JP4236334B2 - Power measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power measuring apparatus, and more particularly to a power measuring apparatus based on a three-phase three-wire two-watt meter method.
[0002]
[Prior art]
When power is supplied to a load by a three-phase three-wire AC circuit, the power consumption can be measured with reference to one channel (phase) and the other two channels (each phase). The power of each is measured, and each of these powers is added. FIG. 10 shows an example of measurement by the three-phase two-wire wattmeter method.
[0003]
In the case of the three-phase two-wire wattmeter method, three clips 101A to 101C for voltage measurement and two clamp sensors 102A and 102B for current measurement are used. The clips 101A to 101C are electrically connected to the electric wires 201A to 201C so as to sandwich the electric wires 201A to 201C having polarities “R”, “S”, and “T”.
[0004]
In this example, the S phase of the electric wire 201 </ b> B is selected as the reference channel, and therefore the clip 101 </ b> A sandwiched between the wires is connected to the terminal “N”, which is the measurement reference terminal of the measuring device main body 103. On the other hand, the R-phase clip 101B and the T-phase clip 101C are respectively connected to the terminal of the number “1” that is the first channel terminal and the terminal of the number “2” that is the second channel terminal. Connected.
[0005]
Clamp sensors 102A and 102B as current sensors are connected to an R phase (electric wire 201A) and a T phase (electric wire 201C) other than the S phase. Each clamp sensor 102A, 102B is the same structure, and is provided with the sensor part 121 and the clamp part 122 as the perspective view of FIG. The sensor unit 121 is connected to the measuring instrument main body 103 by a connection cable. The clamp part 122 has a pair of clamp arms that can be opened and closed, and the measurement electric wire 201A (201C) is inserted into the internal space thereof.
[0006]
Although not shown, a current detection coil is provided in each clamp arm, whereby the clamp unit 122 detects an alternating current flowing through the electric wire 201A (201C) and measures the detection result via the sensor unit 121. To the main body 103. One clamp sensor 102A is connected to the terminal “1” for the first channel provided in the measuring instrument main body 103, and the other clamp sensor 102B is connected to the terminal “2” for the second channel. .
[0007]
The measuring device main body 103 measures the AC voltage between the terminal with the symbol “N” and the terminal with the number “1” using the clips 101A to 101C. This AC voltage is the measurement voltage of the first channel (between R and S). Similarly, the measuring instrument main body 103 measures the AC voltage between the terminal with the symbol “N” and the terminal with the number “2”. This AC voltage is the measurement voltage of the second channel (between T and S). Moreover, the measuring device main body 103 measures the alternating current from the clamp sensors 102A and 102B. These alternating currents are the measurement current of the first channel and the measurement current of the second channel.
[0008]
The measuring device main body 103 performs the following power calculation processing based on the measurement voltage and measurement current of the first channel and the measurement voltage and measurement current of the second channel, and is supplied to the load side. The power Psum is calculated.
[0009]
That is, the measuring instrument main body 103 sets the measurement voltage of the first channel as the vector V1, the measurement current as the vector I1, the measurement voltage of the second channel as the vector V2, and the measurement current as the vector I2. ) And (2) are used to calculate the power P1 of the first channel and the power P2 of the second channel.
P1 = vector V1 · vector I1 (1)
P2 = vector V2 · vector I2 (2)
[0010]
The measuring device main body 103 calculates the electric power Psum consumed by the load using the following equation (3) after calculating the electric power P1 and P2.
Electric power Psum = P1 + P2 (3)
[0011]
The measuring device main body 103 stores the calculated power Psum inside, and ends the power calculation process. Thereafter, the measuring device main body 103 displays the power Psum on the display unit 103A in accordance with the operator's instruction. Moreover, the measuring device main body 103 measures the electric power Psum for a long period of time as necessary, and stores the measurement result therein.
[0012]
By the way, as shown in FIG. 11, the clamp sensors 102A and 102B are provided with an arrow mark 122A indicating the connection direction to the wires to be measured 201A and 201C. An electric wire to be measured is inserted into 122.
[0013]
[Problems to be solved by the invention]
However, even if the clamp sensor has an arrow mark 122A indicating its connection direction, the clamp sensor is connected in the reverse direction (reverse connection) or connected to the wrong phase due to carelessness such as carelessness. There is a case (misconnection). Then, since the measured current vector is reversed or does not become the correct vector, the correct value of the power Psum cannot be calculated.
[0014]
Note that the measuring instrument main body 103 is provided with a memory. Conventionally, however, only the power value as a calculation result is stored due to the limitation of the memory capacity. Even if it turns out, it cannot be recalculated. Of course, it is only necessary to store the basic calculation data of the power value. However, when the power measurement is performed for a long time, the amount of data becomes enormous, and this is not a realistic solution.
[0015]
[Means for Solving the Problems]
The present invention has been made to solve such a problem, and its purpose is to obtain a correct power value without performing measurement again even when it is found that there is a misconnection in the current sensor after the measurement is completed. An object of the present invention is to provide a power measuring apparatus that can be used.
[0016]
In order to achieve the above object, according to the present invention, the same channel and the other two channels (each phase) on the basis of a predetermined one channel (phase) in a three-phase three-wire AC circuit for supplying power to a load. Based on the detection results of each of the current sensors, the voltage detection means for detecting the AC voltage between the two current sensors, the two current sensors including the clamp sensors for measuring the AC currents flowing in the respective channels other than the reference channel, respectively. First computing means for calculating AC power supplied to the load based on each current vector calculated in the above and each voltage vector calculated based on the detection result of the voltage detecting means, and the calculated AC power In the power measuring device including the output means for outputting, from the measurement results of the two current sensors, all connections to the channel lines of the current sensors are made. Assuming the state, the current vectors of the two channels are calculated and supplied to the load using all the calculated current vectors and the voltage vectors calculated by the first calculation means. Second calculating means for calculating each AC power to be stored, and storage means for storing all the AC power calculated by the second calculating means, wherein the second calculating means stores the AC power stored in the storing means. Is read out as necessary and sent to the output means.
[0017]
According to the present invention, assuming that all connection states of the current sensor to the wire to be measured are assumed by the second calculation means, each channel (each phase) is reversely connected or erroneously connected in addition to being correctly connected. Up to the current vector at that time. This is because if the current sensor is not properly connected along the arrow mark above, that is, the operator may accidentally connect the current sensor in the reverse direction or connect it to the wrong phase. This is done assuming a case.
[0018]
Thereafter, the second calculation means calculates AC power supplied to the load for each channel using all the calculated current vectors and each voltage vector calculated by the first calculation means. The storage means stores all AC power calculated by the second calculation means. The second computing means reads the AC power stored in the storage means as necessary and sends it to the output means.
[0019]
As a result, even if it is found that there is an erroneous connection in the current sensor after the measurement is completed, the operator reads the AC power from the storage unit and corrects the AC power calculated by the first calculation unit as necessary. be able to.
[0020]
Thus, since the basic data required for determining the final power Psum is stored in the storage means as the power P1 and P2 of each channel, a large memory capacity can be obtained even in the case of long-time measurement. You do n’t have to.
[0021]
According to a preferred aspect of the present invention, the second calculation means obtains the inverted current vectors -I1 and -I2 from the current vectors I1 and I2 obtained by the current sensors, and further calculates the three-phase from these current vectors. Based on the AC current relational expression, current vectors-(I1 + I2),-(I1-I2),-(-I1 + I2),-(-I1-I2) are obtained for the reference channel, and these eight current vector values are obtained. And eight types of AC powers P1 and P2 are calculated from the voltage vectors V1 and V2 calculated by the voltage detection means and stored in the storage means.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described with reference to the drawings in order to better understand the technical idea of the present invention.
[0023]
First, as shown in the block diagram of FIG. 1, this power measuring device is based on a three-phase three-wire two-watt meter method, and includes an input unit 1, an operation setting unit 2, a CPU (Central Processing Unit) 3, a ROM (Read Only Memory) 4, RAM (Random Access Memory) 5 as a storage means, a display unit 6 and an output unit 7, and the input unit 1, CPU 3 and ROM 4 constitute a first calculation unit and a second calculation unit, respectively. The display unit 6 and the output unit 7 constitute output means. The input unit 1, setting unit 2, ROM 4, RAM 5, display unit 6 and output unit 7 are connected to the CPU 3 by a bus 8.
[0024]
The input unit 1 is connected to two clamp sensors 1A and 1B as current sensors and three clips 1C to 1E as voltage detection means. The clamp sensors 1A and 1B and the clips 1C to 1E are the same as the clamp sensors 102A and 102B and the clips 101A to 101C in FIG.
[0025]
When the input unit 1 receives the alternating current from the clamp sensors 1A and 1B and the alternating voltage of the clips 1D and 1E when the clip 1C is used as a measurement reference, the input unit 1 converts these analog signals into digital signals, Measurement data is sent to the CPU 3.
[0026]
Various settings necessary for measurement are input to the operation setting unit 2 by an operator's operation. The setting items include, for example, a measurement start instruction, a measurement period instruction, and an instruction for outputting measurement data stored therein. The operation setting unit 2 sends signals indicating these instructions to the CPU 3.
[0027]
RAM5 memorize | stores temporarily the alternating voltage and alternating current from the input part 1 by control of CPU3. The display unit 6 displays the measurement result under the control of the CPU 3. The output unit 7 may be a plug for connecting a printer or an external device (for example, a personal computer), and outputs data stored in the RAM 5 to the printer or the plug under the control of the CPU 3. The ROM 4 stores a procedure of processing performed by the CPU 3 in advance.
[0028]
When the CPU 3 receives the digital AC voltage and AC current from the input unit 1, the CPU 3 stores these digital signals in the RAM 5. When the waveform data indicated by the alternating voltage and the waveform data indicated by the alternating current are in a predetermined cycle, for example, when a waveform for one cycle is stored in the RAM 5, the CPU 3 performs the processing procedure stored in the ROM 4 according to the processing procedure stored in FIG. , 3 is performed.
[0029]
That is, the CPU 3 reads the alternating current waveform data detected by the clamp sensor 1A from the RAM 5 (step S1), and calculates a current vector (hereinafter referred to as a current vector) from the alternating current waveform data (step S2). At this time, the current vector calculated by the CPU 3 is the vector I1, which is a detection result of the clamp sensor 1A.
[0030]
After step S2, the CPU 3 inverts the vector I1 and calculates the vector -I1 (step S3). The CPU 3 stores the calculated vector I1 and vector-I1 in the RAM 5 (step S4). For the sake of convenience of explanation, in the following, inversion vectors are also denoted with a minus sign (−).
[0031]
The CPU 3 performs the same process on the alternating current waveform data detected by the clamp sensor 1B, and determines whether or not the calculation of the measurement results from the two clamp sensors 1A and 1B is completed (step S5). When the calculation of the measurement result by the clamp sensor 1B has not ended, the CPU 3 returns the process to step S1. The CPU 3 stores the vector I2 and the vector -I2 obtained by inverting the current vector in the RAM 5 as the detection result of the clamp sensor 1B by repeating steps S1 to S4.
[0032]
The processing in steps S1 to S4 assumes the next connection state of the clamp sensors 1A and 1B. That is, as shown in FIGS. 4 to 9, 24 connection states are assumed in total. For convenience of drawing, each clamp sensor 1A, 1B is shown as a reverse C-shape, and an arrow indicating the correct connection direction is also written on them.
[0033]
Therefore, the connection example shown in FIG. 4 will be described as a representative. Also in this example, as in the connection state of FIG. 10 described above, the S-phase electric wire 201B is used as a reference, one clamp sensor 1A is connected to the R-phase electric wire 201A, and the other clamp sensor 1B is the T-phase electric wire. It is assumed that it is connected to the electric wire 201C. The current flowing through the R-phase electric wire 201A is I1, and the current flowing through the T-phase electric wire 201C is I2.
[0034]
Although not shown, the voltage detection clips 1C to 1E are also connected to the R-phase, S-phase, and T-phase electric wires 201A to 201C, respectively, as in the connection state of FIG. And Note that the voltage vector between R and S is V1, and the voltage vector between T and S is V2.
[0035]
A state in which each clamp sensor 1A, 1B is correctly connected to the R phase (electric wire 201A) and the T phase (electric wire 201C) is the connection state 1. At this time, the R-phase (electric wire 201A) current vector detected by the clamp sensor 1A is a vector I1, and the T-phase (electric wire 201C) current vector detected by the clamp sensor 1B is a vector I2.
[0036]
One clamp sensor 1A is correctly connected to the R phase (electric wire 201A), while the other clamp sensor 1B is connected to the T phase (electric wire 201C) in the opposite direction is the connection state 2. At this time, the current vector of the R phase (electric wire 201A) detected by the clamp sensor 1A is the vector I1, but the current vector of the T phase (electric wire 201C) detected by the clamp sensor 1B is the inverted vector -I2. is there.
[0037]
On the contrary, one clamp sensor 1A is connected in the opposite direction to the R phase (electric wire 201A), while the other clamp sensor 1B is correctly connected to the T phase (electric wire 201C). Is connected state 3. At this time, the R-phase (electric wire 201A) current vector detected by the clamp sensor 1A is an inversion vector -I1, and the T-phase (electric wire 201C) current vector detected by the clamp sensor 1B is a vector I2. .
[0038]
A state in which the clamp sensors 1A and 1B are connected in opposite directions to the R phase (electric wire 201A) and the T phase (electric wire 201C) is a connection state 4. At this time, the R-phase (electric wire 201A) current vector detected by the clamp sensor 1A is an inversion vector -I1, and the T-phase (electric wire 201C) current vector detected by the clamp sensor 1B is also an inversion vector. -I2.
[0039]
Assuming that the above connection states 1 to 4 are present in the actual measurement operation, the CPU 3 reverses the vectors I1 and I2 actually obtained from the R phase (electric wire 201A) and the T phase (electric wire 201C). Vectors -I1 and -I2 are obtained and stored in RAM 5. Thus, at the end of step S5, the RAM 5 stores four vector values I1, -I1, I2, and -I2.
[0040]
Next, the CPU 3 executes steps S6 to S8, obtains the current vector of the reference S phase (electric wire 201B), and stores the vector value in the RAM 5. That is, assuming that the S-phase current vector is I3, the following relational expression is generally established for each of the three-phase AC R-phase, S-phase, and T-phase current vectors.
R phase vector + T phase vector + S phase vector = 0
Therefore,
S phase vector = − (R phase vector + T phase vector) (4)
It becomes.
[0041]
In order to obtain this S-phase vector, the CPU 3 selects two current vectors from the four current vectors (I1, -I1, I2, -I2) stored in the RAM 5 in step S6, and the above equation (4 ) (Step S7).
[0042]
Thus, the following four vector values are obtained for the S-phase vector, and each vector value is stored in the RAM 5 (step S8).
-(I1 + I2),-(I1-I2),-(-I1 + I2),-(-I1-I2)
[0043]
Therefore, at the stage of step S9 when step S8 is completed, the following eight vector values are stored in the RAM 5 in the RAM 5.
▲ 1 ▼ I1,
▲ 2 ▼ -I1,
▲ 3 ▼ I2,
▲ 4 ▼ -I2,
(5)-(I1 + I2),
(6)-(I1-I2),
(7)-(-I1 + I2),
(8)-(-I1-I2)
[0044]
Thereafter, the CPU 3 reads, for example, the voltage V1 between R and S from the RAM 5 (step S10), calculates the voltage vector V1 (step S11), and the current vectors (1) to (8) described above from the RAM 5. (Step S12), the voltage vector V1 is multiplied by the current vectors (1) to (8) above to obtain eight different powers P1 (step S13), and the power P1 is stored in the RAM 5 (step S13). S14).
[0045]
Next, similarly, the voltage V2 between TS is read from the RAM 5 (step S10), the voltage vector V2 is calculated (step S11), and the current vectors (1) to (8) are read ( Step S12), the voltage vector V2 is also multiplied by the current vectors (1) to (8) to obtain eight powers P2 (Step S13), and the power P2 is stored in the RAM 5 (Step S12). S14), the process is terminated (step S15).
[0046]
As a result, the following 16 power values are stored in the RAM 5. That is, for the voltage vector V1, as its power P1,
▲ 1 ▼ I1 × V1,
(2) -I1 × V1,
(3) I2, × V1,
(4) -I2, × V1,
(5)-(I1 + I2) × V1,
(6)-(I1-I2) × V1,
(7)-(-I1 + I2) × V1,
(8)-(-I1-I2) × V1
These eight power values are stored in the RAM 5.
[0047]
Similarly, for the voltage vector V2, as its power P2,
▲ 1 ▼ I1 × V2,
▲ 2 ▼ -I1 × V2,
(3) I2, × V2,
(4) -I2, × V2,
(5)-(I1 + I2) × V2,
(6)-(I1-I2) × V2,
(7)-(-I1 + I2) × V2,
(8)-(-I1-I2) × V2
These eight power values are stored in the RAM 5. In this way, during the measurement period set by the operation setting unit 2, the CPU 3 digitally converts the voltage and current at a predetermined sampling interval, and repeats the above data storage process.
[0048]
In addition to the data storage process, the CPU 3 performs a power calculation process similar to the conventional one. That is, the CPU 3 calculates the electric power Psum supplied to the load side on the assumption that the current connection of the clamp sensors 1A and 1B is correct. The CPU 3 stores the calculated power Psum in the RAM 5. Then, the CPU 3 reads the power Psum currently obtained from the RAM 5 based on the output instruction from the measurement operator after the measurement is completed, and outputs it to the display unit 6 and the output unit 7.
[0049]
By the way, when it is found that the clamp sensors 1A and 1B are erroneously connected after the measurement, the measurement operator operates the operation setting unit 2 to instruct the CPU 3 to output the stored data. As a result, the eight powers P1 for the voltage vector V1 and the eight powers P2 for the voltage vector V2 obtained in step S13 are output to the display unit 6 or the output unit 7. Therefore, the measurement operator can obtain the correct power Psum by referring to the stored data and recalculating the data.
[0050]
As described above, according to the present invention, even if the reverse connection or incorrect connection of the clamp sensors 1A and 1B is noticed after the measurement is completed, the data when the erroneous connection is assumed is stored. Electric power Psum can be obtained.
[0051]
【The invention's effect】
As described above, according to the present invention, when the power consumption value of the load is obtained by the three-phase three-wire two-watt meter method, it is assumed in advance that the clamp sensor (current sensor) is erroneously connected. By calculating the inversion vector from the currently measured current vector, calculating the power P1 and P2 for each channel for each of them, storing the data, and making it possible to read out appropriately, after the measurement is completed Even when an erroneous connection of the clamp sensor is found, the correct power can be obtained based on the stored data without performing the measurement again.
[0052]
Further, since the stored data is the power P1, P2 for each channel, the memory capacity can be reduced accordingly. Therefore, long-time measurement can be handled without using a large-capacity memory.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a flowchart showing a processing procedure of a CPU in the embodiment.
FIG. 3 is a flowchart showing the processing procedure of the CPU in the embodiment.
FIG. 4 is an explanatory diagram showing assumed connection states 1 to 4 of the clamp sensor.
FIG. 5 is an explanatory diagram showing assumed connection states 5 to 8 of the clamp sensor.
FIG. 6 is an explanatory diagram showing assumed connection states 9 to 12 of the clamp sensor.
FIG. 7 is an explanatory diagram showing assumed connection states 13 to 16 of the clamp sensor.
FIG. 8 is an explanatory diagram showing assumed connection states 17 to 20 of the clamp sensor.
FIG. 9 is an explanatory diagram showing assumed connection states 21 to 24 of the clamp sensor.
FIG. 10 is an external view showing a power measuring apparatus using a three-phase three-wire two-watt meter method.
FIG. 11 is a perspective view showing a clamp sensor.
[Explanation of symbols]
1 Input unit 2 Setting unit 3 CPU
4 ROM
5 RAM
6 Display unit 7 Output unit

Claims (2)

Voltage detection that detects the AC voltage between the same channel and the other two channels (each phase) based on a predetermined one channel (phase) in the three-phase three-wire AC circuit that supplies power to the load Means, two current sensors comprising clamp sensors for measuring alternating currents flowing in channels other than the reference channel, current vectors calculated based on detection results of the current sensors, and voltage detection means In a power measuring device comprising: first computing means for calculating AC power supplied to the load by each voltage vector calculated based on the detection result of the output; and output means for outputting the calculated AC power;
From the measurement results of the two current sensors, the current vectors of the two channels are calculated by assuming all the connection states of the current sensors to the channel lines, and all the calculated current vectors, Second calculation means for calculating the AC power supplied to the load using each voltage vector calculated by the first calculation means, and all the AC power calculated by the second calculation means are stored. And a storage unit, wherein the second calculation unit reads the AC power stored in the storage unit as necessary and sends the AC power to the output unit. The second calculating means obtains the inverted current vectors -I1, -I2 from the current vectors I1, I2 obtained by the current sensors, and further, based on the current relational expression of the three-phase alternating current from these current vectors. Thus, current vectors-(I1 + I2),-(I1-I2),-(-I1 + I2),-(-I1-I2) for the reference channel are obtained, and these eight current vector values and the voltage detecting means are used. The power measuring apparatus according to claim 1, wherein eight types of AC power P1, P2 are calculated from the calculated voltage vectors V1, V2, respectively, and stored in the storage means.

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