CN114460359B - Method, device, equipment and storage medium for eliminating power grid harmonic voltage measurement errors - Google Patents
Method, device, equipment and storage medium for eliminating power grid harmonic voltage measurement errors Download PDFInfo
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- G01R22/06—Arrangements for measuring time integral of electric power or current, e.g. electricity meters by electronic methods
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The application relates to a method and a device for eliminating a harmonic voltage measurement error of a power grid. The method comprises the steps of obtaining fundamental positive sequence voltage and fundamental negative sequence voltage corresponding to three-phase line voltage of a power grid, determining negative sequence voltage unbalance degree and positive sequence voltage phase difference of the three-phase line voltage according to the fundamental positive sequence voltage and the fundamental negative sequence voltage, determining three conversion coefficients corresponding to the three-phase line voltage respectively according to the negative sequence voltage unbalance degree, the positive sequence voltage phase difference and a preset negative sequence voltage unbalance degree threshold value, obtaining harmonic data corresponding to the three-phase line voltage respectively, and determining the harmonic data of the three-phase voltage of the power grid according to the harmonic data corresponding to the three-phase line voltage respectively and the three conversion coefficients. The method and the system can obtain accurate harmonic data of the three-phase voltage, accurately evaluate the power quality of the power grid based on the harmonic data of the three-phase voltage, enable staff to accurately judge the power quality condition of the power grid, and facilitate maintenance or optimization of the power grid.
Description
Technical Field
The application relates to the technical field of power grid power quality test, in particular to a method, a device, equipment and a storage medium for eliminating power grid harmonic voltage measurement errors.
Background
With the development of power system technology, the scale of the power grid is larger and larger, and the number of nonlinear loads is increased in an explosive manner. Such as large rectifying equipment, variable-frequency speed regulating devices, electrified railway locomotives, electric arc furnaces and the like, the nonlinear loads inject harmonic currents into a power grid, so that voltage distortion of the power grid is caused, the electric energy quality of the power grid is caused to be problematic, and the reliability of power supply of the power grid is reduced. On the other hand, with the rapid development of modern science and technology, users increasingly use high-precision and sharp power electronic equipment, and meanwhile, a large number of tightly continuous process control systems are adopted to complete work processing and management, which all require a high-quality and high-reliability power grid and power quality suitable for the power grid. In order to ensure the safety, an additional harmonic eliminator is needed to ensure the operation safety of the power grid, but after the additional harmonic eliminator, when exciting current taking 3 times of zero sequence harmonic as a dominant component flows through the harmonic eliminator connected in series on the neutral line of the electromagnetic voltage transformer, the displacement of neutral point voltage is necessarily caused, and further, the error occurs in the harmonic voltage measurement measured on the secondary side, and the generated harmonic voltage measurement error directly affects the measurement result of the electric energy quality, so that the economic, management and technical risks are brought, and the expected benefit of the construction of an electric energy quality on-line monitoring system and the improvement of the electric energy quality management of the power grid by the general measurement work is reduced. Therefore, how to accurately measure the harmonic voltage while ensuring the safety of the operation of the power grid is a problem to be solved at present.
In the prior art, in order to ensure that no error occurs in the measurement of the harmonic voltage, the error of the measurement of the harmonic voltage is eliminated by removing the harmonic eliminator and directly grounding the neutral line of the electromagnetic voltage transformer, so that an accurate measurement result of the harmonic voltage is obtained.
However, from the viewpoint of ensuring safe operation of the electromagnetic voltage transformer, the greater the resistance value of the damper (detuner) that suppresses ferromagnetic resonance, the better the effect. Therefore, in the mode of the traditional technology, as the harmonic eliminator is not additionally arranged, the risk of the electromagnetic voltage transformer in the operation process is too high, and safety accidents are easy to occur.
Disclosure of Invention
Based on this, it is necessary to provide a method, an apparatus, a computer device and a storage medium capable of eliminating a voltage harmonic measurement error while ensuring safety during operation of a power grid in view of the above technical problems.
A method for eliminating harmonic voltage measurement errors of a power grid comprises an electromagnetic voltage transformer, wherein a harmonic eliminator is arranged between a neutral point of a primary winding of the electromagnetic voltage transformer and the ground, the method comprises the steps of obtaining fundamental positive sequence voltage and fundamental negative sequence voltage corresponding to three-phase line voltages of the power grid, determining negative sequence voltage unbalance and positive sequence voltage phase difference of the three-phase line voltages according to the fundamental positive sequence voltage and the fundamental negative sequence voltage, determining three conversion coefficients corresponding to the three-phase line voltages according to the negative sequence voltage unbalance, the positive sequence voltage phase difference and a preset negative sequence voltage unbalance threshold, obtaining harmonic data corresponding to the three-phase line voltages, and determining harmonic data of the three-phase voltages of the power grid according to the harmonic data corresponding to the three-phase line voltages and the three conversion coefficients.
In one embodiment, the acquiring the fundamental positive sequence voltage and the fundamental negative sequence voltage corresponding to the three-phase line voltage of the power grid comprises acquiring the three-phase line voltage of the power grid, determining fundamental voltage amplitude and fundamental voltage phase corresponding to the three-phase line voltage according to the three-phase line voltage, wherein the three-phase line voltage comprises line voltage between A phase and B phase, line voltage between B phase and C phase, line voltage between C phase and A phase, and determining fundamental positive sequence voltage and fundamental negative sequence voltage corresponding to the three-phase line voltage according to fundamental voltage amplitude and fundamental voltage phase corresponding to the three-phase line voltage.
In one embodiment, the method for determining the negative sequence voltage unbalance degree and the positive sequence voltage phase difference of the three-phase line voltage according to the fundamental positive sequence voltage and the fundamental negative sequence voltage comprises the steps of respectively obtaining the amplitude and the phase of the fundamental positive sequence voltage and the fundamental negative sequence voltage, determining the negative sequence voltage unbalance degree of the three-phase line voltage according to the amplitude of the fundamental positive sequence voltage and the amplitude of the fundamental negative sequence voltage, and determining the positive sequence voltage phase difference and the negative sequence voltage phase difference of the three-phase line voltage according to the phase of the fundamental positive sequence voltage and the phase of the fundamental negative sequence voltage.
In one embodiment, the determining three conversion coefficients corresponding to the three phase line voltages according to the negative sequence voltage unbalance degree, the positive and negative sequence voltage phase difference, and a preset negative sequence voltage unbalance degree threshold value includes determining three conversion coefficients corresponding to the three phase line voltages respectively by the following formula:
Wherein α AB is a conversion coefficient of line voltages between a phase and a phase in the three-phase line voltage, α BC is a conversion coefficient of line voltages between a phase and a phase in the three-phase line voltage, α CA is a conversion coefficient of line voltages between a phase and a phase in the three-phase line voltage, θ is a positive-negative sequence voltage phase difference corresponding to the three-phase line voltage, ε is a negative sequence voltage unbalance corresponding to the three-phase line voltage, and γ is the preset negative sequence voltage unbalance threshold.
In one embodiment, the harmonic data of the three-phase voltages comprises a total harmonic distortion ratio of the three-phase voltages and each subharmonic content ratio of the three-phase voltages, the harmonic data of the three-phase voltages comprises the total harmonic distortion ratio of the three-phase voltages and each subharmonic content ratio of the three-phase voltages, the harmonic data corresponding to the three-phase voltages are obtained, the harmonic data of the three-phase voltages of the power grid are determined according to the harmonic data corresponding to the three-phase voltages and the three conversion coefficients, the harmonic data of the three-phase voltages of the power grid are determined according to the total harmonic distortion ratio and the conversion coefficients of line voltages between the phase A and the phase B of the power grid, the total harmonic distortion ratio and the conversion coefficients of line voltages between the phase B and the phase B of the power grid are determined according to the total harmonic distortion ratio and the conversion coefficients of line voltages between the phase B and the phase B of the power grid, and the harmonic distortion ratio of the phase B and each phase of the power grid is determined according to the total harmonic distortion ratio and the conversion coefficients of line voltages between the phase B and the phase B of the power grid, and the harmonic distortion ratio of the phase B and each phase of the power grid is determined according to the total harmonic distortion ratio and the conversion coefficients of line voltages between the phase B and phase of the phase.
In one embodiment, after the three-phase line voltage of the power grid is obtained, the method further comprises the steps of synthesizing the obtained three-phase line voltage to obtain a complete three-phase line voltage of the power grid, and adjusting the phase sequence of the three-phase line voltage to enable the phase sequence of the three-phase line voltage to be positive.
A harmonic voltage measurement error cancellation device for a power grid, the power grid comprising an electromagnetic voltage transformer, a harmonic eliminator being provided between a primary winding neutral point of the electromagnetic voltage transformer and ground, the device comprising:
the voltage fundamental wave determining module is used for obtaining fundamental wave positive sequence voltage and fundamental wave negative sequence voltage corresponding to three-phase line voltage of the power grid;
The voltage parameter determining module is used for determining the negative sequence voltage unbalance degree and the positive sequence voltage phase difference of the three-phase line voltage according to the fundamental wave positive sequence voltage and the fundamental wave negative sequence voltage;
The conversion coefficient determining module is used for determining three conversion coefficients corresponding to the three phase line voltages respectively according to the negative sequence voltage unbalance degree, the positive sequence voltage phase difference and a preset negative sequence voltage unbalance degree threshold value;
the voltage harmonic wave determining module is used for acquiring harmonic wave data corresponding to the three-phase line voltages respectively, and determining the harmonic wave data of the three-phase line voltages of the power grid according to the harmonic wave data corresponding to the three-phase line voltages respectively and the three conversion coefficients.
A computer device comprises a memory and a processor, wherein the memory stores a computer program, the processor realizes the following steps when executing the computer program, the processor obtains fundamental positive sequence voltage and fundamental negative sequence voltage corresponding to three-phase line voltages of a power grid, determines negative sequence voltage unbalance degree and positive sequence voltage phase difference of the three-phase line voltages according to the fundamental positive sequence voltage and the fundamental negative sequence voltage, determines three conversion coefficients corresponding to the three-phase line voltages respectively according to the negative sequence voltage unbalance degree, the positive sequence voltage phase difference and a preset negative sequence voltage unbalance degree threshold value, obtains harmonic data corresponding to the three-phase line voltages respectively, and determines harmonic data of the three-phase voltage of the power grid according to the harmonic data corresponding to the three-phase line voltages respectively and the three conversion coefficients.
A computer readable storage medium having stored thereon a computer program which when executed by a processor performs the steps of obtaining a fundamental positive sequence voltage and a fundamental negative sequence voltage corresponding to three phase voltages of the electrical grid, determining a negative sequence voltage imbalance and a positive sequence voltage phase difference of the three phase voltages from the fundamental positive sequence voltage and the fundamental negative sequence voltage, determining three conversion coefficients corresponding to the three phase voltages respectively from the negative sequence voltage imbalance, the positive sequence voltage phase difference, and a preset negative sequence voltage imbalance threshold, obtaining harmonic data corresponding to the three phase voltages respectively, and determining harmonic data of the three phase voltages of the electrical grid from the harmonic data corresponding to the three phase voltages respectively, and the three conversion coefficients.
A computer program product. The computer program product comprises a computer program, and when the computer program is executed by a processor, the computer program realizes the steps of acquiring fundamental positive sequence voltage and fundamental negative sequence voltage corresponding to three-phase line voltage of the power grid, determining negative sequence voltage unbalance degree and positive sequence voltage phase difference of the three-phase line voltage according to the fundamental positive sequence voltage and the fundamental negative sequence voltage, determining three conversion coefficients corresponding to the three-phase line voltage respectively according to the negative sequence voltage unbalance degree, the positive sequence voltage phase difference and a preset negative sequence voltage unbalance degree threshold value, acquiring harmonic data corresponding to the three-phase line voltage respectively, and determining the harmonic data of the three-phase voltage of the power grid according to the harmonic data corresponding to the three-phase line voltage respectively and the three conversion coefficients.
The method, the device, the equipment and the storage medium for eliminating the harmonic voltage measurement error of the power grid. The power grid comprises an electromagnetic voltage transformer, and a harmonic eliminator is arranged between the neutral point of a primary winding of the electromagnetic voltage transformer and the ground, so that resonance overvoltage generated in the operation process of the electromagnetic voltage transformer is restrained by arranging the harmonic eliminator, and the operation safety of the power grid is ensured. The fundamental wave positive sequence voltage and the fundamental wave negative sequence voltage corresponding to the three-phase line voltage of the power grid are obtained, so that the reference voltage data of the power grid are obtained, the neutral point voltage is displaced after the harmonic eliminator is additionally arranged on the electromagnetic voltage transformer, the phase voltage of the power grid is caused to have errors, the line voltage of the power grid cannot generate errors due to the factors, and the fundamental wave voltage of the power grid is still accurate, so that the fundamental wave voltage of the power grid is determined through the line voltage of the power grid, and the accurate fundamental wave voltage of the power grid can be obtained. Then, according to the positive sequence fundamental wave voltage and the fundamental wave negative sequence voltage of the power grid, the negative sequence voltage unbalance degree and the positive sequence voltage phase difference corresponding to the three-phase line voltage can be calculated. And calculating three conversion coefficients corresponding to the three phase line voltages respectively through the negative sequence voltage unbalance degree, the positive sequence voltage phase difference and the negative sequence voltage phase difference and a preset negative sequence voltage unbalance degree threshold value, wherein the preset negative sequence voltage unbalance degree threshold value is determined according to the national standard of the measuring instrument. And then, respectively acquiring harmonic data corresponding to the three-phase line voltages in a mode of acquiring the measurement data, and respectively converting the harmonic data corresponding to the three-phase line voltages into the harmonic data of the three-phase line voltages of the power grid according to three conversion coefficients corresponding to the three-phase line voltages, so that accurate harmonic data of the three-phase line voltages can be obtained. According to the method, under the condition that safe operation of the power grid is ensured by additionally installing the harmonic eliminator, accurate harmonic data of three-phase voltage can be obtained, so that the power quality of the power grid can be accurately estimated based on the harmonic data of the three-phase voltage, errors in a traditional measurement mode are eliminated, workers can accurately judge the power quality condition of the power grid, and the power grid is convenient to maintain or optimize.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments or the conventional techniques of the present application, the drawings required for the descriptions of the embodiments or the conventional techniques will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present application, and other drawings may be obtained according to the drawings without inventive effort for those skilled in the art.
FIG. 1 is a flow chart of a method for eliminating the measurement error of the harmonic voltage of the power grid in one embodiment;
FIG. 2 is a schematic diagram of an angular connection of a measuring instrument corresponding to an electromagnetic voltage transformer of a neutral-line series detuner in one embodiment;
FIG. 3 is a schematic diagram of a star connection of a measuring instrument corresponding to an electromagnetic voltage transformer with a neutral line directly grounded in another embodiment;
FIG. 4 is a flow chart of a method of determining the fundamental positive sequence voltage and the fundamental negative sequence voltage of the three phase voltages in one embodiment;
FIG. 5 is a schematic diagram of three-phase line voltage synthesis and phase sequence adjustment in one embodiment;
FIG. 6 is a flow chart of a method of determining parameters of a three phase line voltage in one embodiment;
FIG. 7 is a flow chart of a method of determining three phase line voltages and harmonic data transfer coefficients for three phase voltages in one embodiment;
FIG. 8 is a schematic diagram of test wiring in one embodiment;
FIG. 9 is a block diagram of a device for eliminating harmonic voltage measurement errors of a power grid in one embodiment;
fig. 10 is an internal structural view of a computer device in one embodiment.
Detailed Description
In order that the application may be readily understood, a more complete description of the application will be rendered by reference to the appended drawings. Embodiments of the application are illustrated in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.
As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," and/or the like, specify the presence of stated features, integers, steps, operations, elements, components, or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof.
As described in the background art, the method for acquiring the power grid harmonic wave in the prior art has the problem that the safety of the power grid and the accuracy of the power grid harmonic wave cannot be considered. The inventor researches and finds that the reason for the problem is that if the safe operation of the power grid is to be ensured, a harmonic eliminator needs to be arranged between the neutral point of the primary winding of the voltage transformer of the power grid and the ground, but the arrangement of the harmonic eliminator can cause inaccuracy of the measured voltage harmonic of the power grid.
Based on the above reasons, the invention provides a method, a device, equipment and a storage medium for eliminating the harmonic voltage measurement error of a power grid, which can eliminate the harmonic voltage measurement error under the condition that the safety in the running process of the power grid is ensured.
In one embodiment, as shown in fig. 1, a method for eliminating harmonic voltage measurement errors of a power grid is provided, the method is suitable for the wiring condition of a transformer as shown in fig. 2, an electromagnetic voltage transformer 30 adopts a star connection method, an electric energy quality analyzer 40 adopts an angle connection method, the electromagnetic voltage transformer is in a three-phase four-wire system, a harmonic eliminator 10 is arranged between the neutral point of a primary winding 20 of the electromagnetic voltage transformer and the ground, three-phase terminals a, B and C of a secondary winding output of the electromagnetic voltage transformer 30 are correspondingly connected into three-phase A, B, C input terminals of the electric energy quality analyzer 40, an N terminal and a B terminal of the electric energy quality analyzer 40 are in short circuit, a secondary winding output N (neutral line) terminal of the electromagnetic voltage transformer is in suspension, and the terminal of the secondary winding 30 of the electromagnetic voltage transformer is connected with the electric energy quality analyzer 40, so that line voltages between an A phase and a B phase and a line voltage between a B phase and a C phase can be measured through the electric energy quality analyzer. In the transformer connection situation shown in fig. 3, the neutral line of the primary winding 20 of the electromagnetic voltage transformer is grounded, the star connection method is adopted, the power quality analyzer 40 adopts the star connection method, and the a, b, c, n terminals at the output end of the secondary winding 30 of the electromagnetic voltage transformer respectively correspond to the A, B, C, N terminals of the power quality analyzer 40, and no resonance eliminator is connected in series, so that the safety is not high. The power grid comprises an electromagnetic voltage transformer, wherein a harmonic eliminator is arranged between a neutral point of a primary winding of the electromagnetic voltage transformer and the ground, and the method comprises the following steps:
And step S100, acquiring fundamental wave positive sequence voltage and fundamental wave negative sequence voltage corresponding to three-phase line voltage of the power grid.
Specifically, the electromagnetic voltage transformer is a voltage transformer that converts primary voltage into secondary voltage in proportion by electromagnetic induction. Such a transformer is not attached with other electrical components (e.g. capacitors) that change the primary voltage.
Specifically, the positive sequence in the power grid is 120 ° advanced by a phase a and 120 ° advanced by B and 120 ° advanced by C and 120 ° advanced by a phase a in the three-phase sinusoidal quantity. The negative sequence in the power grid is 120 degrees after phase lag of A and B, 120 degrees after phase lag of B and C, and 120 degrees after phase lag of C and A. The periodic alternating current signal is subjected to Fourier series decomposition, and the obtained component signal with the same frequency as the power frequency is called fundamental wave signal.
Step S120, determining the unbalance degree of the negative sequence voltage and the phase difference of the positive sequence voltage and the negative sequence voltage of the three-phase line voltage according to the fundamental wave positive sequence voltage and the fundamental wave negative sequence voltage.
In particular, due to asymmetric faults in the grid, or asymmetric line impedance, or unbalanced loads. The problem of three-phase imbalance of the power grid can result. The degree of imbalance of the three-phase voltages can reflect the degree of imbalance of the three-phase voltages.
Step S140, determining three conversion coefficients corresponding to the three phase line voltages respectively according to the negative sequence voltage unbalance degree, the positive sequence voltage phase difference and a preset negative sequence voltage unbalance degree threshold value.
Specifically, after the harmonic eliminator is additionally arranged on the electromagnetic voltage transformer of the power grid, neutral point voltage can be displaced, so that phase voltage of the power grid is error, line voltage of the power grid can not be error due to the factor, and the power grid is still accurate, and therefore, accurate phase voltage results can be obtained through measuring the line voltage and converting the line voltage into the phase voltage through a conversion coefficient.
Step S160, harmonic data corresponding to the three-phase line voltages are obtained, and the harmonic data of the three-phase line voltages of the power grid are determined according to the harmonic data corresponding to the three-phase line voltages and the three conversion coefficients.
Specifically, the harmonic data of the three-phase voltage includes a total harmonic distortion ratio of the three-phase voltage and each subharmonic content ratio of the three-phase voltage, and the harmonic data of the three-phase voltage includes a total harmonic distortion ratio of the three-phase voltage and each subharmonic content ratio of the three-phase voltage. According to the specification of the national standard GBT 14549-1993 electric energy quality public power grid harmonic, phase voltage is adopted as an index for evaluating electric energy quality in the industry, if line voltage is adopted, measurement results cannot be transversely compared, the meaning of the index is lost, and the limit value given by the standard is based on the phase voltage. Therefore, harmonic data of the line voltage cannot be used to evaluate the power quality of the power grid, and the harmonic data of the phase voltage must be converted by the conversion coefficient to evaluate the power quality of the power grid.
In the embodiment, the power grid comprises the electromagnetic voltage transformer, and the harmonic eliminator is arranged between the neutral point of the primary winding of the electromagnetic voltage transformer and the ground, so that resonance overvoltage generated in the operation process of the electromagnetic voltage transformer is restrained by arranging the harmonic eliminator, and the operation safety of the power grid is ensured. The method comprises the steps of obtaining fundamental positive sequence voltage and fundamental negative sequence voltage corresponding to three-phase line voltage of a power grid, wherein after an harmonic eliminator is additionally arranged on an electromagnetic voltage transformer, neutral point voltage is displaced, so that phase voltage of the power grid is error, line voltage of the power grid is not error due to the factor, and the method is still accurate. Then, according to the positive sequence fundamental wave voltage and the fundamental wave negative sequence voltage of the power grid, the unbalance degree of the negative sequence voltage and the phase difference of the positive sequence voltage corresponding to the three-phase line voltage can be calculated, so that the degree of error of the power grid due to the influence of the harmonic eliminator is determined. And calculating three conversion coefficients corresponding to the three phase line voltages respectively through the negative sequence voltage unbalance degree, the positive sequence voltage phase difference and the negative sequence voltage phase difference and a preset negative sequence voltage unbalance degree threshold value, wherein the preset negative sequence voltage unbalance degree threshold value is determined according to the national standard of the measuring instrument. And then, respectively acquiring harmonic data corresponding to the three-phase line voltages, and respectively converting the harmonic data corresponding to the three-phase line voltages into harmonic data of the three-phase line voltages of the power grid according to three conversion coefficients corresponding to the three-phase line voltages, so that accurate harmonic data of the three-phase line voltages can be obtained. According to the method, under the condition that safe operation of the power grid is ensured by additionally installing the harmonic eliminator, accurate harmonic data of three-phase voltage can be obtained, so that the power quality of the power grid can be accurately estimated based on the harmonic data of the three-phase voltage, errors in a traditional measurement mode are eliminated, workers can accurately judge the power quality condition of the power grid, and the power grid is convenient to maintain or optimize.
In one embodiment, as shown in fig. 4, step S100 includes:
Step S400, three-phase line voltage of the power grid is obtained, and fundamental wave voltage amplitude and fundamental wave voltage phase corresponding to the three-phase line voltage are determined according to the three-phase line voltage.
Specifically, as shown in fig. 2, the three-phase line voltage includes a line voltage between a phase and B phase, a line voltage between B phase and C phase, and a line voltage between C phase and a phase.
Step S420, determining fundamental positive sequence voltage and fundamental negative sequence voltage corresponding to the three-phase line voltage according to the fundamental voltage amplitude and the fundamental voltage phase corresponding to the three-phase line voltage respectively.
Specifically, a fundamental positive sequence voltage and a fundamental negative sequence voltage corresponding to the three-phase line voltage are determined by the following formulas:
Wherein, Is the fundamental wave positive sequence voltage corresponding to the three-phase line voltage,The fundamental negative sequence voltage corresponding to the three-phase line voltage is represented by U AB,1, U BC,1, U CA,1, delta AB,1, delta BC,1, delta CA,1 and delta CA,1, wherein U AB,1 is the fundamental voltage amplitude of the line voltage between the a phase and the B phase in the three-phase line voltage, U BC,1 is the fundamental voltage amplitude of the line voltage between the B phase and the C phase in the three-phase line voltage, delta AB,1 is the fundamental voltage phase of the line voltage between the a phase and the B phase in the three-phase line voltage, and delta CA,1 is the fundamental voltage phase of the line voltage between the C phase and the a phase in the three-phase line voltage.
In this embodiment, the three-phase line voltage of the power grid is obtained through the electric energy quality analyzer and the voltage synthesis mode, then the corresponding fundamental voltage amplitude and fundamental voltage phase are determined according to the three-phase line voltage, and then the fundamental positive sequence voltage and the fundamental negative sequence voltage corresponding to the three-phase line voltage are calculated according to the fundamental voltage amplitude and the fundamental voltage phase, so that subsequent calculation is facilitated.
In one embodiment, after step S400, the method further comprises:
and S500, synthesizing the obtained three-phase line voltages to obtain the complete three-phase line voltage of the power grid.
As shown in fig. 2, the electromagnetic voltage transformer 30 adopts a star connection method, the electric energy quality analyzer 40 adopts an angle connection method, the resonance eliminator 10 is arranged between the neutral point of the primary winding 20 of the electromagnetic voltage transformer and the ground, the terminal of the secondary winding 30 of the electromagnetic voltage transformer is connected with the electric energy quality analyzer 40, the line voltage between the a phase and the B phase and the line voltage between the B phase and the C phase can be measured by the electric energy quality analyzer, and then the line voltage between the C phase and the a phase can be synthesized by the following formula:
uCA(t)＝uCB(t)-uAB(t)
Where u AB (t) is the line voltage between phase A and phase B, u BC (t) is the line voltage between phase B and phase C, and u CA (t) is the line voltage between phase C and phase A.
Step S520, the phase sequence of the three-phase line voltage is adjusted to enable the three-phase line voltage to be in positive sequence, and then the three-phase line voltage obtained through sampling is subjected to fast Fourier transform to obtain three fundamental wave voltage amplitudes and three fundamental wave voltage phases respectively corresponding to the three-phase line voltage.
Specifically, when the three-phase line voltage is positive, the line voltage between A, B phases is advanced by 120 ° of the line voltage between B, C phases, the line voltage between B, C phases is advanced by 120 ° of the line voltage between C, A phases, and the line voltage between C, A phases is advanced by 120 ° of the line voltage between A, B phases, so if the measured phase sequence of the line voltage is not positive, the phase sequence is adjusted by taking a negative number, so that the phase sequences of the three-phase line voltage are positive.
Illustratively, as shown in fig. 5, the line voltage U AB (t) between the B phase and the a phase is measured, the line voltage U CB () between the B phase and the C phase is obtained by synthesis, and the line voltage U AC () between the C phase and the a phase is obtained by synthesis, and in order to make the line voltage between the B phase and the C phase and the other two phase line voltages form a positive sequence, it is necessary to take a negative number for the U CB () to adjust the direction.
In this embodiment, by adjusting the direction of the three-phase line voltage, the phase sequence of the three-phase line voltage is positive, so that subsequent calculation is facilitated.
In one embodiment, as shown in fig. 6, step S120 includes:
And S600, respectively acquiring the amplitude and the phase of the fundamental wave positive sequence voltage and the fundamental wave negative sequence voltage.
Specifically, the amplitude and phase of the fundamental wave positive sequence voltage corresponding to the three-phase line voltage are determined by the following formula:
Wherein U Lp is the amplitude of the fundamental wave positive sequence voltage corresponding to the three-phase line voltage, Is the phase of the fundamental wave positive sequence voltage corresponding to the three-phase line voltage,Is the fundamental wave positive sequence voltage corresponding to the three-phase line voltage.
The amplitude and the phase of the fundamental wave negative sequence voltage corresponding to the three-phase line voltage are determined by the following formula:
Wherein U Ln is the amplitude of the fundamental wave negative sequence voltage corresponding to the three-phase line voltage, Is the phase of the fundamental wave negative sequence voltage corresponding to the three-phase line voltage,Is the fundamental wave negative sequence voltage corresponding to the three-phase line voltage.
Step S620, determining the negative sequence voltage unbalance degree of the three-phase line voltage according to the amplitude of the fundamental wave positive sequence voltage and the amplitude of the fundamental wave negative sequence voltage.
Specifically, the negative sequence voltage imbalance of the three-phase line voltage is determined by the following formula:
Wherein epsilon is the negative sequence voltage unbalance corresponding to the three-phase line voltage, U Ln is the amplitude of the fundamental wave negative sequence voltage corresponding to the three-phase line voltage, and U Lp is the amplitude of the fundamental wave positive sequence voltage corresponding to the three-phase line voltage.
Step S640, determining the positive and negative sequence voltage phase difference of the three-phase line voltage according to the phase of the fundamental wave positive sequence voltage and the phase of the fundamental wave negative sequence voltage.
Specifically, the positive and negative sequence voltage phase difference corresponding to the three-phase line voltage is determined by the following formula:
wherein, theta is the phase difference of positive and negative sequence voltages corresponding to the three-phase line voltage, Is the phase of the fundamental wave positive sequence voltage corresponding to the three-phase line voltage,Is the phase of the fundamental wave negative sequence voltage corresponding to the three-phase line voltage.
In this embodiment, the amplitude and phase of the fundamental wave positive sequence voltage and the amplitude and phase of the fundamental wave negative sequence voltage are extracted, so that parameters of the fundamental wave voltage in the power grid are obtained. And then according to the amplitude values of the fundamental wave positive sequence voltage and the fundamental wave negative sequence voltage in the power grid, the unbalance degree of the negative sequence voltage of the power grid can be determined. And then determining the phase difference of the positive and negative sequence voltages in the power grid through the phases of the positive sequence voltage and the negative sequence voltage of the fundamental wave in the power grid.
In one embodiment, step S140 includes:
Three conversion coefficients corresponding to the three-phase line voltages are determined according to the following formula:
Wherein, α AB is a conversion coefficient of line voltage between a phase and a phase in the three-phase line voltage, α BC is a conversion coefficient of line voltage between a phase and a phase in the three-phase line voltage, α CA is a conversion coefficient of line voltage between a phase and a phase in the three-phase line voltage, θ is a positive and negative sequence voltage phase difference corresponding to the three-phase line voltage, ε is a negative sequence voltage unbalance corresponding to the three-phase line voltage, and γ is a preset negative sequence voltage unbalance threshold.
Specifically, a preset negative sequence voltage unbalance threshold gamma is determined according to the precision grade of a measuring instrument, and the maximum allowable error gamma= ±0.15% of the negative sequence voltage unbalance measurement of a class-A instrument and the maximum allowable error gamma= ±0.2% of the negative sequence voltage unbalance measurement of a class-S instrument are referred to the specification of the national standard GBT 19862-2016 general requirement of electric energy quality monitoring equipment.
In this embodiment, according to the precision requirement of the measuring instrument, the negative sequence voltage unbalance threshold is determined, then according to the negative sequence voltage unbalance threshold, the value formulas of three conversion coefficients corresponding to the three phase line voltages are determined, and then according to the positive and negative sequence voltage phase differences and the negative sequence voltage unbalance of the power grid, the three conversion coefficients corresponding to the three phase line voltages are calculated. Thereby constructing a formula capable of mutually converting the three-phase voltage harmonic measurement parameter and the three-phase voltage harmonic measurement parameter. The conversion of the harmonic measurement results between the three-phase line voltage and the three-phase line voltage is realized.
In one embodiment, the harmonic data of the three-phase voltage includes a total harmonic distortion ratio of the three-phase voltage and each subharmonic content ratio of the three-phase voltage, and the harmonic data of the three-phase voltage includes a total harmonic distortion ratio of the three-phase voltage and each subharmonic content ratio of the three-phase voltage, as shown in fig. 7, step S160 includes:
Step S700, determining the total harmonic distortion rate of the A-phase voltage in the three-phase voltage of the power grid according to the total harmonic distortion rate and the conversion coefficient of the line voltages between the A-phase and the B-phase of the power grid.
Specifically, harmonic data of the three-phase line voltage is measured by an electric energy quality analyzer. And performing fast Fourier transform on the three-phase line voltage sampling data according to the time interval of 10 cycles by using an electric energy quality analyzer to obtain harmonic waves.
The harmonic wave means that the periodic alternating current quantity is subjected to Fourier series decomposition to obtain a sinusoidal component with a frequency which is an integer multiple of the fundamental wave frequency greater than 1. The evaluation indexes of the harmonic waves in the power grid comprise the content rate (HR) of each harmonic wave of the voltage and the total harmonic distortion rate (total harmonic distortion, THD) of the voltage, and the calculation formula of the content rate of each harmonic wave of the voltage is as follows:
wherein HRU (h) is the h harmonic content of the power grid voltage, U h is the h harmonic voltage square root of the power grid, and U 1 is the fundamental wave voltage square root of the power grid.
The calculation formula of the total harmonic distortion rate of the voltage is as follows:
Wherein THD U is the total harmonic distortion of the voltage of the power grid, U h is the voltage of the h-th harmonic of the power grid, U 1 is the square root of the fundamental voltage of the power grid, h=2, 3, N, N is the highest number of considered harmonics.
Step S720, determining the total harmonic distortion rate of the B-phase voltage in the three-phase voltage of the power grid according to the total harmonic distortion rate and the conversion coefficient of the line voltage between the B-phase and the C-phase of the power grid.
Step S740, determining the total harmonic distortion rate of the C-phase voltage in the three-phase voltage of the power grid according to the total harmonic distortion rate and the conversion coefficient of the line voltage between the C-phase and the A-phase of the power grid.
Step S760, determining the harmonic content of the a-phase voltage in the three-phase voltage of the power grid according to the harmonic content and the conversion coefficient of the line voltage between the a-phase and the B-phase of the power grid.
And step S780, determining the content of each subharmonic of the B-phase voltage in the three-phase voltage of the power grid according to the content of each subharmonic of the line voltage between the B-phase and the C-phase of the power grid and the conversion coefficient.
Step S800, determining the content of each subharmonic of the C-phase voltage in the three-phase voltage of the power grid according to the content of each subharmonic of the line voltage between the C-phase and the A-phase of the power grid and the conversion coefficient.
Specifically, the total harmonic distortion rate of the three-phase voltage of the power grid is determined by the following formula:
Wherein, Is the total harmonic distortion of the a-phase voltages in the three-phase voltages of the grid,Is the total harmonic distortion of the B-phase voltage in the three-phase voltages of the grid,Is the total harmonic distortion of the C-phase voltage in the three-phase voltages of the grid,The total harmonic distortion rate of the line voltage between the a phase and the B phase of the power grid,The total harmonic distortion of the line voltage between the B and C phases of the grid,The total harmonic distortion rate of line voltage between the C phase and the A phase of the power grid;
The content of each subharmonic of the three-phase voltage of the power grid is determined by the following formula:
Wherein HRU (h) A is the harmonic content of the a-phase voltage in the three-phase voltages of the power grid, HRU (h) B is the harmonic content of the B-phase voltage in the three-phase voltages of the power grid, HRU (h) C is the harmonic content of the C-phase voltage in the three-phase voltages of the power grid, HRU (h) AB is the harmonic content of the line voltage between the a-phase and the B-phase of the power grid, HRU (h) BC is the harmonic content of the line voltage between the B-phase and the C-phase of the power grid, and HRU (h) CA is the harmonic content of the line voltage between the C-phase and the a-phase of the power grid.
Specifically, according to the specification of the national standard GBT 14549-1993 electric energy quality public power grid harmonic, phase voltage is adopted as an index for evaluating electric energy quality in the industry, if line voltage is adopted, measurement results cannot be transversely compared, meaning of the index is lost, and a limit value given by the standard is based on the phase voltage. Therefore, harmonic data of line voltage cannot be used to evaluate the power quality of the power grid, and the harmonic data of phase voltage must be converted to evaluate the power quality of the power grid.
In this embodiment, the harmonic data corresponding to the three-phase line voltages are respectively converted into the harmonic data of the three-phase line voltages through the conversion coefficients, and because the harmonic data of the three-phase line voltages are accurate values, the accurate harmonic data of the three-phase line voltages are obtained, so that the electric energy quality of the electric network can be accurately analyzed through the harmonic data of the three-phase line voltages. Whether the electric energy quality of the power grid meets the standard can be judged according to whether harmonic data of the three-phase voltage is larger than a specified preset value, and if the electric energy quality of the power grid does not meet the standard, the power grid can be treated in modes of harmonic compensation and the like. Therefore, a worker can accurately judge the electric energy quality condition of the power grid, and the power grid is convenient to maintain or optimize.
As shown in fig. 8, for example, a 10kV bus of a 110kV substation is taken as a monitoring object, and the bus includes two groups of electromagnetic voltage transformers (hereinafter referred to as PT) adopting a three-phase four-wire system wiring mode, which are named as a bus PT1 and a line PT2, respectively. Through the field material information inquiry, the neutral point of the primary winding of the bus PT1 is connected with the rear end of the harmonic elimination device R0 in series, and the neutral point of the primary winding of the line PT2 is directly connected with the ground. 3 measuring instruments with the same type and the accuracy grade of A are selected, secondary signals are respectively obtained from a bus and a line PT to carry out synchronous measurement, wherein the measuring instrument 1 is connected with the bus PT1 in an angle mode (a wiring method shown in fig. 2 in the embodiment is adopted), the measuring instrument 2 is connected with the bus PT1 in a star mode (measurement errors exist), and the measuring instrument 3 is connected with the line PT2 in a star mode (no measurement errors exist). The measurement results of the three final measuring instruments are shown in the table one, and the accuracy of the three-phase voltage calculated by the method of the application is verified in a practical test mode.
And synchronously measuring a 10-cycle data segment as an analysis object, and calculating to obtain negative sequence voltage unbalance epsilon=1.47% and positive and negative sequence voltage phase difference theta=63.7 degrees. It is not difficult to find that epsilon > |gamma|=0.15% at this time, the line-phase voltage conversion coefficient of the three-phase harmonic parameter is calculated. Harmonic data of the three-phase line voltage and the three-phase voltage are then calculated.
As shown in table one.
Wherein, α AB is a conversion coefficient of line voltage between a phase and B phase in the three-phase line voltage, α BC is a conversion coefficient of line voltage between B phase and C phase in the three-phase line voltage, α CA is a conversion coefficient of line voltage between C phase and a phase in the three-phase line voltage, θ is a positive-negative sequence voltage phase difference corresponding to the three-phase line voltage, and ε is a negative sequence voltage unbalance corresponding to the three-phase line voltage.
And the voltage harmonic parameters measured by different measuring instruments are shown in the table I.
As can be seen from table one, since the measurement value of the measuring instrument 3 is a standard value without error, but the measuring instrument 3 is a mounted detuner, the safety is insufficient, but the measurement value is accurate. The measuring instrument 1 is three-phase voltage value harmonic data calculated by using the mode of the application, and the error between the three-phase voltage value harmonic data calculated by using the mode of the application and an actual value is very small, while the error between the three-phase voltage value harmonic data directly measured by using the measuring instrument 2 and the actual value is very large. Both the measuring instrument 1 and the measuring instrument 2 are provided with harmonic elimination devices to ensure the safety of the operation of the power grid, but the harmonic elimination devices cause the error of the measuring instrument 2 to be very large, but the numerical error calculated by the method of the application is particularly small.
It should be understood that, although the steps in the flowcharts of fig. 1, 4, 6, and 7 are shown in order as indicated by the arrows, these steps are not necessarily performed in order as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders. Moreover, at least some of the steps of fig. 1, 4, 6, 7 may comprise a plurality of steps or stages, which are not necessarily performed at the same time, but may be performed at different times, nor does the order in which the steps or stages are performed necessarily follow one another, but may be performed alternately or alternately with at least some of the other steps or stages.
In one embodiment, as shown in fig. 9, there is provided a device for eliminating harmonic voltage measurement error of a power grid, wherein the power grid comprises an electromagnetic voltage transformer, a harmonic eliminator is arranged between a neutral point of a primary winding of the electromagnetic voltage transformer and the ground, and the device comprises a voltage fundamental wave determining module 901, a voltage parameter determining module 902, a conversion coefficient determining module 903 and a voltage harmonic determining module 904, wherein:
the voltage fundamental wave determining module 901 is configured to obtain a fundamental wave positive sequence voltage and a fundamental wave negative sequence voltage corresponding to three-phase line voltages of a power grid.
The voltage parameter determining module 902 is configured to determine a negative sequence voltage unbalance degree and a positive sequence voltage phase difference of the three-phase line voltage according to the fundamental positive sequence voltage and the fundamental negative sequence voltage.
The conversion coefficient determining module 903 is configured to determine three conversion coefficients corresponding to the three phase line voltages respectively according to the negative sequence voltage unbalance, the positive sequence voltage phase difference, and a preset negative sequence voltage unbalance threshold.
The voltage harmonic determination module 904 is configured to obtain harmonic data corresponding to the three-phase voltages, and determine harmonic data of the three-phase voltages of the power grid according to the harmonic data corresponding to the three-phase voltages and the three conversion coefficients.
For specific limitations on the device for eliminating the harmonic voltage measurement error of the power grid, reference may be made to the above limitation on the method for eliminating the harmonic voltage measurement error of the power grid, which is not repeated herein. The modules in the power grid harmonic voltage measurement error eliminating device can be all or partially realized by software, hardware and a combination thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules. It should be noted that, in the embodiment of the present application, the division of the modules is schematic, which is merely a logic function division, and other division manners may be implemented in actual implementation.
In one embodiment, a computer device is provided, the internal structure of which may be as shown in FIG. 10. The computer device includes a processor, a memory, and a network interface connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, computer programs, and a database. The internal memory provides an environment for the operation of the operating system and computer programs in the non-volatile storage media. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is executed by a processor to implement a method for removing measurement errors of harmonic voltages of a power grid.
It will be appreciated by those skilled in the art that the structure shown in FIG. 10 is merely a block diagram of some of the structures associated with the present inventive arrangements and is not limiting of the computer device to which the present inventive arrangements may be applied, and that a particular computer device may include more or fewer components than shown, or may combine some of the components, or have a different arrangement of components.
In one embodiment, a computer device is provided, comprising a memory and a processor, the memory having stored therein a computer program, the processor implementing the steps of the method embodiments described above when the computer program is executed.
In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored which, when executed by a processor, implements the steps of the method embodiments described above.
In an embodiment, a computer program product is provided, comprising a computer program which, when executed by a processor, implements the steps of the method embodiments described above.
Those skilled in the art will appreciate that implementing all or part of the above described methods may be accomplished by way of a computer program stored on a non-transitory computer readable storage medium, which when executed, may comprise the steps of the embodiments of the methods described above. Any reference to memory, storage, database, or other medium used in embodiments provided herein may include at least one of non-volatile and volatile memory. The nonvolatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical Memory, or the like. Volatile memory can include random access memory (Random Access Memory, RAM) or external cache memory. By way of illustration, and not limitation, RAM can be in various forms such as static random access memory (Static Random Access Memory, SRAM) or dynamic random access memory (Dynamic Random Access Memory, DRAM), etc.
In the description of the present specification, reference to the terms "some embodiments," "other embodiments," "desired embodiments," and the like, means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.
The technical features of the above embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.
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