Method for distinguishing lightning interference and fault of flexible HVDC transmission line

Abstract

The application discloses a kind of flexible direct current transmission line lightning interference and fault discrimination method, specifically includes the following steps: step 1, using wavelet transform modulus maximum value method extracts and judges T1 time window inside zero-mode voltage reverse wave head polarity δ1, using zero-mode voltage wave head polarity δ1 positive and negative to judge lightning position;Step 2, based on T1 time window inside line-mode voltage reverse wave data, using wavelet modulus maximum value transformation extracts wave head number n;Step 3, according to the wave head number n obtained in step 2, lightning fault and lightning interference are judged, when it can be judged to belong to lightning fault or lightning interference, the judgment is ended;When no judgment result is obtained, step 4 is executed;Step 4, using wavelet modulus maximum value transformation extracts T2 data window inside reverse wave head number m, if m=2, it is judged as lightning interference, and discrimination is ended;Otherwise, it is lightning fault, and discrimination is ended.The application can improve the reliability of flexible direct current transmission line protection.

Description

Technical Field

[0001] This invention belongs to the field of power system technology and relates to a method for identifying lightning interference and faults in flexible DC transmission lines. Background Technology

[0002] The proposal of my country's "dual carbon" target has further promoted the country's energy transformation and pointed the way for building a clean and low-carbon energy system. Flexible DC transmission technology, with its flexible regulation and control capabilities, has significant technological advantages in clean energy grid integration and is an important direction for the future development of the power grid.

[0003] One of the major challenges facing flexible DC transmission technology is its DC line protection system. Due to the rapid rise and large amplitude of current after a fault, the overcurrent tolerance of primary equipment is limited, thus requiring extremely high response speeds for protection. The main protection system needs to complete fault identification within 3ms after a fault. Currently, research and application of single-ended main protection for flexible DC transmission systems mainly utilize transient quantity characteristics as the basis for protection. Transient quantity protection relies primarily on fault transient information to improve protection accuracy. However, when transmission lines are subjected to lightning interference, the transient process also contains a large number of high-frequency signals, similar to fault signals, which can easily lead to misjudgments by transient quantity protection. Overhead transmission lines are exposed to the elements, traversing various complex geographical environments and variable weather conditions, making them inevitably susceptible to lightning strikes. Numerous statistical results show that for high-voltage transmission lines, lightning-induced faults account for 40% to 70% of line faults. Therefore, correctly identifying lightning interference signals and fault signals in protection devices is crucial. The ability to effectively identify lightning interference directly affects the reliability of high-voltage transmission line protection operations and plays a crucial role in the safe and stable operation of the entire power system.

[0004] Currently, most lightning interference identification methods rely on the energy ratio of high-frequency and low-frequency components after the disturbance occurs for discrimination. However, setting the threshold value is difficult, and the judgment is easily affected by various factors such as lightning current parameters, line parameters, and lightning strike location, leading to insensitivity or even misjudgment. Furthermore, current lightning interference identification methods for flexible DC transmission lines can only identify a limited number of lightning strike types, mostly only distinguishing faults and interference based on a single lightning strike type, which is not comprehensive enough. Therefore, in-depth analysis of the transient traveling wave waveform characteristics of flexible DC transmission systems under different types of lightning strikes, and the proposal of a fast, reliable, and comprehensive lightning interference identification method, are of great significance to the development of protection technology for flexible DC transmission systems and their safe and stable operation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for identifying lightning interference and faults in flexible DC transmission lines, which can improve the reliability of protection for flexible DC transmission lines.

[0006] The technical solution adopted in this invention is a method for identifying lightning interference and faults in flexible DC transmission lines, which specifically includes the following steps:

[0007] Step 1: After the protection element is activated, the polarity δ1 of the first wavefront of the zero-mode voltage reverse traveling wave within the T1 time window is extracted and determined using the wavelet transform modulus maxima method. The polarity δ1 of the first wavefront of the zero-mode voltage traveling wave is used to determine the location of the lightning strike.

[0008] Step 2: Based on the line-mode voltage inverse traveling wave data within the T1 time window, extract the number of wavefronts n using wavelet mode maxima transform;

[0009] Step 3: Based on the wavefront number n obtained in Step 2, determine whether it is a lightning fault or lightning interference. If it can be determined that it is a lightning fault or lightning interference, the judgment ends; if no judgment result can be obtained, proceed to Step 4.

[0010] Step 4: Use wavelet modulus maximum transform to extract the number m of the back-traveling wavefronts within the T2 data window. If m = 2, it is determined to be lightning interference, and the judgment ends; otherwise, it is a lightning fault, and the judgment ends.

[0011] The invention is further characterized by:

[0012] The specific process of step 1 is as follows:

[0013] The method for determining data window T1 is as follows:

[0014] Based on the principle of traveling wave reflection, the arrival time of the traveling wave front at the line edge is analyzed. The arrival time of the traveling wave front at the line boundary is related to the lightning strike point location d, the total line length L, and the traveling wave transmission speed v.

[0015] Data window T1 includes the data window τ1 after protection starts. The duration Δt1 after protection starts is taken, and the margin Δt is considered.

[0016] Δt1=L / v (1);

[0017] τ1=Δt1+Δt (2);

[0018] To effectively extract the initial wave header, data window T1 also includes 0.5ms of data prior to the protection start-up time; therefore, the length of T1 is:

[0019] T1=0.5+τ1 (3);

[0020] The calculation process for the voltage reverse traveling wave is as follows:

[0021] Collect the voltage data of the positive and negative poles, and use this voltage data to calculate the voltage fault components of the positive and negative poles according to equation (4):

[0022]

[0023] In the formula:

[0024] dU P (t), dU N (t) – These are the positive and negative voltage fault components, respectively;

[0025] U P (t), U N (t)——the instantaneous values ​​of the positive and negative voltages after the disturbance occurs;

[0026] U P0 U N0 —These are the initial values ​​of the positive and negative voltages before the disturbance occurred;

[0027] Collect the current data of the positive and negative poles, and use this current data to calculate the fault components of the positive and negative pole currents according to equation (5):

[0028]

[0029] In the formula:

[0030] dI P (t), dI N (t) – representing the fault components of the positive and negative currents, respectively;

[0031] I P (t), I N (t)——The instantaneous values ​​of the positive and negative currents after the disturbance occurs;

[0032] I P0 I N0 —These are the initial values ​​of the positive and negative currents before the disturbance occurred;

[0033] After obtaining the fault components of voltage and current, the line modulus and zero modulus are obtained using the fault components, as shown in equation (6):

[0034]

[0035] In the formula:

[0036] dU1(t) and dU0(t) are the line-mode and zero-mode voltage fault components, respectively.

[0037] dI1(t) and dI0(t) are the fault components of the line-mode and zero-mode currents, respectively.

[0038] dU P (t), dU N (t) – These are the positive and negative voltage fault components, respectively;

[0039] dI P (t), dIN (t) – These are the positive and negative voltage fault components, respectively;

[0040] Based on the linear and zero moduli of voltage and current, the linear and zero moduli of the voltage reverse traveling wave are calculated as shown in equation (7):

[0041]

[0042] In the formula:

[0043] U b1 (t) — represents the inverse traveling wave of the line-mode voltage;

[0044] U b0 (t)——is the zero-mode voltage reverse traveling wave;

[0045] Z c —This refers to the line surge impedance;

[0046] The process of extracting the polarity of the zero-mode traveling wavefront using the wavelet transform modulus maxima method is as follows:

[0047] The wavelet basis function Ψ(t) is taken from the Haar wavelet function:

[0048]

[0049] Taking a scaling factor a = 2 and a translation factor b = 1, the discrete wavelet transform for the function f(t) is:

[0050]

[0051] For zero-mode voltage reverse traveling wave U b0 (t) Perform wavelet transform, that is, let f(t) = U in equation (8) b0 (t), we get:

[0052]

[0053] Taking the fourth wavelet coefficients, i.e., j=4, we get calculate The modulus of the maximum value;

[0054] If all k in a neighborhood of k0 satisfy:

[0055]

[0056] Then k0 is the wavelet transform The maximum point of the modulus, It is the corresponding modulus maximum;

[0057] Signal within the window when k∈T1 The first modulo maximum point k in the middle 0_1 Corresponding modulus maximum The polarity of the zero-mode voltage traveling wave is δ1, which is the polarity of the first wavehead.

[0058]

[0059] When the polarity of the first wavefront of the zero-mode traveling wave is positive (δ1 > 0), it is determined to be the location of a lightning strike on the top of the tower; when the polarity of the first wavefront of the zero-mode traveling wave is negative (δ1 < 0), it is determined to be the location of a lightning strike on the conductor.

[0060] The specific process of step 2 is as follows:

[0061] Linear mode voltage reverse traveling wave U b1 (t) Perform wavelet transform, that is, let f(t) = U in equation (9) b1 (t), we get:

[0062]

[0063] Taking the fourth wavelet coefficients, i.e., j=4, we get calculate The modulus of the maximum value;

[0064] If all k in a neighborhood of k0 satisfy:

[0065]

[0066] Then k0 is the wavelet transform The maximum point of the modulus; within the window when k∈T1 The number of points that satisfy equation (14) is the number of wavefronts of the line-mode voltage inversion wave in window T1.

[0067] The specific process of step 3 is as follows:

[0068] Step 3.1: If the number of wavefronts n≥3, then it is directly judged as a lightning strike fault, and the judgment ends; otherwise, proceed to step 3.2.

[0069] Step 3.2: If the number of wavefronts n = 1, then it is determined to be lightning interference, and the judgment ends; otherwise, proceed to step 3.3.

[0070] Step 3.3: If the number of wavefronts n = 2, extract the polarity δ2 of the second wavefront in the reverse traveling wave data of the line-mode voltage within the window at time T1. If δ2 is positive (i.e., δ2 > 0), it is determined to be a lightning strike fault, and the judgment ends; otherwise, proceed to step 4.

[0071] The method for determining the polarity δ2 of the second wavefront in the inverse traveling wave data of the line mode voltage within the T1 time window is as follows:

[0072] The polarity δ2 of the second head of the line-mode voltage traveling wave is within the window when k∈T1. The second point k in the signal that satisfies equation (14) 0_2The corresponding modulus maximum Polarity correspondence:

[0073]

[0074] The specific process of step 4 is as follows:

[0075] Step 4.1: Data window T2 includes the data window τ2 after protection starts. The duration Δt2 after protection starts is taken, taking into account the margin Δt:

[0076]

[0077] τ2=Δt2+Δt (17);

[0078] To effectively extract the first wave header, data window T2 also includes 0.5ms of data before the protection start time; therefore, the length of T2 is:

[0079] T2=0.5+τ2 (18);

[0080] Step 4.2, the method for determining the number m of the reverse traveling wave head is as follows:

[0081] For the line-mode voltage inverse traveling wave U within the time window t∈T2 b1 (t) Perform wavelet transform, that is, let f(t) = U in equation (9) b1 (t), thus obtaining equation (13);

[0082] Taking the fourth wavelet coefficients, i.e., j=4, we get Calculate the time window within T2 according to formula (13). Modulus maxima;

[0083] If all k in a neighborhood of k0 satisfy equation (14), then k0 is a wavelet transform. The maximum point of the modulus;

[0084] Within the window when k∈T2 The number of points that satisfy equation (14) is the number of wavefronts m of the reverse traveling wave within the T2 data window.

[0085] The beneficial effects of this invention are that it proposes a method for identifying lightning interference and faults in flexible DC transmission lines. Based on the voltage traveling wave reflection and refraction patterns of the positive line voltage after lightning interference and faults, the polarity and time difference of the voltage traveling wave front are extracted. The characteristics of the traveling wave front are then used for rapid identification of lightning faults and lightning interference. Within 75% of the entire line, ultra-high-speed identification of lightning faults can be achieved using only the information within the τ1 data window after the fault. Within the remaining 25%, information within the τ2 data window after the fault can be used to rapidly distinguish between lightning faults and interference, meeting the fast-acting requirements of flexible DC line protection. Furthermore, the principle of this method is clear, requiring no tuning based on experience or simulation results, and it meets practical engineering requirements, possessing strong practical value. Attached Figure Description

[0086] Figure 1 This is a flowchart of the method for identifying lightning interference in flexible DC transmission lines according to the present invention;

[0087] Figure 2 This is a simulation model diagram of a double-ended flexible DC transmission system;

[0088] Figure 3(a) , 3(b) During the simulation verification phase, the results of lightning strike interference on the conductor were verified at a distance of 100km.

[0089] Figure 4(a) , 4(b) During the simulation verification phase, the results of the interference from the top of the lightning tower were verified at a distance of 300km.

[0090] Figure 5(a) , 5(b) During the simulation verification phase, the results of a lightning strike on a conductor were verified at a distance of 200km.

[0091] Figures 6(a) and (b) show the results of verifying a lightning strike on a conductor at a distance of 400 km during the simulation verification phase. Detailed Implementation

[0092] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0093] The present invention provides a method for identifying lightning interference and faults in flexible DC transmission lines, which can achieve lightning interference identification. The method is implemented according to the following steps:

[0094] Step 1: After the protection element is activated, the polarity δ1 of the first wavefront of the zero-mode voltage reverse traveling wave within the time window T1 is extracted and determined using the wavelet transform modulus maxima method. The location of the lightning strike is determined by the polarity δ1 of the first wavefront of the zero-mode voltage traveling wave: when the polarity of the first wavefront of the zero-mode traveling wave is positive, i.e., δ1 > 0, it is determined to be the location of the lightning strike on the top of the tower; when the polarity of the first wavefront of the zero-mode traveling wave is negative, i.e., δ1 < 0, it is determined to be the location of the lightning strike on the conductor.

[0095] In step 1, the process of extracting and determining the polarity δ1 of the first wavefront of the zero-mode voltage traveling wave within the window at time T1 using the wavelet transform modulus maxima method to determine the lightning strike location is as follows:

[0096] Step 1.1, the method for determining data window T1 is as follows:

[0097] Based on the principle of traveling wave reflection, the arrival time of the traveling wave front at the line edge is analyzed. The arrival time of the traveling wave front at the line boundary is related to the lightning strike point location d, the total line length L, and the traveling wave transmission speed v.

[0098] Data window T1 includes the data window τ1 after protection starts, taking the duration Δt1 after protection starts and considering a certain margin Δt:

[0099] Δt1=L / v (1);

[0100] τ1=Δt1+Δt (2);

[0101] To effectively extract the initial wave header, data window T1 also includes 0.5ms of data prior to the protection start-up time; therefore, the length of T1 is:

[0102] T1=0.5+τ1 (3);

[0103] Step 1.2, Calculation method for voltage reverse traveling wave:

[0104] Collect positive and negative line voltage data, and use this voltage data to calculate the positive and negative voltage fault components according to formula (4).

[0105]

[0106] In the formula:

[0107] dU P (t), dU N (t) – These are the positive and negative voltage fault components, respectively;

[0108] U P (t), U N (t)——the instantaneous values ​​of the positive and negative voltages after the disturbance occurs;

[0109] U P0 U N0 —These are the initial values ​​of the positive and negative voltages before the disturbance occurred;

[0110] Collect the current data of the positive and negative poles, and use this current data to calculate the fault components of the positive and negative pole currents according to formula (5).

[0111]

[0112] In the formula:

[0113] dI P (t), dI N (t) – representing the fault components of the positive and negative currents, respectively;

[0114] I P (t), I N (t)——The instantaneous values ​​of the positive and negative currents after the disturbance occurs;

[0115] I P0 I N0 —These are the initial values ​​of the positive and negative currents before the disturbance occurred;

[0116] After obtaining the fault components of voltage and current, the line modulus and zero modulus are obtained using the fault components, as shown in equation (6).

[0117]

[0118] In the formula:

[0119] dU1(t) and dU0(t) are the line-mode and zero-mode voltage fault components, respectively.

[0120] dI1(t) and dI0(t) are the fault components of the line-mode and zero-mode currents, respectively.

[0121] dU P (t), dU N (t) – These are the positive and negative voltage fault components, respectively;

[0122] dI P (t), dI N (t) – These are the positive and negative voltage fault components, respectively;

[0123] Based on the linear and zero moduli of voltage and current, the linear and zero moduli of the voltage reverse traveling wave are calculated as shown in equation (7).

[0124]

[0125] In the formula:

[0126] U b1 (t) — represents the inverse traveling wave of the line-mode voltage;

[0127] U b0 (t)——is the zero-mode voltage reverse traveling wave;

[0128] Z c — This refers to the line wave impedance.

[0129] Step 1.3, the method for extracting the polarity of the zero-mode traveling wavefront using the wavelet transform modulus maxima method is as follows:

[0130] The wavelet basis function Ψ(t) is taken from the Haar wavelet function:

[0131]

[0132] Taking a scaling factor a = 2 and a translation factor b = 1, the discrete wavelet transform for the function f(t) is:

[0133]

[0134] For zero-mode voltage reverse traveling wave U b0 (t) Perform wavelet transform, that is, let f(t) = U in equation (8) b0 (t), we get:

[0135]

[0136] Taking the wavelet coefficients of the fourth layer (i.e., j=4), we obtain Calculate its modulus maxima.

[0137] If all k in a neighborhood of k0 satisfy:

[0138]

[0139] Then k0 is the wavelet transform The maximum point of the modulus, It is the corresponding modulus maximum.

[0140] Signal within the window when k∈T1 The first modulo maximum point k in the middle 0_1 Corresponding modulus maximum The polarity of the zero-mode voltage traveling wave is δ1, which is the polarity of the first wavehead.

[0141]

[0142] Step 2: Calculate the line-mode voltage back-traveling wave data within the window at time T1, and extract the number of wavefronts n using wavelet mode maxima transform;

[0143] Linear mode voltage reverse traveling wave U b1 (t) Perform wavelet transform, that is, let f(t) = U in equation (9) b1 (t), we get:

[0144]

[0145] Taking the wavelet coefficients of the fourth layer (i.e., j=4), we obtain Calculate its modulus maxima.

[0146] If all k in a neighborhood of k0 satisfy:

[0147]

[0148] Then k0 is the wavelet transform The maximum value of the modulus.

[0149] Within the window when k∈T1 The number of points that satisfy equation (14) is the number of wavefronts of the line-mode voltage inversion wave in window T1.

[0150] Step 3: If the number of wavefronts n≥3, then directly determine it as a lightning strike fault and the judgment ends; otherwise, proceed to step 4.

[0151] Step 4: If the number of wavefronts n = 1, then it is determined to be lightning interference, and the judgment ends; otherwise, proceed to step 5.

[0152] Step 5: If the number of wavefronts n = 2, extract the polarity δ2 of the second wavefront in the reverse traveling wave data of the line-mode voltage within the window at time T1. If δ2 is positive, i.e., δ2 > 0, then it is determined to be a lightning strike fault, and the judgment ends; otherwise, proceed to step 6.

[0153] The method for determining the polarity δ2 of the second wavefront in the inverse traveling wave data of the line-mode voltage within the window at time T1 in step 5 is as follows:

[0154] The polarity δ2 of the second head of the line-mode voltage traveling wave is within the window when k∈T1. The second point k in the signal that satisfies equation (14) 0_2 The corresponding modulus maximum Polarity correspondence:

[0155]

[0156] Step 6: Use wavelet modulus maximum transform to extract the number m of the back-traveling wavefronts in the T2 data window. If m = 2, it is determined to be lightning interference, and the judgment ends; otherwise, it is a lightning fault, and the judgment ends.

[0157] Step 6.1, the method for determining time window T2 is as follows:

[0158] Data window T2 includes the data window τ2 after protection starts, taking the duration Δt2 after protection starts and considering a certain margin Δt:

[0159]

[0160] τ2=Δt2+Δt (17);

[0161] To effectively extract the first wave header, data window T2 also includes 0.5ms of data before the protection start time; therefore, the length of T2 is:

[0162] T2=0.5+τ2 (18);

[0163] Step 6.2, the method for determining the number m of the reverse traveling wave head is as follows:

[0164] For the line-mode voltage inverse traveling wave U within the time window t∈T2 b1 (t) Perform wavelet transform, that is, let f(t) = U in equation (9) b1 (t), thus obtaining equation (13).

[0165] Taking the wavelet coefficients of the fourth layer (i.e., j=4), we obtain Calculate its modulus maxima.

[0166] If all k in a neighborhood of k0 satisfy equation (14), then k0 is a wavelet transform. The maximum value of the modulus.

[0167] Within the window when k∈T2 The number of points that satisfy equation (14) is the number of wavefronts m of the reverse traveling wave within the T2 data window.

[0168] As attached Figure 2 The figure shown is a simulation model of a double-ended flexible DC transmission system. This system has a rated voltage of ±500kV, a rated transmission capacity of 3000MVA, and a total transmission line length of 500km. An overhead line frequency-varying parameter model is used, and the sampling frequency during system simulation is 100kHz. In this case, the total line length L = 500km, and the traveling wave propagation speed is approximated as the speed of light v = 3 × 10⁻⁶. 8 Given m / s, τ1 and τ2 are set to 1.7 ms and 2.3 ms respectively, so the time windows T1 and T2 are 2.2 ms and 2.8 ms respectively. (See attached...) Figure 1 The identification process correctly identifies lightning strikes.

[0169] Example 1

[0170] At a distance of 100km from the boundary, the interference of lightning strikes on the conductor was simulated. After collecting the positive voltage data of the line, wavelet modulus decomposition was used, and the processed waveforms are shown in Figures 3(a) and 3(b).

[0171] As shown in Figure 3(a), the first wavefront of the zero-mode voltage is negative, indicating a lightning strike on the conductor. In Figure 3(b), the line-mode waveform does not have a second wavefront reaching the M side within the T1 time window; there is only one wavefront, indicating a lightning interference situation.

[0172] Example 2

[0173] At a distance of 300km from side M, simulating lightning strike interference on the tower top, positive voltage data of the line was collected. Wavelet mode maximum decomposition was then used, and the processed waveforms are shown in Figures 4(a) and 4(b).

[0174] As shown in Figure 4(a), the first wavefront of the zero-mode voltage is positive, indicating a lightning strike on the tower top. In Figure 4(b), the line-mode waveform has a second wavefront reaching the M side within the T1 time window, and its polarity is determined to be negative. Within the T2 time window, no third wavefront arrives, indicating a lightning interference situation.

[0175] Implementation Case 3

[0176] At a distance of 200 km from side M, a lightning strike fault was simulated on the conductor. After collecting the positive voltage data of the line, wavelet modulus decomposition was used, and the processed waveforms are shown in Figures 5(a) and 5(b).

[0177] As shown in Figure 5(a), the first traveling wavefront of the zero-mode voltage is negative, indicating a lightning strike on the conductor. In Figure 5(b), the line-mode waveform has a positive wavefront within the T1 time window, indicating a lightning strike fault.

[0178] Example 4

[0179] At a distance of 400 km from side M, a lightning strike fault was simulated on the conductor. After collecting the positive voltage data of the line, wavelet modulus decomposition was used, and the processed waveforms are shown in Figures 6(a) and 6(b).

[0180] As shown in Figure 6(a), the first wavefront of the zero-mode voltage is positive, indicating a lightning strike on the tower top. In Figure 6(b), the line-mode waveform has three wavefronts within the T1 time window, indicating a lightning strike fault.

[0181] To comprehensively verify the impact of lightning strike distance on the discrimination results, different lightning interference and lightning faults were set at different distances from the line, and the proposed lightning interference identification method was verified based on the simulation results. The verification results are shown in Table 1.

[0182] Table 1. Verification results of lightning interference and faults at different distances.

[0183]

[0184]

Claims

1. A method for distinguishing lightning interference from fault in a flexible HVDC power transmission line, characterized in that: Specifically comprising the following steps: Step 1: After the protection element is activated, extract and judge the modulus maxima using wavelet transform. T 1. Polarity of the first wavehead of the zero-mode voltage reverse traveling wave within the time window δ 1. Utilizing the polarity of the first wavehead of a zero-mode voltage traveling wave δ 1. Determine the location of the lightning strike based on its positive or negative sign; the specific process of step 1 is as follows: data window T The determination method is as follows: According to the principle of traveling wave reflection and refraction, the time when the wave front reaches the line boundary, the time when the wave front reaches the line boundary and the lightning stroke point position are analyzed d , the total length of the line L , and the traveling wave transmission speed v ​ Data window T 1 contains the protection start τ 1 data window, take the protection start t 1 duration and consider the margin t : （1） （2） To effectively extract the first wave head, the data window T 1 also includes the data 0.5 ms before the protection start time T The length of 1 is: （3） The voltage reverse wave calculation process is as follows: collecting positive and negative electrode line voltage data, using the voltage data to calculate the positive and negative electrode voltage fault components according to formula (4): （4） In the formula: dU P ( t )、 dU N ( t ) - positive and negative voltage fault components, respectively; U P ( t )、 U N t ) - the instantaneous values of the positive and negative electrode voltages, respectively, after the disturbance has occurred;​ U P0 , U N0 - the initial values of the positive and negative electrode voltages, respectively, before the disturbance occurs; Collecting positive and negative electrode line current data, using the current data to calculate the positive and negative electrode current fault components according to formula (5): （5） In the formula: dI P t dI N t positive electrode, negative electrode current fault component, respectively​​​ I P ( t )、 I N ( t ) - the instantaneous values of the positive and negative currents, respectively, after the disturbance has occurred; I P0 , I N0 - the initial values of the positive and negative currents before the disturbance, respectively; After obtaining the voltage and current fault components, the line modulus and zero modulus are obtained by using the fault components, as shown in formula (6): （6） wherein: dU 1( t )、 dU 0( t ) - are line mode, zero mode voltage fault components, respectively; dI 1( t ), dI 0( t — These are the line-mode and zero-mode current fault components, respectively; dU P ( t )、 dU N ( t ) - positive and negative voltage fault components, respectively; dI P ( t )、 dI N ( t ) - positive and negative voltage fault components, respectively; According to the line modulus and zero modulus of the voltage and current, the line modulus and zero modulus of the voltage reverse wave are obtained, as shown in formula (7): （7） In the formula: U b1 t is the line mode voltage traveling wave;​ U b0 ( t ) — zero mode voltage counter traveling wave; Z c — is the line wave impedance; The process of extracting the polarity of the zero-mode wave head by using the wavelet transform modulus maximum value method is as follows: Wavelet basis function Ψ (t) taking the Haar wavelet function: （8） Taking the scale factor a = 2, the translation factor b = 1, and the function f The discrete wavelet transform of the function (t) is: （9） Zero mode voltage counter traveling wave U b0 ( t ) is wavelet transformed, i.e. letting f (t)= U b0 ( t ), we obtain: （10） Taking the fourth level wavelet coefficients, i.e., j = 4, we get The modulus maxima of are calculated. If k all of the elements in some neighborhood of 0 satisfy: k all of the elements in some neighborhood of 0 satisfy: （11） then k 0 is the wavelet transform of the modulus maxima, is the corresponding modulus maxima; signals within the time window first modulus maximum point k 0_1 corresponding modulus maximum polarity, i.e. polarity of the first wave front of the zero-mode voltage traveling wave δ 1: （12） When the first wave head polarity of the zero-mode traveling wave is positive, that is, δ 1 > 0, it is judged that the lightning strikes the tower top position; when the first wave head polarity of the zero-mode traveling wave is negative, that is, δ 1 < 0, it is judged that the lightning strikes the conductor position; Step 2, based on T 1, the wave head number of the line mode voltage reverse wave data in the time window is extracted by using the wavelet mode maximum value transform n ; the specific process of the step 2 is that the wavelet transform is performed on the line mode voltage reverse wave U b1 ( t ) to obtain formula (9) in the formula (9) f (t)= U b1 ( t ), and the following is obtained: （13） Taking the fourth level wavelet coefficients, i.e., j = 4, we get The modulus maxima of are calculated. If k all of the elements in some neighborhood of 0 satisfy: k all of the elements in some neighborhood of 0 satisfy: （14） Then k 0 is the modulus maxima point of wavelet transform ; The number of points in the time window The number of points in the time window T 1 is the number of line-mode voltage counter-wavefronts in the time window n ; Step 3, according to the wave head number n obtained in step 2, the lightning stroke fault and the lightning interference are judged, when it can be judged that it belongs to lightning stroke fault or lightning interference, the judgment is ended, when it cannot be judged, step 4 is executed; Step 4, extracting by wavelet modulus maxima transform T 2 the number of the data window reverse wave front m, if m=2, it is judged as lightning interference, and the discrimination ends; otherwise, it is lightning fault, and the discrimination ends; the specific process of the step 4 is: Step 4.1, data window T 2 contains protection after start τ 2 data window, take protection after start Δ t 2 duration and consider margin Δ t : （15） （16） To effectively extract the first wave head, the data window T 2 also includes data 0.5 ms before the protection start time T 2 has a length of: （17） Step 4.2, the determination method of the reverse wave head number m is as follows: On Line mode voltage traveling wave within a time window U b1 ( t ) is wavelet transformed, i.e. letting f (t)= U b1 ( t ), equation (13) is obtained; Taking the fourth level wavelet coefficients, i.e., j = 4, we get , compute the modulus maxima in the time window . like k All in a certain neighborhood of 0 k If all satisfy equation (14), then k 0 is wavelet transform The maximum point of the modulus; the number of points in the time window The number of points in the time window that satisfy equation (14) is T 2 The number of points in the time window that satisfy equation (14) is 2. The method of claim 1, wherein: The specific process of step 3 is as follows: Step 3.1, if the number of wave heads n ≥ 3, it is directly determined as lightning stroke fault, and the discrimination ends. Otherwise, step 3.2 is entered; Step 3.2, if the number of wave heads n = 1, it is determined as lightning interference, and the discrimination ends. Otherwise, step 3.3 is entered; Step 3.3, if the number of wave heads n = 2, extract T 1 the second wave head polarity in the line mode voltage counter wave data in the time window δ 2, if δ 2 is positive polarity, that is, δ 2 > 0, it is judged as lightning stroke fault, and the discrimination ends; otherwise, step 4 is entered; T 1st wave head polarity in line mode voltage counter-propagating data within the 1st time window δ 2 is determined as follows: Second head polarity of line mode voltage traveling wave δ 2 with Within the time window Second point in the signal satisfying equation (14) k 0_2 Corresponding to the mode maximum Corresponding to the polarity of: （18）。

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