A method for locating faults in medium voltage distribution network cable lines

Abstract

The present invention relates to a method for locating faults in medium-voltage distribution network cable lines, including collecting traveling wave signals at a terminal; screening out intermediate-frequency traveling wave signals and high-frequency traveling wave signals; decomposing the intermediate-frequency traveling wave signals and high-frequency traveling wave signals using multi-level wavelet packets, selecting reference bandpass filtering parameters for reference bandpass filtering, and generating reference frequency traveling wave signals; constructing a transient simulation model for line faults, and constructing a reference waveform library; traversing the reference frequency traveling wave signals in the reference waveform library; and outputting distribution network cable fault locating results. The single-ended traveling wave locating technology of the present invention can reduce the number of original device layouts by 50%, and can improve the economy of engineering use; the present invention solves the problem that the initial traveling wave and the reflected traveling wave are easy to overlap in the short line scenario, resulting in the inability to locate, and the fault point can be located based on the reference high-frequency signal; the present invention proposes a large data sample library, which can adapt to distribution network cable lines with different parameters, improve the accuracy of cable fault locating, and reduce the workload of cable fault troubleshooting.

Description

Technical Field

[0001] The present invention relates to the field of electric power technology, and in particular to a method for locating a medium-voltage distribution network cable line fault. Background Art

[0002] Under the "dual carbon" goal, the development of green and low-carbon energy is the general trend. The global energy revolution has led to a significant increase in the proportion of distributed power generation installed. As the main transmission medium, the application scale of cables has been greatly increased. In addition, the undergrounding of overhead lines and the increase in the cable rate are conducive to the improvement of urban landscape environment and the saving of precious land resources. It is an inevitable reflection and development trend of urbanization in the field of distribution networks. The construction of a distribution network that fully meets the electricity demand in the era of electrification is an important support for the development of the power grid. The focus needs to be on solving problems such as rapid isolation and precise positioning of faults after distribution network failures. Due to installation technology, operating environment, electrical shock and other problems, distribution network cable lines will inevitably fail, leading to serious problems such as production suspension. Long-term power outages due to faults will greatly reduce the user's power experience. Therefore, how to quickly locate cable fault points and assist in the troubleshooting of fault points is one of the key directions that power grid people have always paid attention to and studied.

[0003] In recent years, my country's power grid has increased the construction and investment of distribution networks, and has made great progress in the intelligentization and digitization of distribution networks. In terms of the treatment of short circuits and grounding faults in distribution networks, my country has currently achieved the analysis and isolation of fault sections based on various types of intelligent distribution equipment, but it is still difficult to achieve "precise location" for fault detection. After the fault occurs, a lot of manpower and material resources are still needed to find the fault and analyze the cause of the fault, especially for cable lines. Due to problems such as laying scenarios, fault troubleshooting is more difficult. It is usually necessary to dig cables over a large area to determine the exact location of the fault point. The distribution network automation system needs to improve the refinement of the operation and maintenance of cable faults.

[0004] With the development of traveling wave positioning technology, two-terminal traveling wave positioning technology has been widely used in transmission networks and has achieved excellent application effects. The corresponding national standard "GB / T 35721-2017 Distributed Fault Diagnosis System for Transmission Lines" has been formed. In recent years, in order to improve the level of refined operation and maintenance of distribution network faults, two-terminal traveling wave positioning technology has gradually expanded its application from the transmission field to the distribution network fault positioning field. However, there are several major differences in the application of traveling wave positioning technology between the distribution network and the main transmission network: a) The transmission network is usually a long straight line. Combined with the traveling wave transmission attenuation characteristics and positioning effect, a traveling wave positioning device can be installed every 30km, but the distribution network line structure is complex, showing multiple T connections and multiple hybrid situations; b) The transmission network is a neutral point direct grounding system with obvious fault characteristics. The distribution network lines are mostly neutral point ungrounded systems, and the fault characteristics are difficult to find. The above factors have led to a qualitative change in the installation principles of traveling wave devices in distribution network lines. In distribution networks, it is usually necessary to install monitoring devices at the overhead-cable mixed points. For distribution network cable lines, it is usually necessary to install one set of equipment every 2km, and for distribution network overhead equipment, it is usually necessary to install a set of monitoring devices every 5km. The improvement in configuration principles has greatly reduced the economy of the traveling wave system.

[0005] Specifically, combined with the effect of the current application of traveling wave devices in distribution network cables, there are still the following problems to be solved:

[0006] 1. For the traveling wave positioning of distribution network cable line faults, the problem of low engineering economy needs to be solved:

[0007] Traditional distribution network traveling wave monitoring devices usually need to be installed at both ends of the distribution network cable line. Figure 2 As shown in the figure, if there are multiple lines with a common busbar, in order to prevent the traveling wave head from being slow, the problem of not being able to accurately identify the wave head may occur (as shown in the attached figure). Figure 3 The wave head of the waveform shown is difficult to identify. Taking the 1MHz sampling rate as an example, the positioning error corresponding to adjacent wave heads is as high as 175m. The black dot in the figure is an example of the traveling wave head). Currently, traveling wave devices all use double-end positioning. Traveling wave devices need to be installed at both the beginning and the end of the line for fault detection. At this time, the economic efficiency of the system engineering will be greatly reduced.

[0008] 2. In short line scenarios, the initial traveling wave and the reflected traveling wave waveforms are prone to overlap, resulting in the inability to locate the single end:

[0009] Since the traveling wave is transmitted at an extremely high speed in the line (for example, about 170m / μs in the cable), and the fault traveling wave is usually a composite traveling wave signal containing multiple frequency components, and the traveling wave waveform lasts for a long time, the initial traveling wave signal and the reflected wave signal usually overlap, and the initial traveling wave signal and the reflected wave signal cannot be effectively separated.

[0010] 3. The positioning accuracy of distribution network cable lines is high. Due to the influence of line parameters and other factors, the cable positioning accuracy of the existing double-end positioning technology cannot meet the actual needs of the project:

[0011] At present, double-end traveling wave positioning technology adopts a formulaic calculation method, that is, the wave speed in the cable is calculated according to the wave speed of 170m / μs. However, for different loads and different line parameters, the transmission speed of the traveling wave in the cable is different. The cable fault positioning accuracy requirements are extremely high, and the formulaic calculation method cannot be used to perform double-end positioning of the distribution network cable. Summary of the invention

[0012] The technical problem to be solved by the present invention is to provide a method for locating a fault in a medium voltage distribution network cable line to overcome the deficiencies in the above-mentioned prior art.

[0013] The technical solution of the present invention to solve the above technical problem is as follows: A method for locating a fault in a medium voltage distribution network cable line comprises the following steps:

[0014] Step S01: The terminal collects traveling wave signals;

[0015] Step S02: Filter out the medium frequency traveling wave signal and the high frequency traveling wave signal from the traveling wave signal, and enter step S03, the low frequency traveling wave signal in the traveling wave signal waits for the next traveling wave signal of the fault, and then repeats the determination;

[0016] Step S03: Decomposing the intermediate frequency traveling wave signal and the high frequency traveling wave signal using a multi-level wavelet packet, selecting a reference bandpass filter parameter to perform reference bandpass filtering, and generating a reference frequency traveling wave signal;

[0017] Step S04: constructing a line fault transient simulation model according to line parameters, and constructing a reference waveform library;

[0018] Step S05: traverse the reference frequency traveling wave signal in the reference waveform library;

[0019] Step S06: outputting the distribution network cable fault location result according to the waveform traversal result;

[0020] Step S03 specifically includes the following steps:

[0021] Step S31: record the traveling wave signal collected by the terminal as a traveling wave waveform sequence x[n], where n=1,2,3...N-1,N, and the sampling frequency is a known quantity f s , at this time, the signal is the superposition of multiple single-frequency traveling wave waveforms, and N is the number of single-frequency traveling wave waveforms;

[0022] Step S32: Decompose the traveling wave sequence x[n] into M-layer wavelet packets and arrange them according to the frequency components to obtain 2 Mcoefficient matrices, where the jth coefficient matrix C j The corresponding frequency band is [(j-1)*f s / 2 M+1 ,j*f s / 2 M+1 ], where j = 1, 2, 3...2 M , M is the number of wavelet packet decomposition layers;

[0023] Step S33: Calculate the frequency band as [(j-1)*f s / 2 M+1 ,j*f s / 2 M+1 ] signal energy W j , the calculation formula is as follows:

[0024]

[0025] According to the above steps, the energy spectrum of the traveling wave waveform sequence x[n] arranged in each frequency band is obtained;

[0026] Step S34: According to the energy spectrum, take the maximum signal energy W in the energy spectrum jmax The frequency band is taken as the reference bandpass filter parameter, denoted as [f min ,f max ].

[0027] The beneficial effects of the present invention are as follows: (1) The present invention proposes a single-ended traveling wave positioning technology suitable for distribution network cable line scenarios, which can reduce the number of original device layouts by 50%, thereby improving the economy of engineering use; (2) The present invention solves the problem that the initial traveling wave and the reflected traveling wave are prone to overlap in short line scenarios, resulting in the inability to locate the fault point, and the fault point can be located based on the reference high-frequency signal; (3) The present invention proposes a large data sample library that can adapt to distribution network cable lines with different parameters, improve the cable fault positioning accuracy, and reduce the workload of cable fault troubleshooting.

[0028] Based on the above technical solution, the present invention can also be improved as follows.

[0029] Further, step S04 specifically includes the following steps:

[0030] Step S41: different simulation scenario variables are the precise location of the fault point, with the line exit point as the original starting point and 1m as the step length, and the scenarios where the fault point is located at 1m, 2m, 3m...(l-1)m are simulated in sequence, where l is the total length of the line;

[0031] Step S42: According to different fault point location scenarios, the initial traveling wave signal and the reflected traveling wave signal at each discharge point are obtained. The reflected waves corresponding to different locations are distributed differently on the time axis. The traveling wave signal data sets obtained from faults at different locations are used to form a reference waveform library.

[0032] Further, step S05 specifically includes the following steps:

[0033] Step S51: The traveling wave signal collected by the terminal is recorded as a traveling wave waveform sequence x[n], and the reference bandpass filter parameter [f min ,f max ] as the filtering parameter to obtain a new waveform sequence x[n]';

[0034] Step S52: Calculate the similarity between the new waveform sequence x[n]' and each simulation waveform data in the reference waveform library by a similarity algorithm to form a similarity array q = [q1, q2, q3 ... q n ];

[0035] Step S53: Take the maximum value q in the similarity array max As a result, the maximum value q in the reference waveform library max The fault position of the corresponding traveling wave is the distribution network cable fault location result. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of the present invention;

[0037] Figure 2 This is a typical distribution network cable line traveling wave device installation configuration diagram of the present invention;

[0038] Figure 3 This is a schematic diagram of the wave head extraction of the slow wave traveling wave signal of the present invention;

[0039] Figure 4 It is a simulation scene diagram of the present invention;

[0040] Figure 5 It is a schematic diagram of the simulated traveling wave waveform of the present invention;

[0041] Figure 6 The figure is a flow chart of the traversal method of the present invention. DETAILED DESCRIPTION

[0042] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0043] like Figure 1 to Figure 6 As shown, in embodiment 1, a method for locating a medium voltage distribution network cable line fault comprises the following steps:

[0044] Step S01: The terminal collects a traveling wave signal; the traveling wave current signal is a waveform signal containing rich frequency components; the terminal may be a distribution network cable traveling wave device;

[0045] Step S02: Filter out the medium frequency traveling wave signal and the high frequency traveling wave signal from the traveling wave signal, and enter step S03, the low frequency traveling wave signal in the traveling wave signal waits for the next traveling wave signal of the fault, and then repeats the determination;

[0046] Step S03: Decomposing the intermediate frequency traveling wave signal and the high frequency traveling wave signal using a multi-level wavelet packet, selecting a reference bandpass filter parameter to perform reference bandpass filtering, and generating a reference frequency traveling wave signal; the reference frequency traveling wave signal in the present invention is a filtered signal;

[0047] Step S04: constructing a line fault transient simulation model according to line parameters, and constructing a reference waveform library;

[0048] Step S05: traverse the reference frequency traveling wave signal in the reference waveform library;

[0049] Step S06: Output the distribution network cable fault location result according to the waveform traversal result.

[0050] (1) The present invention proposes a single-ended traveling wave positioning technology suitable for distribution network cable line scenarios, which can reduce the number of original device layouts by 50% and improve the economy of engineering use; (2) The present invention solves the problem that the initial traveling wave and the reflected traveling wave are prone to overlap in short line scenarios, resulting in the inability to locate the fault point, and the fault point can be located based on the reference high-frequency signal; (3) The present invention proposes a big data sample library that can adapt to distribution network cable lines with different parameters, improve the cable fault location accuracy, and reduce the workload of cable fault troubleshooting.

[0051] Step S03 specifically includes the following steps:

[0052] Step S31: record the traveling wave signal collected by the terminal as a traveling wave waveform sequence x[n], where n=1,2,3...N-1,N, and the sampling frequency is a known quantity f s , at this time, the signal is the superposition of multiple single-frequency traveling wave waveforms, and N is the number of single-frequency traveling wave waveforms;

[0053] Step S32: Decompose the traveling wave sequence x[n] into M-layer wavelet packets and arrange them according to the frequency components to obtain 2 M coefficient matrices, where the jth coefficient matrix C j The corresponding frequency band is [(j-1)*f s / 2 M+1 ,j*f s / 2 M+1 ], where j = 1, 2, 3...2 M , M is the number of wavelet packet decomposition layers;

[0054] Step S33: Calculate the frequency band as [(j-1)*f s / 2 M+1 ,j*fs / 2 M+1 ] signal energy W j , the calculation formula is as follows:

[0055]

[0056] According to the above steps, the energy spectrum of the traveling wave waveform sequence x[n] arranged in each frequency band is obtained;

[0057] Step S34: According to the energy spectrum, take the maximum signal energy W in the energy spectrum jmax The frequency band is taken as the reference bandpass filter parameter, denoted as [f min ,f max ].

[0058] Embodiment 2: This embodiment is a further improvement on the basis of embodiment 1, and its details are as follows:

[0059] Step S04 specifically includes the following steps:

[0060] Step S41: different simulation scenario variables are the precise location of the fault point, with the line exit point as the original starting point and 1m as the step length, and the scenarios where the fault point is located at 1m, 2m, 3m...(l-1)m are simulated in sequence, where l is the total length of the line;

[0061] Step S42: According to different locations of the fault point, the initial traveling wave signal and the reflected traveling wave signal at each discharge point are obtained (such as Figure 5 As shown in FIG. 1 , the reflected waves corresponding to different positions are distributed differently on the time axis. A reference waveform library is formed based on the traveling wave signal data sets obtained from faults at different positions.

[0062] The simulation of the real power system can be analyzed for multiple scenarios to obtain customized parameters for different scenarios. In view of the deficiency that the precise positioning accuracy of distribution network cable faults is affected by line parameters, the present invention builds a simulation model to simulate the traveling wave waveform signal under fault scenarios at different locations, and finally forms a waveform library for accurate fault positioning. After obtaining specific information such as line parameters and load parameters from the on-site operation and maintenance personnel of the line, the present invention builds a simulation model for distribution network cable lines with different line parameters to carry out simulation of the above scenarios.

[0063] Embodiment 3, this embodiment is a further improvement on the basis of embodiment 2, and its details are as follows:

[0064] Step S05 specifically includes the following steps:

[0065] Step S51: The traveling wave signal collected by the terminal is recorded as a traveling wave waveform sequence x[n], and the reference bandpass filter parameter [f min ,f max] as the filtering parameter to obtain a new waveform sequence x[n]';

[0066] Step S52: Calculate the similarity between the new waveform sequence x[n]' and each simulation waveform data in the reference waveform library by a similarity algorithm to form a similarity array q = [q1, q2, q3 ... q n ];

[0067] Step S53: Take the maximum value q in the similarity array max As a result, the maximum value q in the reference waveform library max The fault position of the corresponding traveling wave is the distribution network cable fault location result.

[0068] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for locating a medium voltage distribution network cable line fault, characterized in that: The steps include: Step S01: The terminal collects traveling wave signals; Step S02: Filter out the medium-frequency traveling wave signal and the high-frequency traveling wave signal from the traveling wave signal, and enter step S03, discard the low-frequency traveling wave signal in the traveling wave signal, wait for the next traveling wave signal of the fault, and repeat the determination; Step S03: Decomposing the intermediate frequency traveling wave signal and the high frequency traveling wave signal using a multi-level wavelet packet, selecting a reference bandpass filter parameter to perform reference bandpass filtering, and generating a reference frequency traveling wave signal; Step S04: constructing a line fault transient simulation model according to line parameters, and constructing a reference waveform library; Step S05: traversing the reference frequency traveling wave signal in the reference waveform library; Step S06: outputting the distribution network cable fault location result according to the waveform traversal result; The step S03 specifically includes the following steps: Step S31: Record the traveling wave signal collected by the terminal as a traveling wave waveform sequence ,in , the sampling frequency is a known quantity , at this time, the signal is the superposition of multiple single-frequency traveling wave waveforms, and is the number of single-frequency traveling wave waveforms; Step S32: Transform the traveling wave waveform sequence conduct The wavelet packet decomposition of the layer is arranged according to the frequency components to obtain coefficient matrix, where Coefficient matrix The corresponding frequency band is ,in , is the number of wavelet packet decomposition layers; Step S33: Calculate the frequency band The signal energy , the calculation formula is as follows: According to the above steps, an energy spectrum of the traveling wave waveform sequence arranged in each frequency band is obtained; Step S34: According to the energy spectrum, take the maximum signal energy in the energy spectrum The frequency band is taken as the reference bandpass filter parameter, denoted as .

2. A method for locating a medium voltage distribution network cable line fault according to claim 1, characterized in that: The step S04 specifically includes the following steps: Step S41: different simulation scenario variables are the precise location of the fault point, with the line exit station as the original starting point and 1m as the step length, and the simulation fault point is located at 1m, 2m, 3m... m scenario, where is the total length of the line; Step S42: According to different fault point location scenarios, the initial traveling wave signal and the reflected traveling wave signal at each discharge point are obtained. The reflected waves corresponding to different locations are distributed differently on the time axis. The traveling wave signal data sets obtained from faults at different locations are used to form a reference waveform library.

3. A method for locating a medium voltage distribution network cable line fault according to claim 2, characterized in that: The step S05 specifically includes the following steps: Step S51: The traveling wave signal collected by the terminal is recorded as a traveling wave waveform sequence , with reference bandpass filter parameters As the filtering parameter, we can get a new waveform sequence. ; Step S52: Calculate a new waveform sequence using a similarity algorithm The similarity with each simulation waveform data in the reference waveform library forms a similarity array ; Step S53: Take the maximum value in the similarity array As a result, the maximum value in the reference waveform library The fault position of the corresponding traveling wave is the distribution network cable fault location result.

Images