CN112051517A - Single-phase earth fault line discrimination method based on zero-sequence fault component transient direction - Google Patents

Single-phase earth fault line discrimination method based on zero-sequence fault component transient direction Download PDF

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CN112051517A
CN112051517A CN202010896643.4A CN202010896643A CN112051517A CN 112051517 A CN112051517 A CN 112051517A CN 202010896643 A CN202010896643 A CN 202010896643A CN 112051517 A CN112051517 A CN 112051517A
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郭国伟
张开轩
陆志欣
刘鹏祥
徐欣慰
吴柏涛
李浩成
李箭
王崇康
王晓然
冯报端
陈锦彪
黄胜
马锋
黄林海
张璧辉
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Guangdong Power Grid Co Ltd
Foshan Power Supply Bureau of Guangdong Power Grid Corp
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Guangdong Power Grid Co Ltd
Foshan Power Supply Bureau of Guangdong Power Grid Corp
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Abstract

The invention provides a single-phase earth fault line distinguishing method based on zero sequence fault component transient direction, which solves the problem of poor accuracy and reliability of the existing small current earth single-phase fault line distinguishing method, firstly collects the zero sequence voltage of the small current earth system to be distinguished and the zero sequence current of each outlet wire, then wavelet transformation, denoising and inverse transformation reconstruction are carried out in sequence, the zero sequence current integral value of each outgoing line current is obtained, then the single-phase earth fault circuit is distinguished according to the positive and negative polarities of the zero sequence current, zero sequence data acquisition is carried out before the judgment, the interference of noise to the zero sequence fault component signal is removed through a denoising process, the accuracy of the reserved semaphore is ensured, the accuracy and the sensitivity of the single-phase earth fault line judgment are improved, the method has guiding significance for the subsequent work of workers, and does not need to specially install discrimination equipment.

Description

Single-phase earth fault line discrimination method based on zero-sequence fault component transient direction
Technical Field
The invention relates to the technical field of single-phase earth fault line judgment, in particular to a single-phase earth fault line judgment method based on a zero-sequence fault component transient direction.
Background
In the electric power system of 35kV and below in China, the mode of neutral point indirect grounding is commonly adopted, for the electric power system of the mode of neutral point grounding through a small resistor, the judgment is easier because the fault zero sequence current is larger, the judgment of the grounding fault circuit can be realized by using the common zero sequence protection, and for the electric power system of the mode of neutral point ungrounded and the mode of neutral point grounding through an arc suppression coil, the current flowing through the grounding point when the grounding fault occurs is small, so the electric power system is also called as a small current grounding system.
According to the fault statistics report of the power department, the probability of single-phase earth fault of the low-current earth system is very high, and the single-phase earth fault accounts for about 80% of the total number of the faults. For a power distribution network with a neutral point not grounded and a power distribution network grounded through an arc suppression coil, when a single-phase ground fault (also called a low-current ground fault) occurs, the fault detection has great technical difficulty due to small fault current and unobvious characteristics.
The currently adopted small current ground fault line distinguishing method mainly comprises a zero sequence current method, an injection signal method and a transient power direction method. The zero sequence current method judges the fault section by comparing the zero sequence current amplitude detected by the distribution automation terminal along the line, which has the advantages of simplicity and feasibility, but in the resonance grounding system, the resistance needs to generate the zero sequence current with enough magnitude in the neutral point input so as to ensure the detection sensitivity; chinese patent No. CN102288872A, 11/21/2011, discloses a single-phase earth fault location method for a low-current grounding system based on a signal injection method, in which a constant-frequency sinusoidal current signal is injected into a secondary side fault phase through a voltage transformer, a zero-sequence current transformer of each line is used to measure the injected signal current flowing through each line, and the line with the largest current amplitude is determined as a fault line, then the fault distance is further measured by a fixed distance measuring device without being influenced by the system structure and the operation mode, the technical scheme discloses a process for judging a single-phase earth fault line by injecting signals, but the technical scheme firstly needs to install signal injection equipment, secondly, before fault location, the reliability of the method for judging the fault line directly through the amplitude of the injected signal current of each line is influenced by the transition resistance and the intermittent arc; the transient power direction method firstly calculates the fault direction by using transient zero module sequence voltage and current, and then selects a fault section by comparing the fault direction measured by the distribution automation terminal.
Disclosure of Invention
In order to solve the problem that the existing small-current grounding single-phase fault line distinguishing method is poor in accuracy and reliability, the invention provides a single-phase grounding fault line distinguishing method based on a zero-sequence fault component transient direction, and accuracy and sensitivity of single-phase grounding fault line distinguishing are improved.
In order to achieve the technical effects, the technical scheme of the invention is as follows:
a single-phase earth fault line distinguishing method based on a zero-sequence fault component transient direction at least comprises the following steps:
s1, numbering each outgoing line in a small current grounding system to be judged in sequence, wherein the number is 1, k, n, n represents the total number of the outgoing lines, and k represents the number of the kth outgoing line;
s2, collecting zero sequence voltage data U of small current grounding system0And zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，In}，IkRepresenting the zero sequence current of the kth outgoing line;
s3, respectively aligning the collected zero sequence voltages U0And carrying out wavelet decomposition on the zero sequence current I of each outgoing line to obtain an approximate component a (k) and a detail component d after wavelet decompositioni(k) I represents the sequence index of the detail component of the ith layer after wavelet decomposition;
s4, according to the detail component di(k) Determining noise threshold lambda for each layeriFor the approximate component a (k) and detail component d after wavelet decompositioni(k) Denoising;
s5, denoising the approximate component a (k) and the detail component di(k) Performing wavelet inverse transformation reconstruction to obtain zero sequence voltage U of the denoised small current grounding system0bAnd zero sequence current I of each outgoing lineb＝{I1b，I2b，...，Ikb，...，Inb}；
S6, calculating a zero sequence current integral value of each outgoing line, sequencing the absolute values of the zero sequence current integral values of the outgoing lines in sequence from high to low, and determining the zero sequence currents of the outgoing lines with the three first-digit absolute value sequencing;
s7, determining the maximum value or the minimum value obtained by the zero sequence current of the outlet wire with the first three absolute values in the time t after the single-phase earth fault occurs, and respectively using the maximum value or the minimum value as a fault line judgment value Imaxx、ImaxyAnd Imaxz；
S8, judging Imaxx、ImaxyAnd ImaxzIf both are greater than the threshold value R, if yes, go to step S9; otherwise, reselecting the discrimination method to discriminate the single-phase earth fault line;
s9. if Imaxx、ImaxyAnd ImaxzAny one of ImaxxfThe positive and negative polarities of (A) are different from the other two, then ImaxxfThe corresponding line is a single-phase earth fault line, ImaxxfIs represented bymaxx、ImaxyAnd ImaxzAny one value of; if Imaxx、ImaxyAnd ImaxzThe positive and negative polarities of the single-phase grounding fault line are the same, and the single-phase grounding fault line is a bus.
Here, after wavelet decomposition, an approximation component a (k) and a detail component d are generatedi(k) The approximate component a (k) characterizes the low-frequency part information after wavelet decomposition, and the detail component di(k) Information of the high frequency part of the signal is characterized.
Preferably, the collected zero sequence voltage U0 satisfies: u0 is greater than UDZ, and the UDZ represents a protection setting voltage value; zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，InThe value of any one of them is the transient capacitance current IcAnd transient inductor current ILThe difference between the two; u shape0＞UDZThe single-phase earth fault line is judged before the single-phase earth fault line is cut off by relay protection, and guiding significance is provided for the subsequent work of workers; in addition, when a single-phase earth fault occurs in a low-current earth system, a fast-decaying transient capacitance current and a slow-decaying transient inductance current are generated at a fault point of a fault line. The amplitude of the zero-sequence fault transient current is mainly determined by the transient capacitance current, the compensation effect of the arc suppression coil is not obvious in the initial stage of the zero-sequence fault transient current, the positive and negative polarities of the transient current cannot be influenced, but the transient capacitance current of a small-current grounding system circuit is weakened to a certain extent.
Preferably, the collected zero sequence voltage data U of step S20And zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，InThe data of the power frequency cycle sampling points comprise data of 0.5 power frequency cycles before the single-phase earth fault, data of 1.5 power frequency cycles after the single-phase earth fault and data in the fault, each power frequency cycle samples 720 points, and the data with the frequency of 300-3000 Hz is used as calculation data.
When a single-phase earth fault occurs, the larger the transient capacitance current amplitude is, the shorter the duration is, and the frequency cycle is about 0.5-1.0; the smaller the amplitude of the transient inductance current is, the frequency is equal to the power frequency, the duration time can usually reach 2-3 power frequency cycles, meanwhile, in order to prevent the occurrence of a boundary effect, on the basis of considering the duration time of the transient inductance current, the acquisition strength of data volume is increased at the head and the tail (before and after a fault) of zero sequence data acquisition, and the influence on the steady-state characteristics of the circuit is eliminated by removing points which are acquired before and after the fault after subsequent noise elimination.
Preferably, the collected zero sequence voltages U are respectively subjected to wavelet pair by db60And zero sequence of each outgoing lineWavelet decomposition is carried out on the current I, and after wavelet decomposition, the approximate component a (k) and the detail component d of each outgoing line arei(k) Respectively satisfy the formula:
Figure BDA0002658659110000031
Figure BDA0002658659110000041
wherein i represents the sequence number of the wavelet ith layer detail component; n represents the total number of outgoing lines, and k represents the number of the kth outgoing line; h denotes a filter series, h0Is a low-pass filtering sequence; h is1For high-pass filtering sequence, i is 1,2, K, 6.
Preferably, step S4 is based on detail component di(k) Determining noise threshold lambda for each layeriThe formula of (1) is:
Figure BDA0002658659110000042
wherein λ isiA noise threshold representing an i-th layer detail component; mean (| d)i(k) |) represents averaging the absolute values of the i-th layer detail components; n is the number of elements of the ith layer of detail component sequence;
for the approximate component a and detail component d after wavelet decompositioni(k) The denoising method is one of a modular maximum reconstruction theory denoising method, a spatial domain denoising method and a soft threshold denoising method.
Here, according to detail component di(k) Determining noise threshold lambda for each layeriThe method makes full use of the variance information of the noise, and is more accurate than other threshold value selection methods.
Preferably, the approximate component a and the detail component d after wavelet decomposition are processedi(k) The process of denoising comprises the following steps: judging approximate component a and detail component d after wavelet decompositioni(k) Whether the wavelet coefficient of (a) is less than the noise threshold lambdaiIf yes, it is smallApproximate component a and detail component d after wave decompositioni(k) Setting the wavelet coefficient of (2) to zero; otherwise, the approximate component a and the detail component d after wavelet decomposition are retainedi(k) The wavelet coefficients of (a).
In the method, the useful zero sequence data has large amplitude and small number, and the wavelet coefficient corresponding to the noise has small amplitude, so that the threshold is set to satisfy the relationship, and the noise in the data can be effectively inhibited.
Preferably, the reconstruction process in step S5 satisfies the following formula:
Figure BDA0002658659110000043
wherein h represents a filter series, h0Is a low-pass filtering sequence; h is1For high-pass filtering sequence, i is 1,2, K, 6.
Preferably, the zero sequence current I for the kth of the outgoing lineskIntegrated value of (2):
Figure BDA0002658659110000051
wherein m represents the total number of sample points; j represents the j sampling point of the zero sequence current of the kth outgoing line; i.e. i0k.jFor j sampling point of the zero sequence current of the k outgoing linesRepresents a sampling period; j-1 represents the first sampling value of the zero sequence current of the k-th outgoing line after the fault.
Preferably, the time t after the occurrence of the single-phase ground fault in step S7 is 2 ms.
Preferably, when Imaxx、ImaxyAnd ImaxzAnd when any value is not greater than the threshold value R, reselecting the discrimination method to discriminate the single-phase earth fault line. When I ismaxx、ImaxyAnd ImaxzAre all greater than the threshold value R, they can be used to determine the polarity of each other.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
the invention provides a single-phase earth fault line distinguishing method based on a zero-sequence fault component transient direction, which comprises the steps of firstly collecting zero-sequence voltage of a small current earth system to be distinguished and zero-sequence current of each outgoing line, then carrying out wavelet transformation, denoising and inverse transformation reconstruction in sequence, obtaining a zero-sequence current integral value of each outgoing line current, distinguishing a single-phase earth fault line according to the positive and negative polarities of the zero-sequence current, carrying out zero-sequence data collection before distinguishing, removing the interference of noise on zero-sequence fault component signals through a denoising process, ensuring the accuracy of the reserved signal quantity, improving the distinguishing accuracy and sensitivity of the single-phase earth fault line, having guiding significance for the subsequent work of workers, and needing no special installation of distinguishing equipment.
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Fig. 1 shows a flow chart of a single-phase earth fault line discrimination method based on a zero-sequence fault component transient direction according to the present invention.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
for better illustration of the present embodiment, certain parts of the drawings may be omitted, enlarged or reduced, and do not represent actual dimensions;
it will be understood by those skilled in the art that certain well-known descriptions of the figures may be omitted.
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
Example 1
Fig. 1 shows a flowchart of a single-phase ground fault line discrimination method based on a transient direction of a zero-sequence fault component, and with reference to fig. 1, the method includes:
s1, numbering each outgoing line in a small current grounding system to be judged in sequence, wherein the number is 1, k, n, n represents the total number of the outgoing lines, and k represents the number of the kth outgoing line;
s2, collecting zero sequence voltage data U of small current grounding system0And zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，In}，IkRepresenting the zero sequence current of the kth outgoing line;
s3, respectively aligning the collected zero sequence voltages U0And carrying out wavelet decomposition on the zero sequence current I of each outgoing line to obtain an approximate component a (k) and a detail component d after wavelet decompositioni(k) I represents the sequence index of the detail component of the ith layer after wavelet decomposition;
s4, according to the detail component di(k) Determining noise threshold lambda for each layeriFor the approximate component a (k) and detail component d after wavelet decompositioni(k) Denoising;
s5, denoising the approximate component a (k) and the detail component di(k) Performing wavelet inverse transformation reconstruction to obtain zero sequence voltage U of the denoised small current grounding system0bAnd zero sequence current I of each outgoing lineb＝{I1b，I2b，...，Ikb，...，Inb}；
S6, calculating a zero sequence current integral value of each outgoing line, sequencing the absolute values of the zero sequence current integral values of the outgoing lines in sequence from high to low, and determining the zero sequence currents of the outgoing lines with the three first-digit absolute value sequencing;
s7, determining the maximum value or the minimum value obtained by the zero sequence current of the outlet wire with the first three absolute values in the time t after the single-phase earth fault occurs, and respectively using the maximum value or the minimum value as a fault line judgment value Imaxx、ImaxyAnd Imaxz(ii) a In the present embodiment, the time t is 2 ms;
s8, judging Imaxx、ImaxyAnd ImaxzIf both are greater than the threshold value R, if yes, go to step S9; otherwise, reselecting the discrimination method to discriminate the single-phase earth fault line;
s9. if Imaxx、ImaxyAnd ImaxzAny one of ImaxxfThe positive and negative polarities of (A) are different from the other two, then ImaxxfThe corresponding line is a single-phase earth fault line, ImaxxfIs represented bymaxx、ImaxyAnd ImaxzAny one value of; if Imaxx、ImaxyAnd ImaxzThe positive and negative polarities of the two are the same, then the single-phase earth fault lineThe way is a bus. When I ismaxx、ImaxyAnd ImaxzAnd when any value is not greater than the threshold value R, reselecting the discrimination method to discriminate the single-phase earth fault line. When I ismaxx、ImaxyAnd ImaxzAre all greater than the threshold value R, they can be used to determine the polarity of each other.
In this embodiment, the collected zero sequence voltage U0Satisfies the following conditions: u shape0＞UDZ，UDZIndicating a protection setting voltage value, and indicating zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，InThe value of any one of them is the transient capacitance current IcAnd transient inductor current ILDifference of U0＞UDZThe single-phase earth fault line is judged before the single-phase earth fault line is cut off by relay protection, and guiding significance is provided for the subsequent work of workers.
In this embodiment, the collected zero sequence voltage data U in step S20And zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，InThe data of the power frequency cycle sampling points comprise data of 0.5 power frequency cycles before the single-phase earth fault, data of 1.5 power frequency cycles after the single-phase earth fault and data in the fault, each power frequency cycle samples 720 points, and the data with the frequency of 300-3000 Hz is used as calculation data. When a single-phase earth fault occurs, the larger the transient capacitance current amplitude is, the shorter the duration is, and the frequency cycle is about 0.5-1.0; the smaller the amplitude of the transient inductive current is, the frequency is equal to the power frequency, the duration time can usually reach 2-3 power frequency cycles, meanwhile, in order to prevent the occurrence of a boundary effect, on the basis of considering the duration time of the transient current, the acquisition strength of data volume is increased at the head and the tail (before and after a fault) of zero sequence data acquisition, and the influence on the steady-state characteristics of the circuit is eliminated by removing points acquired before and after the fault after subsequent noise elimination.
In the embodiment, the collected zero sequence voltages U are respectively subjected to wavelet pair db60And performing wavelet decomposition on the zero sequence current I of each outgoing line, and performing wavelet decomposition on an approximate component a (k) and a detail component d of each outgoing line after the wavelet decompositioni(k) Are respectively full ofFoot formula:
Figure BDA0002658659110000071
Figure BDA0002658659110000072
wherein i represents the sequence number of the wavelet ith layer detail component; n represents the total number of outgoing lines, and k represents the number of the kth outgoing line; h denotes a filter series, h0Is a low-pass filtering sequence; h is1For high-pass filtering sequence, i is 1,2, K, 6. Step S4 according to detail component di(k) Determining noise threshold lambda for each layeriThe formula of (1) is:
Figure BDA0002658659110000073
wherein λ isiA noise threshold representing an i-th layer detail component; mean (| d)i(k) |) represents averaging the absolute values of the i-th layer detail components; n is the number of elements of the detail component sequence of the ith layer, and the method fully utilizes the variance information of the noise and is more accurate than other threshold value selection methods.
For the approximate component a and detail component d after wavelet decompositioni(k) The denoising method is one of a modular maximum reconstruction theory denoising method, a spatial domain denoising method and a soft threshold denoising method, and in this embodiment, the soft threshold denoising method is selected, so that wavelet coefficient oscillation can be avoided, and the continuity is good.
For the approximate component a and detail component d after wavelet decompositioni(k) The process of denoising comprises the following steps: judging approximate component a and detail component d after wavelet decompositioni(k) Whether the wavelet coefficient of (a) is less than the noise threshold lambdaiIf so, the approximate component a and detail component d after wavelet decompositioni(k) Setting the wavelet coefficient of (2) to zero; otherwise, the approximate component a and the detail component d after wavelet decomposition are retainedi(k) The wavelet coefficients of (a). Due to the useful zero sequenceThe data amplitude is large, the number is small, the wavelet coefficient amplitude corresponding to the noise is small, and the threshold is set to meet the relation, so that the noise in the data can be effectively inhibited.
In this embodiment, the reconstruction process in step S5 satisfies the following formula:
Figure BDA0002658659110000081
wherein h represents a filter series, h0Is a low-pass filtering sequence; h is1For high-pass filtering sequence, i is 1,2, K, 6.
For the zero sequence current I of the k-th outgoing line in each outgoing linekIntegrated value of (2):
Figure BDA0002658659110000082
wherein m represents the total number of sample points; j represents the j sampling point of the zero sequence current of the kth outgoing line; i.e. i0k.jFor j sampling point of the zero sequence current of the k outgoing linesRepresents a sampling period; j-1 represents the first sampling value of the zero sequence current of the k-th outgoing line after the fault.
The positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims (10)

1. A single-phase earth fault line distinguishing method based on a zero-sequence fault component transient direction is characterized by at least comprising the following steps:
s1, numbering each outgoing line in a small current grounding system to be judged in sequence, wherein the number is 1, k, n, n represents the total number of the outgoing lines, and k represents the number of the kth outgoing line;
s2, collecting zero sequence voltage data U of small current grounding system0And zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，In}，IkRepresenting the zero sequence current of the kth outgoing line;
s3, respectively aligning the collected zero sequence voltages U0And carrying out wavelet decomposition on the zero sequence current I of each outgoing line to obtain an approximate component a (k) and a detail component d after wavelet decompositioni(k) I represents the sequence index of the detail component of the ith layer after wavelet decomposition;
s4, according to the detail component di(k) Determining noise threshold lambda for each layeriFor the approximate component a (k) and detail component d after wavelet decompositioni(k) Denoising;
s5, denoising the approximate component a (k) and the detail component di(k) Performing wavelet inverse transformation reconstruction to obtain zero sequence voltage U of the denoised small current grounding system0bAnd zero sequence current I of each outgoing lineb＝{I1b，I2b，...，Ikb，...，Inb}；
S6, calculating a zero sequence current integral value of each outgoing line, sequencing the absolute values of the zero sequence current integral values of the outgoing lines in sequence from high to low, and determining the zero sequence currents of the outgoing lines with the three first-digit absolute value sequencing;
s7, determining the maximum value or the minimum value obtained by the zero sequence current of the outlet wire with the first three absolute values in the time t after the single-phase earth fault occurs, and respectively using the maximum value or the minimum value as a fault line judgment value Imaxx、ImaxyAnd Imaxz；
S8, judging Imaxx、ImaxyAnd ImaxzIf both are greater than the threshold value R, if yes, go to step S9; otherwise, reselecting the discrimination method to discriminate the single-phase earth fault line;
s9. if Imaxx、ImaxyAnd ImaxzAny one of ImaxxfThe positive and negative polarities of (A) are different from the other two, then ImaxxfThe corresponding line is a single-phase earth fault line, ImaxxfIs represented bymaxx、ImaxyAnd ImaxzAny one value of; if Imaxx、ImaxyAnd ImaxzThe positive and negative polarities of the single-phase grounding fault line are the same, and the single-phase grounding fault line is a bus.
2. The method for identifying a single-phase earth fault line based on a zero-sequence fault component transient direction as claimed in claim 1, wherein the collected zero-sequence voltage U is0Satisfies the following conditions: u shape0＞UDZ，UDZRepresenting a protection setting voltage value; zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，InThe value of any one of them is the transient capacitance current IcAnd transient inductor current ILThe difference between them.
3. The method for determining a single-phase earth fault line based on a zero-sequence fault component transient direction as claimed in claim 1, wherein the collected zero-sequence voltage data U of step S20And zero sequence current I ═ I of each outgoing line1，I2，...，Ik，...，InThe data of the power frequency cycle sampling points comprise data of 0.5 power frequency cycles before the single-phase earth fault, data of 1.5 power frequency cycles after the single-phase earth fault and data in the fault, each power frequency cycle samples 720 points, and the data with the frequency of 300-3000 Hz is used as calculation data.
4. The method for judging the single-phase earth fault line based on the transient direction of the zero-sequence fault component according to claim 1, wherein the collected zero-sequence voltage U is respectively measured by db6 wavelet0And performing wavelet decomposition on the zero sequence current I of each outgoing line, and performing wavelet decomposition on an approximate component a (k) and a detail component d of each outgoing line after the wavelet decompositioni(k) Respectively satisfy the formula:
Figure FDA0002658659100000021
Figure FDA0002658659100000022
wherein i represents the sequence number of the wavelet ith layer detail component; n represents the total number of outgoing lines, and k represents the number of the kth outgoing line; h denotes a filter series, h0Is a low-pass filtering sequence; h is1For high-pass filtering sequence, i is 1,2, K, 6.
5. The method for determining a single-phase earth fault line based on a zero-sequence fault component transient direction as claimed in claim 4, wherein step S4 is performed according to detail component di(k) Determining noise threshold lambda for each layeriThe formula of (1) is:
Figure FDA0002658659100000023
wherein λ isiA noise threshold representing an i-th layer detail component; mean (| d)i(k) |) represents averaging the absolute values of the i-th layer detail components; n is the number of elements of the ith layer of detail component sequence;
for the approximate component a and detail component d after wavelet decompositioni(k) The denoising method is one of a modular maximum reconstruction theory denoising method, a spatial domain denoising method and a soft threshold denoising method.
6. The method for judging the single-phase earth fault line based on the transient direction of the zero-sequence fault component according to claim 5, wherein the approximate component a and the detail component d after wavelet decomposition are usedi(k) The process of denoising comprises the following steps: judging approximate component a and detail component d after wavelet decompositioni(k) Whether the wavelet coefficient of (a) is less than the noise threshold lambdaiIf so, the approximate component a and detail component d after wavelet decompositioni(k) Setting the wavelet coefficient of (2) to zero;otherwise, the approximate component a and the detail component d after wavelet decomposition are retainedi(k) The wavelet coefficients of (a).
7. The method for determining a single-phase earth fault line based on a zero-sequence fault component transient direction as claimed in claim 6, wherein the reconstruction process in step S5 satisfies the following formula:
Figure FDA0002658659100000031
wherein h represents a filter series, h0Is a low-pass filtering sequence; h is1For high-pass filtering sequence, i is 1,2, K, 6.
8. The single-phase earth fault line distinguishing method based on zero-sequence fault component transient direction of claim 1, wherein zero-sequence current I for k-th outgoing line of each outgoing linekIntegrated value of (2):
Figure FDA0002658659100000032
wherein m represents the total number of sample points; j represents the j sampling point of the zero sequence current of the kth outgoing line; i.e. i0k.jFor j sampling point of the zero sequence current of the k outgoing linesRepresents a sampling period; j-1 represents the first sampling value of the zero sequence current of the k-th outgoing line after the fault.
9. The method according to claim 8, wherein the time t after the occurrence of the single-phase earth fault in step S7 is 2 ms.
10. The method according to claim 9, wherein the method for determining the single-phase earth fault line based on the transient direction of the zero-sequence fault component is characterized in that when I is measuredmaxx、ImaxyAnd ImaxzAnd when any value is not greater than the threshold value R, reselecting the discrimination method to discriminate the single-phase earth fault line.
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