated distribution line. This is because the phase error α varies depending on the current flowing through the distribution line. FIG. 7 is a diagram showing an example of the relationship between the phase error α thus obtained and the energization current (current flowing through the simulated distribution line).
In the present embodiment, the formula representing the straight line 61 shown in FIG. 7 is stored in the storage unit 37 based on an operation by the user. However, as long as the relationship between the phase error α and the energization current is stored in the storage unit 37, it is not always necessary to store the expression representing the straight line 61 in the storage unit 37. For example, a table that stores the phase error α and the energization current in association with each other may be stored in the storage unit 37. When such a table is stored in the storage unit 37, the phase error α corresponding to the energized current not stored in the table can be obtained by performing an interpolation process.
As described above, in the present embodiment, the phase errors Δφ, 2πfΔt, and α are individually stored, and the phase error η is obtained from the equation (3). The units of the phase errors Δφ, 2πfΔt, α, and η may be degrees instead of rad.

Returning to the description of FIG. 2, the current correcting unit 38 includes the induced voltage E _{0 of} the clamp type ammeters 10 a and 10 b captured by the current capturing unit 36 and the coupling coefficient K stored in advance in the storage unit 37. The average value _ave , the number N of turns of the coil 12, and the resistance value R of the resistor 15 are substituted into the equation (1), and the currents I _U and I _W measured by the clamp type ammeter are calculated.
Then, the current correction unit 38 reads the phase error η from the storage unit 37 and subtracts the phase error η from the phase of the currents I _U and I _W measured by the clamp type ammeter (current I measured by the clamp type ammeter). The phase is delayed by a phase error η from the phases of _U and I _W ). In the present embodiment, current I _U was measured by clamping ammeter, by correcting the uptake time of I _W, a current I _U was measured by clamping ammeter, so as to correct the phase of the I _W Yes.

The voltage capturing unit 39 captures digital signals of the voltages V _UV and V _WV into the processing device 33.
The power calculation unit 40 uses the data of the voltages V _UV and V _WV acquired by the voltage acquisition unit 39 and the data of the currents I _U and I _W whose phases have been corrected by the current correction unit 38, to distribute the distribution line. calculates the electric power P _s of the sending end 3, the receiving end 4 and a power P _r.
Here, when s is a number indicating the data acquisition order, i is a symbol for identifying a phase, and M is the number of acquired data, the active power P _i is expressed by the following equation (5). Is done.

Power calculation unit 40, (5) the perform calculations for each of the sending end 3 and receiving end 4, calculates the power P _s of the sending end 3 of distribution lines, the receiving end 4 and a power P _r .
As described above, loss calculation device 34, the power calculation unit 40a, an input inputs the power P _s of the sending end 3 of distribution lines, the power calculation unit 40b, the power P _r of the receiving end 4 of the distribution line and, from the power P _s of the sending end 3, by subtracting the power P _r of the receiving end 4, calculates the power loss P _loss of the power distribution line.
Display device 35, the loss calculation unit 34 inputs the power P _s of the sending end 3 of the distribution line, and inputs a power P _r of the receiving end 4, the power loss P _loss of the power distribution line, display them To do. The display device 35 is, for example, a liquid crystal display.
Here, the case where the loss calculating device 34 calculates the power loss P _loss of the distribution line has been described as an example, but the power P _s of the power transmission end 3 of the distribution line and the power reception end 4 If the power _Pr is calculated and displayed, it is not always necessary to calculate the power loss P _loss of the distribution line. This is because the power loss P _loss of the distribution line can be easily calculated by the user.
As described above, in the present embodiment, for example, the current is obtained by using the input terminal 31, the A / D converter 32, and the current capturing unit 36, the storage unit 37, and the current correcting unit 38 in the processing device 33. An example of a calculation device is realized, and an example of a current measurement device is realized by using the clamp-type ammeter 10 and the current calculation device.

<Winding configuration of clamp-type ammeter>
As described above, in the present embodiment, the coils 12 are distributed over substantially the entire circumference of the iron cores 11a and 11b (see FIG. 3). Hereinafter, the process of doing this will be described.
FIG. 8 shows a state in which the coil 71 is wound only at one position of the linear portion of the closed magnetic path formed by the iron cores 11a and 11b (FIG. 8A), and the coil 71 is thus wound. FIG. 8 is a view showing a state in which a clamp-type ammeter 72 casing the iron cores 11a and 11b sandwiches the U-phase distribution line shown in FIG. 1 (FIG. 8B). The number of turns of the coil 71 and the copper wire used for the coil 71 are the same as those of the coil 12 shown in FIG.

The present inventors set the phase error ψ (the phase error η) when the clamp-type ammeter 72 is rotated (rotation angle θ) from the state shown in FIG. Change in phase error) was determined in the same condition except for the rotation angle of the clamp-type ammeter 72.
FIG. 9 is a diagram illustrating an example of the relationship between the phase error ψ and the rotation angle θ of the clamp-type ammeter 72.
As shown in FIG. 9, the phase error ψ varies greatly depending on the rotation angle θ, and the phase error ψ varies greatly depending on the position of the clamp-type ammeter 72 (ie, the coil 71).
From the results shown in FIG. 9, the present inventors have found that the coil 71 is wound only around a part of the closed magnetic circuit formed by the iron cores 11a and 11b, and the position of the clamp-type ammeter 72 (ie, the coil 71) Accordingly, it has been found that the clamp-type ammeter 72 is affected by the magnetic field generated from the distribution line adjacent to the distribution line to be measured, and as a result, the phase error ψ changes. This phenomenon will be specifically described. First, a magnetic field generated from a distribution line adjacent to a distribution line to be measured enters the iron cores 11a and 11b and then exits from the iron cores 11a and 11b. Here, if the coil 71 is wound only in a partial region of the closed magnetic path formed by the iron cores 11a and 11b, the magnetic field that has entered the iron cores 11a and 11b or the magnetic field that exits from the iron cores 11a and 11b is limited. The coil 71 may not be detected. Then, the induced voltage E _{0 of} the clamp-type ammeters 10a and 10b changes, thereby changing the phase error ψ.

Based on such knowledge, the present inventors can distribute the coil 12 over substantially the entire circumference of the iron cores 11a and 11b as shown in FIG. 3, regardless of the position of the clamp-type ammeter 10. The present inventors have found that the coil 12 can detect both the magnetic field that has entered the iron cores 11a and 11b and the magnetic field that leaves the iron cores 11a and 11b as reliably as possible. In other words, the iron core 11a, the induced voltage E ₀ by the magnetic field that has entered the 11b, because the polarity of the core 11a, the induced voltage E ₀ by the magnetic field exiting 11b are opposite, by detecting both their magnetic fields in the coils 12 For example, the induced voltage E ₀ due to these magnetic fields can be canceled, and thereby the influence of the magnetic field generated from the distribution line adjacent to the distribution line to be measured on the phase error ψ can be reduced.

FIG. 10 is a diagram illustrating an example of the relationship between the phase error ψ and the rotation angle θ of the clamp-type ammeter 10 of the present embodiment.
As shown in FIG. 10, it can be understood that the phase error ψ can be prevented from being changed as much as possible by the rotation angle θ by distributing the coil 12 around the entire circumference of the iron cores 11a and 11b.
From the above, in this embodiment, the coils 12 are distributed (preferably uniformly) on substantially the entire circumference of the iron cores 11a and 11b. Here, the substantially entire circumference of the iron cores 11a and 11b is a portion where winding is difficult (or impossible) due to the structure of the iron core, such as the corner portion of the iron cores 11a and 11b shown in FIG. The entire circumference of the iron core excluding the places where the winding is difficult (or impossible), such as the places where the winding is difficult (or impossible) due to the structure of the case containing the applied iron core.

<Current measurement accuracy>
The present inventors obtained the current amplitude accuracy obtained by the power measuring device of the present embodiment shown in FIG. 3 by changing the current (energization current) flowing through the distribution line.
Here, the current amplitude accuracy (%) is calculated by the following equation (6) (where I _CT and I _shunt indicate the amplitude).
Current amplitude accuracy = [(I _CT amplitude−I _shunt amplitude) / I _shunt amplitude] × 100 (6)
FIG. 11 is a diagram illustrating an example of the relationship between the current amplitude accuracy obtained by the power measurement apparatus of the present embodiment and the energization current.
As shown in FIG. 11, the current amplitude accuracy can be kept within a range of ± 0.2% by using the power measuring apparatus of the present embodiment. The current amplitude accuracy (catalog value) of clamp-type ammeters currently on the market is about ± 0.3% to ± 1%, so that the current amplitude accuracy of the power measuring apparatus of this embodiment should be greatly reduced. You can see that In FIG. 11, the lower limit value of the current amplitude accuracy when the energization current is 1 A is less than −0.2%, but this is output from the clamp-type ammeter 10 because the value of the energization current is small. This is probably because the induced voltage E ₀ is small and the S / N ratio is poor. However, the current amplitude accuracy when the energization current is 1 A can be improved by adjusting the parameters of the clamp-type ammeter 10 (the number of turns of the coil 12, the resistance value of the resistor 15, etc.).
Further, as shown in FIG. 10, the phase error η can be within a range of ± 0.05 degrees, and the current phase accuracy (degree) can be within a range of ± 0.05 degrees. Since the current phase accuracy (catalog value) of clamp-type ammeters currently on the market is about ± 0.5 degrees to ± 1 degrees, the current phase accuracy is also greatly reduced in the power measurement device of this embodiment. You can see that

<Power measurement accuracy>
The inventors arrange the clamp-type ammeters 10a and 10b and the voltage measuring devices 20a and 20b at the power transmission end 3 and the power receiving end 4 of the distribution line, respectively, and the power P _s of the power transmission end 3 of the distribution line. If, were measured and the power P _r of the receiving end 4 at the same time.
FIG. 12 is a diagram illustrating measurement results of the power P _s (power transmission end power) at the power transmission end 3 and the power P _r (power reception end power) at the power reception end 4 of the distribution line. As shown in FIG. 12, the variation in power calculated by the power measurement apparatus of this embodiment is about ± 0.3%, and it can be seen that measurement with small variation is possible.

Further, the present inventors have found that the power loss P _loss of the power distribution line due to the voltage drop method using a shunt resistor, the power loss P _loss of the power distribution line according to the method of the present embodiment was determined several times under the same conditions.
FIG. 13 is a diagram illustrating an example of the result of performing the calculation of the line loss (distribution line power loss P _loss ) by the voltage drop method and the line loss calculation by the method of this embodiment 60 times under the same conditions. is there.
In FIG. 13, the average value of the power loss P _loss of the distribution line by the method of the present embodiment was 17.3 W, and the variation was ± 2 W (± 12%). Moreover, the wattmeter accuracy (%) shown in the following equation (7) is about ± 0.2%, and the wattmeter accuracy (%) can be kept within ± 0.3%. Thus, since the wattmeter accuracy (%) is about ± 0.2%, the variation (± 2 W (± 12%)) of the power loss P _loss is within the allowable range. Moreover, since the power meter accuracy of the power measuring devices currently on the market is several percent, it is possible to measure the power loss with higher accuracy than before by using the power measuring device of this embodiment. I understand. Specifically, it can be seen that a 1.6% loss of the power at the power transmission end 3 can be measured with high accuracy by using the power measurement device of the present embodiment.
Wattmeter accuracy = [(Line loss by the method of this embodiment−Line loss by the voltage drop method) / Line loss by the voltage drop method] × 100 (7)
FIG. 14 is a diagram illustrating an example of a result obtained by performing line loss calculation by the voltage drop method and line loss calculation by the method of the present embodiment by changing the energization current.
As shown in FIG. 14, it can be seen that the line loss can be obtained with high accuracy even if the energization current is changed in the method of the present embodiment.

As described above, in this embodiment, the phase error Δφ caused by the impedance of the clamp-type ammeter 10 and the resistor 15 connected in parallel to the output terminal of the clamp-type ammeter 10, the voltage to be taken in at the same time, and A phase error 2πΔt caused by a difference in current data capture time, and a phase error α caused by the fact that the magnetic flux density in the iron cores 11a and 11b of the clamp-type ammeters 10a and 10b is not proportional to the magnetic field applied to the iron cores 11a and 11b. Is stored in advance. Then, the phases of the currents I _U and I _W measured by the clamp-type ammeter 10 in which the coil 12 is wound around the iron cores 11a and 11b so as to be distributed over substantially the entire circumference of the iron cores 11a and 11b are expressed as these phases. Correction is performed based on the phase error η obtained by adding the errors Δφ, 2πΔt, and α.
By doing this, the effect of the phase error on the power measurement accuracy is within ± 0.1% (current phase accuracy is within ± 0.05 ° when the load power factor is 0.7), and the current amplitude accuracy is ±±. Within 0.2%, power meter accuracy was within ± 0.3%. Therefore, it is possible to measure the line loss of about 1% of the power at the power transmission end 3 with higher accuracy than before. Thereby, it becomes possible to use the power measuring apparatus of this embodiment for the laying design etc. for aiming at the energy-saving of the distribution line in a facility, or to evaluate the efficiency of electric power equipment etc. with high precision.

In the present embodiment, the phases of the currents I _U and I _W measured by the clamp type ammeter are corrected based on the phase error η obtained by adding the phase errors Δφ, 2πΔt, and α. However, this is not always necessary. For example, the phase of the currents I _U and I _W measured by the clamp-type ammeter 10 can be corrected using at least one of the phase error Δφ and 2πΔt, α (for example, only the phase error α). .
Further, if the phase errors Δφ, 2πΔt, and α are stored individually as in the present embodiment, the phase error Δφ and 2πΔt depending on the configuration of the power measurement device and the condition of the distribution line to be measured. The phase of the currents I _U and I _W measured by the clamp-type ammeter 10 can be corrected using only the phase error selected by the user from among α. However, the phase error (for example, phase error η) obtained by adding the phase errors Δφ, 2πΔt, and α may not be stored individually.

Further, in the present embodiment, the acquisition time difference Δt of data to be acquired at the same time is obtained from the result of the experiment, but this may be obtained from the specifications of the apparatus. In addition, in order to reduce the burden of the user's input operation or to let the user use the default value, any or all of the phase errors Δφ, 2πΔt, α and information for obtaining these are measured with power. You may make it memorize | store in the memory | storage part 37 before the measurement by an apparatus (for example, before shipment of an electric power measurement apparatus).
In the present embodiment, the case where the iron cores 11a and 11b are U-shaped cores has been described as an example. However, the shapes of the iron cores 11a and 11b are not limited to this. For example, a semicircular or semi-elliptical iron core may be used.

Of the embodiments of the present invention described above, the processing performed by the processing device 33 can be realized by a computer executing a program. Further, a means for supplying the program to the computer, for example, a computer-readable recording medium such as a CD-ROM recording such a program, or a transmission medium for transmitting such a program may be applied as an embodiment of the present invention. it can. A program product such as a computer-readable recording medium that records the program can also be applied as an embodiment of the present invention. The programs, computer-readable recording media, transmission media, and program products are included in the scope of the present invention.
In addition, each of the above-described embodiments is merely a specific example for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. . That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

DESCRIPTION OF SYMBOLS 1 Three-phase alternating current power supply 2 Three-phase load 3 Power transmission end 4 Power receiving end 10 Clamp type ammeter 11 Iron core 12 Coil 15 Resistance 20 Voltage measuring device 30 Power calculation device 31 Input terminal 32 A / D converter 33 Processing device 34 Loss calculation device 35 display devices

Claims (6)

A pair of iron cores that can be separated and a coil wound around the iron core, and when the pair of iron cores are combined, a closed magnetic circuit is formed in the pair of iron cores, and the closed magnetic circuit A clamp-type ammeter that measures the current flowing through the distribution line that passes through the space inside
A current calculation device that calculates a current flowing through the distribution line using the current measured by the clamp-type ammeter, and a current measurement device comprising:
The current calculation device includes a storage unit that stores in advance a phase error that is a difference between a phase of a current actually passed through the distribution line and a phase of a current obtained based on a measurement by the clamp-type ammeter. ,
Correction means for correcting the phase of the current based on the phase error stored in the storage means when inputting current data based on the measurement by the clamp type ammeter for the calculation of the power of the distribution line And a current measuring device. The storage means, as the phase error,
A first phase error caused by an impedance of the clamp-type ammeter and a resistor connected in parallel to an output terminal of the clamp-type ammeter;
A second phase error caused by a difference in voltage and current data acquisition time to be acquired at the same time in the current calculation device;
The magnetic flux density in the iron core included in the clamp-type ammeter is individually stored at least one of a third phase error caused by not being proportional to the magnetic field applied to the iron core, The current measuring device according to claim 1. The first phase error is a value calculated in advance from the impedance of the clamp-type ammeter and a resistance connected in parallel to the output terminal of the clamp-type ammeter,
The second phase error is a value calculated in advance from the voltage and current capture time difference in the simulated distribution line,
The third phase error includes the prior measurement result of the phase of the current flowing through the shunt resistor arranged in the simulated distribution line, and the preliminary phase of the current of the simulated distribution line measured by the clamp-type ammeter. The current measurement device according to claim 2, wherein the current measurement device is a value calculated in advance from a measurement result and the values of the first phase error and the second phase error calculated in advance. The first phase error and the second phase error are constant values,
The current measuring apparatus according to claim 3, wherein the third phase error is a value that changes according to a current.   The current measuring device according to any one of claims 1 to 4, wherein the coil is distributed in substantially the entire circumference of the pair of iron cores. The coil is configured by connecting a plurality of coils in series,
The current measuring device according to claim 5, wherein a plurality of coils are wound around each of the pair of iron cores.

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