Method and device for calculating initial time point of power distribution cable fault arcing

Abstract

The application discloses a kind of power distribution cable fault arc initial time point calculation method and device, method includes the following steps: obtaining the single-phase ground fault recording data of distribution line, the single-phase ground fault recording data includes zero sequence voltage and zero sequence current data;By zero sequence voltage, determine fault starting and ending time point;Extract zero sequence current data between fault starting and ending time point, and carry out band-pass filtering processing;Two zero-crossing points of zero sequence current are 1 section;Data between 2 zero-crossing points are as 1 time arc extinguishing process, and are recorded as F (n);Calculate the waveform similarity coefficient ρ (n) between each section F (n) of filtered zero sequence current data;According to similarity coefficient ρ (n), judge specific starting time.The application can accurately judge the arc time of cable fault, provide reliable data for effective evaluation and early warning of the state of cable.

Description

Technical Field

[0001] This invention relates to a method and apparatus for calculating the initial time point of arcing in a power distribution cable fault, belonging to the field of power distribution line fault monitoring technology. Background Technology

[0002] The power cables used in 10-35kV distribution networks are all cross-linked polyethylene (XLPE) cables. During the breakdown process of XLPE dielectric insulation, tree discharge is particularly prominent. After the cable is energized, an electric field is formed at the interface. When the electric field strength reaches a certain value, micro-spark discharge occurs at the interface between the two organic insulation layers, producing a small amount of carbonized particles. These carbon particles are conductive, thus weakening the insulation performance of the organic insulation interface, reducing the interface breakdown voltage, and leading to the formation of an electric arc between the cable conductor and the ground, ultimately developing into a grounding fault. The deterioration and defect development of cables are statistically significant, with varying rates of development, but most have a certain development period. During this period, accurate detection of relevant parameters such as the time and intensity of arc discharge can provide data for effective assessment and early warning of the cable's condition.

[0003] The patent application No. 201210425483.0, entitled "High-resistance grounding fault detection method based on the intermittent judgment of zero-sequence current zero crossing point", proposes a method to determine the occurrence of high-resistance grounding fault by the time when the sampled value of the zero-sequence current is less than the threshold after the zero crossing point, but does not explain the applicability of arc grounding fault.

[0004] The patent application No. 202111580059.9, entitled "A Method and System for Predicting the Arcing Time of a Potential Powered Arc", proposes to obtain a potential powered arc image, preprocess the potential powered arc image, and perform multivariate fitting regression on the arcing time to obtain an arcing time regression model, and then perform a method for predicting the arcing time. This method is mainly for predicting arcing in enclosed spaces such as circuit breakers, and does not explain its applicability to open spaces or cable arcing.

[0005] Patent application number 202210885471.X, entitled "A Ground Fault Type Identification Method Based on Zero-Sequence Current Characteristic Curve", provides a method that constructs a zero-sequence current amplitude change trend function and uses curve fitting to identify the type of ground fault occurring in the power distribution line, especially tree-line faults. However, it does not specify the type of ground fault. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a method and apparatus for calculating the initial arcing time of a power distribution cable fault, which enables accurate calculation of the arcing time of the fault, thus providing a basis for effective assessment of the cable's condition.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: In a first aspect, the present invention provides a method for calculating the initial time point of arcing in a power distribution cable fault, comprising the following steps: Step 1: Obtain single-phase ground fault recording data of the power distribution line, wherein the single-phase ground fault recording data includes zero-sequence voltage and zero-sequence current data; Step 2: Determine the start and end times of the fault using the zero-sequence voltage; Step 3: Extract the zero-sequence current data between the start and end times of the fault and perform bandpass filtering. Step 4: The two zero-crossing points of the zero-sequence current are considered as one segment; the data between the two zero-crossing points is taken as one arc ignition and extinguishing process, denoted as F(n), n≥1, where n represents the nth arc ignition and extinguishing process; Step 5: Calculate the waveform similarity coefficient ρ(n) between each segment F(n) of the filtered zero-sequence current data: In the formula, i 01 i 02 These are the zero-sequence currents of two adjacent arc-ignition processes, with sampling start point k=1 as the initial time, k as the sampling sequence, and N as the data length. Step 6: Determine the specific start time based on the similarity coefficient ρ(n).

[0008] As one possible implementation of this embodiment, the starting point for determining the zero-sequence voltage is determined using three half-waves, with the first five cycles preceding the first half-wave as the starting point.

[0009] As one possible implementation of this embodiment, the zero-sequence voltage determination ends at the end time point, which is the end of three half-waves, and the third half-wave ends.

[0010] As one possible implementation of this embodiment, the bandpass filtering process involves using an FIR 9th-order bandpass filter with a passband frequency of 150Hz to 4000Hz to filter out DC, power frequency, and high-frequency data from the zero-sequence current data.

[0011] As one possible implementation of this embodiment, the calculation process for the zero-crossing point is as follows: Let A0 and A1 be the sampled values ​​of two sampling points adjacent to the zero point. The case where the sampling point exactly passes the zero point is regarded as a special case where one of A0 and A1 is zero. The zero-crossing point is determined based on the time relationship between the sampling point and the zero point: in, The interval between the zero-crossing point and the second sampling point is T, where T is the sampling interval time.

[0012] As one possible implementation of this embodiment, the step of determining the specific start time based on the similarity coefficient ρ(n) includes: If the similarity coefficient ρ(n) ≥ 0.6, denote ρ(n) = 1; if the similarity coefficient ρ(n) < 0.6, denote ρ(n) = 0. If P(n) = 1, P(n+1) = 0, and P(n+2) = 1, then F(n+1) is considered to be the initial time point of arc ignition. If P(n) = 0, P(n+1) = 1, and P(n+2) = 1, then F(n) is considered to be the initial time point of arc ignition. If P(n) = 1, P(n+1) = 1, and P(n+2) = 0, then F(n+2) is considered to be the initial time point of arc burning.

[0013] Secondly, an embodiment of the present invention provides a device for calculating the initial time point of arcing in a power distribution cable fault, comprising: The data acquisition module is used to acquire single-phase ground fault recording data of the power distribution line, wherein the single-phase ground fault recording data includes zero-sequence voltage and zero-sequence current data. The fault start and end time point determination module is used to determine the start and end time points of a fault by using the zero-sequence voltage. The bandpass filter processing module is used to extract zero-sequence current data between the start and end times of the fault and perform bandpass filtering processing. The arc ignition and extinction process determination module is used to define the segment between two zero-crossing points of the zero-sequence current; the data between the two zero-crossing points is taken as one arc ignition and extinction process, denoted as F(n), where n≥1, and n represents the nth arc ignition and extinction process; The similarity coefficient calculation module is used to calculate the waveform similarity coefficient ρ(n) between each segment F(n) of the filtered zero-sequence current data. In the formula, i 01 i 02 These are the zero-sequence currents of two adjacent arc-ignition processes, with sampling start point k=1 as the initial time, k as the sampling sequence, and N as the data length. The start time determination module is used to determine the specific start time based on the similarity coefficient ρ(n).

[0014] As one possible implementation of this embodiment, the starting point for judging the zero-sequence voltage is three half-waves, with the first half-wave being the five cycles before the first half-wave as the starting point; the ending point for judging the zero-sequence voltage is the end of three half-waves, with the third half-wave being the end point.

[0015] As one possible implementation of this embodiment, the bandpass filter processing module uses an FIR 9th order bandpass filter with a passband frequency of 150Hz to 4000Hz to filter out DC, power frequency and high frequency data in the zero-sequence current data.

[0016] As one possible implementation of this embodiment, the calculation process for the zero-crossing point is as follows: Let A0 and A1 be the sampled values ​​of two sampling points adjacent to the zero point. The case where the sampling point exactly passes the zero point is regarded as a special case where one of A0 and A1 is zero. The zero-crossing point is determined based on the time relationship between the sampling point and the zero point: in, The interval between the zero-crossing point and the second sampling point is T, where T is the sampling interval time.

[0017] As one possible implementation of this embodiment, the start time determination module is specifically used for: If the similarity coefficient ρ(n) ≥ 0.6, denote ρ(n) = 1; if the similarity coefficient ρ(n) < 0.6, denote ρ(n) = 0. If P(n) = 1, P(n+1) = 0, and P(n+2) = 1, then F(n+1) is considered to be the initial time point of arc ignition. If P(n) = 0, P(n+1) = 1, and P(n+2) = 1, then F(n) is considered to be the initial time point of arc ignition. If P(n) = 1, P(n+1) = 1, and P(n+2) = 0, then F(n+2) is considered to be the initial time point of arc burning.

[0018] The technical solutions of the embodiments of the present invention can have the following beneficial effects: The technical solution of this invention acquires fault recording data of power distribution cables and performs precise analysis and calculation of the fault initiation time and arcing time using zero-sequence voltage and zero-sequence current to obtain the accurate arcing time of the fault. This invention can accurately determine the arcing time of cable faults, providing reliable data for effective assessment and early warning of cable conditions. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating a method for calculating the initial time point of arcing in a power distribution cable fault, according to an exemplary embodiment. Figure 2 This is a schematic diagram of a device for calculating the initial time point of arcing in a power distribution cable fault, according to an exemplary embodiment. Figure 3This is a schematic diagram illustrating the relationship between sampling points and zero points in waveform data according to an exemplary embodiment. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments: To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings. The following disclosure provides many different embodiments or examples for implementing different structures of the invention. To simplify the disclosure of the invention, components and arrangements of specific examples are described below. Furthermore, reference numerals and / or letters may be repeated in different examples. This repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. It should be noted that the components illustrated in the drawings are not necessarily drawn to scale. Descriptions of well-known components, processing techniques, and processes are omitted in this invention to avoid unnecessarily limiting the invention.

[0021] like Figure 1 As shown in the figure, an embodiment of the present invention provides a method for calculating the initial time point of arcing in a power distribution cable fault, comprising the following steps: Step 1: Obtain single-phase ground fault recording data of the power distribution line. The single-phase ground fault recording data includes zero-sequence voltage and zero-sequence current data.

[0022] Step 2: Determine the start and end times of the fault using the zero-sequence voltage. The start time for determining the zero-sequence voltage is based on three half-waves, with the first five cycles preceding the first half-wave as the starting point. The end time for determining the zero-sequence voltage is the end of the third half-wave.

[0023] Step 3: Extract the zero-sequence current data between the start and end times of the fault and perform bandpass filtering. The bandpass filtering process uses an FIR 9th-order bandpass filter with a passband frequency of 150Hz to 4000Hz to filter out DC, power frequency, and high-frequency data from the zero-sequence current data, retaining the maximum energy portion of the arc.

[0024] Step 4: The two zero-crossing points of the zero-sequence current are considered as one segment; the data between the two zero-crossing points is taken as one arc ignition and extinguishing process, denoted as F(n), n≥1, where n represents the nth arc ignition and extinguishing process.

[0025] The calculation process for the zero-crossing point is as follows: like Figure 3 As shown, let the sampled values ​​of two sampling points adjacent to the zero-crossing point be A0 and A1, respectively. The zero-crossing point is determined based on the time relationship between the sampling point and the zero point: in, The interval between the zero-crossing point and the second sampling point is T, where T is the sampling interval time.

[0026] Where T = TL0 + TR0, TL0 is the time interval from sampling point A0 to the zero-crossing point, TR0 is the time interval from sampling point A1 to the zero-crossing point, and the sampling point is negative when it is below the zero axis and positive when it is above the zero axis.

[0027] If there is a sampling point that exactly crosses zero, it is considered a special case where one of A0 and A1 is zero.

[0028] Step 5: Calculate the waveform similarity coefficient ρ(n) between each segment F(n) of the filtered zero-sequence current data: In the formula, i 01 i 02 These are the zero-sequence currents of two adjacent arc-ignition processes, with sampling start point k=1 as the initial time, k as the sampling sequence, and N as the data length. The similarity coefficient ρ(n) reflects the similarity between two fixed waveforms i 01 (k) and i 02 The similarity of (k) is defined by its value in the interval [0,1]. When the two signal waveforms are completely similar, ρ(n) reaches its maximum value of 1; when they are completely dissimilar, it is 0.

[0029] Step 6: Determine the specific start time based on the similarity coefficient ρ(n).

[0030] The determination of the specific start time based on the similarity coefficient ρ(n) includes: If the similarity coefficient ρ(n) ≥ 0.6, we denote ρ(n) = 1; if the similarity coefficient ρ(n) < 0.6, we denote ρ(n) = 0. ρ(n) is the integer result of the similarity coefficient ρ(n). If P(n) = 1, P(n+1) = 0, and P(n+2) = 1, then F(n+1) is considered to be the initial time point of arc ignition. If P(n) = 0, P(n+1) = 1, and P(n+2) = 1, then F(n) is considered to be the initial time point of arc ignition. If P(n) = 1, P(n+1) = 1, and P(n+2) = 0, then F(n+2) is considered to be the initial time point of arc burning.

[0031] like Figure 2 As shown in the figure, an embodiment of the present invention provides a device for calculating the initial time point of arcing in a power distribution cable fault, comprising: The data acquisition module is used to acquire single-phase ground fault recording data of the power distribution line, wherein the single-phase ground fault recording data includes zero-sequence voltage and zero-sequence current data. The fault start and end time point determination module is used to determine the start and end time points of a fault by using the zero-sequence voltage. The bandpass filter processing module is used to extract zero-sequence current data between the start and end times of the fault and perform bandpass filtering processing. The arc ignition and extinction process determination module is used to define the segment between two zero-crossing points of the zero-sequence current; the data between the two zero-crossing points is taken as one arc ignition and extinction process, denoted as F(n), where n≥1, and n represents the nth arc ignition and extinction process; The similarity coefficient calculation module is used to calculate the waveform similarity coefficient ρ(n) between each segment F(n) of the filtered zero-sequence current data. In the formula, i 01 i 02 These are the zero-sequence currents of two adjacent arc-ignition processes, with sampling start point k=1 as the initial time, k as the sampling sequence, and N as the data length. The start time determination module is used to determine the specific start time based on the similarity coefficient ρ(n).

[0032] As one possible implementation of this embodiment, the starting point for judging the zero-sequence voltage is three half-waves, with the first half-wave being the five cycles before the first half-wave as the starting point; the ending point for judging the zero-sequence voltage is the end of three half-waves, with the third half-wave being the end point.

[0033] As one possible implementation of this embodiment, the bandpass filter processing module uses an FIR 9th order bandpass filter with a passband frequency of 150Hz to 4000Hz to filter out DC, power frequency and high frequency data in the zero-sequence current data, while retaining the maximum energy part of the arc.

[0034] As one possible implementation of this embodiment, the calculation process for the zero-crossing point is as follows: like Figure 3 As shown, let the sampled values ​​of the two sampling points adjacent to the zero-crossing point be A0 and A1, respectively. The zero-crossing point is determined based on the time relationship between the sampling point and the zero point: in, The interval between the zero-crossing point and the second sampling point is T, where T is the sampling interval time.

[0035] If there is a sampling point that exactly crosses zero, it is considered a special case where one of A0 and A1 is zero.

[0036] The similarity coefficient ρ(n) reflects the similarity between two fixed waveforms i 01 (k) and i 02The similarity of (k) is defined by its value in the interval [0,1]. When the two signal waveforms are completely similar, ρ(n) reaches its maximum value of 1; when they are completely dissimilar, it is 0.

[0037] As one possible implementation of this embodiment, the start time determination module is specifically used for: If the similarity coefficient ρ(n) ≥ 0.6, denote ρ(n) = 1; if the similarity coefficient ρ(n) < 0.6, denote ρ(n) = 0. If P(n) = 1, P(n+1) = 0, and P(n+2) = 1, then F(n+1) is considered to be the initial time point of arc ignition. If P(n) = 0, P(n+1) = 1, and P(n+2) = 1, then F(n) is considered to be the initial time point of arc ignition. If P(n) = 1, P(n+1) = 1, and P(n+2) = 0, then F(n+2) is considered to be the initial time point of arc burning.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for calculating the initial time point of arcing during a power distribution cable fault, characterized in that, Includes the following steps: Step 1: Obtain single-phase ground fault recording data of the power distribution line, wherein the single-phase ground fault recording data includes zero-sequence voltage and zero-sequence current data; Step 2: Determine the start and end times of the fault using the zero-sequence voltage; Step 3: Extract the zero-sequence current data between the start and end times of the fault and perform bandpass filtering. Step 4: The two zero-crossing points of the zero-sequence current are considered as one segment; the data between the two zero-crossing points is taken as one arc ignition and extinguishing process, denoted as F(n), n≥1, where n represents the nth arc ignition and extinguishing process; Step 5: Calculate the waveform similarity coefficient ρ(n) between each segment F(n) of the filtered zero-sequence current data: In the formula, i 01 i 02 These are the zero-sequence currents of two adjacent arc-ignition processes, with sampling start point k=1 as the initial time, k as the sampling sequence, and N as the data length. Step 6: Determine the specific start time based on the similarity coefficient ρ(n); The determination of the specific start time based on the similarity coefficient ρ(n) includes: If the similarity coefficient ρ(n) ≥ 0.6, then denote ρ(n) = 1; If the similarity coefficient ρ(n) < 0.6, denote ρ(n) = 0; If P(n) = 1, P(n+1) = 0, and P(n+2) = 1, then F(n+1) is considered to be the initial time point of arc ignition. If P(n) = 0, P(n+1) = 1, and P(n+2) = 1, then F(n) is considered to be the initial time point of arc ignition. If P(n) = 1, P(n+1) = 1, and P(n+2) = 0, then F(n+2) is considered to be the initial time point of arc burning.

2. The method for calculating the initial time point of arcing in a power distribution cable fault according to claim 1, characterized in that, The starting point for determining the zero-sequence voltage is determined using three half-waves, with the first five cycles preceding the first half-wave as the starting point.

3. The method for calculating the initial time point of arcing in a power distribution cable fault according to claim 1, characterized in that, The zero-sequence voltage determination ends at the end time point, which marks the end of three half-waves, with the third half-wave ending.

4. The method for calculating the initial time point of arcing in a power distribution cable fault according to claim 3, characterized in that, The bandpass filtering process involves using an FIR 9th-order bandpass filter with a passband frequency of 150Hz to 4000Hz to filter out DC, power frequency, and high-frequency data from the zero-sequence current data.

5. The method for calculating the initial time point of arcing in a power distribution cable fault according to claim 1, characterized in that, The calculation process for the zero-crossing point is as follows: Let A0 and A1 be the sampled values ​​of two sampling points adjacent to the zero point. The case where the sampling point exactly passes the zero point is regarded as a special case where one of A0 and A1 is zero. The zero-crossing point is determined based on the time relationship between the sampling point and the zero point: in, The interval between the zero-crossing point and the second sampling point is T, where T is the sampling interval time.

6. A device for calculating the initial time point of arcing in a power distribution cable fault, characterized in that, include: The data acquisition module is used to acquire single-phase ground fault recording data of the power distribution line, wherein the single-phase ground fault recording data includes zero-sequence voltage and zero-sequence current data. The fault start and end time point determination module is used to determine the start and end time points of a fault by using the zero-sequence voltage. The bandpass filter processing module is used to extract zero-sequence current data between the start and end times of the fault and perform bandpass filtering processing. The arc ignition and extinction process determination module is used to define the segment between two zero-crossing points of the zero-sequence current; the data between the two zero-crossing points is taken as one arc ignition and extinction process, denoted as F(n), where n≥1, and n represents the nth arc ignition and extinction process; The similarity coefficient calculation module is used to calculate the waveform similarity coefficient ρ(n) between each segment F(n) of the filtered zero-sequence current data. In the formula, i 01 i 02 These are the zero-sequence currents of two adjacent arc-ignition processes, with sampling start point k=1 as the initial time, k as the sampling sequence, and N as the data length. The start time determination module is used to determine the specific start time based on the similarity coefficient ρ(n); The start time determination module is specifically used for: If the similarity coefficient ρ(n) ≥ 0.6, denote ρ(n) = 1; if the similarity coefficient ρ(n) < 0.6, denote ρ(n) = 0. If P(n) = 1, P(n+1) = 0, and P(n+2) = 1, then F(n+1) is considered to be the initial time point of arc ignition. If P(n) = 0, P(n+1) = 1, and P(n+2) = 1, then F(n) is considered to be the initial time point of arc ignition. If P(n) = 1, P(n+1) = 1, and P(n+2) = 0, then F(n+2) is considered to be the initial time point of arc burning.

7. The calculation device for the initial time point of arcing in a power distribution cable fault according to claim 6, characterized in that, The starting point for determining the zero-sequence voltage is based on three half-waves, with the first five cycles preceding the first half-wave as the starting point; the ending point for determining the zero-sequence voltage is the end of the three half-waves, with the third half-wave being the end point.

8. The device for calculating the initial time point of arcing in a power distribution cable fault according to claim 6, characterized in that, The bandpass filter processing module uses an FIR 9th-order bandpass filter with a passband frequency of 150Hz to 4000Hz to filter out DC, power frequency and high frequency data in the zero-sequence current data.

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