JP2598889Y2 - Three-phase AC measuring device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-phase AC measuring apparatus capable of measuring a positive-phase, negative-phase, or zero-phase voltage or current of a three-phase AC with high accuracy.

[0002]

2. Description of the Related Art For example, as shown in FIG. 5, a three-phase current measuring device 2 is used at a measuring point 1 when evaluating an equivalent negative-sequence current in a generator 3 from a power system side to a power plant side. Conventionally, three-phase AC measurement is performed by synchronously sampling each of the three-phase current signals, digitizing the signals, and calculating the positive, negative, and zero-phase components of the three-phase current by digital arithmetic processing. ing. In this case, the three-phase current measuring device 2 generally has a fundamental wave positive-phase current of C
When about 10% of T rating, 2-3% of 10%,
That is, it is necessary to evaluate an equivalent reverse phase current of 0.2 to 0.3% of the CT rating. Therefore, the accuracy of measuring the equivalent negative-sequence current must be 0.05% or less of the CT rating.

[0003]

However, in the three-phase AC measurement, a gain error and a phase error between the respective phases of the measuring device become a problem.

Here, the effect of a measurement error on the negative-phase current I2 at the time of three-phase perfect symmetry will be considered.

First, the reverse-phase current I2 is expressed by the following equation.

[0006]

(Equation 1)

Here, as shown in the vector diagram of FIG.
The B-phase current Ib and the C-phase current I are based on the A-phase current Ia.
If the measurement relative error of c is ± ΔI, ± Δθ,

[0008]

(Equation 2)

[0009]

(Equation 3)

## EQU1 ## Substituting these into [Equation 1] and approximately calculating the maximum error, ΔI = 0.5%, Δθ =
At 0.5 °, the error of the negative-phase current I2 is about 0.8%.

[0011] As described above, in order to perform measurement at 0.05% or less of the CT rating, the gain error and the phase error must be kept extremely low, and it is very difficult to satisfy such accuracy. It was something. The same applies to the negative-sequence voltage.

Although the gain error and the phase error of the measuring instrument itself have the greatest effect on the measurement of the negative-phase signal, they also have an effect on the measurement of the positive-phase signal and the zero-phase signal, which also lowers the measurement accuracy. .

It is an object of the present invention to provide a three-phase AC measuring apparatus capable of measuring three-phase AC with high accuracy even if the gain error and phase error inherent in the measuring device itself are relatively large.

[0014]

According to a first aspect of the present invention, there is provided a three-phase alternating current measuring apparatus comprising: terminals for inputting voltage signals or current signals for three phases of A phase, B phase, and C phase; A means for A / D converting each of the signals input from the input terminals to obtain input data of each phase; and a component extracting and calculating means for obtaining a positive phase component, a negative phase component, or a zero phase component from the input data of each phase. In the phase alternating current measurement device, the input terminals are connected in series, and reference signal input means for inputting a single-phase alternating current reference signal, and in the input state of the reference signal, the rotation of phase A → phase B → phase C is positive. In the case of the direction, the apparent positive-phase component obtained by shifting the B-phase input signal by -120 ° and the C-phase input signal by + 120 ° with reference to the A-phase input signal is a reference correction to the reference signal. Reference correction vector extraction as a vector Output means, and correction means for correcting the positive-phase component by subtracting the proportional component of the reference correction vector from the positive-phase component of the three-phase AC signal obtained by the component extraction operation. And

A three-phase AC measuring apparatus according to a second aspect of the present invention includes a terminal for inputting voltage signals or current signals for three phases of A phase, B phase, and C phase, and a signal input from each input terminal. Are respectively A / D converted to obtain input data of each phase, and a three-phase AC measuring apparatus comprising component extraction operation means for obtaining a positive phase component, a negative phase component, or a zero phase component from the input data of each phase. While connecting each input terminal in series,
A reference signal input means for inputting a single-phase AC reference signal, and in the case where the rotation of A-phase → B-phase → C-phase is set to the positive direction in the input state of the reference signal, the input signal of A-phase The phase input signal is shifted by + 120 °, and the phase C input signal is shifted by -1.
A reference correction vector extracting means for obtaining an apparent negative phase component shifted by 20 ° as a reference correction vector for the reference signal; and a reference correction for the negative phase component of the three-phase AC signal obtained by the component extraction operation. Correction means for correcting the inverse phase component by subtracting the proportional component of the vector.

According to a third aspect of the present invention, there is provided a three-phase alternating current measuring device, comprising a terminal for inputting a voltage signal or a current signal for three phases of A phase, B phase and C phase, and a signal input from each input terminal. Are respectively A / D converted to obtain input data of each phase, and a three-phase AC measuring apparatus comprising component extraction operation means for obtaining a positive phase component, a negative phase component, or a zero phase component from the input data of each phase. While connecting each input terminal in series,
Reference signal input means for inputting a single-phase AC reference signal, reference correction vector extraction means for obtaining an apparent zero-phase component as a reference correction vector for the reference signal in the input state of the reference signal, and Correction means for correcting the zero-phase component by subtracting the proportional component of the reference correction vector from the obtained zero-phase component of the three-phase AC signal.

[0017]

In the three-phase AC measuring device according to the first aspect, the A-phase,
In a state where terminals for inputting voltage signals or current signals for three phases of B phase and C phase are respectively connected in series and a single phase AC signal is input, an apparent positive phase component is corrected for the reference signal with respect to the reference signal. The proportional component of the reference correction vector is subtracted from the positive phase component of the three-phase AC signal, which is the signal under measurement, and the correction is performed.

That is, the apparent positive-phase component obtained in the input state of the single-phase AC signal is caused by a gain error and a phase error between the respective phases, and the apparent positive-phase component is input. Although there is a possibility of a somewhat non-linear motion depending on the value of the voltage or current, it is considered that the motion becomes a substantially proportional vector. Therefore, it is considered that an offset multiplied by the ratio of the voltage or current of the signal under measurement to the single-phase AC signal has occurred with respect to the reference correction vector, and by removing the offset, the gain error between each phase and The error component due to the phase error is canceled, and highly accurate measurement of the normal phase component becomes possible.

In the three-phase AC measuring device according to claim 2, A
Terminals for inputting voltage signals or current signals for three phases of phase, phase B and phase C are connected in series, and in a state where a single-phase AC signal is input, an apparent reverse-phase component is compared with the reference signal. The correction is performed by subtracting the proportional component of the reference correction vector from the negative phase component of the three-phase AC signal that is the signal under measurement, which is obtained as the reference correction vector.

That is, the apparent negative-phase component obtained in the input state of the single-phase AC signal is caused by a gain error and a phase error between the respective phases, and the apparent negative-phase component is inputted. Although there is a possibility of a somewhat non-linear motion depending on the value of the voltage or current, it is considered that the motion becomes a substantially proportional vector. Therefore, it is considered that an offset multiplied by the ratio of the voltage or current of the signal under measurement to the single-phase AC signal has occurred with respect to the reference correction vector, and by removing the offset, the gain error between each phase and The error component due to the phase error is cancelled, and the accurate measurement of the negative phase component becomes possible.

In the three-phase AC measuring device according to claim 3, A
Terminals for inputting voltage signals or current signals for three phases of phase, phase B and phase C are connected in series, and in a state where a single-phase AC signal is input, an apparent zero-phase component is compared with the reference signal. The correction is performed by subtracting the proportional component of the reference correction vector from the zero-phase component of the three-phase AC signal that is the signal under measurement, which is obtained as the reference correction vector.

That is, the apparent zero-phase component obtained in the input state of the single-phase AC signal is caused by a gain error and a phase error between respective phases, and the apparent zero-phase component is inputted. Although there is a possibility of a somewhat non-linear motion depending on the value of the voltage or current, it is considered that the motion becomes a substantially proportional vector. Therefore, it is considered that an offset multiplied by the ratio of the voltage or current of the signal under measurement to the single-phase AC signal has occurred with respect to the reference correction vector, and by removing the offset, the gain error between each phase and The error component due to the phase error is canceled, and the zero-phase component can be measured with high accuracy.

[0023]

FIG. 1 is a block diagram showing the configuration of a three-phase alternating current measuring apparatus according to an embodiment of the present invention. In FIG. 1, reference numeral 4 denotes a power system as a circuit to be measured, 5a, 5b, and 5c denote transformers for detecting respective phase currents, and 6 denotes a three-phase AC current measuring device main body. CHa, CHb and CHc are signal input terminals for three phases, and switches 19a, 19b and 19c
Are in the normal state, the auxiliary transformers 7a, 7
The secondary sides of the transformers 5a, 5b, 5c are connected to the primary sides of b, 7c. The A / D converters 8a, 8b, 8c sample the signals of the auxiliary transformers 7a, 7b, 7c in synchronization with a predetermined clock signal and convert the signals into digital data. The memory 10 stores a ROM in which a program to be executed by the CPU 9 is written in advance, sampling data and the like, and uses the ROM as a working area for various arithmetic processing.
AM. The CPU 9 executes a program previously written in the ROM to perform three-phase AC measurement. The display 12 displays the measurement result and the like, and the CPU 9 controls the display via the interface 11. The printer 14 prints out the measurement result, and the CPU 9 controls the printing via the interface 13. The communication interface 15 transmits data to and from a device externally connected via the connector 16. The switch 17 is used when setting various measurement modes and conditions. Furthermore, CPU is I / O port 2
The switching control of the switches 19a, 19b, and 19c is performed via 0. In FIG. 1, reference numeral 18 denotes a single-phase AC current source. When the switches 19a, 19b, and 19c are in the states shown in the figure, the primary sides of the auxiliary transformers 7a, 7b, and 7c are connected in series and the single-phase AC current source 18 is connected. In this state, by obtaining the positive phase component, it is obtained as a reference correction vector for the positive phase component, and by obtaining the negative phase component, it is obtained as a reference correction vector for the negative phase component, and further, a zero phase component is obtained. Thereby, it is obtained as a reference correction vector for the zero-phase component.

Next, the procedure of the three-phase AC measurement is shown as a flowchart in FIGS.

FIG. 2 shows a procedure for measuring the normal phase component. First, as shown in FIG. 1, the changeover switches 19a, 19b, 1
9c is switched to the calibration side, and a reference single-phase AC signal Ir (peak value of the reference single-phase AC signal) is input.
Sampling and A conversion by D converters 8a, 8b, 8c
The / D-converted data is sequentially written into the memory 10, and then the normal phase component I1 'is calculated as a reference correction vector for the normal phase component. This is, for example, based on the input signal of the input terminal CHa, the value of the signal, the value of the point obtained by shifting the input signal of the input terminal CHb by −120 °, and the value of the point obtained by shifting the input signal of the input terminal CHc by + 120 °. The values are sequentially added to obtain a composite waveform, one-third of the amplitude of the composite waveform is obtained as a scalar quantity, and the phase of the composite waveform based on the input signal of the input terminal CHa is calculated by, for example, a product addition type operation. , And this is obtained as the direction of the vector. Thereafter, the changeover switch 19 shown in FIG.
a, 19b, and 19c are switched to the normal side (measurement side) to input the signal to be measured, and A / D converters 8a, 8b, and 8
The digital data obtained by c is sequentially stored in the memory 10.
And then calculates the positive-phase component I1 in the same manner. Subsequently, the average value I of the peak values of the phase currents Ia, Ib, Ic is calculated. After that, correction is performed by subtracting a value obtained by multiplying the already obtained reference correction vector I1 'by a coefficient of (I / Ir) from the positive-phase component I1 of the signal under measurement.

FIG. 3 shows a procedure for measuring the reverse phase component. First, as shown in FIG. 1, the changeover switches 19a, 19b, 1
9c is switched to the calibration side, and a reference single-phase AC signal Ir (peak value of the reference single-phase AC signal) is input.
Sampling and A conversion by D converters 8a, 8b, 8c
The / D-converted data is sequentially written into the memory 10, and then the anti-phase component I2 'is calculated as a reference correction vector for the anti-phase component. This is, for example, based on the input signal of the input terminal CHa, the value of the signal, the value of the point obtained by shifting the input signal of the input terminal CHb by + 120 °, and the value of the point obtained by shifting the input signal of the input terminal CHc by −120 °. The values are sequentially added to obtain a composite waveform, one-third of the amplitude of the composite waveform is obtained as a scalar quantity, and the phase of the composite waveform based on the input signal of the input terminal CHa is calculated by, for example, a product addition type operation. , And this is obtained as the direction of the vector. Thereafter, the changeover switch 19 shown in FIG.
a, 19b, and 19c are switched to the normal side (measurement side) to input the signal to be measured, and A / D converters 8a, 8b, and 8
The digital data obtained by c is sequentially stored in the memory 10.
, And then calculate the negative-phase component I2 in the same manner. Subsequently, the average value I of the peak values of the phase currents Ia, Ib, Ic is calculated. After that, correction is performed by subtracting a value obtained by multiplying the already obtained reference correction vector I2 'by a coefficient of (I / Ir) from the negative-phase component I2 of the signal under measurement.

FIG. 4 shows a procedure for measuring the zero-phase component. First, as shown in FIG.
b, 19c are switched to the calibration side, and the reference single-phase AC signal I
r, and each A / D converter 8a, 8b, 8
The data sampled and A / D converted by c is sequentially written into the memory 10, and then the zero-phase component I0 'is calculated as a reference correction vector for the zero-phase component. For example, the input signals of the input terminals CHa, CHb, and CHc are sequentially added to obtain a composite waveform, one-third of the amplitude of the composite waveform is obtained as a scalar amount, and the input signal of the input terminal CHa is obtained. The phase of the reference composite waveform is obtained by, for example, a product addition type operation, and this is obtained as the direction of the vector. Thereafter, as shown in FIG. 1, the signal under measurement is inputted, and the digital data similarly obtained by the A / D converters 8a, 8b, 8c are sequentially written into the memory 10,
Thereafter, the zero-phase component I0 is calculated in the same manner. Subsequently, the average value I of the peak values of the phase currents Ia, Ib, Ic is calculated. Thereafter, a correction is performed by subtracting a value obtained by multiplying the already obtained reference correction vector I0 'by a coefficient of (I / Ir) from the zero-phase component I0 of the signal under measurement.

Although the examples shown in FIGS. 1 to 4 show the measurement of three-phase alternating current, the present invention can be similarly applied to an apparatus for measuring three-phase alternating current.

[0029]

According to the present invention, the gain error and the phase error between the phases are corrected when measuring the positive phase, the negative phase, or the zero phase component of the three-phase AC voltage or current. Can be measured with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a three-phase alternating current measuring device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure for measuring a normal phase component.

FIG. 3 is a flowchart showing a procedure for measuring a reversed-phase component.

FIG. 4 is a flowchart showing a procedure for measuring a zero-phase component.

FIG. 5 is a diagram showing an example of a three-phase AC current measurement state.

FIG. 6 is a diagram illustrating an influence of a measurement relative error on measurement accuracy of a negative-sequence current.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01R 19/00-19/32 G01R 29/00-29/26

Claims (3)

(57) [Scope of request for utility model registration] 1. A terminal for inputting voltage signals or current signals for three phases of A phase, B phase, and C phase, and A / D conversion of a signal input from each input terminal to input data of each phase. And a three-phase AC measuring device comprising a component extraction operation means for obtaining a positive phase component, a negative phase component, or a zero phase component from the input data of each phase. A reference signal input means for inputting a reference signal; and in the case where the rotation of A phase → B phase → C phase is in the positive direction in the input state of the reference signal, the input signal of B phase Is shifted by -120 °, and the C-phase input signal is shifted by + 120 °.
A reference correction vector extracting means for obtaining an apparent positive phase component shifted by 120 ° as a reference correction vector for the reference signal; and the reference correction for the positive phase component of the three-phase AC signal obtained by the component extraction operation. Correction means for subtracting the proportional component of the vector to correct the positive phase component. 2. A terminal for inputting a voltage signal or a current signal for three phases of A phase, B phase and C phase, and A / D conversion of a signal input from each input terminal to input data of each phase. And a three-phase AC measuring device comprising a component extraction operation means for obtaining a positive phase component, a negative phase component, or a zero phase component from the input data of each phase. A reference signal input means for inputting a reference signal; and in the case where the rotation of A phase → B phase → C phase is in the positive direction in the input state of the reference signal, the input signal of B phase Is shifted by + 120 °, and the C-phase input signal is
A reference correction vector extracting means for obtaining an apparent negative phase component shifted by 120 ° as a reference correction vector for the reference signal; and a reference correction for the negative phase component of the three-phase AC signal obtained by the component extraction operation. Correction means for subtracting a proportional component of the vector to correct the negative phase component. 3. A terminal for inputting voltage signals or current signals for three phases of A phase, B phase and C phase, and A / D conversion of a signal input from each input terminal to input data of each phase. And a three-phase AC measuring device comprising a component extraction operation means for obtaining a positive phase component, a negative phase component, or a zero phase component from the input data of each phase. Reference signal input means for inputting a reference signal, reference correction vector extraction means for obtaining an apparent zero-phase component as a reference correction vector for the reference signal in the input state of the reference signal, and three phases obtained by the component extraction operation Correction means for correcting the zero-phase component by subtracting the proportional component of the reference correction vector from the zero-phase component of the AC signal.