A method for lightning strike disconnection warning of medium-voltage insulated lines

Abstract

The present invention discloses a medium-voltage insulated line lightning disconnection early warning method, comprising: S1: let i = 1, calculate the total number K of disturbance time periods of an overvoltage record, if K < 3, determine that no lightning-induced disconnection will occur, otherwise execute S2; S2: if i > K-2, determine that there is no possibility of subsequent lightning-induced disconnection, otherwise execute S3; S3: determine whether the i-th disturbance is an induced lightning overvoltage, if not, let i = i + 1, return to S2, otherwise, issue an "induced lightning overvoltage alarm" message, and execute S4; S4: Determine whether #imgabs0# is true. If not, set i=i+1 and return to S2. Otherwise, issue a "flashover alarm" message and continue to execute S5; S5: Determine whether the i+1th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue an "arc grounding overvoltage alarm" and execute S6; S6: Determine whether the i+2th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue a "lightning strike line break warning".

Description

Technical Field

[0001] The present invention relates to the field of lightning strikes on power distribution lines in power systems, and in particular to a method for early warning of lightning-strike disconnection of medium-voltage insulated lines. Background Art

[0002] my country is a vast country with extensive distribution lines. As the "last mile" of power transmission from the power system to users, their safe operation is crucial to residents' happiness with electricity. The use of insulation in distribution lines is accelerating in my country. While the use of insulation offers many advantages, such as corrosion resistance and protection against electric shock, its large-scale application also presents some challenges.

[0003] Medium-voltage lines generally have low insulation levels, making them highly susceptible to lightning strikes, especially induced lightning. High-amplitude induced lightning can penetrate the conductor insulation, creating a pinhole. The subsequent power-frequency arc, blocked by the insulation, can then continue to burn the pinhole. Ultimately, the arc's thermal and mechanical effects can cause a lightning-induced line break, leading to numerous adverse consequences. These include threats to the safety of nearby residents and disrupted power supply balance due to phase loss.

[0004] Therefore, timely warnings before lightning strikes and power outages will alert power grid workers, allowing them to prepare for possible accidents, invest in repairs earlier, and improve the reliability of electricity supply to residents. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a medium-voltage insulated line lightning break warning method. When distinguishing various overvoltage types, this method uses a threshold method and constructs multi-level support vector machines SVMA and SVMB to make the determined overvoltage type more accurate. By successively judging the overvoltage type of each stage, it is finally determined whether it can cause lightning break, and the false alarm probability is low.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for warning of medium-voltage insulated line disconnection caused by lightning strike is provided, the method being based on overvoltage records collected by a system and comprising the following steps:

[0008] S1: Let i = 1, calculate the total number of disturbance time periods K of an overvoltage record. If K < 3, then end and confirm that the overvoltage record will not cause lightning strike disconnection. Otherwise, continue to S2;

[0009] S2: If i>K-2, then end and confirm that the overvoltage record has no possibility of causing lightning strike and disconnection in the future. Otherwise, continue to S3;

[0010] S3: Determine whether the i-th disturbance is an induced lightning overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue an "induced lightning overvoltage alarm" message and continue to execute S4.

[0011] S4: Judgment Is it true? If not, set i=i+1 and return to S2; otherwise, issue a "flashover alarm" message and continue to execute S5;

[0012] S5: Determine whether the i+1th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue an "arc grounding overvoltage alarm" message and continue to execute S6.

[0013] S6: Determine whether the i+2th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue a "lightning break warning" message, where i represents the disturbance number. Indicates the three-phase minimum effective value of the single-phase-to-ground flashover overvoltage, U 阈值 Indicates the set threshold.

[0014] Furthermore, in S1 , the wavelet sliding window energy is used to calculate the disturbance start time and end time, thereby determining the disturbance time period.

[0015] Furthermore, the threshold method and support vector machine are used to determine the overvoltage type corresponding to the disturbances in S3, S5 and S6.

[0016] Furthermore, the threshold method and support vector machine are used to determine the overvoltage types corresponding to the disturbances in S3, S5 and S6, including:

[0017] S11: Divide the disturbance time period into the period before the disturbance t 12 , disturbance t 23 , after disturbance t 34 ;

[0018] S12: Extracting the characteristic value U of the overvoltage corresponding to the disturbance 12rmsmax 、U 34rmsmax 、S mean , K, α max 、E qianwu 、E houer ,λ;

[0019] S13: Judge U 12rmsmax 12rmsmax阈值 Is it true? If so, it is determined that the overvoltage is an air-to-close overvoltage, and the process ends; if not, executing S14;

[0020] S14: Judge U 34rmsmax 34rmsmax阈值 ​​Is it true? If so, it is determined that the overvoltage is an overvoltage of the switching transformer, and the process ends. If not, the process proceeds to S15.

[0021] S15: The feature quantity S mean and K are input into a first support vector machine SVMA to distinguish whether the overvoltage type corresponding to the disturbance is a first overvoltage type or a second overvoltage type, wherein the first overvoltage type includes an induced lightning or an isolated light grounding overvoltage, and the second overvoltage type includes a closed capacitor bank, a closed no-load line, or a direct lightning overvoltage;

[0022] S16: The feature value α max 、E qianwu 、E houer and λ are input into the second support vector machine SVMB to distinguish the overvoltage type corresponding to the disturbance, induced lightning or isolated light grounding overvoltage, where U 12rmsmax Indicates t 12 The maximum effective value of the three-phase voltage during the time period, U 12rmsmax阈值 The set t 12 The maximum effective value threshold of the three-phase voltage within the time period, U 34rmsmax Indicates t 34 The maximum effective value of the three-phase voltage during the time period, U 34rmsmax阈值 The set t 34 The maximum effective value threshold of the three-phase voltage within the time period, S mean represents the average value of the three-phase waveform similarity, K represents the line mode and zero mode voltage ratio of the overvoltage, α max Indicates the overvoltage steepness, E qianwu It represents the sum of detail energy of the first five levels of wavelet transform, E houer It represents the sum of detail energy of the two scales after wavelet transform, and λ is E houer With E qianwu The ratio.

[0023] Furthermore, U 12rmsmax阈值 and U 34rmsmax阈值 Both are set to 0.2.

[0024] Furthermore, in S4, U 阈值 Set to 0.1.

[0025] The beneficial effects of the present invention are:

[0026] The proposed early warning method, based on the developmental stages of lightning-induced line failure ("induced lightning - flashover - arcing"), is practical. Because it sequentially identifies the overvoltage type at each stage, it offers a low false alarm rate and high accuracy. It can issue early warnings before a line failure occurs, enabling maintenance personnel to act quickly.

[0027] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which:

[0029] Figure 1 A schematic flow chart of a lightning strike line breakage early warning method;

[0030] Figure 2 Partition diagram for disturbance time period;

[0031] Figure 3 It is the flow chart for overvoltage identification;

[0032] Figure 4 is the waveform of induced lightning overvoltage;

[0033] Figure 5 The diagram of the start and end time of the sliding window energy of phase A;

[0034] Figure 6 is the starting and ending time diagram corresponding to the sum of the wavelet detail components of phase A;

[0035] Figure 7 is the induced lightning overvoltage energy distribution;

[0036] Figure 8 The arc grounding overvoltage energy distribution. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the preferred embodiments are only for illustrating the present invention, and are not intended to limit the scope of protection of the present invention.

[0038] This application proposes a lightning-induced disconnection warning method for medium-voltage insulated lines. This method sequentially determines the overvoltage type at each stage, resulting in a low false alarm rate and high accuracy. It can issue warning information in time before the line breaks, allowing maintenance personnel to take prompt action.

[0039] Figure 1 It is a schematic flow chart of the lightning strike line break warning method.

[0040] Since lightning-induced line breakage is caused by three stages, namely "induced lightning-flashover-arc", combined with Figure 1 The method is based on the overvoltage records collected by the system and includes the following steps:

[0041] S1: Let i = 1 (i represents the disturbance sequence number), calculate the total number of disturbance time periods K of an overvoltage record. If K < 3, then end and determine that the overvoltage record will not cause a lightning break (that is, when the total number of disturbances in the disturbance time period is less than 3, it is insufficient to form an arc, which means that the overvoltage record will not cause cumulative breakage). Otherwise, continue to S2;

[0042] S2: If i>K-2, then end and confirm that the overvoltage record has no possibility of causing lightning strike and disconnection in the future. Otherwise, continue to S3;

[0043] S3: Determine whether the i-th disturbance is an induced lightning overvoltage. If not, continue to determine the next disturbance, i.e., set i=i+1, and return to S2. Otherwise, if the i-th disturbance is determined to be an induced lightning overvoltage, issue an "induced lightning overvoltage alarm" message, and continue to execute S4.

[0044] S4: Judgment Is it established? If not, set i=i+1 and return to S2. Otherwise, issue a "flashover alarm" message and continue to execute S5.

[0045] S5: Determine whether the i+1th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue an "arc grounding overvoltage alarm" message and continue to execute S6.

[0046] S6: Determine whether the i+2th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue a "lightning break warning" message. Where i represents the disturbance number. Indicates the three-phase minimum effective value of the single-phase-to-ground flashover overvoltage, U 阈值 Indicates the set threshold.

[0047] In some embodiments, step S1 can use wavelet sliding window energy to calculate the disturbance start and end times, thereby determining the disturbance time period. The following example uses 462 waveforms with a sampling frequency of 200 kHz and a sampling time of 100 ms to illustrate the wavelet sliding window energy calculation steps and the accuracy of overvoltage identification.

[0048] Among them, the calculation formula of wavelet sliding window energy is:

[0049]

[0050] In formula (1), k represents the signal sampling point number, d j It is the detail component from the 1st layer to the 7th layer after wavelet transform, which basically covers the frequency distribution of the overvoltage signal. Its frequency band range is shown in Table 1 below. wis the size of the wavelet window, which can be optionally 50, k = 1, 2, …, N - N w + 1, where N is the total number of signal sampling points and can be taken as 20000. Since the frequency distribution range of ferroresonance overvoltage is mainly within 1 / 2 power frequency to 3 times power frequency, its E(k) value is small, and ferroresonance overvoltage can be avoided from being statistically counted after the following calculation steps.

[0051] Table 1 Frequency band ranges corresponding to decomposed signals of each layer

[0052]

[0053]

[0054] The specific steps to determine the start and end times of disturbances using wavelet sliding window energy can include:

[0055] 1): Calculate the maximum and minimum values of the sliding window energy of each undisturbed waveform and ferroresonance overvoltage according to Equation (1), and statistically count the distribution range [E1, E2] of the sliding window energy during normal system operation and resonance, then execute 2);

[0056] 2): If the maximum value of the overvoltage sliding window energy in 1) is greater than E2, then continue to execute 3) and let k = 1, otherwise go to 5);

[0057] 3): Judge whether k < N - N w - 4 holds. If k < N - Nw - 4 does not hold, then go to 5). If k < N - Nw - 4 holds, then calculate Equation (2) and further judge whether △E max (k) ≥ △E 阈值 holds. If △E max (k) ≥ △E 阈值 does not hold, let k = k + 1 and go to 3). If △E max (k) ≥ △E 阈值 holds, then let k1 = k and go to 4);

[0058] △E max (k) = max{E(k + 5), E(k + 4),..., E(k + 1)} - E(k) (2)

[0059] 4): Let k = k + 1 and judge whether k < N - N w + 1 holds. If k < N - N w + 1 does not hold, then go to 5). If k < N - N w + 1 holds, then judge whether E(k) < E2 holds. If E(k) < E2 holds, then let k2 = k, determine the sampling points corresponding to the disturbance time period as [k1, k2], and go to 3) to continue calculating the next disturbance time period. If E(k) < E2 does not hold, then go to 4);

[0060] 5): Count the total number of all disturbance time periods K.

[0061] After calculation, △E 阈值 The value of is taken as 0.0012, and the distribution range of the sliding window energy when the system is operating normally and resonance occurs is [0.01, 0.5]. Figure 4 The waveform of the induced lightning overvoltage is shown below. Figure 4 The waveform shown in is used as an example to verify the effectiveness of the above steps. Among them, the disturbance start sampling point and end sampling point obtained after performing the above steps on phase A are as follows: Figure 5 As shown, the starting sampling point and the ending sampling point corresponding to the sum of the actual wavelet detail components are as follows Figure 6 The comparison between the two is shown in Table 2.

[0062] Table 2 Figure 5 and Figure 6 Corresponding start and end timetable

[0063]

[0064] From the results in Table 2, it can be seen that the start and end times of the disturbance of phase A determined by using the wavelet sliding window energy are not much different from the start and end times corresponding to the sum of the actual wavelet detail components. Therefore, the wavelet sliding window energy can be used to determine the disturbance time period.

[0065] In some embodiments, the threshold method and support vector machine can be used to determine the overvoltage type corresponding to the disturbances in S3, S5 and S6. First, a disturbance time period can be divided into the period before the disturbance t 12 , disturbance t 23 , after disturbance t 34 ,like Figure 2 Then extract the overvoltage characteristic quantity U in each interruption time period rms 、S mean , K, α max 、E qianwu 、E houer , λ, and finally combined with the threshold method, the multi-level support vector machine is used to realize the overvoltage type judgment.

[0066] Specifically, combined Figure 3 , using the threshold method and support vector machine to determine the overvoltage type corresponding to the disturbances in S3, S5 and S6 may include:

[0067] S11: Divide the disturbance time period into the period before the disturbance t 12 , disturbance t 23 , after disturbance t 34 ;

[0068] S12: Extracting the characteristic value U of the overvoltage corresponding to the disturbance 12rmsmax 、U 34rmsmax 、S mean , K, α max 、E qianwu 、E houer ,λ;

[0069] S13: Judge U 12rmsmax 12rmsmax阈值 Is it true? If so, it is determined that the overvoltage is a closed transformer (i.e., closed air transformer) overvoltage, and the process ends; if not, execute S14;

[0070] S14: Judge U 34rmsmax 34rmsmax阈值 Is it true? If so, it is determined that the overvoltage is an overvoltage of the tripped transformer (i.e., the empty transformer), and the process ends. If not, execute S15;

[0071] S15: The feature quantity S mean and K are input into a first support vector machine SVMA to distinguish whether the overvoltage type corresponding to the disturbance is a first overvoltage type or a second overvoltage type, wherein the first overvoltage type includes an induced lightning or an isolated light grounding overvoltage, and the second overvoltage type includes a closed capacitor bank, a closed no-load line (i.e., a closed empty line), or a direct lightning overvoltage;

[0072] S16: The feature value α max 、E qianwu 、E houer The sum λ is input into the second support vector machine SVMB to distinguish the overvoltage type corresponding to the disturbance as induced lightning or isolated light grounding overvoltage.

[0073] The method disclosed in this application first eliminates overvoltage of the open transformer and the closed transformer by the threshold method, and then constructs a multi-level support vector machine: SVMA and SVMB. 12rmsmax t 12 The maximum effective value of the three-phase voltage during the time period, U 34rmsmax t 34 The maximum effective value of the three-phase voltage during the time period. 12 or t 34 During the time period, the effective values of the opening and closing overvoltages are small, so the threshold method is used to eliminate these two overvoltages. The multi-level support vector machine includes SVMA and SVMB. Among them, since the induced lightning overvoltage and arc grounding overvoltage are highly similar in three phases, SVMA selects S mean , K characteristic quantity to distinguish other overvoltages; compared with the induced lightning overvoltage, the arc grounding overvoltage has a smaller steepness and its energy is mainly concentrated below 3kHz, so SVMB chooses α max 、E qianwu ​​、E houer , λ characteristic quantities to distinguish between the two overvoltages.

[0074] The calculation formulas for each feature value are shown in formula (3) to formula (7).

[0075]

[0076] Among them, U rms Represents the effective value of phase voltage, N is the number of sampling points, and U(n) represents the voltage sampling sequence value. For the 462 waveforms with a sampling frequency of 200kHz and a sampling time of 100ms, the U of each type of overvoltage collected is calculated. rms , which are summarized in Table 3. Among them, U 12rmsmax t 12 The maximum effective value of the three-phase voltage during the time period, U 34rmsmax t 34 The maximum effective value of the three-phase voltage within the time, U 34rmsmin t 34 The minimum effective value of the three-phase voltage within the time.

[0077] Since the three-phase voltage waveform after the transformer is opened becomes zero after a short high-frequency oscillation, while the waveform after the transformer is closed is just the opposite, U can be selected. 12rmsmax and U 34rmsmax Two characteristic quantities distinguish these two overvoltages from all overvoltages. As shown in Table 3, the U 12rmsmax Minimum, U of the disconnecting transformer 34rmsmax The minimum value verifies the validity of these two characteristic quantities. Therefore, in overvoltage identification, the threshold method can be used to exclude these two overvoltages. 12rmsmax阈值 and U 34rmsmax阈值 Set to 0.2.

[0078] Table 3 U rms Calculation results

[0079]

[0080]

[0081] Among them, S AB Indicates the similarity between the waveforms of phase A and phase B, S BC Indicates the similarity between the B-phase and C-phase waveforms, S CA Indicates the similarity between the C-phase and A-phase waveforms, S mean Represents the average value of the three-phase waveform similarity, x(n) and y(n) represent the voltage sampling sequence values of any two phases in the three-phase overvoltage. If the three-phase waveforms are more similar, then S mean The larger the value, the closer it is to 1.

[0082]

[0083] Among them, U A 、U B and U C where U0 represents the zero-mode voltage component, U1 and U2 represent the line-mode voltage components, and K represents the ratio of the line-mode to zero-mode voltages. The more similar the three-phase waveforms are, the smaller the line-mode voltages U1 and U2 are, which in turn reduces K.

[0084] Since the three-phase waveforms of induced lightning overvoltage and arc grounding overvoltage are highly similar, S mean And K can be used as the characteristic quantity to distinguish the induced lightning overvoltage and arc grounding overvoltage from other overvoltages. According to formula (4) and formula (5), the similarity average S of the five types of overvoltages, induced lightning, direct lightning, closed capacitor bank, closed no-load line and arc grounding, is calculated. mean The results are shown in Table 4. The S of induced lightning overvoltage and arc grounding overvoltage mean Close to 1, greater than the other three types of overvoltage, while the line mode and zero mode voltage ratio K is smaller than the other three types of overvoltage. This calculation result shows that S mean The K characteristic quantity can effectively distinguish induced lightning and arc grounding overvoltage from the five types of overvoltage.

[0085] Table 4 S mean , K calculation results

[0086]

[0087]

[0088] Among them, α max is the overvoltage steepness, △U A (n), △U B (n) and △U C (n) represents the difference of the three-phase voltage sampling sequence at a certain interval, and △n represents the interval length.

[0089]

[0090] Among them, D j (n) is the detail component of the j-th level after wavelet transform, E qianwu is the sum of the detail energy of the first five levels, E houer is the sum of the detail energy of the last two levels, and λ is E houer With E qianwu The ratio.

[0091] Compared to the induced lightning overvoltage, the arc grounding overvoltage has a smaller steepness, and its energy is mainly concentrated below 3kHz. Therefore, it is foreseeable that the sum of the detailed energy of the two layers after the arc grounding overvoltage is much greater than the sum of the first five layers, and the ratio λ will also be greater than that of the induced lightning overvoltage. The energy distribution of the two overvoltages is calculated, and the results are as follows: Figure 7 and Figure 8 The comparison of the characteristic quantities of the two is shown in Table 5. From the results in Table 5, it can be seen that compared with the induced lightning overvoltage, the E houer ,λ is large,E qianwu , α max The smaller the value, the more effective these four features are.

[0092] Table 5 E qianwu 、E houer ,λ,α max Calculation results

[0093]

[0094] Overvoltage identification flow chart as follows Figure 3 As shown. First, the threshold method is used to eliminate the overvoltage of the open transformer and the closed transformer, and then a multi-level support vector machine is constructed: SVMA and SVMB. Specifically, after obtaining the overvoltage, the U of the overvoltage can be determined first. 12rmsmax 12rmsmax阈值 Is it true? If so, it is determined to be an air-to-air overvoltage. If not, further determine U 34rmsmax 34rmsmax阈值 Is it true? If so, it is determined to be a short-circuit transformer overvoltage. If not, it is distinguished based on the multi-level support vector machine SVMA and SVMB (SVMA can distinguish induced lightning or solitary light grounding from closed capacitor groups, closed short lines, and direct lightning; SVMB can distinguish induced lightning from solitary light grounding).

[0095] In the embodiment of the present invention, 12rmsmax阈值 and U 34rmsmax阈值 The value can be set to 0.2. A portion of the collected overvoltages is put into SVMA and SVMB for training, and the remaining overvoltages are used to test the accuracy of the multi-level support vector machine, as shown in Table 6. The results in Table 6 show that the overvoltage type identification method proposed in the present invention is accurate and effective.

[0096] Table 6 Recognition accuracy of multi-level support vector machine

[0097]

[0098] In an optional embodiment, the S4 can determine U by a large number of statistical single-phase to ground flashover voltage effective values. 阈值 ​​Specifically, when a single phase flashes over to ground, the voltage of the fault phase drops to a very low level, while the voltage of the non-fault phase increases. In the embodiment of the present invention, the three-phase minimum effective value of the single phase to ground flashover overvoltage in 462 overvoltage records is counted. Select a suitable threshold U 阈值 , the value can be 0.1. When it is established, a "flashover alarm" message is issued.

[0099] In addition, in the description of the present invention, the terms used are for illustrative purposes only and are not intended to limit the scope of the present invention. The terms "comprise" and / or "include" are used to specify the presence of the elements, steps, operations and / or components, but do not exclude the presence or addition of one or more other elements, steps, operations and / or components. The terms "first", "second" and the like may be used to describe various elements, do not represent an order, and do not limit these elements. In addition, in the description of the present invention, unless otherwise specified, the meaning of "plurality" is two or more. These terms are only used to distinguish one element from another. These and / or other aspects become apparent in conjunction with the following drawings, and it is easier for a person of ordinary skill in the art to understand the description of the embodiments of the present invention. The accompanying drawings are used to depict the embodiments of the present invention for illustrative purposes only. Those skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods shown in the present invention can be adopted without departing from the principles of the present invention.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for warning of medium voltage insulated line disconnection caused by lightning, characterized in that: Lightning-induced line breakage is caused by three stages: induced lightning, flashover, and arcing. The method is based on overvoltage records collected by the system and includes the following steps: S1: Let i = 1, calculate the total number of disturbance time periods K of an overvoltage record. If K < 3, then end and confirm that the overvoltage record will not cause lightning strike disconnection. Otherwise, continue to S2; S2: If i>K-2, then end and confirm that the overvoltage record has no possibility of causing lightning strike and disconnection in the future. Otherwise, continue to S3; S3: Determine whether the i-th disturbance is an induced lightning overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue an "induced lightning overvoltage alarm" message and continue to execute S4. S4: Judgment Is it true? If not, set i=i+1 and return to S2; otherwise, issue a "flashover alarm" message and continue to execute S5; S5: Determine whether the i+1th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue an "arc grounding overvoltage alarm" message and continue to execute S6. S6: Determine whether the i+2th disturbance is an arc grounding overvoltage. If not, set i=i+1 and return to S2. Otherwise, issue a "lightning break warning" message, where i represents the disturbance number. Indicates the three-phase minimum effective value of the single-phase-to-ground flashover overvoltage. Indicates the set threshold; The overvoltage types corresponding to the disturbances in S3, S5, and S6 are determined by using the threshold method and support vector machine, including: S11: Divide the disturbance time period into the period before the disturbance t 12 , disturbance t 23 , after disturbance t 34 ; S12: Extracting the characteristic value U of the overvoltage corresponding to the disturbance 12rmsmax 、U 34rmsmax 、S mean , K, α max 、E qianwu 、E houer ,λ; S13: Judge U 12rmsmax < Is it true? If so, it is determined that the overvoltage is an air-to-close overvoltage, and the process ends; if not, executing S14; S14: Judge U 34rmsmax < Is it true? If so, it is determined that the overvoltage is an overvoltage of the switching transformer, and the process ends. If not, the process proceeds to S15. S15: The feature quantity S mean and K are input into a first support vector machine SVMA to distinguish whether the overvoltage type corresponding to the disturbance is a first overvoltage type or a second overvoltage type, wherein the first overvoltage type includes an induced lightning or an isolated light grounding overvoltage, and the second overvoltage type includes a closed capacitor bank, a closed no-load line, or a direct lightning overvoltage; S16: The feature value α max 、E qianwu 、E houer and λ are input into the second support vector machine SVMB to distinguish the overvoltage type corresponding to the disturbance, induced lightning or isolated light grounding overvoltage. Among them, U 12rmsmax Indicates t 12 The maximum effective value of the three-phase voltage within the time period, is the maximum effective value threshold of the three-phase voltage in the set t12 time period, U 34rmsmax Indicates t 34 The maximum effective value of the three-phase voltage within the time period, The set t 34 The maximum effective value threshold of the three-phase voltage within the time period, S mean represents the average value of the three-phase waveform similarity, K represents the line mode and zero mode voltage ratio of the overvoltage, α max Indicates the overvoltage steepness, E qianwu It represents the sum of detail energy of the first five levels of wavelet transform, E houer It represents the sum of detail energy of the two scales after wavelet transform, and λ is E houer With E qianwu The ratio.

2. The medium voltage insulated line lightning break warning method according to claim 1, characterized in that: In S1, the wavelet sliding window energy is used to calculate the disturbance start time and end time, thereby determining the disturbance time period.

3. The lightning-breakage warning method according to claim 1, characterized in that: and Both are set to 0.

2.

4. The lightning strike disconnection warning method according to claim 1, characterized in that: The S4 Set to 0.1.

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