Method for identifying lightning interference of flexible direct current transmission line based on instantaneous traveling wave power

Abstract

The application discloses a lightning stroke interference identification method of a flexible direct current (HVDC) transmission line based on instantaneous traveling wave power, and specifically comprises the following steps: step 1, calculating line mode voltage reverse traveling wave and line mode current reverse traveling wave; step 2, obtaining line mode voltage reverse traveling wave high-frequency component and low-frequency component and line mode current reverse traveling wave high-frequency component and low-frequency component through a digital filter respectively; step 3, obtaining instantaneous traveling wave power high-frequency component by calculating the absolute value of the product of the voltage and current reverse traveling wave high-frequency components, and obtaining instantaneous traveling wave power low-frequency component by calculating the absolute value of the product of the voltage and current reverse traveling wave low-frequency components; and step 4, calculating the ratio of the integral value of P h (k1) in a time window of 1 ms after the start of a fault element to determine whether lightning stroke interference occurs. According to the difference in instantaneous traveling wave power frequency domain energy distribution, the application identifies lightning stroke interference, has high transition resistance resistance, and has low requirements on a sampling frequency.

Description

Technical Field

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

[0002] In power systems, accurate identification of lightning interference is crucial for ensuring the safe operation of transmission lines. Traditional lightning interference identification methods mainly rely on time-domain characteristics, but these methods have some obvious limitations.

[0003] First, time-domain characteristic-based methods typically focus on waveform change trends. As mentioned in the literature, these methods may use the current change before and after a lightning strike or fault as a feature. However, the traveling wave after a lightning strike undergoes reflection and refraction, and the traveling wave during a fault may also have a zero-crossing point, making the reliability of time-domain characteristic-based methods insufficient. Furthermore, these methods are significantly affected by the busbar structure, and their operational performance needs improvement under conditions of abnormal data transmission or noise interference. Second, time-domain characteristics are highly sensitive to interference from transition resistance. The presence of transition resistance can lead to inaccurate impedance measurements in distance protection, potentially causing the protection to fail to operate or to malfunction. The magnitude and characteristics of the transition resistance have a significant impact on distance protection, especially in short-line scenarios.

[0004] In contrast, frequency domain-based methods exhibit significant advantages. Frequency domain methods typically employ time-frequency analysis tools such as wavelet transform and Hilbert-Huang transform to reveal the energy distribution characteristics of faults and lightning interference. These methods can effectively distinguish between lightning interference and short-circuit faults because they focus on the spectral components of the signal, rather than a single time-domain indicator. Frequency domain features are less dependent on lightning parameters and transition resistance, thus exhibiting better adaptability and robustness. Summary of the Invention

[0005] The purpose of this invention is to provide a method for identifying lightning interference in flexible DC transmission lines based on instantaneous traveling wave power. This method identifies lightning interference based on the difference in frequency domain energy distribution of instantaneous traveling wave power, has high tolerance to transition resistance, and has low requirements for sampling frequency.

[0006] The technical solution adopted in this invention is a method for identifying lightning interference in flexible DC transmission lines based on instantaneous traveling wave power, which specifically includes the following steps:

[0007] Step 1, Calculate the line-mode voltage reverse traveling wave and line mode current reverse traveling wave ;

[0008] Step 2: Based on the calculation results of Step 1, the high-frequency components of the line-mode voltage inverse traveling wave are obtained through digital filters. Low-frequency components High-frequency components of the reverse traveling wave of the line-mode current Low-frequency components ;

[0009] Step 3: Obtain the instantaneous traveling wave power high-frequency component by calculating the absolute value of the product of the high-frequency components of the voltage and current reverse traveling waves. P h ( k The instantaneous traveling wave power low-frequency component is obtained by calculating the absolute value of the product of the low-frequency components of the voltage and current reverse traveling waves. P l ( k );

[0010] Step 4, calculate separately P h ( k 1) P l ( k 1) The ratio of the integral values ​​within a 1 ms time window after the faulty component starts up. To determine whether lightning interference has occurred.

[0011] The invention is further characterized by:

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

[0013] Step 1.1: After the protection starting element starts, take 0.5 ms before starting and 1.0 ms after starting as the protection time window, read the voltage and current data in the data window, and read the positive voltage at the protection installation location. Negative voltage Positive current Negative current The values ​​were compared with the average positive voltage 10 ms before protection activation. Average negative electrode voltage Average positive current Average negative current Subtraction, positive voltage fault component Negative voltage fault component Positive current fault component With negative current fault component The calculation formula is shown in equation (1):

[0014] (1)

[0015] Step 1.2, calculate the line-mode voltage fault component within the time window using the following formula (2). Linear current fault component :

[0016] (2)

[0017] Step 1.3: Calculate the line-mode voltage reverse traveling wave within the time window using the following formula (3). :

[0018] (3)

[0019] In the formula, The line-mode impedance;

[0020] Step 1.4: Calculate the reverse traveling wave of the line-mode current within the time window using the following formula (4). :

[0021] (4).

[0022] The specific process of step 2 is as follows:

[0023] Step 2.1: Construct the type and parameters of the high-pass digital filter and the type and parameters of the low-pass digital filter, respectively;

[0024] Step 2.2, reverse the traveling wave of the line-mode voltage. and line mode current reverse traveling wave Substituting into the difference equation of the high-pass filter shown in equation (5), and As input electrical quantity x [ k ], thus obtaining the output high-frequency electrical components. y h [ k [1], that is, the high-frequency component of the reverse traveling wave of the line-mode voltage. High-frequency components of the reverse traveling wave of the line mode current ; Invert the traveling wave of the line-mode voltage and line mode current reverse traveling wave Substituting into the difference equation of the low-pass filter shown in equation (5), and As input electrical quantity x [ k ], thus obtaining the output high-frequency electrical components. y l [ k [1], that is, the low-frequency component of the line-mode voltage reverse traveling wave. High-frequency components of the reverse traveling wave of the line mode current :

[0025] (5)

[0026] In the formula:y h [ k 1]、 y h [ k 2]、 y h [ k 3]、 y h [ k 4] y h [ k [5] is the output electrical quantity calculated using the difference equation of a high-pass filter. , ; y l [ k 1]、 y l [ k 2]、 y l [ k 3]、 y l [ k 4] y l [ k [5] is the output electrical quantity calculated through the differential equation of the low-pass filter. , ; x [ k ]、 x [ k 1]、 x [ k– 2]、 x [ k– 3]、 x [ k– 4] x [ k 5] represents the current and previous input electrical quantities. , ; k These are time-domain sampling points.

[0027] The specific process of step 3 is as follows:

[0028] Step 3.1: Calculate the instantaneous traveling wave power high-frequency component by using equation (6) to obtain the absolute value of the product of the high-frequency components of the voltage and current reverse traveling waves from the start-up time of the faulty component to 1 ms after start-up. P h ( k ):

[0029] (6)

[0030] Step 3.2: Calculate the absolute value of the product of the low-frequency components of the reverse traveling wave of voltage and current from the start-up time of the faulty component to 1 ms after start-up using equation (7) to obtain the low-frequency component of the instantaneous traveling wave power. P l ( k ):

[0031] (7).

[0032] The specific process of step 4 is as follows:

[0033] Calculate using equation (8) P h ( k 1) P l ( k 1) The ratio between the integral values ​​within a 1 ms time window after the faulty component starts up. :

[0034] (8)

[0035] In the formula, 0≤ k 1≤ N -1; N This represents the number of sampling points from the moment the faulty component starts up to 1.0 ms after startup;

[0036] like > set If so, it is determined that a malfunction has occurred; if < set If so, it is judged to be lightning interference.

[0037] The beneficial effects of this invention are that it identifies lightning interference based on the frequency domain energy distribution characteristics of the instantaneous traveling wave power at a single end of the line. This method can be used in both bounded and unbounded flexible DC power grids, and it provides rapid identification, strong resistance tolerance, and low sampling frequency requirements. It can still effectively identify lightning interference even with 0 Ω and 500 Ω transition resistances and sampling frequencies of 50 kHz and 25 kHz. Attached Figure Description

[0038] Figure 1 This is a flowchart of the lightning interference identification method for flexible DC transmission lines based on instantaneous traveling wave power according to the present invention;

[0039] Figure 2 This is a simulation model diagram of a true bipolar MMC flexible DC transmission system at both ends;

[0040] Figure 3(a) shows the simulation verification stage, specifically the instantaneous traveling wave power time-domain waveform of the bipolar flexible DC system with an in-situ grounding fault at 250 km and a transition resistance of 500Ω, and the judgment results using the lightning interference identification method for flexible DC transmission lines based on instantaneous traveling wave power of this invention.

[0041] Figure 3(b) shows the frequency domain energy distribution ratio of the instantaneous traveling wave power time domain waveform after wavelet decomposition of the bipolar flexible DC system with an in-area ground fault at 250 km and a transition resistance of 500Ω in the simulation verification stage.

[0042] Figure 4 This is a simulation model diagram of a four-terminal MMC flexible DC transmission network;

[0043] Figure 5(a) shows the simulation verification stage, such as Figure 4 The time-domain waveform of the instantaneous traveling wave power of the four-terminal flexible DC power grid within a 100 km radius is compared with the judgment results of the lightning interference identification method for flexible DC transmission lines based on instantaneous traveling wave power of the present invention.

[0044] Figure 5(b) shows the simulation verification stage, such as... Figure 4 The frequency domain energy distribution ratio of the instantaneous traveling wave power time domain waveform of the lightning interference around the four-terminal flexible DC power grid at a distance of 100 km is shown after wavelet decomposition.

[0045] Figure 6 This is a simulation model diagram of a four-terminal "mesh-type" MMC flexible DC transmission network;

[0046] Figure 7(a) shows the simulation verification stage, such as Figure 6 The instantaneous traveling wave power in the time domain and waveform domain of the four-terminal "mesh-type" flexible DC system at a distance of 100 km for lightning strike fault identification is compared with the determination results of the lightning interference identification method for flexible DC transmission lines based on instantaneous traveling wave power of the present invention.

[0047] Figure 7(b) shows the simulation verification stage, such as Figure 6 The instantaneous traveling wave power time-domain waveform of the four-terminal "mesh-type" flexible DC system at a distance of 100 km for lightning strike fault identification is shown in the frequency domain energy distribution ratio diagram after wavelet decomposition. Detailed Implementation

[0048] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0049] This invention presents a method for identifying lightning interference in flexible DC transmission lines based on the frequency domain energy distribution of instantaneous traveling wave power. By analyzing the frequency domain characteristics of the traveling wave signal on the line after a lightning strike, the unique frequency domain energy distribution characteristics of lightning interference are extracted. Compared with traditional time-domain analysis methods, frequency-domain analysis can more comprehensively reflect the essential characteristics of lightning interference, effectively improving identification accuracy. Furthermore, this method can achieve rapid response and real-time monitoring, significantly enhancing the reliability and safety of flexible DC transmission systems.

[0050] A method for identifying lightning interference in flexible DC transmission lines based on the frequency domain energy distribution of instantaneous traveling wave power, such as... Figure 1 As shown, the specific steps include the following:

[0051] Step 1: After the protection starting element starts, take 0.5 ms before starting and 1.0 ms after starting as the protection time window, and read the voltage and current data within the time window. Calculate the positive voltage fault component. Negative voltage fault component With negative current fault component Then, the line-mode voltage fault component is calculated from this. Linear current fault component Finally, the reverse traveling wave of the line-mode voltage was calculated based on this. Linear current reverse traveling wave The specific process of step 1 is as follows:

[0052] Step 1.1: After the protection starting element starts, take 0.5 ms before starting and 1.0 ms after starting as the protection time window, and read the voltage and current data within the data window. Read the positive voltage at the protection installation location. Negative voltage Positive current Negative current The values ​​were compared with the average positive voltage 10 ms before protection activation. Average negative electrode voltage Average positive current Average negative current Subtraction, positive voltage fault component Negative voltage fault component Positive current fault component With negative current fault component The calculation formula is shown in equation (1):

[0053] (1)

[0054] Step 1.2: Calculate the line-mode voltage fault component within the time window. Linear current fault component The calculation formula is shown in equation (2):

[0055] (2)

[0056] Step 1.3: Calculate the line-mode voltage back-traveling wave within the time window. The calculation formula is shown in equation (3):

[0057] (3)

[0058] In the formula, The impedance of the line mode wave is given.

[0059] Step 1.4: Calculate the reverse traveling wave of the line-mode current within the time window. The calculation formula is shown in equation (4):

[0060] (4)

[0061] In the formula, The impedance of the line mode wave is given.

[0062] Step 2, take the inverse traveling wave of the line-mode voltage from Step 1. Reverse traveling wave of line mode current The high-frequency components of the line-mode voltage inverse traveling wave were obtained by using digital filters. Low-frequency components High-frequency components of the reverse traveling wave of the line-mode current Low-frequency components The specific process of step 2 is as follows:

[0063] Step 2.1: Based on the significant difference in energy distribution between fault and interference energy proportions in the instantaneous traveling wave power distribution from 0 to 1.5 kHz, the 0-1.5 kHz range is defined as the low-frequency band, and frequencies above 1.5 kHz as the high-frequency band. The high-pass digital filter type and parameters are constructed as follows: Chebyshev Type II high-pass filter, stopband cutoff frequency 1.5 kHz, passband cutoff frequency 2.5 kHz, stopband attenuation 30 dB, and passband ripple 1 dB. The low-pass digital filter type and parameters are also constructed as follows: Chebyshev Type II low-pass filter, stopband cutoff frequency 1.0 kHz, passband cutoff frequency 1.5 kHz, stopband attenuation 30 dB, and passband ripple 1 dB.

[0064] Step 2.2, reverse the traveling wave of the line-mode voltage. and line mode current reverse traveling wave Substituting into the difference equation of the high-pass filter shown in equation (5), and As input electrical quantity x [ k ], thus obtaining the output high-frequency electrical components. y h [ k [1], that is, the high-frequency component of the reverse traveling wave of the line-mode voltage. High-frequency components of the reverse traveling wave of the line mode current ; Invert the traveling wave of the line-mode voltage and line mode current reverse traveling wave Substituting into the difference equation of the low-pass filter shown in equation (5), and As input electrical quantity x [ k ], thus obtaining the output high-frequency electrical components. y l [ k [1], that is, the low-frequency component of the line-mode voltage reverse traveling wave. High-frequency components of the reverse traveling wave of the line mode current :

[0065] (5)

[0066] In the formula: y h [ k 1]、 y h [ k 2]、 y h [ k 3]、 y h [ k 4] y h [ k [5] is the output electrical quantity calculated using the difference equation of a high-pass filter. , ; y l [ k 1]、 y l [ k 2]、 y l [ k 3]、 yl [ k 4] y l [ k [5] is the output electrical quantity calculated through the differential equation of the low-pass filter. , ; x [ k ]、 x [ k 1]、 x [ k– 2]、 x [ k– 3]、 x [ k– 4] x [ k 5] represents the current and previous input electrical quantities. , ; k These are time-domain sampling points.

[0067] Step 3: Obtain the instantaneous traveling wave power high-frequency component by calculating the absolute value of the product of the high-frequency components of the voltage and current reverse traveling waves. P h ( k The instantaneous traveling wave power low-frequency component is obtained by calculating the absolute value of the product of the low-frequency components of the voltage and current reverse traveling waves. P l ( k ).

[0068] The specific process of step 3 is as follows:

[0069] Step 3.1: Calculate the instantaneous traveling wave power high-frequency component by using equation (6) to obtain the absolute value of the product of the high-frequency components of the voltage and current reverse traveling waves from the start-up time of the faulty component to 1 ms after start-up. P h ( k ):

[0070] (6)

[0071] Step 3.2: Calculate the absolute value of the product of the low-frequency components of the reverse traveling wave of voltage and current from the start-up time of the faulty component to 1 ms after start-up using equation (7) to obtain the low-frequency component of the instantaneous traveling wave power. P l ( k ):

[0072] (7).

[0073] Step 4, calculate separately P h ( k 1) P l ( k 1) The ratio of the integral values ​​within a 1 ms time window after the faulty component starts up. The specific process of step 4 is as follows:

[0074] Calculate using equation (8) P h ( k 1) P l ( k 1) The ratio between the integral values ​​within a 1 ms time window after the faulty component starts up. .

[0075] (8)

[0076] In the formula, 0≤ k 1≤ N -1; N This represents the number of sampling points from the moment the faulty component starts up to 1.0 ms after startup.

[0077] Step 5, if > set If so, it is determined that a malfunction has occurred; if < set If so, it is judged to be lightning interference.

[0078] The specific process of step 5 is as follows:

[0079] like > set If so, it is determined that a malfunction has occurred; if < set If the time is right, it is determined to be lightning interference. The obtained ratio is then... With threshold value set In comparison, as shown in equation (9), according to The relationship between the magnitude of the threshold value and the lightning strike disturbance is used as a criterion for identification.

[0080] (9)

[0081] Based on the differences in the frequency domain distribution of instantaneous traveling wave power during fault occurrence and lightning interference, and the simulation test results, a threshold value is selected. set =5.

[0082] As attached Figure 2 The figure shown is a simulation model diagram of a two-terminal flexible DC transmission system. The figure includes a current-limiting reactor. L =0.2H, MMC1 and MMC2 are modular converters, and P1 and P2 are line boundary protection measuring points. f 1, f 2 and f 3 represents the location of the disturbance. This system has a rated voltage of ±500 kV, a rated transmission capacity of 3000 MVA, and a total transmission line length of 500 km. An overhead line frequency-varying parameter model is used, and its line surge impedances are Z... c0 =320 Z c1 =260 During system simulation, the sampling frequency was 100 kHz, and a 1.2 / 50 μs standard lightning current model was used to simulate lightning strikes. The entire text uses Line 1, measuring point P1 as an example; the fault distance is the distance from the fault location to measuring point P1, as shown in the attached figure. Figure 1 The identification process identifies grounding faults.

[0083] Example 1

[0084] As shown in Figure 3(a), in the case of Figure 2 In the dual-ended flexible DC transmission system shown, a transition resistance of 500 Ω occurs 250 km from the protection measuring point P1. The simulated value of the line-mode voltage reverse traveling wave measured at the protection measuring point during a positive ground fault. After the protection element starts, the line-mode voltage reverse traveling wave data of the 50 sampling points before start-up and the 100 sampling points after start-up are read. Calculation. The value is determined as a fault, and the protection system operates. Figure 3(b) shows a bar chart of the frequency domain energy distribution of the instantaneous traveling wave power, proving the correctness of the protection principle.

[0085] As attached Figure 4 The figure shown is a simulation model diagram of a four-terminal MMC flexible DC transmission network. The figure includes a current-limiting reactor. L =0.2H, MMC1, MMC2, MMC3, and MMC4 are modular converters, and P1 and P2 are line boundary protection measurement points. f 1 represents the location of the disturbance. The rated voltage between MMC1 and MMC2 is ±500 kV, the rated transmission capacity is 3000 MVA, and the total length of the transmission line is 207.9 km. An overhead line frequency-varying parameter model is used, and the line surge impedances are Z... c0 =310 Z c1 =250 During system simulation, the sampling frequency was 100 kHz, and a 1.2 / 50 μs standard lightning current model was used to simulate lightning strikes. The four-terminal flexible DC power grid structure is highly symmetrical. This paper takes Line 1, measurement point P1 as an example. The fault distance is the distance from the fault location to measurement point P1, as shown in the attached figure. Figure 1 The identification process identifies lightning interference.

[0086] Example 2

[0087] As shown in Figure 5(a), in the case of Figure 4 The simulated line-mode voltage back-traveling wave value measured at the protection measuring point in the four-terminal MMC flexible DC transmission network shown is obtained when a lightning strike occurs 100 km from the protection installation location. After the protection element is activated, line-mode voltage back-traveling wave data from the first 50 sampling points and the last 100 sampling points are read. Calculations are then performed. The value was determined to be lightning interference, and the protection was activated. Figure 5(b) shows a bar chart of the frequency domain energy distribution of the instantaneous traveling wave power, proving the correctness of the protection principle.

[0088] As attached Figure 6 The diagram shown is a simulation model of a four-terminal "mesh-type" MMC flexible DC transmission network. The diagram includes a current-limiting reactor. L =0.2H, MMC1, MMC2, MMC3, and MMC4 are modular converters, and P1 and P2 are line boundary protection measurement points. f 1 represents the location of the disturbance. The rated voltage between MMC1 and MMC2 is ±500 kV, the rated transmission capacity is 3000 MVA, and the total length of the transmission line is 207.9 km. An overhead line frequency-varying parameter model is used, and the line surge impedances are Z... c0 =310 Z c1 =250 During system simulation, the sampling frequency was 100 kHz, and a 1.2 / 50 μs standard lightning current model was used to simulate lightning strikes. The four-terminal "mesh-type" flexible DC power grid structure is highly symmetrical. This paper takes Line 1 and measuring point P1 as an example. The fault distance is the distance from the fault location to measuring point P1, as shown in the attached figure. Figure 1 The identification process identifies lightning strike faults.

[0089] Example 3

[0090] As shown in Figure 7(a), in the case of Figure 6 The simulated line-mode voltage back-traveling wave value measured at the protection measuring point is shown in the four-terminal "mesh-type" flexible DC transmission system. When a ground fault occurs 100km from the protection installation location, the back-traveling wave data of the line-mode voltage at the protection measuring point is recorded. After the protection element is activated, the line-mode voltage back-traveling wave data of the 50 sampling points before activation and the 100 sampling points after activation are read. Calculations are then performed. The value is determined as a fault, and the protection system operates. Figure 7(b) shows a bar chart of the frequency domain energy distribution of the instantaneous traveling wave power, proving the correctness of the protection principle.

[0091] To comprehensively verify the impact of fault distance, transition resistance, sampling frequency, and system type on the protection method, grounding fault and lightning interference simulations were conducted at the beginning, end, and midpoint of a bipolar DC transmission system, a four-terminal flexible DC grid, and a four-terminal "mesh-type" flexible DC grid. The lightning interference identification method was then validated based on the simulation results.

[0092] Table 1 provides simulation data for different fault distances and transition resistances on bipolar flexible DC transmission lines. Data within the time window shows that during lightning interference... Less than 5; in the event of a ground fault, Greater than 5. Lightning interference can be identified at different fault distances.

[0093] Table 1 Simulation results for different fault distances and transition resistances

[0094]

[0095] Table 2 provides simulation data for a four-terminal flexible DC power grid and a four-terminal "mesh-type" flexible DC power grid. Data within the time window shows that during lightning interference... Less than 5; in the event of a ground fault, Greater than 5. Lightning interference can be identified under grounding faults with different transition resistances.

[0096] Table 2 Simulation results for different system types

[0097]

[0098] Table 3 provides simulation data for grounding faults and lightning interference in a four-terminal flexible DC power grid and a four-terminal "mesh-type" flexible DC power grid. Data within the time window shows that during lightning interference... Less than 5; in the event of lightning strikes or grounding faults, Greater than 5. The sampling frequency has no significant impact on the protection performance, and both can effectively identify lightning interference.

[0099] Table 3 Simulation results at different sampling frequencies

[0100]

[0101] This invention utilizes the fact that during a fault, the instantaneous traveling wave power has a higher proportion of low-frequency energy, while during lightning interference, the instantaneous traveling wave power has a higher proportion of high-frequency energy. High- and low-frequency components of the instantaneous traveling wave power are extracted using a digital filter, and their proportions are calculated accordingly. This method identifies lightning interference based on the difference in the frequency domain energy distribution of the instantaneous traveling wave power. The combination of frequency domain protection principles and time-domain algorithms enables rapid identification, strong resistance tolerance, and low sampling frequency requirements. Furthermore, because its lightning identification principle, built using inverse traveling waves, can be used in both bounded and unbounded flexible DC power grids.

Claims

1. A method for identifying lightning interference in flexible DC transmission lines based on instantaneous traveling wave power, characterized in that: Specifically, the steps include the following: Step 1, Calculate the line-mode voltage reverse traveling wave and line mode current reverse traveling wave The specific process of step 1 is as follows: Step 1.1: After the protection starting element starts, take 0.5 ms before starting and 1.0 ms after starting as the protection time window, read the voltage and current data in the data window, and read the positive voltage at the protection installation location. Negative voltage Positive current Negative current The values ​​were compared with the average positive voltage 10 ms before protection activation. Average negative electrode voltage Average positive current Average negative current Subtraction, positive voltage fault component Negative voltage fault component Positive current fault component With negative current fault component The calculation formula is shown in equation (1): （1） Step 1.2, calculate the line-mode voltage fault component within the time window using the following formula (2). Linear current fault component : （2） Step 1.3: Calculate the line-mode voltage reverse traveling wave within the time window using the following formula (3). : （3） In the formula, The line-mode impedance; Step 1.4: Calculate the reverse traveling wave of the line-mode current within the time window using the following formula (4). : （4） Step 2: Based on the calculation results of Step 1, the high-frequency components of the line-mode voltage inverse traveling wave are obtained through digital filters. Low-frequency components ; High-frequency components of the reverse traveling wave of the linear mode current Low-frequency components The specific process of step 2 is as follows: Step 2.1: Construct the type and parameters of the high-pass digital filter and the type and parameters of the low-pass digital filter, respectively; Step 2.2, reverse the traveling wave of the line-mode voltage. and line mode current reverse traveling wave Substituting into the difference equation of the high-pass filter shown in equation (5), and As input electrical quantity x [ k ], thus obtaining the output high-frequency electrical components. y h [ k [1], that is, the high-frequency component of the reverse traveling wave of the line-mode voltage. High-frequency components of the reverse traveling wave of the line mode current ; Invert the traveling wave of the line-mode voltage and line mode current reverse traveling wave Substituting into the difference equation of the low-pass filter shown in equation (5), and As input electrical quantity x [ k ], thus obtaining the output high-frequency electrical components. y l [ k [1], that is, the low-frequency component of the line-mode voltage reverse traveling wave. High-frequency components of the reverse traveling wave of the line mode current : （5） In the formula: y h [ k 1]、 y h [ k 2]、 y h [ k 3]、 y h [ k 4] y h [ k [5] is the output electrical quantity calculated using the difference equation of a high-pass filter. , ; y l [ k 1]、 y l [ k 2]、 y l [ k 3]、 y l [ k 4] y l [ k [5] is the output electrical quantity calculated through the differential equation of the low-pass filter. , ; x [ k ]、 x [ k 1]、 x [ k– 2]、 x [ k– 3]、 x [ k– 4] x [ k 5] represents the current and previous input electrical quantities. , ; k For time-domain sampling points; Step 3: Obtain the instantaneous traveling wave power high-frequency component by calculating the absolute value of the product of the high-frequency components of the voltage and current reverse traveling waves. P h ( k The instantaneous traveling wave power low-frequency component is obtained by calculating the absolute value of the product of the low-frequency components of the voltage and current reverse traveling waves. P l ( k ); The specific process of step 3 is as follows: Step 3.1: Calculate the instantaneous traveling wave power high-frequency component by using equation (6) to obtain the absolute value of the product of the high-frequency components of the voltage and current reverse traveling waves from the start-up time of the faulty component to 1 ms after start-up. P h ( k ): （6） Step 3.2: Calculate the absolute value of the product of the low-frequency components of the reverse traveling wave of voltage and current from the start-up time of the faulty component to 1 ms after start-up using equation (7) to obtain the low-frequency component of the instantaneous traveling wave power. P l ( k ): （7） Step 4, calculate separately P h ( k 1) P l ( k 1) The ratio of the integral values ​​within a 1 ms time window after the faulty component starts up. To determine whether lightning interference has occurred; the specific process of step 4 is as follows: calculate using formula (8) P h ( k 1) P l ( k 1) The ratio between the integral values ​​within a 1 ms time window after the faulty component starts up. : （8） In the formula, 0≤ k 1≤ N -1; N This represents the number of sampling points from the moment the faulty component starts up to 1.0 ms after startup; like > set If so, it is determined that a malfunction has occurred; if < set If so, it is judged to be lightning interference.

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