CN111707856B - Power system fault current measuring method designed by utilizing waveform superposition principle - Google Patents

Power system fault current measuring method designed by utilizing waveform superposition principle Download PDF

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CN111707856B
CN111707856B CN202010572650.9A CN202010572650A CN111707856B CN 111707856 B CN111707856 B CN 111707856B CN 202010572650 A CN202010572650 A CN 202010572650A CN 111707856 B CN111707856 B CN 111707856B
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frequency
current
fault current
impedance
value
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CN111707856A (en
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林湘
孙向飞
谢广宇
韩坤
蔡静飞
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Kunming University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
    • G01R31/086—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution networks, i.e. with interconnected conductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/08—Locating faults in cables, transmission lines, or networks
    • G01R31/088—Aspects of digital computing

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Abstract

The invention relates to a method for measuring fault current of a power system designed by utilizing a waveform superposition principle, and belongs to the technical field of relay protection of the power system. The technical scheme provided by the invention firstly extracts the maximum value and the minimum value of the fault current measured by the Fourier algorithm by means of waveform superposition and current magnitude comparison, corrects the error measured by the Fourier algorithm by using the influence of frequency fluctuation on the boundary of the measured value of the Fourier algorithm on the extreme value of the measured current, and corrects the impedance deviation of the current value with the corrected measurement error of the Fourier algorithm due to the inductive impedance. By carrying out frequency offset correction and impedance offset correction on the fault current, the influence of frequency fluctuation on fault current measurement is reduced, the sensitivity of current protection during frequency fluctuation is improved, and the stable operation of the power system is effectively guaranteed.

Description

Power system fault current measuring method designed by utilizing waveform superposition principle
Technical Field
The invention discloses a method for measuring fault current of a power system by utilizing a waveform superposition principle, and belongs to the technical field of relay protection of the power system.
Background
With the rapid increase of electric power demand and the rapid promotion of energy development in China, the characteristics of a power grid become more and more complex, and asynchronous networking is implemented in some areas for optimizing the structure of the power grid, reducing the risk of parallel operation of alternating current and direct current. The implementation of the measure optimizes the structure of the power grid, improves the reliability of power supply, ensures the safety of energy supply and the like. But at the same time, asynchronous networking also brings new problems, among which the frequency stability problem is highlighted. The frequency in the grid is subject to dynamic fluctuations, and particularly in an island operation state, the frequency is highly likely to fluctuate to a large extent. When the frequency fluctuates, a frequency measurement method such as a fourier algorithm is involved, and the measured fault electrical quantity not only oscillates, but also causes the deviation of the electrical quantity measurement amplitude, which causes relatively serious influence on the sensitivity and selectivity of fault detection, and even causes protection rejection under extreme conditions, thereby causing serious threat to the stable operation of a power system.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for measuring the fault current of the power system designed by utilizing the waveform superposition principle, reducing the influence of frequency fluctuation on the measurement of the fault current by carrying out frequency deviation correction and impedance deviation correction on the fault current, improving the sensitivity of current protection during the frequency fluctuation and effectively ensuring the stable operation of the power system.
In order to solve the above problems, the present invention provides a method for measuring a fault current of a power system designed by using a waveform superposition principle, wherein the method specifically comprises the following steps:
A. measuring fault current by Fourier algorithm, delaying the measured current waveform for multiple times in one period by signal delay principle, superposing the delayed waveforms, and obtaining maximum value I of fault current by using larger and smaller modefmaxAnd minimum value Ifmin；
B. And B, performing frequency offset correction on the current waveform obtained in the step A, wherein the specific correction is performed by adopting the following formulas (1) to (7):
by fourier transform, the real part and imaginary part of the fundamental component are calculated as shown in equation (1):
Figure GDA0002985769980000011
when the frequency is shifted, the calculation formulas of the fundamental wave and each harmonic component are shown as formula (2) and formula (3):
Figure GDA0002985769980000021
Figure GDA0002985769980000022
obtain f0The phase is calculated as the fundamental amplitude of the electrical quantity at the fundamental frequency, as shown in equation (4):
Figure GDA0002985769980000023
further, the amplitude-frequency characteristic coefficient is obtained as H, as shown in formula (5):
Figure GDA0002985769980000024
when the frequency fluctuates, order
Figure GDA0002985769980000025
Is F, when therein
Figure GDA0002985769980000026
When is 0, F is F0When is coming into contact with
Figure GDA0002985769980000027
At 1, F is F, and the functional relationship is shown in formula (6):
Figure GDA0002985769980000031
Kchangethe method is used for describing the oscillation boundary when the Fourier algorithm measures the fundamental wave under different frequency conditions, and the work is calculated by utilizing the oscillation boundaryAnd (3) measuring a frequency-time Fourier algorithm, as shown in formula (7):
Figure GDA0002985769980000032
in the above formula, Δ f ═ f-f0Where f is the actual frequency, f0Is the fundamental frequency, deltaf is the frequency difference,
Figure GDA0002985769980000033
is an initial phase angle, ω0At an electrical angle, ImIs a frequency of f0Amplitude of current in time, IReIs the real part of the current at frequency f, IImIs the imaginary part of the current at frequency f, Im1.fFor measuring the amplitude of the current, n is the number of harmonics, T0Is the period of the fundamental wave, IfmaxFor measuring the maximum value of the current at frequency f, IfminFor measuring the minimum value of the current at frequency f, If0For the corrected power frequency time Fourier algorithm measured value at the same fault point, Kchange(max)Is the upper boundary of the amplitude-frequency characteristic coefficient, Kchange(min)The lower boundary of the amplitude-frequency characteristic coefficient;
C. and C, performing impedance deviation correction on the current waveform obtained in the step B, wherein the specific correction is performed by adopting the following formulas (8) to (11):
the total impedance of the system includes the generating impedance XGTransformer impedance XTAnd transmission line impedance XLThe total impedance of the system is calculated as shown in equation (8):
Figure GDA0002985769980000034
the current values actually measured at this time are:
Figure GDA0002985769980000035
the position of the fault point at this time is:
Figure GDA0002985769980000036
at this time, a fault point position l is obtained, and the fault current at this position is converted into a fault current value under the power frequency by using l, as shown in formula (11):
Figure GDA0002985769980000041
wherein:
Figure GDA0002985769980000042
wherein E is the generator terminal voltage, XsysIs the total impedance of the system, LG、LT、LLInductance coefficients of a generator, a transformer and a power transmission line respectively, omega is an electrical angular velocity, ItrueFor the actual measured current value, ItransFor converting into a fault current value under power frequency.
The technical scheme provided by the invention firstly extracts the maximum value and the minimum value of the fault current measured by the Fourier algorithm by means of waveform superposition and current magnitude comparison, corrects the error measured by the Fourier algorithm by using the influence of frequency fluctuation on the boundary of the measured value of the Fourier algorithm on the extreme value of the measured current, and corrects the impedance deviation of the current value with the corrected measurement error of the Fourier algorithm due to the inductive impedance. By carrying out frequency offset correction and impedance offset correction on the fault current, the influence of frequency fluctuation on fault current measurement is reduced, the sensitivity of current protection during frequency fluctuation is improved, and the stable operation of the power system is effectively guaranteed.
Drawings
FIG. 1 is a schematic diagram of waveform superposition to obtain a maximum value;
FIG. 2 is a graph of amplitude-frequency characteristics provided by the present invention;
in the figure: 1-superposed waveform, 2-original waveform, 3-delayed waveform, 4-delayed waveform and 5-amplitude-frequency characteristic curve.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments, but not all embodiments, of the present invention; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1 and fig. 2, the technical solution provided by the present invention firstly extracts the maximum value and the minimum value of the fault current measured by the fourier algorithm by means of waveform superposition and comparison of the magnitudes of the currents, corrects the error measured by the fourier algorithm by using the influence of the frequency fluctuation on the boundary of the measured value of the fourier algorithm, and corrects the impedance offset of the current value corrected the measurement error of the fourier algorithm because the impedance is inductive. By carrying out frequency offset correction and impedance offset correction on the fault current, the influence of frequency fluctuation on fault current measurement is reduced, the sensitivity of current protection during frequency fluctuation is improved, and the stable operation of the power system is effectively guaranteed.
The measuring method provided by the invention specifically comprises the following steps:
A. measuring fault current by Fourier algorithm, delaying the measured current waveform for multiple times in one period by signal delay principle, superposing the delayed waveforms, and obtaining maximum value I of fault current by using larger and smaller modefmaxAnd minimum value Ifmin；
B. And B, performing frequency offset correction on the current waveform obtained in the step A, wherein the specific correction is performed by adopting the following formulas (1) to (7):
in the measurement of the signal of the power system, the real part and the imaginary part of the fundamental component are calculated by Fourier transformation, wherein the real part and the imaginary part are shown in an equation (1):
Figure GDA0002985769980000051
when the frequency is shifted, the calculation formulas of the fundamental wave and each harmonic component are shown as formula (2) and formula (3):
Figure GDA0002985769980000052
Figure GDA0002985769980000053
obtain f0The phase is calculated as the fundamental amplitude of the electrical quantity at the fundamental frequency, as shown in equation (4):
Figure GDA0002985769980000061
further, the amplitude-frequency characteristic coefficient is obtained as H, as shown in formula (5):
Figure GDA0002985769980000062
when the frequency fluctuates, order
Figure GDA0002985769980000063
Is F, when therein
Figure GDA0002985769980000064
When is 0, F is F0When is coming into contact with
Figure GDA0002985769980000065
At 1, F is F, and the functional relationship is shown in formula (6):
Figure GDA0002985769980000066
Kchangeto describe the oscillation boundaries when the fourier algorithm measures the fundamental wave in different frequency situations,and (3) calculating a power frequency time Fourier algorithm measured value by using the oscillation boundary, wherein the formula (7) is as follows:
Figure GDA0002985769980000067
in the above formula, Δ f ═ f-f0Where f is the actual frequency, f0Is the fundamental frequency of the signal to be measured, delta f is the frequency difference,
Figure GDA0002985769980000068
is an initial phase angle, ω0At an electrical angle, ImIs a frequency of f0Amplitude of current in time, IReIs the real part of the current at frequency f, IImIs the imaginary part of the current at frequency f, Im1.fFor measuring the amplitude of the current, n is the number of harmonics, T0Is the period of the fundamental wave, IfmaxFor measuring the maximum value of the current at frequency f, IfminFor measuring the minimum value of the current at frequency f, If0For the corrected power frequency time Fourier algorithm measured value at the same fault point, Kchange(max)Is the upper boundary of the amplitude-frequency characteristic coefficient, Kchange(min)The lower boundary of the amplitude-frequency characteristic coefficient;
C. and C, performing impedance deviation correction on the current waveform obtained in the step B, wherein the specific correction is performed by adopting the following formulas (8) to (11):
the total impedance of the system includes the generating impedance XGTransformer impedance XTAnd transmission line impedance XLThe total impedance of the system is calculated as shown in equation (8):
Figure GDA0002985769980000071
the current values actually measured at this time are:
Figure GDA0002985769980000072
the position of the fault point at this time is:
Figure GDA0002985769980000073
at this time, a fault point position l is obtained, and the fault current at this position is converted into a fault current value under the power frequency by using l, as shown in formula (11):
Figure GDA0002985769980000074
wherein:
Figure GDA0002985769980000075
wherein E is the generator terminal voltage, XsysIs the total impedance of the system, LG、LT、LLInductance coefficients of a generator, a transformer and a power transmission line respectively, omega is an electrical angular velocity, ItrueFor the actual measured current value, ItransFor converting into a fault current value under power frequency.
The measuring method is applied to current protection, can correct the current error measured by the Fourier module caused by frequency, can correct the impedance value measuring error caused by frequency fluctuation, and finishes the work of relay protection by comparing with a setting value set by taking power frequency as a reference.
While the present invention has been described in detail with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, and various changes can be made without departing from the spirit of the present invention within the knowledge of those skilled in the art.

Claims (1)

1. A method for measuring fault current of a power system designed by utilizing a waveform superposition principle is characterized by comprising the following steps of: the method comprises the following steps:
A. measuring fault current by Fourier algorithm, delaying the measured current waveform for multiple times in one period by signal delay principle, and delaying the waveformMutually overlapped, and a large and small mode is adopted to obtain the maximum value I of the fault currentfmaxAnd minimum value Ifmin；
B. And B, performing frequency offset correction on the current waveform obtained in the step A, wherein the specific correction is performed by adopting the following formulas (1) to (7):
by fourier transform, the real part and imaginary part of the fundamental component are calculated as shown in equation (1):
Figure FDA0002985769970000011
after the frequency shift occurs, the calculation formulas of the fundamental wave and each harmonic component are shown as formula (2) and formula (3):
Figure FDA0002985769970000012
Figure FDA0002985769970000013
obtain f0The phase is calculated as the fundamental amplitude of the electrical quantity at the fundamental frequency, as shown in equation (4):
Figure FDA0002985769970000021
further, the amplitude-frequency characteristic coefficient is obtained as H, as shown in formula (5):
Figure FDA0002985769970000022
when the frequency fluctuates, order
Figure FDA0002985769970000023
Is F, when therein
Figure FDA0002985769970000024
When is 0, F is F0When is coming into contact with
Figure FDA0002985769970000025
At 1, F is F, and the functional relationship is shown in formula (6):
Figure FDA0002985769970000026
Kchangethe method is used for describing the oscillation boundary when the Fourier algorithm measures the fundamental wave under different frequency conditions, and the Fourier algorithm measured value when the power frequency is calculated by using the oscillation boundary, and is shown in the formula (7):
Figure FDA0002985769970000027
in the above formula, Δ f ═ f-f0Where f is the actual frequency, f0Is the fundamental frequency, deltaf is the frequency difference,
Figure FDA0002985769970000028
is an initial phase angle, ω0At an electrical angle, ImIs a frequency of f0Amplitude of current in time, Im1.fFor measuring the amplitude of the current, n is the number of harmonics, T0Is the period of the fundamental wave, IfmaxFor measuring the maximum value of the current at frequency f, IfminFor measuring the minimum value of the current at frequency f, If0For the corrected power frequency time Fourier algorithm measured value at the same fault point, Kchange(max)Is the upper boundary of the amplitude-frequency characteristic coefficient, Kchange(min)The lower boundary of the amplitude-frequency characteristic coefficient;
C. and C, performing impedance deviation correction on the current waveform obtained in the step B, wherein the specific correction is performed by adopting the following formulas (8) to (11):
the total impedance of the system includes the generating impedance XGTransformer impedance XTAnd transmission line impedance XLIs a system ofThe total impedance is calculated as shown in equation (8):
Figure FDA0002985769970000031
the current values actually measured at this time are:
Figure FDA0002985769970000032
the position of the fault point at this time is:
Figure FDA0002985769970000033
at this time, a fault point position l is obtained, and the fault current at this position is converted into a fault current value under the power frequency by using l, as shown in formula (11):
Figure FDA0002985769970000034
wherein:
Figure FDA0002985769970000035
wherein E is the generator terminal voltage, XsysIs the total impedance of the system, LG、LT、LLInductance coefficients of a generator, a transformer and a power transmission line respectively, omega is an electrical angular velocity, ItrueFor the actual measured current value, ItransFor converting into a fault current value under power frequency.
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CN101446614A (en) * 2008-12-19 2009-06-03 中国电力科学研究院 Fault current testing method for direct-current transmission converter valve
CN108872843A (en) * 2018-06-14 2018-11-23 国网湖北省电力有限公司电力科学研究院 A kind of one or two fusion measurement methods of 10kV pole-mounted circuit breaker protection feature
CN109560558A (en) * 2018-12-28 2019-04-02 江苏华冠电器集团有限公司 A kind of current transformer master control device that applied to low-voltage network there is resonance to inhibit function

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