Power transmission line fault discrimination method

Abstract

The invention discloses a power transmission line fault discrimination method, which comprises the following steps: S1, collecting a terminal voltage signal of a fault phase to obtain voltage waveforms at two ends of a fault line; s2, decomposing the fault signal into a low-frequency part and a high-frequency part; s3, performing n-level division on a low-frequency part and a high-frequency part of the fault signal by adopting wavelet packet analysis to obtain a decomposed fault signal x (t); s4, extracting energy values of the fault signal on different frequency bands, and selecting energy characteristic values in a specified frequency band to construct an energy characteristic vector; s5, calculating an energy characteristic ratio Ec by using the wavelet packet energy characteristic vector; s6, setting a threshold value of an energy characteristic ratio; judging whether the fault signal energy characteristic ratio is greater than a threshold value, if so, judging that the fault is a permanent fault, otherwise, judging that the fault is an instantaneous fault; the fault type can be quickly judged, corresponding safety measures can be taken conveniently, and the stable and reliable performance of a power supply system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power transmission line fault determination, and in particular relates to a power transmission line fault determination method. Background Art

[0002] Transmission line faults are divided into two types: transient faults and permanent faults. Transient faults refer to power supply interruptions caused by some sudden external factors. After emergency repairs, the insulation at the fault point returns to normal levels. After the circuit breaker is closed, the power supply system returns to normal. Permanent faults refer to power supply interruptions caused by line breakage, tower collapse, or insulator damage. Before this type of fault is completely repaired, even if the circuit breaker is closed, the system will trip again to protect the power supply system because the fault still exists.

[0003] When a power supply line fails, whether it is a transient fault or a permanent fault, the circuit breaker will be closed to ensure the continuity and reliability of the power supply system. However, the closing of the circuit breaker is only suitable for the recovery of transient faults, and does not play a positive role in the recovery of permanent faults. Instead, it will cause some negative effects. Therefore, in order to ensure the safety and reliability of the power supply system's post-fault recovery, it is necessary to immediately identify the type of fault that has occurred, so that different measures and processing methods can be taken for different types of faults to ensure the safety and stability of the power supply system.

[0004] Therefore, in order to solve the above problems, it is necessary to develop a transmission line fault identification method. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a method for determining a power transmission line fault, so as to quickly determine the type of fault, facilitate the adoption of corresponding safety measures, and improve the stability and reliability of the power supply system.

[0006] The object of the present invention is achieved in this way: a method for determining a power transmission line fault comprises the following steps:

[0007] S1. When a line fault occurs and the circuit breaker trips, the terminal voltage signal of the fault phase is collected to obtain the voltage waveform at both ends of the fault line;

[0008] S2, decomposing the fault signal into a low-frequency part and a high-frequency part; using a wavelet function to decompose the voltage signal at the fault phase end within a specified time period, and dividing the voltage waveform at both ends of the line into different characteristic frequency bands according to the corresponding frequency intervals;

[0009] S3, using wavelet packet analysis to divide the low-frequency part and the high-frequency part of the fault signal into n levels to obtain the decomposed fault signal x(t);

[0010] S4, extracting the energy values ​​of the fault signal in different frequency bands, selecting the energy characteristic values ​​in the specified frequency band to construct an energy characteristic vector;

[0011] S5. Use the wavelet packet energy eigenvector to calculate the energy eigenvalue ratio E. c ;

[0012] S6. Set a threshold value of the energy characteristic ratio; determine whether the energy characteristic ratio of the fault signal is greater than the threshold value, if so, determine it as a permanent fault, otherwise it is a transient fault.

[0013] Furthermore, in step S2, a Meyer wavelet function is used to decompose the fault phase terminal voltage signal.

[0014] Furthermore, in step S3, wavelet packet analysis is used to perform n-layer wavelet packet decomposition on the fault signal x(t) to obtain:

[0015]

[0016] , where

[0017]

[0018] , ψ j,k,i (t) is a wavelet packet with scale index j, location index k and frequency index i.

[0019] Furthermore, the energy characteristic vector constructed in step S4 specifically includes: the total energy of the fault signal is:

[0020]

[0021] , according to the orthogonality of wavelet packets:

[0022]

[0023] , where is the total signal energy in the i-th frequency band,

[0024] Furthermore, in step S5, the energy characteristic ratio E c It is expressed as:

[0025]

[0026] , where E2 is the energy characteristic of the frequency band where the power frequency is located, and E1 is the energy characteristic of the frequency band where the free oscillation component lower than the low-frequency component is located.

[0027] Due to the adoption of the above technical scheme, the beneficial effects of the present invention are as follows: the fault signal is decomposed by wavelet function, the voltage waveform at both ends of the line is divided into different characteristic frequency bands according to the corresponding frequency intervals, and the low-frequency part and the high-frequency part of the fault signal are further divided into multiple levels by wavelet packet analysis, the energy value of the fault signal in different frequency bands is extracted, the energy characteristic value in the specified frequency band is selected to construct an energy characteristic vector, and the characteristic vector is used to judge different fault types, so that the fault type can be quickly identified, which is convenient for taking corresponding safety measures and improving the stability and reliability of the power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0030] like Figure 1 As shown, a method for determining a transmission line fault comprises the following steps:

[0031] S1. When a line fault occurs and the circuit breaker trips, the terminal voltage signal of the faulty phase is collected to obtain the voltage waveform at both ends of the faulty line.

[0032] S2. Decompose the fault signal into a low-frequency part and a high-frequency part; use a wavelet function to decompose the fault phase terminal voltage signal within a specified time period, and divide the voltage waveform at both ends of the line into different characteristic frequency bands according to the corresponding frequency intervals; preferably, use a Meyer wavelet function to decompose the fault phase terminal voltage signal.

[0033] S3. Use wavelet packet analysis to divide the low-frequency part and the high-frequency part of the fault signal into n layers to obtain the decomposed fault signal x(t); preferably, use wavelet packet analysis to perform n-layer wavelet packet decomposition on the fault signal x(t) to obtain:

[0034]

[0035] , where

[0036]

[0037] , ψ j,k,i (t) is a wavelet packet with scale index j, location index k and frequency index i.

[0038] S4. Extract the energy values ​​of the fault signal in different frequency bands, and select the energy characteristic values ​​in the specified frequency band to construct an energy characteristic vector; preferably, constructing the energy characteristic vector specifically includes: the total energy of the fault signal is:

[0039]

[0040] , according to the orthogonality of wavelet packets:

[0041]

[0042] , where is the total signal energy in the i-th frequency band,

[0043] S5. Use the wavelet packet energy eigenvector to calculate the energy eigenvalue ratio E. c ; Preferably, the energy characteristic ratio E c It is expressed as:

[0044]

[0045] , where E2 is the energy characteristic of the frequency band where the power frequency is located, and E1 is the energy characteristic of the frequency band where the free oscillation component lower than the low-frequency component is located.

[0046] S6. Set a threshold value of the energy characteristic ratio; determine whether the energy characteristic ratio of the fault signal is greater than the threshold value, if so, determine it as a permanent fault, otherwise it is a transient fault.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for determining a power transmission line fault, characterized in that: The following steps are involved: S1. When a line fault occurs and the circuit breaker trips, the terminal voltage signal of the fault phase is collected to obtain the voltage waveform at both ends of the fault line; S2, decomposing the fault signal into a low-frequency part and a high-frequency part; using a wavelet function to decompose the voltage signal at the fault phase end within a specified time period, and dividing the voltage waveform at both ends of the line into different characteristic frequency bands according to the corresponding frequency intervals; S3, using wavelet packet analysis to divide the low-frequency part and the high-frequency part of the fault signal into n levels to obtain the decomposed fault signal x(t); S4, extracting the energy values ​​of the fault signal in different frequency bands, selecting the energy characteristic values ​​in the specified frequency band to construct an energy characteristic vector; S5. Use the wavelet packet energy eigenvector to calculate the energy eigenvalue ratio E. c ; S6. Set a threshold value of the energy characteristic ratio; determine whether the energy characteristic ratio of the fault signal is greater than the threshold value, if so, determine it as a permanent fault, otherwise it is a transient fault.

2. A method for determining a power transmission line fault according to claim 1, characterized in that: In step S2, the fault phase terminal voltage signal is decomposed using the Meyer wavelet function.

3. A method for determining a power transmission line fault according to claim 1, characterized in that: In step S3, wavelet packet analysis is used to perform n-layer wavelet packet decomposition on the fault signal x(t) to obtain: ， In the formula, ， ψ j,k,i (t) is a wavelet packet with scale index j, location index k and frequency index i.

4. A method for determining a power transmission line fault according to claim 3, characterized in that: The energy characteristic vector constructed in step S4 specifically includes: the total energy of the fault signal is: v According to the orthogonality of wavelet packets, we get: ， In the formula, is the total signal energy in the i-th frequency band, 5. A method for determining a power transmission line fault according to claim 1, characterized in that: The energy characteristic ratio E of step S5 c It is expressed as: ， Where E2 is the energy characteristic of the frequency band where the power frequency is located, and E1 is the energy characteristic of the frequency band where the free oscillation component lower than the low-frequency component is located.

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