Power distribution network cable fault wave head identification and positioning method and system based on sheath traveling wave

Abstract

The invention relates to a power distribution network cable fault wave head identification and positioning method and system based on sheath traveling waves, and belongs to the field of power system relay protection. According to the invention, cable fault condition identification is carried out by adopting a sheath traveling wave analysis method. The method comprises the following steps: carrying out identification and fault positioning on a power distribution network cable fault wave head by combining time-frequency analysis with high-pass filtering based on traveling wave time-frequency characteristics of a cable sheath. Firstly, traveling wave measuring points are set at the head end and the tail end of a cable sheath, transient information of the head end and the tail end of the sheath during cable operation is recorded in real time, zero-sequence voltage is set as a fault judgment quantity during cable fault, high-frequency transient quantity information of the cable fault is extracted for high-pass filtering, namely interference variables such as noise and harmonic waves in traveling waves are removed, and the fault judgment quantity is calculated. For the traveling wave signal after filtering processing, each wave head information of the fault traveling wave is calibrated by adopting time-frequency analysis, fault positioning is performed through position information of a fault initial wave head and each catadioptric wave head, a criterion is formed for cable fault positioning, the criterion is simple and reliable, the coupling degree with an actual line is relatively good, and the selectivity and the sensitivity are relatively high.

Description

Technical Field

[0001] The invention relates to a method and system for identifying and locating a fault wave head of a distribution network cable based on the time-frequency characteristics of a sheath traveling wave, and belongs to the field of relay protection of power systems. Background Art

[0002] As the key focus of building a new power system, the urban distribution network has gradually replaced the traditional single-end power supply network with multiple power sources or mesh power supply networks to improve the power supply reliability of the distribution network system. Compared with overhead line construction, the urban distribution network adopts cable laying. The cable line in the distribution network has the advantages of long service life, relatively stable power transmission quality, and less external interference. Compared with overhead lines, it has the characteristics of beautifying the environment with less environmental transformation. For distribution network systems below 10kV voltage level, cable lines account for a large proportion in urban distribution network systems due to their advantages such as convenient laying, small operating circulation and beautification of the environment compared with overhead lines. When a fault occurs, the probability of cable failure is also high. Most of the faults in the distribution network system are cable faults, but the urban distribution network system often uses three-core cables for laying. When a fault occurs, the coupling between the three phases of the three-core cable increases, the distributed capacitance current increases, and the injected current is shunted. The signal attenuates rapidly, which makes detection and fault judgment difficult. However, due to the complexity of the cable line and the mutual coupling between the three phases, the capacitive current is large and the fault point is not easy to find. In particular, the distribution network cable line fault brings difficulties to the subsequent fault inspection and maintenance, which greatly affects the time for the fault line to recover. The reliability detection of the traveling wave and the correct calibration of the wave head information are the foundation of the cable fault traveling wave positioning. The data collected by the current traveling wave positioning device are the phase current values ​​of each circuit connected to the substation. By recording and analyzing the entire process of the current traveling wave during the fault period, different signal processing technologies are used to identify and mark the initial traveling wave and subsequent wave heads. However, compared with the initial traveling wave, the subsequent traveling wave is more severely attenuated, and it becomes more difficult to distinguish it from the interference wave, which makes the identification and calibration of the second wave head required in the single-ended positioning technology more challenging.

[0003] In order to improve power supply reliability and ensure safe and stable operation of the power grid, it is particularly important to study an efficient, accurate and reliable method for locating single-phase grounding faults in cables. Summary of the invention

[0004] The present invention aims to solve the above-mentioned technical problems of the prior art by providing a method and system for identifying and locating the fault wave head of a distribution network cable based on the time-frequency characteristics of the sheath traveling wave. The method can achieve accurate fault detection and reliable positioning.

[0005] The technical solution of the present invention is: a method for identifying and locating the fault wave head of a cable in a distribution network based on sheath traveling waves, comprising the following steps:

[0006] Step 1: Use the signal acquisition module to monitor the signal quantity at each location of the cable sheath in real time;

[0007] Step 2: Start according to the cable zero-sequence voltage;

[0008] Step 3: Use high-pass filtering to process the transient fault components of each cable sheath current;

[0009] Step 4: Use the time-frequency feature mining of traveling waves to analyze the filtered signal and calibrate the information of each wave head;

[0010] Step 5: Establish a fault location equation based on the calibrated wave head position information, and the optimal solution of the equation norm criterion is the cable fault location.

[0011] Furthermore, in Step 1, several measuring points are installed on each cable segment, and the sheath signal quantity of each cable segment is monitored in real time through a signal acquisition module.

[0012] Further, in Step 2, when the acquisition module detects the instantaneous value of the cable zero-sequence voltage u n (t) is greater than the set threshold, the fault location module starts immediately, where u n (t) is 1.15 per unit.

[0013] Furthermore, in the Step 3, the current components of each cable sheath after the fault are processed by high-pass filtering, and the high-frequency components are obtained by performing 1-mode transient filtering on them.

[0014] Furthermore, in Step 4, the high-frequency component is subjected to short-time fractional Fourier transform analysis using the time-frequency characteristics of the traveling wave, and the wave head information of each fault is calibrated according to the obtained time-frequency spectrum of the traveling wave energy.

[0015] The system used for the cable fault wave head identification and positioning method based on sheath traveling wave in distribution network comprises: a data acquisition module, which is used to collect the electrical quantity data of the cable line in real time and calculate the spatial modulus signal of the electrical quantity, that is, to calculate and collect the zero-sequence voltage and sheath current value of the cable;

[0016] A numerical calculation module is used to calculate the cumulative amount of the spatial modulus signal change of the electrical quantity of the sheath within a set time window to construct a fault detection signal;

[0017] The fault detection module continuously collects three consecutive fault detection signals to determine whether they are all greater than the set detection threshold. If not, it returns to continue collecting and calculating. If so, it is a fault on this line and a protection start signal is issued.

[0018] It also includes: a data preprocessing module for analyzing and processing the collected electrical quantities of the distribution network cables, reducing the amount of calculation in the system and saving time.

[0019] Furthermore, the data acquisition module specifically includes:

[0020] The cable current acquisition unit is used to collect the sheath current signal from the cable line;

[0021] The cable voltage acquisition unit is used to collect the zero-sequence voltage signal from the cable line;

[0022] The signal output unit is used to send the data collected by the data acquisition module to the next module unit.

[0023] Furthermore, the numerical calculation module specifically includes:

[0024] A signal receiving unit, used for receiving a signal from a data acquisition module;

[0025] A modulus change calculation unit is used to perform spatial modulus transformation on the data collected on the cable line, so as to obtain a zero modulus and a one modulus;

[0026] An integral calculation unit, used for performing integral calculation on the data obtained by the modulus transformation;

[0027] The signal output unit is used to send the data processed by the numerical calculation module to the next module.

[0028] Furthermore, the fault detection module specifically includes:

[0029] A signal receiving unit, used for receiving a signal sent from a numerical calculation module;

[0030] The logic comparison unit is used to compare the data sent by the numerical calculation module with the set detection threshold, and then determine whether the line is faulty and transmit the yes / no signal to the next unit;

[0031] The execution output unit is used to execute the signal from the logic comparison unit. If a "yes" signal is received, a protection signal is issued; if a "no" signal is received, the data acquisition module is returned to continue to collect real-time signals. The beneficial effects of the present invention are:

[0032] 1. The present invention can effectively overcome the problems of phase coupling and increased capacitive current when a grounding fault occurs in a cable, which leads to difficulty in positioning and difficulty in determining the fault point, and achieve correct positioning.

[0033] 2. The present invention uses time-frequency analysis to perform sheath traveling wave mining analysis when a distribution network cable line fails, providing a certain method for multi-branch line fault analysis, effectively saving troubleshooting time when a cable grounding fault occurs, and greatly improving the speed of power supply restoration for operation and maintenance personnel.

[0034] 3. The present invention processes the cable sheath current and zero-sequence voltage based on electromagnetic time inversion, effectively reduces the error, has a simple and reliable criterion, has high selectivity and sensitivity, and can accurately locate.

[0035] 4. The acquisition device analyzes the cable sheath signal. Different from the traditional cable core signal acquisition and analysis method, it effectively avoids the interference and noise caused by the three-phase coupling inside the three-core cable, reduces the calculation amount for the subsequent traveling wave signal time-frequency analysis, and greatly improves the fault location accuracy.

[0036] 5. The high-pass filter used in the present invention does not require a high test sampling rate and has a certain noise resistance capability.

[0037] 6. The present invention has carried out a large number of digital simulations, and the results show that the method is effective and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without carrying out creative work.

[0039] Figure 1 This is a topological diagram of a distribution network according to an embodiment of the present invention.

[0040] Figure 2 It is the algorithm flow chart of the present invention.

[0041] Figure 3 This is a high-pass filtering processing diagram of an embodiment of the present invention.

[0042] Figure 4 This is a time-frequency analysis fault wave head identification diagram of an embodiment of the present invention.

[0043] Figure 5 This is a diagram showing the arrival time of a traveling wave of the sheath current according to an embodiment of the present invention.

[0044] Figure 6 This is a traveling wave path analysis diagram of the sheath current at each measuring point of the line according to an embodiment of the present invention.

[0045] Figure 7 FIG. 4 is a diagram of a fault location system according to an embodiment of the present invention.

[0046] Figure 8 This is a diagram of a cable signal acquisition device according to an embodiment of the present invention.

[0047] Fig. 9 It is a system block diagram of the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] Example 1

[0050] The purpose of the present invention is to provide a method and system for identifying and locating the fault wave head of a distribution network cable based on the time-frequency characteristics of the sheath traveling wave, aiming to solve the problems of inaccurate fault location and difficulty in finding the fault point in the existing distribution network cable. The present invention first builds a distribution line model cable line in PSCAD with a sampling frequency of 10kHz. The fault line is a cable line. Measuring points are installed on the sheath at the beginning and end of each cable section. A total of 3 high-frequency CTs are arranged, the direction into the ground is positive, and the fault phase is selected as phase B. Permanent single-phase grounding faults are set at the main line, branch line, and end, respectively. The transition resistance is 10Ω and the fault angle is 90°. The specific steps include: Step 1: Real-time monitoring of the signal quantity at various locations on the cable through the signal acquisition module;

[0051] Step 2: Start according to the cable zero-sequence voltage;

[0052] Step 3: Use high-pass filtering to process the transient fault components of each cable sheath current;

[0053] Step 4: Analyze the filtered signal and calibrate the information of each wave head by mining the time-frequency characteristics of the sheath traveling wave; Step 5: Establish the fault location equation according to the calibrated wave head position information;

[0054] Step 1.1: Install several measuring points at each cable section, arrange high-frequency CT, with the direction of entering the ground as positive, and obtain the zero-sequence signal of each cable through the signal acquisition module;

[0055] Step 2.1: When the acquisition module detects the instantaneous value of the cable zero-sequence voltage u n (t) is greater than the set threshold, the fault location module starts immediately, where u n (t) is 1.15 per unit;

[0056] Step 3.1: Use high-pass filtering to process the sudden change of cable line sheath current before and after the fault. For the fault sheath traveling wave signal, the high-pass filter amplitude-frequency response expansion is:

[0057]

[0058] In the formula, D0 is the cutoff frequency of the filter, especially when D0=0, the square amplitude response of the denominator in the expression is zero at all levels, and |H(u,v)| can achieve the maximum value here, and the amplitude-frequency response characteristic is the flattest; D(u,v) is the turning frequency, when D0=D(u,v), the frequency attenuation is drastic; n is the system order. Therefore, the cutoff frequency and circuit transfer function of the high-pass filter are:

[0059]

[0060] In the formula, f c It is the cut-off frequency of the second-order filter, and its value depends on the resistance and capacitance of the positive and negative ends of the operational amplifier in the filter; H(s) is the transfer function of the Butterworth filter; H(s)2 is the transfer function of the Butterworth second-order filter; A max is the filter circuit gain coefficient, that is, the ratio of resistances; ω n is the natural frequency of the signal oscillation, which can be expanded into ω n =1 / R 2 C 2 ; ε is the damping coefficient, which is specifically expanded to ε=(3-A max ) / 2.

[0061] Step 3.2: Use the following formula to calculate the sheath current recorded by the acquisition module to obtain the 1-mode component, and use high-pass filtering to process it into a high-frequency component. The fault current relationship is:

[0062]

[0063] In the formula, It is the 1 mode component of sheath current when each cable fails; The acquisition module records the sheath current of each cable when it fails;

[0064] Step 4.1: In Step 4, the time-frequency characteristics of the sheath traveling wave are used to perform short-time fractional Fourier transform analysis on the high-frequency component, and the formula is expressed as follows:

[0065]

[0066] Where u is the fractional Fourier transform domain index; h α,σ (τ) is expressed by the Gaussian rotation window function, and its characteristics can be controlled by adjusting the parameters σ and α to control the width and rotation angle of the time window, so as to analyze and identify the multi-components of the sheath traveling wave signal in the time and frequency domain. At the same time, in order to ensure the analysis of the sheath traveling wave signal in complex scenes, the traveling wave signal has a better time-frequency focusing.

[0067] Step 4.2: Calibrate based on the initial wave head in the fault traveling wave head of each line in the cable network and the reflected wave at the fault point;

[0068] In Step 5.1: Based on the position information of the initial wave head of the sheath traveling wave and each refracted and reflected wave head, the fault location equation is established according to electromagnetic time inversion (EMTR) as follows: The maximum value of the change of the inverted current signal is analyzed by the formula.

[0069]

[0070] In the formula, x f The actual fault location.

[0071] In Step 5.2: When considering the actual cable network application, the fault waveform time is limited to T; therefore, the inversion waveform time is T; the maximum value of the fault current is i g (T). The criterion for determining the fault location by the norm of the inverted fault current waveform amplitude or signal energy is called the norm criterion. The specific expression is:

[0072] 1) Quantity criterion (2-norm criterion)

[0073]

[0074] In the formula, x fr is the real fault location; E is the guessed fault location x g The current i g (x g ,t) energy.

[0075] 2) Peak criterion (∞-norm)

[0076]

[0077] 3) Transfer function criterion (ρ HH -norm)

[0078]

[0079] In the formula, ρ HH It represents the forward current traveling wave transfer function H z The inverted current traveling wave transfer function H j The mutual correlation coefficient between them; σ is expressed as the square root of the energy of the fault current signal. Therefore, the norm criterion is

[0080]

[0081] In Step 5.2: the optimal solution of the equation norm criterion is the precise location of the cable fault; a fault location equation is established based on the position information of the initial wave head of the sheath traveling wave and each refraction and reflection wave head, and the optimal solution of the equation is the precise location of the cable fault; according to the optimal solution of the equation, it can be obtained that the fault occurs at 1570m, 392m away from the C11 transfer box, and the error range is ≤10m.

[0082] The system adopted by the cable fault wave head identification and positioning method of the distribution network cable based on sheath traveling wave includes: a data acquisition module, which is used to collect the electrical quantity data of the cable line in real time and calculate the spatial modulus signal of the electrical quantity, that is, calculate and collect the zero-sequence voltage and sheath current value of the cable;

[0083] A numerical calculation module is used to calculate the cumulative amount of the spatial modulus signal change of the electrical quantity of the sheath within a set time window to construct a fault detection signal;

[0084] The fault detection module continuously collects three consecutive fault detection signals to determine whether they are all greater than the set detection threshold. If not, it returns to continue collecting and calculating. If so, it is a fault on this line and sends a protection start signal.

[0085] The data preprocessing module is used to analyze and process the collected electrical quantities of the distribution network cables, reduce the amount of calculation in the system, and save time.

[0086] The data acquisition module specifically includes:

[0087] The cable current acquisition unit is used to collect the sheath current signal from the cable line;

[0088] The cable voltage acquisition unit is used to collect the zero-sequence voltage signal from the cable line;

[0089] The signal output unit is used to send the data collected by the data acquisition module to the next module unit.

[0090] The numerical calculation module specifically includes:

[0091] A signal receiving unit, used for receiving a signal from a data acquisition module;

[0092] A modulus change calculation unit is used to perform spatial modulus transformation on the data collected on the cable line, so as to obtain a zero modulus and a one modulus;

[0093] An integral calculation unit, used for performing integral calculation on the data obtained by the modulus transformation;

[0094] The signal output unit is used to send the data processed by the numerical calculation module to the next module.

[0095] The fault detection module specifically includes:

[0096] A signal receiving unit, used for receiving a signal sent from a numerical calculation module;

[0097] The logic comparison unit is used to compare the data sent by the numerical calculation module with the set detection threshold, and then determine whether the line is faulty and transmit the yes / no signal to the next unit;

[0098] The execution output unit is used to execute the signal from the logic comparison unit. If a "yes" signal is received, a protection signal is issued; if a "no" signal is received, it returns to the data acquisition module to continue collecting real-time signals.

Claims

1. A method for identifying and locating cable fault wave heads in a distribution network based on sheath traveling waves, characterized in that: Step 1: Use the signal acquisition module to monitor the signal quantity at each location of the cable sheath in real time; Step 2: Start according to the cable zero-sequence voltage; Step 3: Use high-pass filtering to process the transient fault component of each cable sheath current; Step 4: Use the time-frequency feature mining of traveling waves to analyze the filtered signal and calibrate the information of each wave head; Step 5: Establish a fault location equation based on the calibrated wave head position information, and the optimal solution of the equation norm criterion is the cable fault location.

2. The method for identifying and locating cable fault wave head in distribution network based on sheath traveling wave according to claim 1 is characterized in that: In the Step 1, several measuring points are installed on each cable segment, and the sheath signal quantity of each cable segment is monitored in real time through a signal acquisition module.

3. The method for identifying and locating cable fault wave head in distribution network based on sheath traveling wave according to claim 1 is characterized in that: In Step 2, when the acquisition module detects the instantaneous value of the cable zero-sequence voltage u n (t) is greater than the set threshold, the fault location module starts immediately, where u n (t) is 1.15 per unit.

4. The method for identifying and locating cable fault wave head in distribution network based on sheath traveling wave according to claim 1 is characterized in that: In the Step 3, the current components of each cable sheath after the fault are processed by high-pass filtering, and the high-frequency components are obtained by performing 1-mode transient filtering on the current components.

5. The method for identifying and locating cable fault wave head in distribution network based on sheath traveling wave according to claim 1 is characterized in that: In the Step 4, the high-frequency component is subjected to short-time fractional Fourier transform analysis and processing using the time-frequency characteristics of the traveling wave, and the wave head information of each fault is calibrated according to the obtained time-frequency spectrum of the traveling wave energy.

6. A system for the method for identifying and locating cable fault wave head based on sheath traveling wave in distribution network according to claim 1, characterized in that: include: The data acquisition module is used to collect the electrical quantity data of the cable line in real time and calculate the spatial modulus signal of the electrical quantity, that is, to calculate and collect the zero-sequence voltage and sheath current value of the cable; A numerical calculation module is used to calculate the cumulative amount of the spatial modulus signal change of the electrical quantity of the sheath within a set time window to construct a fault detection signal; The fault detection module continuously collects three consecutive fault detection signals to determine whether they are all greater than the set detection threshold. If not, it returns to continue collecting and calculating. If so, it is a fault on this line and a protection start signal is issued.

7. The system according to claim 6, characterized in that Also includes: The data preprocessing module is used to analyze and process the collected electrical quantities of the distribution network cables, reduce the amount of calculation in the system, and save time.

8. The system according to claim 6, characterized in that The data acquisition module specifically includes: The cable current acquisition unit is used to collect the sheath current signal from the cable line; The cable voltage acquisition unit is used to collect the zero-sequence voltage signal from the cable line; The signal output unit is used to send the data collected by the data acquisition module to the next module unit.

9. The system according to claim 6, characterized in that The numerical calculation module specifically includes: A signal receiving unit, used for receiving a signal from a data acquisition module; A modulus change calculation unit is used to perform spatial modulus transformation on the data collected on the cable line, so as to obtain a zero modulus and a one modulus; An integral calculation unit, used for performing integral calculation on the data obtained by the modulus transformation; The signal output unit is used to send the data processed by the numerical calculation module to the next module.

10. The system according to claim 6, characterized in that The fault detection module specifically includes: a signal receiving unit, which is used to receive a signal sent from the numerical calculation module; The logic comparison unit is used to compare the data sent by the numerical calculation module with the set detection threshold, and then determine whether the line is faulty and transmit the yes / no signal to the next unit; The execution output unit is used to execute the signal from the logic comparison unit. If a "yes" signal is received, a protection signal is issued; if a "no" signal is received, it returns to the data acquisition module to continue collecting real-time signals.

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