Method for identifying lightning interference of flexible direct current line based on traveling wave correlation coefficient

Abstract

This invention discloses a method for identifying lightning interference on flexible straight lines based on traveling wave correlation coefficient, specifically including the following steps: Step 1, calculate the traveling wave u of the line-mode voltage. f (k) Linear voltage reverse traveling wave u b (k); Step 2, take q points after the starting point of the traveling wave of the local line-mode voltage, and denote them as u. fm1 (t), u fm1 (t) is sent to the other end, and simultaneously receives the line-mode voltage traveling wave data u of the q points after the start point from the other end. fn1 (t); Step 3, find the second wavefront point of the reverse traveling wave of the line-mode voltage at this end and the other end, K. 2m and K 2n Step 4, for u bm (k), from K 2m Then select q points, denoted as u. bm1 (t), for u bn (k), from K 2n Then select q points, denoted as u. bn1 (t), calculate u bm1 (t) and u fn1 The correlation coefficients ρ1 and u of (t) bn1 (t) and u fm1 The correlation coefficient ρ2 of (t) is used to send ρ1 to the other end, while simultaneously receiving ρ2 sent by the other end. Step 5: Set the lightning interference threshold value b, and compare ρ1 with ρ2 and b. If ρ1 > b or ρ2 > b, then it is determined that lightning interference has occurred on the line. This method can quickly and accurately determine whether lightning interference has occurred on the line, providing an important basis for the correct operation of flexible DC transmission line protection devices.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system fault discrimination, and relates to a lightning interference identification method for a flexible DC line based on a traveling wave correlation coefficient. BACKGROUND

[0002] Under the background of the "double carbon" target, the power grid in China has undergone profound changes. Compared with traditional DC power transmission technology, flexible DC power transmission technology has no commutation failure and reactive power compensation problem, can provide active and reactive power to the AC system, has obvious advantages in new energy grid connection, can realize large-scale and multi-form new energy collection and complementation, improve energy utilization rate, and enhance power supply reliability.

[0003] Due to the high power electronic degree of the flexible DC power transmission system adopting MMC, it is a "low inertia" system. If a fault occurs in the line of the flexible DC power transmission system, the system will overcurrent within a few milliseconds. If the fault line cannot be accurately and timely discriminated and isolated, the valve hall overcurrent protection of the converter station will be triggered and locked out, which has high requirements for the reliability of the line protection criterion.

[0004] There are two common protection schemes for the flexible DC power transmission system, one is single-ended protection, and the other is longitudinal protection. Most single-ended protection principles are simple and fast in action, and are usually used as main protection, but have low sensitivity to high resistance faults and poor anti-lightning interference ability. The longitudinal protection as backup protection uses double-ended information for fault detection and has high selectivity and reliability.

[0005] The line protection of the flexible DC power transmission system needs to accurately identify the internal fault and external fault, and correctly act when a line internal fault occurs to remove the fault line. However, in the actual operation process of the flexible DC power transmission system, the line may also be subjected to lightning interference. When a certain place in the internal area is subjected to lightning interference without causing a fault, the protection device should not act. Most of the current backup protection researches ignore the lightning interference condition, and the protection only distinguishes between internal faults and external faults. When lightning interference occurs, the protection device is prone to misoperation. The transient traveling wave waveform characteristics of the flexible DC power transmission system under different types of faults and lightning interference are analyzed in depth, and a lightning interference identification criterion for the flexible DC power transmission system is proposed, which takes into account the rapidity and reliability, accurately discriminates whether the system has a fault and whether it is subjected to lightning interference, and ensures the correct action of the protection device. It has important value for the development of new type of power system relay protection. SUMMARY

[0006] The purpose of the present application is to provide a method for identifying lightning interference of HVDC transmission lines based on traveling wave correlation coefficient, which can be used in conjunction with longitudinal protection of flexible DC transmission lines, and can quickly and accurately determine whether the transmission line has failed or been interfered by lightning, thereby providing an important basis for the correct action of the protection device of the flexible DC transmission line.

[0007] The technical solution adopted by the present application is a method for identifying lightning interference of HVDC transmission lines based on traveling wave correlation coefficient, which specifically comprises the following steps:

[0008] Step 1, calculate the forward traveling wave of line mode voltage u f (k) and the backward traveling wave of line mode voltage u b (k);

[0009] Step 2, take the starting point and the next q points of the forward traveling wave of the line mode voltage at the local end, denoted as u fm1 (t), t = 1, 2, 3... q, and send them to the opposite end, and at the same time, receive the forward traveling wave data of the line mode voltage sent by the opposite end u fn1 (t), t = 1, 2, 3... q;

[0010] Step 3, find the second wave head point K 2m of the backward traveling wave of the line mode voltage at the local end and the second wave head point K 2n of the backward traveling wave of the line mode voltage at the opposite end;

[0011] Step 4, after the protection main criterion has determined that the line has not failed outside, for u bm (k), take q points after K 2m , denoted as u bm1 (t), for u bn (k), take q points after K 2n , denoted as u bn1 (t), calculate the correlation coefficient ρ1 of u bm1 (t) and u fn1 (t), and calculate the correlation coefficient ρ2 of u bn1 (t) and u fm1 (t), send ρ1 to the opposite end, and at the same time, receive ρ2 sent by the opposite end;

[0012] Step 5, set the threshold value b of the internal lightning interference, compare ρ1 with ρ2 and b, if ρ1 > b or ρ2 > b, it is determined that the transmission line has been interfered by lightning, otherwise, it is not lightning interference.

[0013] The present application is also characterized in that:

[0014] The specific process of step 1 is:

[0015] Step 1.1, when the protection starting element is started, read the positive voltage u p (k), positive current i p (k), negative voltage u n (k), negative current i n (k), respectively, the average value of the positive voltage u p0 , the average value of the positive current i p0 , the average value of the negative voltage u n0 , the average value of the negative current i n0 Subtracting, the positive voltage fault component du p (k), positive current fault component di p (k), negative voltage fault component du n (k) and negative current fault component di n (k), the calculation formula is shown in formula (1):

[0016]

[0017] Step 1.2, calculate the line mode voltage fault component Δu(k) and the line mode current fault component Δi(k) in the data window, the calculation formula is shown in formula (2):

[0018]

[0019] Step 1.3, calculate the line mode voltage forward wave u f (k) and the line mode voltage backward wave u b (k), the calculation formula is shown in formula (3) and formula (4):

[0020]

[0021]

[0022] In the formula, Z c is the line wave impedance.

[0023] The specific process of step 2 is:

[0024] For u fm (k), take q points after the starting point, usually q is 300, and mark as u fm1 (t), t=1, 2, 3...q. For u fn (k), take q points after the starting point, and mark as u fn1 (t), t=1, 2, 3...q. Send u fm1 (t) to the opposite end, and receive u fn1 (t) sent by the opposite end at the same time.

[0025] The specific process of step 3 is:

[0026] For the local line mode voltage anti-travel wave u bm (k), take p points from the local fault starting point, denoted as u bm2 (t), t = 1, 2, 3...p, for the opposite line mode voltage anti-travel wave u bn (k), take p points from the opposite fault starting point, denoted as u bn2 (t), t = 1, 2, 3...p; from the formula (5), formula (6), formula (7), formula (8) respectively to u bm2 (t) and u bn2 (t), carry out wavelet transform, adopt wavelet transform modulus maximum value method, calculate the second wave head point K bm (k) of the local line mode voltage anti-travel wave u 2m (k) and the second wave head point K bn (k) of the opposite line mode voltage anti-travel wave u 2n ;

[0027] The process of extracting the second wave head of line mode voltage anti-travel wave by wavelet transform modulus maximum value method is as follows:

[0028] The wavelet base function Ψ(t) takes Haar wavelet function as shown in formula (5):

[0029]

[0030] The discrete wavelet transform of the function f(t) is as follows:

[0031]

[0032] Carry out wavelet transform on u bm2 (t) and u bn2 (t), that is, let f(t) = u bm2 (t) and f(t) = u bn2 (t) in formula (6) respectively to obtain:

[0033]

[0034]

[0035] Take the first layer wavelet coefficient, that is, j = 1, to obtain X m (1,k) and X n (1,k), calculate the modulus maximum value of X m (1,k) and X n (1,k);

[0036] If all k in a neighborhood of k p and k g satisfy:

[0037] |X m (1,k)|<|X m (1,k p )| (9)

[0038] |X n (1,k)|<|X n (1,k g )| (10)

[0039] then k p is the modulus maximum point of wavelet transform X m (1,k), |X m (1,k p )| is the modulus maximum, k g is the modulus maximum point of wavelet transform X n (1,k), |X n (1,k g )| is the corresponding modulus maximum, then K 2m =k p , K 2n =k g .

[0040] The specific process of step 4 is as follows:

[0041] After the protection main criterion has determined that the line has not occurred an external fault, for u bm (k), take q points from K 2m , denoted as u bm1 (t), t=1, 2, 3...q, for u bn (k), take q points from K 2n , denoted as u bn1 (t), t=1, 2, 3...q, according to formula (11) and formula (12), calculate the correlation coefficient p1 of u bm1 (t) and u fn1 (t), calculate the correlation coefficient p2 of u bn1 (t) and u fm1 (t), send p1 to the opposite end, and receive p2 sent by the opposite end.

[0042]

[0043]

[0044] The specific process of step 5 is as follows:

[0045] Set the in-zone lightning interference threshold value b, and compare with b, if any one of formula (13) and formula (14) is established, it is determined as lightning interference, otherwise it is determined as an internal fault, which is as follows:

[0046] p1>b (13)

[0047] p2>b (14).

[0048] The method has the advantages that the method for identifying lightning interference of the HVDC line based on the traveling wave correlation coefficient can determine whether lightning interference occurs on the power transmission line according to the waveform characteristics of the forward traveling wave and the backward traveling wave of the line mode at both ends of the line. The method can accurately distinguish between different types of internal faults (such as lightning tower, lightning transmission line, ordinary internal short-circuit fault, etc.) and internal lightning interference. The identification method meets the requirements of the HVDC power transmission system for protection selectivity and reliability. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is a flowchart of the method for identifying lightning interference of the HVDC line based on the traveling wave correlation coefficient;

[0050] Figure 2 is a simulation model diagram of a certain two-terminal true bipolar MMC HVDC power transmission system;

[0051] Figure 3 is the voltage waveform of the forward traveling wave and the backward traveling wave at the local end when a positive pole grounding short circuit with a transition resistance of 0Ω occurs at 100km in the simulation verification stage;

[0052] Figure 4 is the voltage waveform of the forward traveling wave and the backward traveling wave at the opposite end when a positive pole grounding short circuit with a transition resistance of 0Ω occurs at 100km in the simulation verification stage;

[0053] Figure 5 is the voltage waveform of the forward traveling wave and the backward traveling wave at the local end when an inter-pole fault with a transition resistance of 500Ω occurs at 200km in the simulation verification stage;

[0054] Figure 6 is the voltage waveform of the forward traveling wave and the backward traveling wave at the opposite end when an inter-pole fault with a transition resistance of 500Ω occurs at 200km in the simulation verification stage;

[0055] Figure 7 is the voltage waveform of the forward traveling wave and the backward traveling wave at the local end when a lightning bipolar shielding failure fault occurs at 50km in the simulation verification stage;

[0056] Figure 8 is the voltage waveform of the forward traveling wave and the backward traveling wave at the opposite end when a lightning bipolar shielding failure fault occurs at 50km in the simulation verification stage;

[0057] Figure 9 is the voltage waveform of the forward traveling wave and the backward traveling wave at the local end when lightning interference occurs at 450km in the simulation verification stage;

[0058] Figure 10 is the voltage waveform of the forward wave and the backward wave of the line at the opposite end when the lightning interference occurs at 450km in the simulation verification stage. DETAILED DESCRIPTION

[0059] The application will be described in detail below with reference to the drawings and specific embodiments.

[0060] The lightning interference identification method for the HVDC transmission line based on the correlation coefficient of the traveling wave, by calculating the correlation coefficient of the traveling wave voltage at both ends of the flexible HVDC transmission line after the fault occurs, can distinguish the two cases of the internal fault and the lightning interference, and the flow is as shown in Figure 1 The following steps are implemented in detail:

[0061] Step 1, after the protection starting element is started, the fault starting point is recorded as the 0th sampling point, the positive voltage fault component du(k) is calculated p , the positive current fault component di(k) is calculated p , the negative voltage fault component du(k) is calculated n , and the negative current fault component di(k) is calculated n , according to which the line mode voltage fault component Au(k) and the line mode current fault component Ai(k) are calculated, and finally the line mode voltage forward wave u(k) and the line mode voltage backward wave u(k) are calculated by using the line mode fault component. The line mode voltage forward wave and the line mode voltage backward wave at the opposite end are u(k) and u(k). f b fm bm fn bn

[0062] The specific process of step 1 is as follows:

[0063] Step 1.1, after the protection starting element is started, the positive voltage u(k) at the protection installation, the positive current i(k) at the protection installation, the negative voltage u(k) at the protection installation, and the negative current i(k) at the protection installation are read. p p n n p0 p0 n0 n0 p p n n ​​​​​​​​​​​​​​​​​(k), the calculation formula is shown in formula (1):

[0064]

[0065] Step 1.2, the line mode voltage fault component Δu(k) and the line mode current fault component Δi(k) in the data window are calculated, the calculation formula is shown in formula (2):

[0066]

[0067] Step 1.3, the line mode voltage forward wave u f (k) and the line mode voltage backward wave u b (k) are calculated, the calculation formula is shown in formula (3) and formula (4):

[0068]

[0069]

[0070] In the formula, Z c is the line wave impedance.

[0071] Step 2, the q points after the starting point of the line mode voltage forward wave at the local end are taken and recorded as u fm1 (t), t=1, 2, 3...q, usually q is 300, and are sent to the opposite end, and the q sampling points after the starting point of the line mode voltage forward wave data u fn1 (t), t=1, 2, 3...q sent by the opposite end are received.

[0072] The specific process of step 2 is as follows:

[0073] For u fm (k), the q points after the starting point are taken and recorded as u fm1 (t), t=1, 2, 3...q. For u fn (k), the q points after the starting point are taken and recorded as u fn1 (t), t=1, 2, 3...q. u fm1 (t) is sent to the opposite end, and u fn1 (t) sent by the opposite end is received.

[0074] Step 3, the second wave head point K bm of the line mode voltage backward wave u 2m (k) at the local end and the second wave head point K bn of the line mode voltage backward wave u 2n (k) at the opposite end are found.

[0075] The specific process of step 3 is as follows:

[0076] The opposite end line mode voltage backward wave u bm (k) is taken from p points after the opposite end fault starting point, denoted as u bm2 (t), t = 1, 2, 3...p, and p is usually 450. bn (k) is taken from p points after the opposite end fault starting point, denoted as u bn2 (t), t = 1, 2, 3...p. bm2 (t) and u bn2 (t) are respectively subjected to wavelet transform according to formula (5), formula (6), formula (7) and formula (8), and the second wave head point K bm (k) of the opposite end line mode voltage backward wave u 2m (k) is calculated by using the wavelet transform modulus maximum value method. bn (k) of the opposite end line mode voltage backward wave u 2n (k) is calculated by using the wavelet transform modulus maximum value method.

[0077] The process of extracting the second wave head of the line mode voltage backward wave by using the wavelet transform modulus maximum value method is as follows:

[0078] The wavelet base function Ψ(t) takes the Haar wavelet function as shown in formula (5):

[0079]

[0080] Taking the scale factor a = 2 and the translation factor b = 1, the discrete wavelet transform of the function f(t) is as follows:

[0081]

[0082] The wavelet transform of u bm2 (t) and u bn2 (t) is performed, that is, f(t) = u bm2 (t) and f(t) = u bn2 (t) in formula (6) are respectively taken to obtain:

[0083]

[0084]

[0085] The first layer wavelet coefficient is taken, that is, j = 1, to obtain X m (1, k) and X n (1, k), and the modulus maximum value of X m (1, k) and X n (1, k) is calculated.

[0086] If all k in a certain neighborhood of k p and k g satisfy:

[0087] |X m (1,k)|<|X m (1,k p )| (9)

[0088] |X n (1,k)|<|X n (1,k g )| (10)

[0089] then k p is the modulus maximum point of wavelet transform X m (1,k), |X m (1,k p )| is the modulus maximum, k g is the modulus maximum point of wavelet transform X n (1,k), |X n (1,k g )| is the corresponding modulus maximum, then K 2m =k p , K 2n =k g .

[0090] Step 4, after the main protection criterion has determined that no external fault has occurred on the line, for u bm (k), take q points from K 2m , denoted as u bm1 (t), t = 1, 2, 3...q, for u bn (k), take q points from K 2n , denoted as u bn1 (t), t = 1, 2, 3...q, the correlation coefficient p1 of u bm1 (t) and u fn1 (t) is calculated by the local protection, and the correlation coefficient p2 of u bn1 (t) and u fm1 (t) is calculated by the remote protection. p1 is sent to the remote protection, and p2 sent by the remote protection is received.

[0091] The specific process of step 4 is as follows:

[0092] After the main protection criterion has determined that no external fault has occurred on the line, for u bm (k), take q points from K 2m , usually q is 300, denoted as u bm1 (t), t = 1, 2, 3...q, for u bn (k), take q points from K 2n , denoted as u bn1 (t), t = 1, 2, 3...q, according to formula (11) and formula (12), ubm1 (t) and u fn1 (t) and u bn1 (t) and u fm1 (t) and u bm1 (t) and u fn1 (t) and u bn1 (t) and u fm1 (t) and u

[0093]

[0094]

[0095] Step 5, set the threshold value b of the intra-zone lightning disturbance, compare ρ1 with ρ2 and b, if ρ1 > b or ρ2 > b, determine that the transmission line has lightning disturbance, and the protection returns to normal, otherwise, determine that the transmission line has intra-zone fault, and the protection acts.

[0096] The specific process of Step 5 is as follows:

[0097] Set the threshold value b of the intra-zone lightning disturbance, and compare ρ1 with ρ2 and b, if either formula (13) or formula (14) is true, determine that it is lightning disturbance, otherwise, determine that it is intra-zone fault.

[0098] ρ1 > b (13)

[0099] ρ2 > b (14).

[0100] The setting method of the threshold value b in Step 5 is as follows:

[0101] Simulate different types of lightning disturbance and intra-zone fault at 10%, 60% and 90% of the line from the line head, according to the specific process of Step 4, calculate u bm1 (t) and u fn1 (t) and u bn1 (t) and u fm1 (t) and u

[0102] As can be seen from Table 1, when the line has intra-zone fault, the correlation coefficients ρ1 and ρ2 are both less than 0, and the size of the transition resistance has an effect on the correlation coefficients ρ1 and ρ2, the greater the transition resistance, the greater the correlation coefficients ρ1 and ρ2. When the line has intra-zone lightning fault, the correlation coefficients ρ1 and ρ2 are both less than -0.35, and when the line has lightning disturbance, the correlation coefficients ρ1 and ρ2 are both greater than 0.95, which is significantly greater than the above two cases, so the threshold value b is set to 0.8.

[0103] Table 1: Correlation coefficient calculation results under different faults

[0104]

[0105]

[0106] As Figure 2 shown, it is a certain two-terminal true bipolar MMC flexible HVDC transmission system simulation model. The system rated DC voltage is ±500 kV, the rated operating current is 2.5 kA, the rated capacity is 2500 MW, the transmission line is 500 km long, the overhead line frequency-varying parameter model is used, and the sampling frequency is 100 kHz. In the figure, MMC is the converter station, R is the line protection resistor, L b is the line smoothing reactor, the inductance value is 0.2 mH, and it is discriminated according to the flow chart shown in Figure 1 .

[0107] Example 1

[0108] As Figure 3 and Figure 4 shown, after a positive ground short circuit with a transition resistance of 0Ω occurs at a distance of 100 km from the installation of the distance protection, the second wave head point K2m of the local line mode voltage traveling wave u bm (k) and the second wave head point K2n of the opposite end line mode voltage traveling wave u bn (k) appear, K2m=68 and K2n=68 are obtained, u bm1 (t) and the correlation coefficient ρ1 of u fn1 (t) are calculated, u bn1 (t) and the correlation coefficient ρ2 of u fm1 (t) are calculated, ρ1=-0.72 and ρ2=-0.39 are obtained, which are less than the threshold value 0.8, so it is determined that the line has an internal fault.

[0109] Example 2

[0110] As Figure 5 and Figure 6 shown, after an inter-terminal fault with a transition resistance of 500Ω occurs at a distance of 200 km from the installation of the distance protection, the protection element starts, the second wave head point K2m of the local line mode voltage traveling wave u bm (k) and the second wave head point K2n of the opposite end line mode voltage traveling wave u bn (k) are calculated, K 2m =68 and K 2n =68 are obtained, u bm1 (t) and the correlation coefficient ρ1 of u fn1 (t) are calculated, u bn1 (t) and the correlation coefficient ρ2 of u fm1 (t) are calculated, ρ1=-0.42 and ρ2=-0.41 are obtained, which are less than the threshold value 0.8, so it is determined that the line has an internal fault.

[0111] Example 3

[0112] like Figure 7 and Figure 8 As shown, after a bipolar lightning strike fault occurs 50km from the protection installation location, the protection components activate. The reverse traveling wave u of the local line-mode voltage is calculated. bm (k) The second wavefront point K2m and the reverse traveling wave u of the opposite line-mode voltage. bn (k) The second wavefront point K2n appears, and K2m = 70 is calculated. 2n =304, calculate u bm1 (t) and u fn1 The correlation coefficient ρ1 of (t) is used to calculate u. bn1 (t) and u fm1 The correlation coefficient ρ2 of (t) yields ρ1 = -0.71 and ρ2 = -0.64, which are less than the threshold value of 0.8. Therefore, it is determined that the line has an internal fault.

[0113] Example 4

[0114] like Figure 9 and Figure 10 As shown, after a lightning strike occurs 450km from the protection installation location, the protection components activate. The reverse traveling wave u of the local line-mode voltage is calculated. bm (k) The second wavefront point K2m and the reverse traveling wave u of the opposite line-mode voltage. bn (k) The second wavefront point K2n appears, and we calculate K2m = 34, K2n = 304. Calculate u. bm1 (t) and u fn1 The correlation coefficient ρ1 of (t) is used to calculate u. bn1 (t) and u fm1 The correlation coefficient ρ2 of (t) is obtained as ρ1=0.96ρ2=0.98, which is greater than the threshold value of 0.8. Therefore, it is determined that the line has been affected by lightning interference.

[0115] To comprehensively verify the impact of disturbance distance and transition resistance on the discrimination results, different types of lightning strikes and different types of ordinary short-circuit faults inside and outside the zone were set at distances of 50km, 100km, 200km, 300km, and 450km. For the ordinary short-circuit faults, transition resistances of 0Ω, 100Ω, and 500Ω were set respectively, with a lightning current parameter of 1.2 / 50μs. The proposed method for identifying faults inside the zone and lightning interference was verified based on simulation results. The verification results are shown in Table 2.

[0116] Table 2. Calculation results of correlation coefficients under different fault conditions.

[0117]

[0118]

[0119]

[0120] It can be seen that for different intra-zone, extra-zone ordinary short circuit faults and different types of lightning, the intra-zone fault and lightning interference identification method proposed by the application can accurately and quickly distinguish, and the discrimination result is not affected by the transition resistance, fault distance, etc.

Claims

1. A method for identifying lightning interference of a flexible direct current (HVDC) transmission line based on a traveling wave correlation coefficient, characterized in that, Specifically comprising the following steps: Step 1, the notebook end line mode voltage forward wave and line mode voltage backward wave are and , the opposite end line mode voltage forward wave and line mode voltage backward wave are and , the line mode voltage forward wave , the line mode voltage backward wave are calculated; the specific process of the step 1 is that: Step 1.1, when the protection starting element is started, the positive electrode voltage at the protection installation site is read , the positive electrode current , the negative electrode voltage , the negative electrode current , respectively, are subtracted from the average values of the positive electrode voltage , the positive electrode current , the negative electrode voltage , and the negative electrode current 10 ms before the protection is started, to obtain the positive electrode voltage fault component , the positive electrode current fault component , the negative electrode voltage fault component , and the negative electrode current fault component , and the calculation formula is shown in formula (1): （1） Step 1.2, calculating the line-mode voltage fault component within the data window , the line-mode current fault component , the calculation formula is shown in equation (2): （2） Step 1.3, calculating the forward wave of the line-mode voltage and the backward wave of the line-mode voltage The formulas are shown in equations (3) and (4): （3） （4） wherein Z is the line wave impedance; Step 2, take the q points after the starting point of the line mode voltage forward wave of the local end, denoted as , =1, 2, 3...q, send to the opposite end, and receive the line mode voltage forward wave data of the q points after the starting point sent by the opposite end , =1, 2, 3...q; the specific process of step 2 is: for , take the q points after the starting point, usually q is 300, denoted as , for , take the q points after the starting point, denoted as , send to the opposite end, and receive sent by the opposite end Step 3, finding the second wave head point of the backward wave of the local line mode voltage and the second wave head point of the backward wave of the opposite line mode voltage ; the specific process of the step 3 is that: For the line mode voltage anti-travel wave of the local end , take p points from the starting point of the fault of the local end, denoted as , =1, 2, 3...p, for the line mode voltage anti-travel wave of the opposite end , take p points from the starting point of the fault of the opposite end, denoted as , =1, 2, 3...p; from the wavelet transform of and respectively according to the following formula (5), formula (6), formula (7), formula (8), calculate the second wave head point of the line mode voltage anti-travel wave of the local end and the second wave head point of the line mode voltage anti-travel wave of the opposite end ; the process of extracting the second wave head of the line mode voltage anti-travel wave by the wavelet transform modulus maxima method is as follows: the wavelet base function Ψ (t) takes the Haar wavelet function as shown in formula (5): （5） For the function the discrete wavelet transform is: （6） The wavelet transform is performed on and respectively, i.e. let and be the wavelet transform of and respectively. （7） （8） Taking the first level wavelet coefficients, i.e. j = 1, we get and the modulus maxima of and are calculated. If With All satisfy: （9） （10） then is a modulus maxima point of the wavelet transform , is a modulus maxima, is a modulus maxima point of the wavelet transform , is the corresponding modulus maxima, then , ; Step 4, after the protection main criterion has determined that the line has not occurred out-of-area fault, for , from after taking q points, recorded as , for , from after taking q points, recorded as , the correlation coefficient of and is calculated , the correlation coefficient of and is calculated , send to the opposite end, while receiving sent by the opposite end; Step 5, set the lightning interference threshold value in the area , if , then , and , if , then , it is determined that the transmission line is subjected to lightning interference, otherwise, it is not lightning interference.

2. The method of claim 1, wherein the method is based on a correlation coefficient of a traveling wave. The specific process of step 4 is as follows: After the protection main criterion has determined that no external fault has occurred on the line, for , from after q points, recorded as , =1, 2, 3...q, for , from after q points, recorded as , according to formula (11) and formula (12), the correlation coefficient of is calculated , the correlation coefficient of is calculated , and is sent to the opposite end, and sent by the opposite end is received simultaneously （11） （12） wherein = 1, 2, 3...q.

3. The method of claim 2, wherein the method is based on a correlation coefficient of a traveling wave. The specific process of step 5 is as follows: Setting the in-zone lightning interference threshold value And If either equation (13) or equation (14) is true, then the lightning interference is determined, otherwise the in-zone failure is determined, as follows: （13） （14） wherein is with the correlation coefficient of is with the correlation coefficient of

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