Cable line high-frequency signal identification method

Abstract

The invention relates to a cable line high-frequency signal identification method, and the method comprises the steps: building a cable line frequency change model in ATP-EMTP according to the actual structure parameters of a cable; according to the cable line frequency variation model, obtaining an amplitude attenuation law of the single-frequency signal in a cable line propagation process, and based on the law, obtaining a relation between a cable line attenuation coefficient and a signal frequency; obtaining a high-frequency signal of the current cable line, and obtaining an energy distribution diagram of the high-frequency signal by adopting wavelet transform; and identifying the high-frequency signals based on the energy distribution diagram and the relationship between the cable line attenuation coefficient and the signal frequency, wherein the high-frequency signals comprise a short-circuit fault signal, a fault lightning stroke, a non-fault lightning stroke, a circuit breaker operation signal and a partial discharge signal. The method can evaluate the operation state of the cable line according to the high-frequency signal of the cable line, and is of great significance to early warning the fault hidden danger of the cable line and improving the stable operation capability of a power system.

Description

Technical Field

[0001] The present invention relates to the technical field of signal recognition, and in particular to a method for recognizing high-frequency signals of a cable line. Background Art

[0002] When a cable line fails or is disturbed, high-frequency signals may appear on the line in addition to the power frequency signal. There are many types of high-frequency signals that may appear on the cable line, and the reasons for the generation of the signals are different.

[0003] For example: the length of transmission cables in urban power grids is getting longer and longer, and there are more and more short-circuit faults in cable lines, and most of the faults are single-phase short-circuit faults. When a short-circuit fault occurs in a cable line, a high-frequency fault signal can be detected on the line. When the insulation of the cable line ages or deteriorates, it may cause partial discharge in the cable insulation. At this time, a partial discharge signal will appear on the line. Cable lines are generally laid underground and are not directly affected by lightning signals. However, when the cable line is connected to the overhead line, the lightning signal may be transmitted to the cable line through the overhead line and affect the cable insulation. At this time, a high-frequency lightning signal can be detected on the cable line. The circuit breaker of the closed line will also generate a high-frequency transient signal on the line.

[0004] Different high-frequency signals cause different disasters and require different solutions. Therefore, there is an urgent need to provide a cable line high-frequency signal recognition method to identify the high-frequency signal. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for identifying high-frequency signals of a cable line.

[0006] To solve the above problems, the technical solution adopted by the present invention is:

[0007] A method for identifying high-frequency signals in a cable line, the method comprising:

[0008] According to the actual structural parameters of the cable, a frequency-variable model of 10KV cable line is established in ATP-EMTP;

[0009] According to the cable line frequency variation model, the attenuation law of the amplitude of a single frequency signal during the propagation of the cable line is obtained, and based on the law, the relationship between the cable line attenuation coefficient and the signal frequency is obtained;

[0010] Acquire a high-frequency signal of the current cable line, and use wavelet transform to obtain an energy distribution diagram of the high-frequency signal;

[0011] The high-frequency signal is identified based on the energy distribution diagram, the relationship between the cable line attenuation coefficient and the signal frequency, and the high-frequency signal includes a short-circuit fault signal, a fault lightning strike, a non-fault lightning strike, a circuit breaker operation signal and a partial discharge signal.

[0012] As an embodiment of the invention, the method further comprises:

[0013] According to the local discharge amount and local discharge energy characteristics of the partial discharge signal of the high-frequency signal, based on fuzzy evaluation theory, a multi-index comprehensive evaluation system for the operation status of the cable line is constructed.

[0014] Construct the time domain feature map of high-frequency signals.

[0015] As an implementation mode of the invention, the relationship between the cable line attenuation coefficient and the signal frequency is generated as follows:

[0016] Acquire the original voltage traveling wave signals of the head end, the end end and the midpoint, perform phase mode transformation on each of the original voltage traveling wave signals, and obtain the original line mode voltage traveling wave signals;

[0017] Generate the line mode voltage traveling wave amplitude attenuation constant at any frequency according to the original line mode voltage traveling wave signal;

[0018] Measuring the amplitudes of signal components of multiple different frequency components in the first wave header signal of different data window lengths corresponding to the original line mode voltage traveling wave signal;

[0019] The relationship between the amplitude attenuation constant and the amplitudes of the signal components of multiple different frequency components in the first wave header signal of different data window lengths is obtained.

[0020] As an implementation method of the invention, the following formula is used to generate the line mode voltage traveling wave amplitude attenuation constant at any frequency:

[0021]

[0022] Wherein, R and G are the line mode resistance and conductance of the line at frequency fn, respectively; j is an imaginary unit; L and C are the power frequency line mode inductance and capacitance of the line, respectively; and w is the corresponding angular frequency.

[0023] As an implementation mode of the invention, the method of obtaining the high frequency signal of the current cable line is as follows:

[0024] Get the additional fault component U under short-circuit fault state b Under the action of the fault current traveling wave and voltage traveling wave generated and propagating to both ends of the line are the high-frequency signals.

[0025] As an implementation mode of the invention, the method of obtaining the energy distribution diagram of the high-frequency signal by wavelet transform includes:

[0026] The high-frequency signal is passed through a low-pass filter and a high-pass filter in sequence, and their outputs represent the first-order approximate parameter A1 and detail parameter D1 respectively. The output signal with a bandwidth equal to half of the original signal can be downsampled;

[0027] The approximate parameters of the first-stage output are further filtered through low-pass filters and high-pass filters to obtain A2 and D2 and the approximate parameters and detail parameters of the next stage; in each wavelet decomposition process, the frequency resolution is doubled after filtering, and the time resolution is halved after downsampling;

[0028] The energy values ​​of the detail parameters are calculated after the signal is subjected to wavelet decomposition, and the energy distribution diagram is obtained according to a plurality of energy values.

[0029] As an implementation method of the invention, the wavelet energy E at any scale i Reconstruct the signal D at this scale i The sum of squares of (K):

[0030]

[0031] The beneficial effects of adopting the above technical solution are:

[0032] The cable line high-frequency signal identification method provided by the present invention can evaluate the operating status of the cable line according to the high-frequency signal of the cable line, which is of great significance for early warning of hidden faults of the cable line and improving the stable operation capability of the power system. The present invention studies the high-frequency signals that appear at a higher frequency when the cable line is running, and analyzes the generation mechanism of different types of high-frequency signals in the cable line. A 10kV cable line model and a cable line frequency variation model are established, the transmission characteristics of high-frequency signals in the cable line are studied, a feature recognition algorithm for high-frequency signals of the cable line is proposed, and a high-frequency signal feature recognition criterion is constructed. Finally, a high-frequency signal feature monitoring and fault warning mechanism for the cable line is established, and a cable line health status evaluation method is proposed, which helps managers and operation and maintenance personnel to grasp the operating status of the cable line in real time and ensure the reliable operation of the cable line. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a short circuit fault decomposition schematic diagram provided by an embodiment of the present invention.

[0034] Figure 2 This is another short circuit fault decomposition schematic diagram provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is clearly and completely described below in conjunction with specific embodiments.

[0036] An embodiment of the present invention provides a method for identifying a high-frequency signal of a cable line, the method comprising:

[0037] Step 1: Establish a 10KV cable line frequency-variable model in ATP-EMTP based on the actual cable structural parameters;

[0038] There are only 50Hz power frequency signals on the line. When the cable line is disturbed or fails, abundant high-frequency signals will be generated on the line. By establishing a 10kV cable line frequency variation model, the transmission characteristics of high-frequency signals in the cable line can be studied.

[0039] Step 2: obtaining the attenuation law of the amplitude of a single frequency signal during the propagation of the cable line according to the cable line frequency variation model, and obtaining the relationship between the cable line attenuation coefficient and the signal frequency based on the law;

[0040] This step includes:

[0041] Step S201, obtaining original voltage traveling wave signals at the head end, the end end and the midpoint, performing phase mode transformation on each of the original voltage traveling wave signals, and obtaining original line mode voltage traveling wave signals;

[0042] Step S202, generating a line mode voltage traveling wave amplitude attenuation constant at any frequency according to the original line mode voltage traveling wave signal;

[0043] Step S203, measuring the amplitudes of signal components of multiple different frequency components in the first wave header signal of different data window lengths corresponding to the original line mode voltage traveling wave signal;

[0044] Step S204: Obtain the relationship between the amplitude attenuation constant and the amplitudes of the signal components of multiple different frequency components in the first wave header signal of different data window lengths.

[0045] The following formula is used to generate the line mode voltage traveling wave amplitude attenuation constant at any frequency:

[0046]

[0047] Where R and G are the frequencies f n The line mode resistance and conductance of the lower line; j is an imaginary unit; L and C are the power frequency line mode inductance and capacitance of the line respectively; w is the corresponding angular frequency.

[0048] Step 3: Obtain the high-frequency signal of the current cable line, and use wavelet transform to obtain the energy distribution diagram of the high-frequency signal.

[0049] like Figure 1 and Figure 2As shown, E is the power supply, m is the busbar, when a short circuit grounding fault occurs in the single-ended power supply cable line at A, the fault state after the short circuit can be equivalent to Figure 2 A normal component U is shown a and a fault additional component U b Under the action of the fault component, a fault current traveling wave and a voltage traveling wave will be generated and propagate to both ends of the line, and a high-frequency fault signal can be detected on the cable line.

[0050] Therefore, in this step, the additional fault component U under the short-circuit fault state is obtained. b Under the action of the fault current traveling wave and voltage traveling wave generated and propagating to both ends of the line are the high-frequency signals.

[0051] In 1974, based on the research of Fourier transform, French engineer Morlet first proposed the method of using wavelet transform to process signals. After years of research, the method of using wavelet transform to process signals has become more mature. Fourier transform is one of the classic methods in signal processing. The traditional Fourier analysis method is suitable for processing stable signals, but it has limitations in analyzing non-stationary high-frequency signals on cable lines. Wavelet transform can simultaneously characterize the characteristic information of signals in the time domain and frequency domain, and is particularly suitable for processing non-stationary mutation signals such as high-frequency signals on cable lines.

[0052] In engineering, it is often necessary to use computers and other tools to analyze and process signals. Therefore, in the process of signal processing and analysis, continuous wavelet transform cannot be used directly. The signal needs to be discretized in advance to make it a discrete sequence value. The wavelet transform of the signal is equivalent to using high-pass and low-pass filters to process the signal, decomposing the original signal into two frequency bands: high-frequency component and low-frequency component. Repeat the above steps for the low-frequency part of the signal in the wavelet decomposition for further decomposition.

[0053] In a possible implementation, the method of using wavelet transform to obtain the energy distribution diagram of the high-frequency signal includes:

[0054] The high-frequency signal is passed through a low-pass filter and a high-pass filter in sequence, and their outputs represent the first-order approximate parameter A1 and detail parameter D1 respectively. The output signal with a bandwidth equal to half of the original signal can be downsampled;

[0055] The approximate parameters of the first-level output are further filtered through low-pass filters and high-pass filters to obtain A2 and D2. The same method can be used to obtain the approximate parameters and detail parameters of the next level. In each wavelet decomposition process, the frequency resolution is doubled after filtering, and the time resolution is halved after downsampling;

[0056] The energy value of the detail parameter calculated after the signal is subjected to wavelet decomposition, and the energy distribution diagram is obtained according to a plurality of energy values;

[0057] Among them, the wavelet energy E at any scale i Reconstruct the signal D at this scale i The sum of squares of (K):

[0058]

[0059] Step 4: Identify the high-frequency signal based on the energy distribution diagram, the relationship between the cable line attenuation coefficient and the signal frequency, wherein the high-frequency signal includes a short-circuit fault signal, a fault lightning strike, a non-fault lightning strike, a circuit breaker operation signal and a partial discharge signal.

[0060] Hereinafter, the present invention will respectively explain the formation mechanism of partial discharge signal, the formation mechanism of lightning strike signal and the formation mechanism of short circuit fault signal, so as to illustrate that the present invention can identify the high-frequency signal based on the relationship between the energy distribution diagram, the cable line attenuation coefficient and the signal frequency.

[0061] 1. Analysis of the formation mechanism of partial discharge signal

[0062] Partial discharge of cable lines refers to the discharge phenomenon that discharge occurs in some areas of the insulation of the cable line, but the insulation as a whole is not penetrated. Some small defects in the cable insulation layer during manufacturing, the influence of the environment during long-term operation, and the damage caused by human laying will cause insulation defects in the insulation layer. When the cable core is energized, the electric field at the cable insulation defect is distorted, and the average breakdown field strength at the good insulation is higher than the breakdown field strength at the defect, so partial discharge will first occur at the insulation defect. In the early stage of partial discharge, the partial discharge is relatively weak, and the insulation layer of the cable will not be immediately broken down by the partial discharge phenomenon, but the partial discharge phenomenon will further damage the insulation layer of the cable line, expanding the scope of the insulation defect area. As the number of partial discharges at the defect increases, the insulation of the cable line gradually deteriorates, and eventually the cable insulation is directly broken down and fails.

[0063] The partial discharge phenomenon of cable line insulation is mainly caused by the following reasons:

[0064] (1) Due to human factors such as improper installation and bumps during transportation, a certain metal component of the cable line is damaged, making its potential to the ground not zero. When the cable line is energized, a potential difference will be generated on this component. When the potential difference is greater than a certain potential, partial discharge will occur.

[0065] (2) When the cable is manufactured, there are residual bubbles or impurities in the insulation layer. Under the action of the electric field, the electric field strength at the well-insulated area is lower than the electric field strength at the air gap or bubble area. Therefore, the air gap or the area containing bubbles in the insulation layer will be broken down first.

[0066] (3) When the cable line is long, it is necessary to connect the cable lines through cable joints. If the cable joint production process is not precise, moisture will enter the cable joint on rainy or humid days. When the cable is energized, the moisture inside the cable joint causes uneven voltage distribution on different insulating medium surfaces, further causing electric field distortion and discharge in the joint.

[0067] 2. Analysis of the formation mechanism of lightning strike signals

[0068] Lightning overvoltage is an atmospheric overvoltage for power systems, which may cause insulation failure and power outages in power systems. In nature, lightning discharge will generate a downward linear negative lightning signal. When a lightning signal hits an overhead line, it can be seen as a process in which a lightning current wave with a high amplitude propagates along the channel to the overhead line, and the lightning high-frequency signal will propagate on the wire. If the overhead line is connected to a cable line, the lightning signal will be transmitted to the cable line through the wire, affecting the cable line. When the lightning current amplitude is large, the lightning signal transmitted to the cable line may damage the insulation of the cable line, causing insulation failure of the cable line.

[0069] 3. Analysis of the formation mechanism of short circuit fault signal

[0070] The operating environment of cables in power systems is somewhat complex. When the cable lines are in operation for a long time, insulation damage, aging, or mechanical damage caused by laying cables may cause short circuit failures in power cables. Short circuit failure refers to a failure caused by the insulation resistance at the fault point of the cable being less than the characteristic impedance of the cable itself, or even close to 0.

[0071] Step 5: According to the local discharge amount and local discharge energy characteristics of the partial discharge signal of the high-frequency signal and based on fuzzy evaluation theory, a multi-index comprehensive evaluation system for the operation status of the cable line is constructed.

[0072] The evaluation of the health status of the cable line first needs to determine the evaluation index of the health status of the cable. During the operation of the cable line, the partial discharge signal can reflect the insulation state and operation state of the cable line. The partial discharge amount is one of the important parameters of the partial discharge signal, which can quantitatively reflect the strength of the partial discharge signal, and then reflect the insulation state of the cable. The energy released by each partial discharge phenomenon is also closely related to the insulation state of the cable. Therefore, the present invention uses the partial discharge amount and the partial discharge energy as indicators for evaluating the state of the cable line. On this basis, combined with the on-site cable and cable well identification, the number of partial discharge signals occurring in the cable line and the average partial discharge value are introduced as evaluation indicators of the cable line operation status index, and at the same time, this is used as an opportunity to improve the on-site cable path map and the identification of the cable and cable well. There is a slow process for the cable insulation to change, and the trend of insulation degradation also has a certain impact on the operation state of the cable line, but there are few studies that consider the role of this factor. Therefore, the present invention also introduces the change in partial discharge amount, the average change in partial discharge, the change in the number of partial discharges, and the change in partial discharge energy as evaluation indicators of the cable operation state.

[0073] An evaluation system is established to warn of abnormal conditions based on the monitored data and analysis results. Combined with the improved cable and cable well identification on site, the status evaluation results of specific cable lines and line status warning information are given.

[0074] The cable line high-frequency signal identification method provided by the present invention can evaluate the operating status of the cable line according to the high-frequency signal of the cable line, which is of great significance for early warning of hidden faults of the cable line and improving the stable operation capability of the power system. The present invention studies the high-frequency signals that appear at a higher frequency when the cable line is running, and analyzes the generation mechanism of different types of high-frequency signals in the cable line. A 10kV cable line model and a cable line frequency variation model are established, the transmission characteristics of high-frequency signals in the cable line are studied, a feature recognition algorithm for high-frequency signals of the cable line is proposed, and a high-frequency signal feature recognition criterion is constructed. Finally, a high-frequency signal feature monitoring and fault warning mechanism for the cable line is established, and a cable line health status evaluation method is proposed, which helps managers and operation and maintenance personnel to grasp the operating status of the cable line in real time and ensure the reliable operation of the cable line.

Claims

1. A method for identifying high-frequency signals in a cable line, characterized in that: The method comprises: According to the actual structural parameters of the cable, a frequency-variable model of 10KV cable line is established in ATP-EMTP; According to the cable line frequency variation model, the attenuation law of the amplitude of a single frequency signal during the propagation of the cable line is obtained, and based on the law, the relationship between the cable line attenuation coefficient and the signal frequency is obtained; Acquire a high-frequency signal of the current cable line, and obtain an energy distribution diagram of the high-frequency signal by using wavelet transform; The high-frequency signal is identified based on the energy distribution diagram, the relationship between the cable line attenuation coefficient and the signal frequency, and the high-frequency signal includes a short-circuit fault signal, a fault lightning strike, a non-fault lightning strike, a circuit breaker operation signal and a partial discharge signal.

2. A cable line high frequency signal identification method according to claim 1, characterized in that: The method further comprises: According to the local discharge amount and local discharge energy characteristics of the partial discharge signal of the high-frequency signal, based on fuzzy evaluation theory, a multi-index comprehensive evaluation system for the operation status of the cable line is constructed.

3. A cable line high frequency signal identification method according to claim 1, characterized in that: The relationship between the cable line attenuation coefficient and the signal frequency is generated as follows: Acquire the original voltage traveling wave signals of the head end, the end end and the midpoint, perform phase mode transformation on each of the original voltage traveling wave signals, and obtain the original line mode voltage traveling wave signals; Generate the line mode voltage traveling wave amplitude attenuation constant at any frequency according to the original line mode voltage traveling wave signal; Measuring the amplitudes of signal components of multiple different frequency components in the first wave header signal of different data window lengths corresponding to the original line mode voltage traveling wave signal; The relationship between the amplitude attenuation constant and the amplitudes of the signal components of multiple different frequency components in the first wave header signal of different data window lengths is obtained.

4. A cable line high frequency signal identification method according to claim 3, characterized in that: The following formula is used to generate the line mode voltage traveling wave amplitude attenuation constant at any frequency: Where R and G are the frequencies f n The line mode resistance and conductance of the lower line; j is an imaginary unit; L and C are the power frequency line mode inductance and capacitance of the line respectively; w is the corresponding angular frequency.

5. A cable line high frequency signal identification method according to claim 1, characterized in that: The method of obtaining the high frequency signal of the current cable line is as follows: Get the additional fault component U under short-circuit fault state b Under the action of the fault current traveling wave and voltage traveling wave generated and propagating to both ends of the line are the high-frequency signals.

6. A cable line high frequency signal identification method according to claim 1, characterized in that: The method of using wavelet transform to obtain the energy distribution diagram of the high-frequency signal includes: The high-frequency signal is passed through a low-pass filter and a high-pass filter in sequence, and their outputs represent the first-order approximate parameter A1 and detail parameter D1 respectively. The output signal with a bandwidth equal to half of the original signal can be downsampled; The approximate parameters output from the first stage are further filtered through low-pass filters and high-pass filters to obtain A2 and D2, as well as the approximate parameters and detail parameters of the next stage; in each wavelet decomposition process, the frequency resolution is doubled after filtering, and the time resolution is halved after downsampling; The energy values ​​of the detail parameters are calculated after the signal is subjected to wavelet decomposition, and the energy distribution diagram is obtained according to a plurality of energy values.

7. A cable line high frequency signal identification method according to claim 6, characterized in that: Wavelet energy E at any scale i Reconstruct the signal D at this scale i The sum of squares of (K):

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