CN114152840B - LCC-MMC hybrid direct current transmission line fault distance measurement method and system - Google Patents
LCC-MMC hybrid direct current transmission line fault distance measurement method and system Download PDFInfo
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- 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
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- 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
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- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
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Abstract
The invention relates to a fault location method and a system for an LCC-MMC hybrid direct-current transmission line, and belongs to the technical field of relay protection of a power system. The method comprises the steps that traveling wave coupling box current signals are respectively collected from a rectification side (LCC) and an inversion side (MMC) of a hybrid direct current power transmission system (LCC-MMC), and ranging signals are respectively constructed; respectively calculating frequency spectrums of ranging signals at two ends, and screening out equal-interval frequency spectrums reflecting fault positions; respectively calculating frequency difference values of frequency spectrums at two ends, calculating a ratio of the frequency difference values at the two ends, and calculating a ranging estimation result k%, (1-k)%, by using the ratio; and respectively calculating double-end check signals, comparing whether the difference of the double-end check signals is smaller than a preset check threshold, if so, determining the fault distance measurement result to be max [ k%, (1-k)% ], and if not, determining the fault distance measurement result to be min [ k%, (1-k)% ]. The invention does not need to identify the properties of the traveling wave head, calibrate the arrival time of the wave, synchronize the clocks at the two ends and is not influenced by the steepness of the traveling wave head, the missing of the wave head, the data defect of the traveling wave and the wave speed.
Description
Technical Field
The invention relates to a fault location method and a system for an LCC-MMC hybrid direct-current transmission line, and belongs to the technical field of relay protection of a power system.
Background
The traditional high-voltage direct-current transmission (LCC-HVDC) technology based on the phase control converter tends to be mature, has the advantages of large transmission capacity, low cost, mature operation technology and the like, is not influenced by power transmission distance, and solves the problem of stable power angle in an alternating-current system, so the phase control converter (LCC) is an important means for solving the interconnection between power long-distance transmission and a power grid. However, when the LCC is used as an inverter, there are the following problems: firstly, there is the risk of commutation failure, secondly the transmission voltage level is lower, at the bottom of the harmonic number of times that the side formed exchanges, need install the wave filter, thirdly LCC transverter absorbs a large amount of reactive power, requires very high to reactive power compensation arrangement. Compared with the LCC converter, the flexible direct current based on the full-control device IGBT and the PWM modulation technology has no commutation failure and small harmonic wave, can be connected with a weak alternating current and passive system and can be used for black start after power grid faults, has the remarkable characteristics and advantages in many aspects, and becomes an important technical means for solving the problem of large-scale direct current power feed limitation outside a receiving end system receiving area. By integrating the advantages of LCC and MMC (modular multilevel converter), the LCC is used as a rectifying side, the MMC is used as an inverting side, and the formed hybrid high-voltage direct-current transmission system (LCC-MMC) gradually becomes the mainstream mode of direct-current remote transmission engineering.
The fault location technology of the LCC-MMC hybrid direct-current transmission line can be divided into a traveling wave method, a natural frequency method and a fault analysis method in principle. The traveling wave method is characterized in that a traveling wave method is used for calibrating a wave head of a fault traveling wave reaching a measuring end by using a signal processing method, and calculating a fault distance according to a constraint relation between traveling wave reaching time and the fault distance, and the key point is precise calibration of the traveling wave head; the fault analysis method realizes fault positioning by optimizing and solving according to the mathematical relationship between the line parameters and the electrical quantity; the fault location based on the natural frequency method mainly utilizes the mathematical relationship between the main frequency component of fault traveling wave and the fault distance to realize fault location, and the location precision is influenced by the accurate extraction of main frequency, frequency spectrum aliasing, frequency spectrum leakage, system boundary conditions and the like, and has not been practically applied.
Disclosure of Invention
The invention aims to solve the technical problem of providing a fault location method and a fault location system for an LCC-MMC hybrid direct current transmission line, which are used for solving the problems in the prior art in the aspect of fault location.
The technical scheme of the invention is as follows: a fault location method and a system for an LCC-MMC hybrid direct current transmission line can construct a location equation by respectively utilizing data of a rectifying side and data of an inverting side, and compared with a traveling wave location method, the method does not need to accurately detect and calibrate a wave head, double-end communication does not need synchronous time synchronization, and the anti-noise interference capability and the anti-transition resistance capability are stronger; compared with the natural frequency method, the mixed direct current system has different system physical boundaries at two ends, inconsistent wave velocity, no error of system control response to the ranging result, no influence of the accuracy of the natural frequency main frequency value, and elimination of frequency spectrum aliasing caused by fault point refraction and reflection.
The method comprises the following specific steps:
step1: and respectively acquiring current signals of the traveling wave coupling box from the rectifying side and the inverting side of the hybrid direct-current power transmission system, and respectively constructing ranging signals.
Step2: and respectively calculating the frequency spectrums of the ranging signals at the two ends, and screening out the equal-interval frequency spectrums reflecting the fault positions.
Step3: and respectively calculating the frequency difference values of the frequency spectrums at the two ends, calculating the ratio of the frequency difference values at the two ends, and calculating the distance measurement estimation result k%, (1-k)%, by using the ratio.
Step4: and respectively calculating double-end check signals, comparing whether the difference of the double-end check signals is smaller than a preset check threshold, if so, determining the fault distance measurement result to be max [ k%, (1-k)% ], and if not, determining the fault distance measurement result to be min [ k%, (1-k)% ].
The Step1 is specifically as follows:
step1.1: and respectively collecting current signals of the traveling wave coupling box from a rectification side and an inversion side of the hybrid direct-current power transmission system.
Step1.2: decoupling a direct current line through a Karenbauer transformation matrix, and solving polar space modulus current signals of an rectifying side and an inverting side as ranging signals.
The Step2 is specifically as follows:
step2.1: and respectively calculating frequency spectrums of ranging signals on the rectifying side and the inverting side.
Step2.2: and judging whether the frequency spectrums of the frequency domain signals at the two ends are at equal intervals, if not, executing Step2.3, and if so, respectively calculating the frequency difference of the signals at the two ends.
Step2.3: and respectively calculating power transformation signals of the ranging signals at the two ends of the direct current transmission line, and returning to Step2.1.
The power transformation refers to an odd power.
The Step3 specifically comprises the following steps:
step3.1: frequency values of spectral peak positions of the double-end equal interval frequency spectrums are respectively extracted, any two adjacent frequency values are subjected to difference, and frequency differences corresponding to the frequency spectrums at the two ends are obtained.
Step3.2: the ratio omega of the two-end frequency difference is obtained according to the formula (1) MN M denotes a rectification side of the double-ended dc system, and N denotes an inversion side of the double-ended dc system.
In the formula (1), Δ ω M 、Δω N Respectively representing the angular frequency difference, delta f calculated by the M terminal and the N terminal M 、Δf N Respectively representing the frequency difference obtained by the calculation of the M end and the N end, wherein the double-end frequency difference and the angular frequency difference respectively satisfy the relational expressions of the expressions (2) and (3).
Step3.3: using the ratio omega of the frequency differences of both ends MN And (4) obtaining a ranging estimation result k% by the constructed ranging formula (4).
In the formula (4), x f And the distance of a fault point relative to the end M is expressed, k% represents the percentage of the distance of the fault point relative to the end M in the total length of the line, and l represents the total length of the direct current line.
The Step3.2 can also be that the ratio omega of the double-end frequency difference is obtained according to the formula (5) NM 。
The Step3.3 can also be realized by utilizing the ratio omega of double-end frequency difference NM The constructed distance measurement formula (6) obtains the distance measurement result (1-k)%.
The Step4 is specifically as follows:
step4.1: the absolute value of the difference between the ratio of the two-terminal frequency differences and 1 is calculated.
Step4.2: judging whether the absolute value of the difference between the double-end frequency difference ratio and 1 is greater than a preset threshold value, if so, determining that the fault distance measurement result is k%, otherwise, executing Step4.3
Step4.3: respectively calculating the change rate K between three adjacent sampling points of the wave head detected at the first two ends M And K N 。
Step4.4: comparison K M -K N And if the detection result is smaller than the preset check threshold, executing Step4.5, otherwise executing Step4.6.
Step4.5: the fault location result was max [ k%, (1-k)% ].
Ste4.6: the fault location result is min [ k%, (1-k)% ].
A LCC-MMC mixed direct current transmission line fault distance measuring system comprises:
and the signal acquisition module is used for respectively acquiring current signals of the traveling wave coupling box from the rectifying side and the inverting side of the hybrid direct-current power transmission system.
And the signal preprocessing module is used for constructing a ranging signal.
And the frequency domain signal analysis module is used for respectively calculating the frequency spectrums of the ranging signals at the two ends and screening out the equal interval frequency spectrums reflecting the fault positions.
And the frequency domain signal processing module is used for calculating the equal interval frequency difference value of the frequency domain signal and calculating the ratio of the frequency difference values at two ends.
And the fault distance measurement module is used for calculating and recording fault distance measurement results.
And the signal checking module is used for calculating the checking signal.
The signal acquisition module includes:
and the voltage and current transmitting unit is used for converting the voltage and current signals on the secondary side of the transformer into signals acquired by the traveling wave device A/D.
And the analog quantity acquisition unit is used for converting the voltage and current analog quantity signals into digital signals.
And the data storage unit is used for naming the wave recording data files according to the time stamps and storing the wave recording data files in the local memory.
And the abrupt change starting unit is used for judging whether the waveform abrupt change is larger than a set starting threshold value or not, and storing the voltage and current signals into a recording data file if the waveform abrupt change is larger than the set starting threshold value.
The signal preprocessing module comprises:
and the numerical value calculation unit 1 is used for decoupling the direct current line by using a Karenbauer transformation matrix to obtain a polar space current modulus traveling wave transient signal.
And the numerical value calculating unit 2 is used for calculating power transformation signals of the ranging signals at the two ends of the direct current transmission line respectively.
The frequency domain signal analysis module comprises:
and the time-frequency transformation unit is used for extracting frequency domain signals of the related signals at the two ends of the direct current transmission line.
And the frequency spectrum calculating unit is used for calculating the frequency spectrums of the frequency domain signals at the two ends.
And the frequency spectrum judging unit is used for judging whether the frequency spectrums of the frequency domain signals at the two ends are at equal intervals.
The frequency domain signal processing module includes:
and the frequency difference calculating unit is used for extracting the frequency values of the spectral peak positions of the double-end equally-spaced frequency spectrums, and performing difference on any two adjacent frequency values to obtain the frequency differences corresponding to the frequency spectrums at the two ends.
A ratio calculation unit for calculating a ratio omega of the two-terminal frequency difference MN 、Ω NM M denotes one end of the double-ended dc system, and N denotes the other end of the double-ended dc system.
The signal verification module includes:
and the checking signal calculating unit 1 is used for calculating the absolute value of the difference between the double-ended frequency difference ratio and 1.
A check signal calculating unit 2 for calculating the change rate K between three adjacent sampling points of the first detected wave head at both ends M And K N 。
And the check signal comparison unit 1 is used for comparing whether the absolute value of the difference between the double-end frequency difference ratio and 1 is greater than a preset threshold value.
A check signal comparison unit 2 for comparing K M -K N Whether the value is less than a preset check threshold value.
The invention has the beneficial effects that:
1. the method is not influenced by different system boundary conditions of the LCC side and the MMC side, and avoids errors caused by unreliable traveling wave head identification and inaccurate wave arrival time calibration. .
2. According to the invention, a ranging equation is constructed by using the frequency difference ratio obtained at the LCC side and the MMC side, the ranging precision is not influenced by wave head distortion, waveform defect and head wave head loss, the influence of wave velocity attenuation is mathematically reduced, and the method does not depend on double-end synchronous time setting and has better robustness on weak fault modes such as high-resistance fault and the like.
3. The invention can be realized by utilizing the traveling wave signals collected by the traveling wave distance measuring device and the signals collected by the fault recorder, is not influenced by interference signals, channel noise and channel synchronism, is used as supplement and assistance of the existing traveling wave distance measuring algorithm, reduces the distance measuring result to the number of the tower, does not participate in distance measuring calculation of the line length, and has the precision not influenced by the actual change of the line length.
Drawings
FIG. 1 is a system diagram according to an embodiment;
FIG. 2 is a schematic diagram of a system boundary on the rectifying side according to the first embodiment;
FIG. 3 is a schematic diagram of a current ranging signal obtained by a corresponding M-port traveling-wave coupling box according to the first embodiment;
FIG. 4 is a schematic diagram of current ranging signals obtained by the corresponding N-terminal traveling-wave coupling box in the first embodiment;
FIG. 5 is a M-terminal spectrum according to an embodiment;
FIG. 6 shows an N-terminal spectrum according to an embodiment;
fig. 7 is a schematic flow chart of a fault location method for an LCC-MMC hybrid dc transmission line according to a second embodiment of the present invention;
FIG. 8 is a flowchart illustrating the detailed steps of Step1 according to the second embodiment;
FIG. 9 is a flowchart illustrating the detailed steps of Step2 according to the second embodiment;
FIG. 10 is a flowchart illustrating the detailed steps of Step3 according to the second embodiment;
FIG. 11 is a flowchart illustrating the detailed steps of Step4 according to the second embodiment;
fig. 12 is a functional block diagram of a system corresponding to the LCC-MMC hybrid dc transmission line fault ranging of the second embodiment.
Detailed Description
The invention is further described with reference to the following drawings and detailed description.
As shown in FIG. 1, the +/-800 kV true bipolar double-ended hybrid direct current transmission system (LCC-MMC) is built under a PSCAD/EMTDC environment. The rectification side is an M end, an LCC converter is adopted, the inversion side is an N end, and an MMC converter is adopted. Each pole of the rectifying unit at the rectifying side is formed by connecting double 12 pulse converters in series. The direct current transmission line is a six-split conductor, the line length is 1500km, and 400mH smoothing reactors are arranged on two sides of the line.
Fig. 2 is a schematic diagram of the physical boundary formed by the smoothing reactor and the dc filter. As shown in FIG. 2, the characteristic harmonic frequency of the DC side is Kp, where p is the number of pulses of the inverter and K is any positive integer, so that the DC filter is selected to be 12A/24/36 triple tuned filter. The parameters are as follows: l =400mH, L 1 ＝39.09mH、L 2 ＝26.06mH、L 3 ＝19.545mH、L 4 ＝34.75mH、 C 1 ＝0.9μF、C 2 ＝0.9μF、C 3 ＝1.8μF、C 4 =0.675 μ F. In the figure B 1 ～B 4 、D 1 、D 2 The lightning arresters are respectively a direct current filter, a smoothing reactor and a direct current bus. The smoothing reactor can be regarded as an open circuit within the traveling wave frequency range. The boundary of the inversion side is the smoothing reactor.
Example 1: assume a unipolar metallic short fault at 400km from the M end, with a sampling rate of 200kHz. The specific implementation steps are as follows:
step1: collecting traveling wave coupling box current signals from a rectification side (LCC) and an inversion side (MMC) of a hybrid direct current power transmission system (LCC-MMC) respectively, and constructing ranging signals respectively.
Step1.1: and respectively acquiring current signals of the traveling wave coupling box from the rectifying side and the inverting side of the hybrid direct-current power transmission system.
Step1.2: decoupling a direct current line through a Karenbauer transformation matrix, and solving polar space modulus current signals on the rectifying side and the inverting side as ranging signals, as shown in fig. 3 and 4.
Step2: and respectively carrying out Fourier transform on the ranging signals at the two ends to obtain corresponding frequency spectrums, and screening out the equidistant frequency spectrums reflecting the fault positions.
Step2.1: the frequency spectrums of the ranging signals on the rectifying side and the inverting side are calculated respectively as shown in fig. 5 and 6.
Step2.2: and judging whether the frequency spectrums of the frequency domain signals at the two ends are at equal intervals, if not, executing Step2.3, and if so, respectively calculating the frequency difference of the signals at the two ends.
Step2.3: and respectively calculating power transformation signals of the ranging signals at the two ends of the direct current transmission line, and returning to Step2.1.
The power transformation refers to an odd power.
Step3: respectively calculating frequency difference values of frequency spectrums at two ends, calculating a ratio of the frequency difference values at the two ends, and calculating a ranging estimation result k%, (1-k)%, by using the ratio, specifically comprising:
step3.1: frequency values ω of spectral peak positions of the double-ended equally spaced spectrum are extracted respectively, as indicated by circles in fig. 4 and 5.
And (5) according to the formulas (7) and (8), carrying out difference on any two adjacent frequency values to obtain the frequency difference corresponding to the frequency spectrums at the two ends.
Δω M ＝ω M (k 2 +1)-ω M (k 2 ) (7)
Δω N ＝ω N (k 2 +1)-ω N (k 2 ) (8)
The calculation result is obtained by calculation according to the formulas (2), (3), (7) and (8): Δ f M ＝372.5Hz，Δf N ＝135.45Hz。 k 2 =1,2, \8230: (length (ω) -1), length (ω) represents the length of the sequence of spectral peak frequencies ω.
Step3.2: the ratio omega of the double-end frequency difference is obtained according to the formula (1) MN M denotes a rectification side (LCC) of the double-ended dc system, and N denotes an inversion side (MMC) of the double-ended dc system.
In the formula (1), Δ ω M 、Δω N Respectively representing the angular frequency difference, delta f calculated by the M terminal and the N terminal M 、Δf N Respectively representing the frequency difference calculated by the M end and the N end, wherein the double-end frequency difference and the angular frequency difference respectively satisfy the relational expressions of the expressions (2) and (3).
The ratio omega of the two-end frequency difference is obtained according to the formula (1) MN ＝2.75。
Step3.3 uses the ratio omega of the two-terminal frequency differences MN And (4) obtaining a ranging estimation result k% by the constructed ranging formula (4).
In the formula (4), x f The distance between the fault point and the end M is shown, k% represents the percentage of the distance between the fault point and the end M to the total length of the line, and l represents the total length of the direct current line. k% =26.47%.
It is also possible to pass the ratio Ω of the two-terminal frequency differences NM To obtain a fault location result, the method specifically comprises the following steps:
omega calculated by the formula (5) NM Using the ratio omega of the frequency differences of both ends NM The constructed distance measurement formula (6) gave a distance measurement result of (1-k)%, (1-k)% =73.53%.
Step4: and respectively calculating double-end check signals, comparing whether the difference of the double-end check signals is smaller than a preset check threshold, if so, determining the fault distance measurement result to be max [ k%, (1-k)% ], and if not, determining the fault distance measurement result to be min [ k%, (1-k)% ].
Step4.1: calculating the absolute value of the difference between the ratio of the two end frequency differences and 1, abs (omega) MN -1)＝1.75。
Step4.2: and judging whether the absolute value of the difference between the double-end frequency difference ratio and 1 is greater than a preset threshold value, setting the absolute value to be 0.05, and if so, determining that the fault distance measurement result is k% =26.47%.
Example 2: as shown in fig. 7, a method for locating a fault of an LCC-MMC hybrid dc transmission line includes the following steps:
step1: collecting traveling wave coupling box current signals from a rectification side (LCC) and an inversion side (MMC) of a hybrid direct current transmission system (LCC-MMC) respectively, and constructing ranging signals respectively.
Step2: and respectively calculating the frequency spectrums of the ranging signals at the two ends, and screening out the equal-interval frequency spectrums reflecting the fault positions. .
Step3: and respectively calculating the frequency difference values of the frequency spectrums at the two ends, calculating the ratio of the frequency difference values at the two ends, and calculating the distance measurement estimation result k%, (1-k)%, by using the ratio.
Step4: and respectively calculating double-end check signals, comparing whether the difference of the double-end check signals is smaller than a preset check threshold, if so, determining the fault distance measurement result to be max [ k%, (1-k)% ], and if not, determining the fault distance measurement result to be min [ k%, (1-k)% ].
As shown in fig. 8, step1 is specifically:
step1.1: and respectively collecting current signals of the traveling wave coupling box from a rectification side and an inversion side of the hybrid direct-current power transmission system.
Step1.2: decoupling a direct current line through a Karenbauer transformation matrix, and solving polar space modulus current signals of an rectifying side and an inverting side as ranging signals.
As shown in fig. 9, step2 is specifically:
step2.1: and respectively calculating frequency spectrums of ranging signals on the rectifying side and the inverting side.
Step2.2: and judging whether the frequency spectrums of the frequency domain signals at the two ends are at equal intervals, if not, executing Step2.3, and if so, respectively calculating the frequency difference of the signals at the two ends.
Step2.3: and respectively calculating power transformation signals of the ranging signals at the two ends of the direct current transmission line, and returning to Step2.1.
The power transformation refers to an odd power.
As shown in fig. 10, step3 is specifically:
step3.1: frequency values of spectral peak positions of the double-end equal interval frequency spectrums are respectively extracted, any two adjacent frequency values are subjected to difference, and frequency differences corresponding to the frequency spectrums at the two ends are obtained.
Step3.2: the ratio omega of the double-end frequency difference is obtained according to the formula (1) MN M denotes a rectification side (LCC) of the double-ended dc system, and N denotes an inversion side (MMC) of the double-ended dc system.
In the formula (1), Δ ω M 、Δω N Respectively representing the angular frequency difference, delta f calculated by the M terminal and the N terminal M 、Δf N Respectively representing the frequency difference obtained by the calculation of the M end and the N end, wherein the double-end frequency difference and the angular frequency difference respectively satisfy the relational expressions of the expressions (2) and (3).
Step3.3: using the ratio omega of the frequency differences of both ends MN And (4) obtaining a ranging estimation result k% by using the constructed ranging formula (4).
In the formula (4), x f And the distance of a fault point relative to the end M is expressed, k% represents the percentage of the distance of the fault point relative to the end M in the total length of the line, and l represents the total length of the direct current line.
The ratio of the double-end frequency difference is obtained in Step3.2, and omega calculated by the formula (5) is also included NM Using the ratio omega of the frequency differences of both ends NM The constructed distance measurement formula (6) obtains the distance measurement result (1-k)%.
As shown in fig. 11, step4 is specifically:
step4.1: the absolute value of the difference between the ratio of the two-terminal frequency differences and 1 is calculated.
Step4.2: judging whether the absolute value of the difference between the double-end frequency difference ratio and 1 is larger than a preset threshold value, if so, determining that the fault distance measurement result is k%, otherwise, executing Step4.3
Step4.3: respectively calculating the change rate K between three adjacent sampling points of the wave head detected at the first two ends M And K N 。
Step4.4: comparison K M -K N And if the detection result is smaller than the preset check threshold, executing Step4.5, otherwise executing Step4.6.
Step4.5, the failure ranging result is max [ k%, (1-k)% ].
Step4.6, the failure ranging result is min [ k%, (1-k)% ].
As shown in fig. 12, an LCC-MMC hybrid dc transmission line fault location system includes:
the signal acquisition module 201 is configured to acquire traveling wave coupling box current signals from a rectification side (LCC) and an inversion side (MMC) of a hybrid direct current power transmission system (LCC-MMC), respectively.
A signal preprocessing module 202 for constructing ranging signals.
And the frequency domain signal analysis module 203 is used for respectively calculating frequency spectrums of the ranging signals at the two ends and screening out an equal interval frequency spectrum reflecting the fault position.
The frequency domain signal processing module 204 is configured to calculate an equally spaced frequency difference value of the frequency domain signal, and calculate a ratio of the two end frequency difference values.
And the fault distance measurement module 205 is used for calculating and recording a fault distance measurement result.
And a signal checking module 206 for calculating a checking signal.
The signal acquisition module 201 includes:
and the voltage-current transmitting unit 2011 is configured to convert a voltage-current signal at the secondary side of the transformer into a signal acquired by the traveling wave device a/D.
The analog acquisition unit 2012 is configured to convert the voltage-current analog signal into a digital signal.
And the data storage unit 2013 is used for naming the wave recording data file according to the time mark and storing the wave recording data file in a local memory.
And the abrupt change starting unit 2014 is used for judging whether the waveform abrupt change is larger than a set starting threshold value or not, and if so, storing the voltage and current signals into a wave recording data file.
The signal preprocessing module 202 includes:
the numerical calculation unit 2021 is configured to decouple the dc line by using a Karenbauer transformation matrix to obtain a polar space current modulus traveling wave transient signal.
A numerical calculation unit 2022 for calculating power conversion signals for respectively calculating distance measurement signals at two ends of the DC transmission line
The frequency domain signal analysis module 203 comprises:
the time-frequency transform unit 2031 is configured to extract frequency domain signals of the signals associated with the two ends of the dc transmission line.
A spectrum calculating unit 2032 is configured to calculate the spectrum of the two-end frequency domain signal.
The frequency domain signal processing module 204 includes:
the frequency difference calculating unit 2041 is configured to extract frequency values at spectral peak positions of the double-end equally-spaced frequency spectrums, and perform a difference between any two adjacent frequency values to obtain equal frequency differences corresponding to the frequency spectrums at the two ends.
A ratio calculation unit 2042 for calculating a ratio Ω of the two-terminal frequency difference MN 、Ω NM M represents one end of the double-ended DC system, and N represents the other end of the double-ended DC system.
The signal verification module 206 includes:
a check signal calculation unit 2061 for calculating the absolute value of the difference between the double-ended frequency difference ratio and 1.
A check signal calculation unit 2062 for calculating the change rate K between three adjacent sampling points of the first detected wave head at the two ends M And K N 。
A check signal comparing unit 2063 for comparing whether the absolute value of the difference between the double-ended frequency difference ratio and 1 is greater than a preset threshold value
A check signal comparison unit 2064 for comparing K M -K N Whether the value is less than a preset check threshold value.
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 and scope of the present invention.
Claims (9)
1. A fault location method for an LCC-MMC hybrid direct current transmission line is characterized by comprising the following steps:
step1: respectively acquiring current signals of a traveling wave coupling box from a rectifying side and an inverting side of the hybrid direct-current power transmission system, and respectively constructing ranging signals;
step2: respectively calculating frequency spectrums of ranging signals at two ends, and screening out equal-interval frequency spectrums reflecting fault positions;
step3: respectively calculating frequency difference values of frequency spectrums at two ends, calculating a ratio of the frequency difference values at the two ends, and calculating a ranging estimation result k%, (1-k)%, by using the ratio;
the Step3 specifically comprises the following steps:
step3.1: respectively extracting frequency values of spectral peak positions of double-end equally-spaced frequency spectrums, and differencing any two adjacent frequency values to obtain equal frequency differences corresponding to the frequency spectrums at the two ends;
step3.2: the ratio omega of the two-end frequency difference is obtained according to the formula (1) MN M represents the rectification side of the double-end direct-current system, and N represents the inversion side of the double-end direct-current system;
in the formula (1), Δ ω M 、Δω N Respectively representing the angular frequency difference, delta f calculated by the M terminal and the N terminal M 、Δf N Respectively representing the frequency difference calculated by the M terminal and the N terminal, and two terminalsThe frequency difference and the angular frequency difference respectively satisfy the relational expressions of the expressions (2) and (3);
step3.3: using the ratio omega of the frequency differences of both ends MN The constructed distance measurement formula (4) obtains a distance measurement estimation result k%;
in the formula (4), x f The distance between a fault point and the end M is represented, k% represents the percentage of the distance between the fault point and the end M in the total length of the line, and l represents the total length of the direct-current line;
the Step3.2 can also be used for calculating the ratio omega of the double-end frequency difference according to the formula (5) NM ；
The Step3.3 can also be realized by utilizing the ratio omega of double-end frequency difference NM The constructed distance measurement formula (6) obtains a distance measurement result (1-k)%;
step4: and respectively calculating double-end check signals, comparing whether the difference of the double-end check signals is smaller than a preset check threshold, if so, determining the fault distance measurement result to be max [ k%, (1-k)% ], and if not, determining the fault distance measurement result to be min [ k%, (1-k)% ].
2. The LCC-MMC hybrid direct current transmission line fault location method of claim 1, wherein Step1 specifically is:
step1.1: respectively collecting current signals of a traveling wave coupling box from a rectifying side and an inverting side of the hybrid direct-current power transmission system;
step1.2: decoupling the direct current line through a Karenbauer transformation matrix, and solving space modulus current signals of an rectification side pole and an inversion side pole to serve as ranging signals.
3. The LCC-MMC hybrid direct current transmission line fault location method of claim 1, wherein Step2 specifically is:
step2.1: respectively calculating frequency spectrums of ranging signals on a rectifying side and a inverting side;
step2.2: judging whether the frequency spectrums of the frequency domain signals at the two ends are at equal intervals, if not, executing Step2.3, and if so, respectively calculating the frequency difference of the signals at the two ends;
step2.3: and respectively calculating power transformation signals of the ranging signals at the two ends of the direct current transmission line, and returning to Step2.1.
4. The LCC-MMC hybrid direct current transmission line fault location method of claim 1, wherein Step4 specifically is:
step4.1: calculating the absolute value of the difference between the ratio of the two end frequency differences and 1;
step4.2: judging whether the absolute value of the difference between the double-end frequency difference ratio and 1 is greater than a preset threshold value, if so, determining that the fault distance measurement result is k%, otherwise, executing Step4.3
Step4.3: respectively calculating the change rate K between three adjacent sampling points of the wave head detected by the first two ends M And K N ；
Step4.4: comparison K M -K N Whether the current value is smaller than a preset check threshold value or not, if yes, step4.5 is executed, and if not, step4.6 is executed;
step4.5: the fault location result is max [ k%, (1-k)% ];
step 4.6: the fault location result is min [ k%, (1-k)% ].
5. A system using the LCC-MMC hybrid direct current transmission line fault location method of claim 1, comprising:
the signal acquisition module is used for respectively acquiring current signals of the traveling wave coupling box from the rectifying side and the inverting side of the hybrid direct-current power transmission system;
the signal preprocessing module is used for constructing a ranging signal;
the frequency domain signal analysis module is used for respectively calculating frequency spectrums of the ranging signals at the two ends and screening out the equal interval frequency spectrums reflecting the fault positions;
the frequency domain signal processing module is used for calculating the equal-interval frequency difference value of the frequency domain signal and calculating the ratio of the frequency difference values at the two ends;
the fault distance measurement module is used for calculating and recording a fault distance measurement result;
the signal checking module is used for calculating a checking signal;
the frequency domain signal processing module includes:
the frequency difference calculating unit is used for extracting frequency values of spectral peak positions of the double-end equal-interval frequency spectrums, and performing difference on any two adjacent frequency values to obtain the corresponding equal frequency differences of the frequency spectrums at the two ends;
a ratio calculation unit for calculating a ratio omega of the two-terminal frequency differences MN 、Ω NM M denotes one end of the double-ended dc system, and N denotes the other end of the double-ended dc system.
6. The system of the LCC-MMC hybrid direct current transmission line fault location method of claim 5, characterized in that said signal acquisition module comprises:
the voltage and current transmission unit is used for converting a voltage and current signal on the secondary side of the transformer into a signal acquired by the traveling wave device A/D;
the analog quantity acquisition unit is used for converting the voltage and current analog quantity signals into digital signals;
the data storage unit is used for naming the wave recording data files according to the time stamps and storing the wave recording data files in a local memory;
and the abrupt change starting unit is used for judging whether the waveform abrupt change is larger than a set starting threshold value or not, and storing the voltage and current signals into a recording data file if the waveform abrupt change is larger than the set starting threshold value.
7. The system of the LCC-MMC hybrid direct current transmission line fault ranging method of claim 5, wherein the signal pre-processing module comprises:
the numerical calculation unit 1 is used for decoupling the direct current line by using a Karenbauer transformation matrix and solving polar space current modulus traveling wave transient signals;
and the numerical value calculating unit 2 is used for calculating power transformation signals of the ranging signals at the two ends of the direct current transmission line respectively.
8. The system of the LCC-MMC hybrid direct current transmission line fault location method of claim 5, wherein the frequency domain signal analysis module comprises:
the time-frequency transformation unit is used for extracting frequency domain signals of related signals at two ends of the direct current transmission line;
the frequency spectrum calculating unit is used for calculating the frequency spectrum of the frequency domain signals at the two ends;
and the frequency spectrum judging unit is used for judging whether the frequency spectrums of the frequency domain signals at the two ends are at equal intervals.
9. The system of the LCC-MMC hybrid direct current transmission line fault ranging method of claim 5, wherein the signal verification module comprises:
the check signal calculating unit 1 is used for calculating the absolute value of the difference between the double-end frequency difference ratio and 1;
a check signal calculating unit 2 for calculating the change rate K between three adjacent sampling points of the first detected wave head at both ends M And K N ；
The check signal comparison unit 1 is used for comparing whether the absolute value of the difference between the double-end frequency difference ratio and 1 is greater than a preset threshold value or not;
a check signal comparison unit 2 for comparing K M -K N Whether or not it is less than presetAnd checking the threshold value.
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