An overhead line fault location method and system based on dual-frequency signals

Abstract

The application relates to an overhead line fault positioning method and system based on a dual-frequency signal, and the method comprises the following steps: S1, inputting a dual-frequency alternating current signal to an overhead line; S2, collecting a dual-frequency alternating current signal and a power frequency interference signal at a current overhead line position to obtain an initial collection signal; S3, sequentially performing signal windowing, signal zero padding, Fourier transform operation, amplitude correction recovery calculation and amplitude filtering calculation operation on the initial collection signal to obtain a processed signal; S4, calculating a resistive current and a capacitive current at the current overhead line position based on the processed signal; S5, determining a total current value calculation formula based on a fault positioning mode, and calculating a total current value at the current overhead line position based on the total current value calculation formula, the resistive current and the capacitive current or based on the total current value calculation formula and the processed signal; and S6, repeatedly performing steps S1-S5 at different positions of the overhead line, and positioning a fault based on changes of the resistive current, the capacitive current and the total current value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of overhead line fault positioning of medium and low voltage distribution network, and particularly relates to an overhead line fault positioning method and system based on double-frequency signals. BACKGROUND

[0002] The overhead line is a power transmission circuit erected on the ground, with insulators fixing the power transmission line on the pole tower standing on the ground to transmit electric energy. The overhead line is mostly used in a small current grounding system. The small current grounding system is a three-phase system with non-effective grounding mode of neutral point non-grounding or grounding through arc suppression coil and high impedance, also known as neutral point indirect grounding system. The common line fault of this system is single-phase grounding fault, i.e. single-phase short circuit grounding fault.

[0003] Most of the medium and low voltage distribution network power systems of 6-35kV in China adopt neutral point non-effective grounding mode, i.e. small current grounding system. In the small current grounding system, the common temporary fault is line single-phase grounding fault. If the single-phase grounding fault occurs and the power grid is operated for a long time, the voltage of the non-fault two phases to ground is increased, which may cause breakdown of the weak link of insulation, cause inter-phase short circuit, and affect normal power use of users. It may also cause serious saturation of the voltage transformer core to cause overloading and burnout. The arc grounding fault may also cause overvoltage of the whole system to cause equipment damage and destroy the safe operation of the system. Therefore, it is necessary to find out the fault line and locate the fault point in time.

[0004] At present, the main network of the power supply system of the distribution network in China is overhead line, and the common fault checking means includes:

[0005] 1. First, the fault interval is isolated by pulling the disconnecting switch, and then the line is manually patrolled and checked.

[0006] 2. The section is checked by the fault indicator.

[0007] 3. The fault is located and checked by the overhead line fault finding device.

[0008] Method one is time-consuming and laborious, and it is difficult to effectively and quickly find hidden faults such as insulator and porcelain bottle cracks.

[0009] Method two has low accuracy for grounding faults, and can only measure the fault interval and cannot accurately locate the fault.

[0010] Method three, the current mainstream fault finding device method, injects a current signal of a certain frequency, realizes accurate positioning of the fault point by judging the change of the signal parameter before and after the fault point, and has the disadvantage of being unable to find high resistance faults. SUMMARY

[0011] In view of the above problems existing in the prior art, the application provides an overhead line fault positioning method and system based on a dual-frequency signal, which can realize accurate positioning of a fault point by judging the change of signal parameters before and after the fault point.

[0012] The application adopts the following technical solutions:

[0013] An overhead line fault positioning method based on a dual-frequency signal comprises the following steps:

[0014] S1, inputting a dual-frequency alternating current signal to the overhead line;

[0015] S2, collecting the dual-frequency alternating current signal and the power frequency interference signal at the current overhead line position to obtain an initial collected signal;

[0016] S3, sequentially performing signal windowing, signal zero padding, Fourier transform operation, amplitude correction and recovery calculation, and amplitude filtering calculation on the initial collected signal to obtain a processed signal;

[0017] S4, calculating the resistive current and the capacitive current at the current overhead line position based on the processed signal;

[0018] S5, determining a total current value calculation formula based on the fault positioning mode, and calculating the total current value at the current overhead line position based on the total current value calculation formula, the resistive current, and the capacitive current or based on the total current value calculation formula and the processed signal;

[0019] S6, repeatedly performing steps S1-S5 at different positions of the overhead line, and positioning the fault based on the changes of the resistive current, the capacitive current, and the total current value.

[0020] As a preferred solution, in step S3, the Fourier transform operation result is subjected to amplitude correction and recovery calculation, and the calculation formula is:

[0021]

[0022]

[0023] wherein, FFTout f represents the result of amplitude correction and recovery calculation on the Fourier transform result of the signal with the frequency f, FFTout 2f represents the result of amplitude correction and recovery calculation on the Fourier transform result of the signal with the frequency 2f, k amp represents the amplitude equal recovery coefficient, k power represents the power equal recovery coefficient, RMS f represents the amplitude root mean square value of the signal with the frequency f, RMS 2f represents the amplitude root mean square value of the signal with the frequency 2f.

[0024] As a preferred solution, RMS f , RMS 2f The calculation formulae are respectively:

[0025]

[0026]

[0027] wherein FFTout f (i) represents the Fourier transform operation result of the i-th frequency point within a preset range around the frequency f, FFTout 2f (i) represents the Fourier transform operation result of the i-th frequency point within a preset range around the frequency 2f, (N+r) represents the total number of signal points of the Fourier transform operation result, N represents the signal point number of the initial collected signal, r represents the number of signal zero padding, and width1+width2 represents the effective frequency width.

[0028] As a preferred solution, in step S3, the amplitude filtering calculation operation is calculated according to the following formula:

[0029]

[0030]

[0031] wherein M is the sliding filtering window width, FFTout f represents FFTout f after the amplitude filtering calculation operation, FFTout 2f represents FFTout 2f after the amplitude filtering calculation operation, respectively represent the maximum value and the minimum value of the Fourier transform operation result in all frequency points within a preset range around the frequency f, respectively represent the maximum value and the minimum value of the Fourier transform operation result in all frequency points within a preset range around the frequency 2f.

[0032] As a preferred solution, in step S4, the calculation formula of the resistive current is:

[0033]

[0034] wherein I r represents the resistive current value, k 2ftof represents a preset ratio coefficient of the signal with the frequency f and the signal with the frequency 2f.

[0035] As a preferred solution, in step S4, the calculation formula of the capacitive current is:

[0036]

[0037] wherein, I c represents the capacitive current value.

[0038] As a preferred solution, in step S5, the fault location mode is a low resistance AC positioning mode or a high resistance AC positioning mode.

[0039] As a preferred solution, the total current value calculation formula of the low resistance AC positioning mode is:

[0040]

[0041] wherein, I total represents the total current value, I distance represents the signal amplitude calculated from the distance of the overhead line from the given position, I ref represents the reference current value parameter of the given position.

[0042] As a preferred solution, the total current value calculation formula of the high resistance AC positioning mode is:

[0043]

[0044] wherein, I total represents the total current value, k represents the calibration coefficient, magnification represents the gain value, k sensor represents the magnetic resistance sensor coefficient, r represents the distance between the hook and the center of the cable, μ0 represents the vacuum permeability.

[0045] Also provided is an overhead line fault location system based on a dual-frequency signal, based on the overhead line fault location method based on a dual-frequency signal described above, comprising a signal acquisition module, a signal processing module, a calculation module, and a fault location module connected in sequence, and further comprising a signal transmission module;

[0046] The signal transmission module is configured to continuously output a dual-frequency AC signal to the overhead line.

[0047] The signal acquisition module is configured to acquire the dual-frequency AC signal and the power frequency interference signal at the corresponding position of the overhead line to obtain an initial acquisition signal.

[0048] The signal processing module is configured to sequentially perform signal windowing, signal zero padding, Fourier transform operation, amplitude correction and recovery calculation, and amplitude filtering calculation operation on the initial acquisition signal to obtain a processed signal.

[0049] The calculation module is configured to calculate the resistive current and the capacitive current at the current position of the overhead line based on the processed signal.

[0050] The computing module also determines a total current value calculation formula based on the fault location mode, and calculates the total current value at the current overhead line position based on the total current value calculation formula, the resistive current, the capacitive current, or based on the total current value calculation formula and the processed signal;

[0051] The fault location module locates the fault based on the changes of the resistive current, the capacitive current and the total current value at different positions of the overhead line.

[0052] The present application has the following advantages:

[0053] The present application injects a double-frequency alternating current signal, and then collects the double-frequency signal through a sensor and analyzes and calculates the double-frequency signal through a receiver to determine the changes of parameters such as line resistance and capacitance, thereby accurately and quickly locating the fault of the overhead line, and the high-resistance fault can also be easily found.

[0054] Due to the inevitable non-integer period truncation of the sampling signal, the signal spectrum leakage problem occurs before the windowing and zero padding. The present application significantly improves the spectrum leakage problem by adding a window function and zero padding, accurately restores the amplitude of the double-frequency signal, and ensures the calculation accuracy of subsequent parameters such as the resistive current value, the resistive current percentage, and the total current value.

[0055] To solve the interference jitter problem caused by pulse data, the calculated signal result is added to a filter mode combining sliding filtering and median value average filtering to obtain a processed signal, thereby further ensuring the calculation accuracy of subsequent parameters such as the resistive current value, the resistive current percentage, and the total current value. BRIEF DESCRIPTION OF DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0057] Figure 1 is a flow chart of the overhead line fault location method based on the double-frequency signal according to the present application.

[0058] Figure 2 is a component schematic diagram of the initial collected signal.

[0059] Figure 3 is a time domain comparison diagram before and after windowing and zero padding.

[0060] Figure 4 is a frequency domain comparison diagram before and after windowing and zero padding.

[0061] Figure 5It is a structural schematic diagram of an overhead line fault location system based on a dual-frequency signal. DETAILED DESCRIPTION

[0062] The advantages and effects of the present application can be easily understood by those skilled in the art from the description. The present application can also be implemented or applied by different specific embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0063] Embodiment one:

[0064] Referring to Figure 1 The embodiment provides an overhead line fault location method based on a dual-frequency signal, comprising the steps of:

[0065] S1, inputting a dual-frequency alternating current signal into the overhead line through a transmitter;

[0066] S2, collecting the dual-frequency alternating current signal and the 50Hz power frequency interference signal at the current overhead line position through a receiver to obtain an initial collection signal, and the initial collection signal components can refer to Figure 2 The sampling rate is set to 500Hz, and the sampling point number reaches 500 points.

[0067] S3, sequentially performing signal windowing, signal zero padding, Fourier transform operation, amplitude correction and recovery calculation, and amplitude filtering calculation operation on the initial collection signal to obtain a processed signal;

[0068] S4, calculating the resistive current and the capacitive current at the current overhead line position based on the processed signal;

[0069] S5, determining a total current value calculation formula based on the fault location mode, and calculating the total current value at the current overhead line position based on the total current value calculation formula, the resistive current and the capacitive current, or based on the total current value calculation formula and the processed signal;

[0070] S6, repeatedly performing steps S1-S5 for different positions of the overhead line, and locating the fault based on the changes of the resistive current, the capacitive current and the total current value.

[0071] The line ground fault of the small current grounding system, the overhead line has the characteristics of long line, many branches, large capacitive current, etc. Single frequency signal cannot accurately determine the fault point position. The invention uses a dual-frequency alternating signal, which contains a sinusoidal alternating proportional composite signal with frequencies f and 2f, which can accurately and quickly calculate the resistance current percentage, total current value, resistance current value and other parameters. Before the fault point, the current in the line mainly contains capacitive current and resistance current, and the resistance current percentage parameter is large; after the fault point, the current in the line is mainly capacitive current, and the resistance current percentage parameter decreases to a small value. By comparing the change trend of the three-dimensional parameters of the total current value parameter, the resistance circuit percentage parameter, and the resistance current value parameter, the overhead line fault can be accurately and quickly located.

[0072] Due to the inevitable non-integer period truncation of the sampling signal, the signal spectrum leakage problem occurs before windowing and zero padding. The invention significantly improves the spectrum leakage problem by adding a window function after zero padding, accurately restores the amplitude of the dual-frequency signal, and ensures the accuracy of the calculation of subsequent resistance current value, resistance current percentage, total current value and other parameters. In this embodiment, the zero padding is to 512 points.

[0073] Referring to Figure 3 , Figure 4 , it is obtained from the waveform diagram that the time domain graph and the frequency domain graph before and after windowing and zero padding both contain f and 2f dual-frequency signals and 50Hz power frequency interference signals. Due to the inevitable non-integer period truncation of the sampling signal, the amplitude of the f and 2f dual-frequency signals is affected, resulting in a signal spectrum leakage problem in the time domain graph and the frequency domain graph before windowing and zero padding. By adding a window function after zero padding, it is analyzed from the time domain graph and the frequency domain graph after windowing and zero padding that the spectrum leakage problem is significantly improved, the amplitude of the dual-frequency signal is accurately restored, and the accuracy of the calculation of subsequent resistance current value, resistance current percentage, total current value and other parameters is ensured.

[0074] Specifically:

[0075] In step S3, the initial collected signal is:

[0076] x(n), n=0, 1, … N-1.

[0077] The window function is:

[0078] w(n), n=0, 1, … N-1.

[0079] The initial collected signal is subjected to a windowing operation, i.e. a time domain multiplication operation, to obtain:

[0080] y(n)=x(n)×w(n), n=0, 1, … N-1.

[0081] The data after the windowing operation is zero padded, i.e. time domain zero padding, and the number of zero padding is r, to obtain:

[0082] y'(n) = y(n), n = 0, 1,... N-1;

[0083] y'(n) = 0, n = N,... N+r-1.

[0084] The windowed and zero-padded data is subjected to FFT operation to obtain:

[0085]

[0086] The Fourier transform results of the signals with frequencies f and 2f are subjected to amplitude-equalized recovery coefficient k amp and power-equalized recovery coefficient k power to obtain:

[0087]

[0088]

[0089] wherein FFTout f represents the result of amplitude-modified recovery calculation on the Fourier transform result of the signal with frequency f, FFTout 2f represents the result of amplitude-modified recovery calculation on the Fourier transform result of the signal with frequency 2f, k amp represents the amplitude-equalized recovery coefficient, k power represents the power-equalized recovery coefficient, RMS f represents the root mean square value of the amplitude of the signal with frequency f, RMS 2f represents the root mean square value of the amplitude of the signal with frequency 2f.

[0090] The calculation formulas of RMS f and RMS 2f are respectively:

[0091]

[0092]

[0093] wherein FFTout f (i) represents the Fourier transform operation result of the i-th frequency point within a preset range above and below the frequency f, FFTout 2f (i) represents the Fourier transform operation result of the i-th frequency point within a preset range above and below the frequency 2f, (N+r) represents the total number of signal points of the Fourier transform operation result, N represents the number of signal points of the initial collected signal, r represents the number of signal zero padding, and width1+width2 represents the effective frequency width.

[0094] To solve the problem of interference jitter caused by pulse data, the calculated signal result is added to the filter mode combining sliding filter and median value average filter, and the following is obtained:

[0095]

[0096]

[0097] wherein M is the sliding filter window width, FFTout f represents FFTout f After the amplitude filtering calculation operation, the result is FFTout 2f represents FFTout 2f After the amplitude filtering calculation operation, respectively represent the maximum and minimum values of the Fourier transform operation results of all frequency points within the preset range above and below the frequency f, respectively represent the maximum and minimum values of the Fourier transform operation results of all frequency points within the preset range above and below the frequency 2f.

[0098] Based on the signal amplitude, substitute the relevant formula to obtain the resistive current value I r and the capacitive current value I c The calculation formula of the resistive current is:

[0099]

[0100] wherein I r represents the resistive current value, k 2ftof represents the preset ratio coefficient of the signal with the frequency f and the signal with the frequency 2f.

[0101] The calculation formula of the capacitive current is:

[0102]

[0103] wherein I c represents the capacitive current value.

[0104] The resistive current percentage parameter percent ir is:

[0105]

[0106] More specifically, in step S5, the fault location mode is a low resistance AC location mode or a high resistance AC location mode.

[0107] Among them, the low resistance AC location mode is suitable for small DC impedance and small AC impedance; large output current and low voltage; T-shaped sensor is used to collect signals, so there is no need to climb the pole; there is no need to remove the line grounding PT.

[0108] High resistance AC positioning mode is suitable for DC impedance small, AC impedance large; output current is small, voltage is high; using suspension sensor, need to climb the pole; without removing the line grounding PT.

[0109] The total current value calculation formula of low resistance AC positioning mode is:

[0110]

[0111] Among them, I total represents the total current value, I distance represents the signal amplitude calculated at the given position of the overhead line, I ref represents the reference current value parameter of the given position.

[0112] The total current value calculation formula of high resistance AC positioning mode is:

[0113]

[0114] Among them, I total represents the total current value, k represents the calibration coefficient, magnification represents the gain value, k sensor represents the magnetic resistance sensor coefficient, r represents the distance between the hook and the center of the cable, μ0 represents the vacuum permeability.

[0115] Example two:

[0116] Referring to Figure 5 The embodiment provides an overhead line fault positioning system based on a double-frequency signal, based on the overhead line fault positioning method based on the double-frequency signal described in example one, comprising a signal acquisition module, a signal processing module, a calculation module and a fault positioning module connected in turn, and further comprising a signal transmitting module;

[0117] The signal transmitting module is used for continuously outputting double-frequency AC signals to the overhead line.

[0118] The signal acquisition module is used for acquiring double-frequency AC signals and power frequency interference signals at corresponding positions of the overhead line to obtain initial acquisition signals.

[0119] The signal processing module is used for sequentially performing signal windowing, signal zero padding, Fourier transform operation, amplitude correction and recovery calculation and amplitude filtering calculation operation on the initial acquisition signals to obtain processed signals.

[0120] The calculation module calculates resistive current and capacitive current at the current position of the overhead line based on the processed signals.

[0121] The computing module also determines a total current value calculation formula based on the fault location mode, and calculates the total current value at the current overhead line position based on the total current value calculation formula, the resistive current, the capacitive current, or based on the total current value calculation formula and the processed signal;

[0122] The fault location module locates the fault based on the changes of the resistive current, the capacitive current and the total current value at different positions of the overhead line.

[0123] It should be noted that the overhead line fault location system based on the dual-frequency signal provided in the embodiment is similar to the overhead line fault location method based on the dual-frequency signal described in the first embodiment, and thus will not be described in detail here.

[0124] The above-described embodiments merely describe the preferred embodiments of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope of the present application.

Claims

1. A method for overhead line fault location based on dual frequency signals, characterized in that, The method comprises the steps of: S1, inputting a double-frequency alternating current signal to an overhead line; S2, collecting the double-frequency alternating current signal and the power frequency interference signal at the current position of the overhead line to obtain an initial collected signal; S3, sequentially performing signal windowing, signal zero padding, Fourier transform operation, amplitude correction recovery calculation, and amplitude filtering calculation on the initial collected signal to obtain a processed signal; S4, calculating the resistive current and the capacitive current at the current position of the overhead line based on the processed signal; S5, determining a total current value calculation formula based on a fault positioning mode, and calculating the total current value at the current position of the overhead line based on the total current value calculation formula, the resistive current, and the capacitive current, or based on the total current value calculation formula and the processed signal; S6, repeatedly performing steps S1-S5 at different positions of the overhead line, and positioning the fault based on the changes of the resistive current, the capacitive current, and the total current value; In step S3, the amplitude correction recovery calculation is performed on the Fourier transform operation result, and the calculation formula is: ； ； wherein, represents the result of amplitude correction recovery calculation on the Fourier transform result of the signal with frequency represents the result of amplitude correction recovery calculation on the Fourier transform result of the signal with frequency represents the result of amplitude correction recovery calculation on the Fourier transform result of the signal with frequency represents the result of amplitude correction recovery calculation on the Fourier transform result of the signal with frequency represents the amplitude equal recovery coefficient, represents the power equal recovery coefficient, represents the amplitude root mean square value of the signal with frequency represents the amplitude root mean square value of the signal with frequency represents the amplitude root mean square value of the signal with frequency represents the amplitude root mean square value of the signal with frequency In step S3, the amplitude filtering calculation operation is performed, and the calculation formula is: ； ； wherein, is a sliding filter window width, denotes a result after an amplitude filtering calculation operation, denotes a result after an amplitude filtering calculation operation, , denote a maximum value and a minimum value of the Fourier transform operation result among all frequency points with the frequency in a preset range above and below , , denote a maximum value and a minimum value of the Fourier transform operation result among all frequency points with the frequency in a preset range above and below . In step S4, the calculation formula of the resistive current is: ； wherein, represents a resistive current value, represents a frequency of a frequency of a preset ratio coefficient of the signal; In step S4, the calculation formula of the capacitive current is: ； wherein, represents a capacitive current value.

2. The overhead line fault location method based on dual-frequency signals according to claim 1, characterized in that, , The calculation formulas of the above are respectively: ； ； wherein, represents the Fourier transform operation result of the first frequency point within a preset range above and below the frequency, represents the Fourier transform operation result of the first frequency point within a preset range above and below the frequency, represents the Fourier transform operation result of the first frequency point within a preset range above and below the frequency, represents the total number of signal points of the Fourier transform operation result, represents the number of signal points of the initial acquisition signal, represents the number of signal zeros, represents the effective frequency width.

3. The overhead line fault location method based on dual-frequency signals according to claim 1, characterized in that, In step S5, the fault positioning mode is a low-resistance alternating current positioning mode or a high-resistance alternating current positioning mode.

4. The overhead line fault location method based on dual-frequency signals according to claim 3, characterized in that, The total current value calculation formula of the low-resistance alternating current positioning mode is: ； wherein, represents the total current value, represents the signal amplitude calculated from the distance to the overhead line, represents the reference current value parameter for the intended position.

5. The overhead line fault location method based on dual-frequency signals according to claim 3, characterized in that, The total current value calculation formula of the high-resistance alternating current positioning mode is: ； wherein, represents a total current value, represents a calibration coefficient, represents a gain value, represents a magnetoresistance sensor coefficient, represents a distance of the hook from the cable center, represents a vacuum permeability.

6. A double frequency signal based overhead line fault location system based on the double frequency signal based overhead line fault location method of any one of claims 1-5, characterized in that, The method comprises a signal collection module, a signal processing module, a calculation module, and a fault positioning module connected in sequence, and further comprises a signal transmission module; The signal transmission module is used for continuously outputting a double-frequency alternating current signal to the overhead line; The signal collection module is used for collecting the double-frequency alternating current signal and the power frequency interference signal at the corresponding position of the overhead line to obtain an initial collected signal; The signal processing module is used for sequentially performing signal windowing, signal zero padding, Fourier transform operation, amplitude correction recovery calculation, and amplitude filtering calculation on the initial collected signal to obtain a processed signal; The calculation module calculates the resistive current and the capacitive current at the current position of the overhead line based on the processed signal; The calculation module further determines a total current value calculation formula based on a fault positioning mode, and calculates the total current value at the current position of the overhead line based on the total current value calculation formula, the resistive current, and the capacitive current, or based on the total current value calculation formula and the processed signal; The fault positioning module positions the fault based on the changes of the resistive current, the capacitive current, and the total current value at different positions of the overhead line.

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