A frequency difference-based three-phase adaptive reclosing method and system for wind farm transmission lines

Abstract

The present application relates to a kind of wind farm transmission line three-phase adaptive reclosing method and system based on frequency difference, belong to the field of power system relay protection.The method first in the maximum sliding time window, using capacitor voltage transformer (CVT) acquisition line M end voltage wave data and pre-processing;Using Fourier transform (FFT) to voltage signal is spectrum analyzed, obtain the amplitude-frequency curve with frequency as abscissa and amplitude as ordinate;Calibrate amplitude-frequency curve local peak, calculate the difference between the frequency corresponding to each peak;Adjacent sliding time window is judged whether the difference of frequency is equal, if equal, fault still exists, not reclosing circuit breaker, if the difference of frequency is not equal, then judge fault disappears, calculate the moment of fault disappearance, combined with the ionization after fault disappearance and determine reclosing time, output closing signal.The present application has lower sampling rate requirement, smaller error, easy to realize.

Description

Technical Field

[0001] This invention relates to a three-phase adaptive reclosing method and system for wind farm transmission lines based on frequency difference, belonging to the field of power system relay protection. Background Technology

[0002] Currently, in China's wind farms, the main power generation equipment is doubly-fed and permanent magnet direct-drive wind turbines. These two types of generators each occupy a certain proportion, forming a diverse group of wind turbine units.

[0003] For 220kV wind farm transmission lines, automatic reclosing systems typically set a fixed time delay after a circuit breaker trips before allowing the circuit breakers at both ends to reclose. However, this method does not determine the nature of the fault before reclosing. If the fault persists, the power electronic equipment within the wind farm may suffer secondary damage. Based on long-term operational experience, approximately 90% of transmission line faults are transient, meaning that in most cases, reclosing can be performed without waiting for a fixed time delay. Therefore, developing an adaptive reclosing strategy capable of reliably identifying the nature of faults is crucial for wind farm transmission lines.

[0004] Many researchers have conducted extensive research on reclosing technology for wind power transmission lines, achieving some valuable results. Some have proposed reclosing methods based on bus voltage de-voltage and line voltage detection, as well as continuous bus voltage de-voltage detection, to improve the success rate of reclosing. However, these methods mainly focus on whether reclosing can be successfully initiated, and do not address the secondary impact that reclosing may cause to the wind power transmission system under permanent fault conditions. Other researchers have proposed an adaptive reclosing strategy based on the ratio of active to reactive power of the faulty phase, but this method requires processing multiple frequency components, making filtering difficult. Additionally, some researchers have proposed an active detection-based adaptive reclosing method that injects a low current into the transmission line and uses the integral of the injected current amplitude to determine the nature of the fault. This method requires the installation of signal injection equipment and may require modifications to the existing equipment structure, resulting in relatively high costs. Therefore, existing adaptive reclosing methods for wind farm transmission lines still have shortcomings, and new methods need to be found to meet the adaptive reclosing requirements of wind farm transmission lines. Summary of the Invention

[0005] The purpose of this invention is to provide a three-phase adaptive reclosing method and system for wind farm transmission lines based on frequency difference, aiming to solve the technical problem that existing adaptive reclosing methods for wind farm transmission lines require the installation of signal injection equipment and may require modifications to the equipment structure of existing projects, resulting in relatively high costs.

[0006] In view of the above, after the circuit breakers at both ends of the transmission line trip, the systems on both sides stop supplying energy to the line. The residual energy in the line continuously decays and dissipates, and the voltage is in a free oscillation state. Its oscillation frequency reflects the fault location. Therefore, the nature of the line fault can be identified using the frequency domain signal of the residual voltage. The presence or absence of a fault can be identified by detecting whether the stable frequency difference of the residual voltage signal is equal. The frequency difference of the fault traveling wave spectrum... It is only related to the fault distance, and is not related to the measurement end back-side system and fault boundary conditions. It has low requirements for sampling rate, small error, and is easy to implement.

[0007] The technical solution of this invention is: a three-phase adaptive reclosing method and system for wind farm transmission lines based on frequency difference. It uses a capacitive voltage transformer (CVT) to collect traveling wave data of the voltage at the M end of the line, performs spectral analysis on the voltage signal using Fourier transform (FFT) within the maximum sliding time window, calculates the frequency difference between each peak value, and uses whether the frequency difference within adjacent sliding time windows is equal to determine whether a fault exists. Based on this, the reclosing time is calculated to achieve adaptive reclosing.

[0008] The specific steps are as follows:

[0009] Step 1: Collect traveling wave data of voltage at the M end of the line using a capacitive voltage transformer (CVT); specifically, a capacitive voltage transformer is installed at the M end on the wind farm side of the transmission line, and the voltage of the fault phase is sampled when a fault occurs in the transmission line.

[0010] Step 2: Preprocess the acquired voltage traveling wave data;

[0011] Step 3: Use Fourier Transform (FFT) to perform spectrum analysis on the preprocessed voltage traveling wave data within the sliding time window to obtain the amplitude-frequency curve with frequency on the horizontal axis and amplitude on the vertical axis.

[0012] Step 4: Calibrate the local peaks of the amplitude-frequency curve and calculate the frequency difference between each peak.

[0013] Step 5: Within the maximum discrimination time limit, determine whether the frequency difference between adjacent sliding time windows is equal. If they are equal, the fault still exists, and the circuit breaker is not closed. If the frequency difference is not equal, the fault is determined to have disappeared, and Step 6 is executed.

[0014] Step 6: Calculate the time when the fault disappears, combine the deionization after the fault disappears to determine the reclosing time, and output the closing signal.

[0015] Step 2 specifically refers to:

[0016] Step 2.1: Perform phase mode transformation on the voltage traveling wave data at terminal M;

[0017] Step 2.2: Perform differential transformation on the data after phase mode transformation.

[0018] Step 3 specifically refers to:

[0019] Step 3.1: Define the length of the sliding time window as T;

[0020] Step 3.2: Perform spectrum analysis on the differentially transformed voltage signal using FFT within a sliding time window;

[0021] Step 3.3: Obtain the amplitude-frequency curve of the spectrum analysis.

[0022] Step 4 specifically refers to:

[0023] Step 4.1: Obtain the frequencies corresponding to the peak values ​​of the amplitude-frequency curve within the i-th (i=1,2,3,…n) sliding time window, and define them as follows: ;

[0024] Step 4.2: Calculate the difference between adjacent frequencies , , , The mode of the frequency difference is defined as the frequency difference within the sliding time window. .

[0025] Step 5 specifically includes:

[0026] Step 5.1: Set the maximum discrimination time limit :

[0027]

[0028] In the formula, For automatic reclosing, a fixed time is set. The time when the circuit breaker trips after the fault occurs. Deionization time after the fault disappears;

[0029] Step 5.2: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit:

[0030]

[0031] Then it is determined that the fault disappears within the i+2 time window, where, It is the mode of the frequency difference within the window at time i+1. It is the mode of the frequency difference within the window at time i+2;

[0032] Step 5.3: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit:

[0033]

[0034] Then it is determined that the fault still exists within the window at time i+2.

[0035] Step 6 specifically refers to:

[0036] Step 6.1: Calculate the time when the fault disappears based on the obtained fault disappearance sliding window number i+2:

[0037]

[0038] In the formula, The moment the fault disappears;

[0039] Step 6.2: Combine the deionization time after the fault disappears The reclosing time is determined as follows:

[0040]

[0041] In the formula, This is the reclosing time.

[0042] To achieve the above objectives, this application also proposes a three-phase adaptive reclosing system for wind farm transmission lines based on frequency difference, comprising:

[0043] Electrical signal acquisition module, used for acquiring and processing data;

[0044] The numerical calculation module is used to calculate the frequency difference of each sliding time window. ;

[0045] The fault nature determination module is used to determine whether the fault has disappeared within the maximum determination time limit by combining a sliding time window, and output the determination result;

[0046] The reclosing execution module is used to receive the closing execution signal or closing lockout signal output by the fault nature determination module and execute the action.

[0047] The electrical signal acquisition module includes:

[0048] The voltage measurement unit is used to acquire the analog voltage signal on the secondary side of the CVT;

[0049] An analog-to-digital converter is used to convert analog signals into digital signals.

[0050] The numerical calculation module includes:

[0051] The phase-mode conversion unit is used to calculate the phase-mode components of the traveling wave of the voltage at the M terminal.

[0052] The numerical calculation unit is used to calculate the difference of the data after phase mode transformation, and uses FFT to perform spectral analysis on the preprocessed data and calculate the difference between the frequency peaks of each sliding time window.

[0053] The fault nature determination module includes:

[0054] The time limit setting unit is used to set the maximum discrimination time limit;

[0055] The fault nature discrimination unit is used to construct fault nature identification criteria and, within the maximum discrimination time limit, combine a sliding time window to determine the fault disappearance time. ;

[0056] The closing signal unit is used to output the closing execution signal or the closing lockout signal.

[0057] The reclosing execution module includes:

[0058] The closing start unit is used to initiate the reclosing of the circuit breakers at both ends of the transmitting line;

[0059] The closing interlocking unit is used to interlock the reclosing of the circuit breakers at both ends of the sending line.

[0060] The beneficial effects of this invention are:

[0061] (1) Compared with traditional reclosing, this invention can quickly determine the nature of the fault and take corresponding actions when a fault occurs in the power grid. For transient faults, it can automatically reclose the circuit breaker to restore power supply, thereby greatly reducing the number of power outages and the power outage time, and improving the reliability of power supply;

[0062] (2) Frequency difference of the fault traveling wave spectrum of the present invention It is only related to the fault distance, and is not related to the measurement end back-side system or fault boundary conditions, thus improving the discrimination accuracy. Attached Figure Description

[0063] Figure 1 This is a topology diagram of the simulation system of the present invention;

[0064] Figure 2 This is a flowchart of the adaptive reclosing process of the present invention;

[0065] Figure 3 This is a functional block diagram of the adaptive reclosing system of the present invention;

[0066] Figure 4 This is a diagram showing the voltage waveform analysis results on the secondary side of the CVT after a fault occurs in this invention.

[0067] Figure 5 This is a spectrum analysis diagram of Embodiment 1 of the present invention. Figure 5 (a) is the spectrum distribution diagram after the fault. Figure 5(b) is the spectrum distribution diagram after the circuit breaker is disconnected. Figure 5 (c) is the spectrum distribution after the fault disappeared;

[0068] Figure 6 This is a spectrum analysis diagram of Embodiment 2 of the present invention. Detailed Implementation

[0069] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0070] Example 1: The topology of the wind farm's AC transmission system is as follows: Figure 1 As shown. The transmission line is 358km long and uses overhead power transmission. A two-phase short-circuit fault (BC) is set to occur at time 0, 50km from end M on the transmission line MN. The fault is described as transient. After the fault occurs... Circuit breaker tripping, fault duration The sampling rate is 200kHz.

[0071] A three-phase adaptive reclosing method for wind farm transmission lines based on frequency difference. The workflow of this invention is as follows: Figure 2 As shown, the specific implementation steps are as follows:

[0072] Step 1: Use a capacitive voltage transformer (CVT) to collect the traveling wave data of the voltage at the M end of the line.

[0073] Specifically, the transmitting line at relative time 0 After a two-phase short-circuit fault occurs at point B and C, the residual voltage signal at terminal M is sampled using a capacitive voltage transformer. The voltage waveform analysis results are as follows: Figure 4 As shown; at the same time, the circuit breakers installed at both ends of the faulty line are... The circuit breaker trips all three phases at any time to isolate the fault.

[0074] Step 2: Preprocess the acquired voltage traveling wave data, specifically as follows:

[0075] Step 2.1: Perform phase mode transformation on the voltage traveling wave data at terminal M;

[0076] Step 2.2: Perform differential transformation on the data after phase mode transformation.

[0077] Step 3: Within the sliding time window, perform spectral analysis on the preprocessed voltage traveling wave data using Fourier Transform (FFT) to obtain the amplitude-frequency curve with frequency on the horizontal axis and amplitude on the vertical axis. Specifically:

[0078] Step 3.1: Define a sliding time window with a duration T of 20ms and a sliding factor s of 20ms. In this example, the window slides 38 times.

[0079] Step 3.2: Perform spectrum analysis on the differentially processed voltage signal using FFT within the sliding time window;

[0080] Step 3.3: Obtain the amplitude-frequency curve of the spectrum analysis. The analysis results are as follows: Figure 5 As shown.

[0081] Step 4: Calibrate the local peak values ​​of the amplitude-frequency curve and calculate the frequency differences corresponding to each peak value. Specifically:

[0082] Step 4.1: Obtain the frequencies corresponding to the peak values ​​of the amplitude-frequency curve within the i-th (i=1,2,3,…n) sliding time window, and define them as follows: In this embodiment, i = (1, 2, 3, ..., 38).

[0083] Step 4.2: Calculate the difference between adjacent frequencies , , , The mode of the frequency difference is defined as the frequency difference within the sliding time window. In this example, when time window i=1, i=2... ;i=3, i=4…i=38 .

[0084] Step 5: Within the maximum judgment time limit, determine whether the frequency difference within adjacent sliding time windows is equal. If they are equal, the fault still exists, and the circuit breaker is not closed. If the frequency difference is not equal, the fault is determined to have disappeared, and Step 6 is executed, specifically:

[0085] Step 5.1: Set the maximum discrimination time limit :

[0086]

[0087] In the formula, For automatic reclosing, a fixed time is set. The time when the circuit breaker trips after the fault occurs. The deionization time after the fault disappears; in this embodiment... , , ;

[0088] so In this example, the window slides a total of 38 times.

[0089] Step 5.2: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit:

[0090]

[0091] Then it is determined that the fault disappears within the i+2 time window, where, It is the mode of the frequency difference within the window at time i+1. It is the mode of the frequency difference within the window at time i+2;

[0092] Step 5.3: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit:

[0093]

[0094] Then it is determined that the fault still exists within the window at time i+2.

[0095] In this embodiment, This indicates that the fault disappeared within the third sliding time window, and proceed to Step 6.

[0096] Step 6: Calculate the fault disappearance time, combine it with the deionization after the fault disappearance to determine the reclosing time, and output the closing signal. Specifically:

[0097] Step 6.1: Based on the fault disappearance sliding window number i=3 obtained in Step 5.2, calculate the fault disappearance time. : ;

[0098] Step 6.2: Combine the deionization time after the fault disappears The reclosing time is determined as follows: Output closing signal.

[0099] The functional block diagram of a three-phase adaptive reclosing system for wind farm transmission lines based on frequency difference provided by this invention is as follows: Figure 3 As shown, it includes:

[0100] Electrical signal acquisition module, used to acquire voltage signals and process data;

[0101] The numerical calculation module is used to calculate the frequency difference of each sliding time window. In this example, when time window i=1, i=2... ;i=3, i=4…i=38 ;

[0102] The fault nature discrimination module is used to determine whether the fault has disappeared within the maximum discrimination time limit by combining a sliding time window, and output the discrimination result; in this example, when the time window i=3, it is determined that the fault has disappeared.

[0103] The reclosing execution module is used to receive the closing execution signal or closing lockout signal output by the fault nature determination module and execute the corresponding action.

[0104] The electrical signal acquisition module includes:

[0105] The voltage measurement unit is used to acquire the analog voltage signal on the secondary side of the CVT;

[0106] An analog-to-digital converter is used to convert analog signals into digital signals.

[0107] The numerical calculation module includes:

[0108] The phase-mode conversion unit is used to calculate the phase-mode components of the voltage traveling wave at the measurement terminal.

[0109] The numerical calculation unit is used to calculate the difference of the data after phase mode transformation. Within the maximum sliding time window, it uses FFT to perform spectral analysis on the preprocessed data and calculate the difference between the frequency peaks of each sliding time window.

[0110] The fault nature determination module specifically includes:

[0111] Time limit setting unit: used to set the maximum discrimination time limit, in this example The time window slid a total of 38 times;

[0112] The fault nature discrimination unit is used to construct fault nature identification criteria and, within the maximum discrimination time limit, combine a sliding time window to determine the fault disappearance time. In this example ;

[0113] The closing signal unit is used to output the closing execution signal or the closing lockout signal.

[0114] The reclosing execution module specifically includes:

[0115] The closing start unit is used to initiate the reclosing of the circuit breakers at both ends of the transmitting line;

[0116] The closing interlocking unit is used to interlock the reclosing of the circuit breakers at both ends of the sending line.

[0117] Example 2: The topology of the wind farm transmission system via AC lines is as follows Figure 1 As shown. The transmission line is 358km long and uses overhead power transmission. A two-phase short-circuit fault (BC) is set to occur at time 0, 10km from end M on the transmission line MN. The fault is permanent. After the fault occurs... The circuit breaker tripped, the fault duration was infinite, and the sampling rate was 200kHz.

[0118] A three-phase adaptive reclosing method for wind farm transmission lines based on frequency difference. The workflow of this invention is as follows: Figure 2 As shown, the specific implementation steps are as follows:

[0119] Step 1: Use a capacitive voltage transformer (CVT) to collect the traveling wave data of the voltage at the M end of the line.

[0120] Specifically, the transmission line is in After a two-phase short-circuit fault occurs (phases B and C), the residual voltage signal at terminal M is sampled using a capacitive voltage transformer. Simultaneously, the circuit breakers installed at both ends of the faulty line... The circuit breaker trips all three phases at any time to isolate the fault.

[0121] Step 2: Preprocess the collected voltage traveling wave data, specifically as follows;

[0122] Step 2.1: Perform phase mode transformation on the voltage traveling wave data at terminal M;

[0123] Step 2.2: Perform differential transformation on the data after phase mode transformation.

[0124] Step 3: Within the sliding time window, perform spectral analysis on the preprocessed voltage traveling wave data using Fourier Transform (FFT) to obtain the amplitude-frequency curve with frequency on the horizontal axis and amplitude on the vertical axis. Specifically:

[0125] Step 3.1: Define a sliding time window with a duration T of 20ms and a sliding factor s of 20ms.

[0126] Step 3.2: Perform spectrum analysis on the differentially processed voltage signal using FFT within the sliding time window;

[0127] Step 3.3: Obtain the amplitude-frequency curve of the spectrum analysis.

[0128] Step 4: Calibrate the local peak values ​​of the amplitude-frequency curve and calculate the frequency differences corresponding to each peak value. Specifically:

[0129] Step 4.1: Obtain the frequencies corresponding to the peak values ​​of the amplitude-frequency curve within the i-th (i=1,2,3,…n) sliding time window, and define them as follows: In this embodiment, i = (1, 2, 3, ..., 25).

[0130] Step 4.2: Calculate the difference between adjacent frequencies , , , The mode of the frequency difference is defined as the frequency difference within the sliding time window. In this embodiment, the frequency difference of each sliding time window is as follows: Figure 6 As shown in the figure, the frequency difference of each sliding time window is equal.

[0131] Step 5: Within the maximum judgment time limit, determine whether the frequency difference within adjacent sliding time windows is equal. If they are equal, the fault still exists, and the circuit breaker is not closed. If the frequency difference is not equal, the fault is determined to have disappeared, and Step 6 is executed, specifically:

[0132] Step 5.1: Set the maximum discrimination time limit :

[0133]

[0134] In the formula, For automatic reclosing, a fixed time is set. The time when the circuit breaker trips after the fault occurs. The deionization time after the fault disappears; in this embodiment... , , ;

[0135] so In this example, there are a total of 25 slides.

[0136] Step 5.2: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit:

[0137]

[0138] Then it is determined that the fault disappears within the i+2 time window, where, It is the mode of the frequency difference within the window at time i+1. It is the mode of the frequency difference within the window at time i+2;

[0139] Step 5.3: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit:

[0140]

[0141] Then it is determined that the fault still exists within the window at time i+2.

[0142] In this embodiment, as Figure 6 The frequency differences of the four time windows shown are all equal, and there is no case where the adjacent frequency differences are not equal. The fault nature identification criterion is not met, the fault nature is identified as a permanent fault, a blocking signal is output, and no reclosing operation is performed.

[0143] The technical features of the three-phase adaptive reclosing system for wind farm transmission lines based on frequency difference in this embodiment are the same as those in Embodiment 1, and will not be repeated here.

[0144] The frequency difference-based adaptive reclosing method proposed in this invention is designed through Embodiments 1 and 2 to verify its applicability under different fault conditions. Embodiment 1 mainly targets transient fault scenarios, using frequency difference detection and adaptive logic judgment to quickly realize reclosing operations and restore power supply. Embodiment 2 targets permanent fault scenarios, using frequency difference analysis and fault type identification to avoid performing reclosing under permanent faults, thereby preventing secondary impact. The comparison of the two embodiments demonstrates that the method has high reliability and applicability under various fault conditions.

[0145] Currently, traditional reclosing schemes are commonly used in wind farm transmission line projects. This scheme, when a circuit breaker trips due to a fault in the transmission line, indiscriminately performs a reclosing operation after a preset time delay, regardless of whether the fault is temporary or permanent. However, if reclosing occurs on a permanent fault, or if the secondary arc has not yet extinguished at the time of closing, the reclosing will fail. This not only causes secondary shocks to the power system but also threatens the stable operation of the system. This invention proposes an innovative method that can accurately determine the fault type before the circuit breaker reclosing: if the fault is identified as permanent, reclosing will be locked; if it is determined to be a transient fault, the exact time when the fault disappears will be calculated, and a precise reclosing timing will be set accordingly, thereby quickly restoring power supply. This invention has extremely important value for improving the reliability of wind power transmission systems and ensuring the safe and stable operation of power equipment.

[0146] While the foregoing description has elaborated on the specific implementation methods of the present invention in conjunction with the illustrations, the scope of application of the present invention is not limited to these embodiments. Within the scope of professional knowledge possessed by those skilled in the art, various adjustments and innovations can be made without departing from the core concept of the present invention.

Claims

1. A three-phase adaptive reclosing method for wind farm transmission lines based on frequency difference, characterized in that, Includes the following steps: Step 1: Use a capacitive voltage transformer (CVT) to collect the traveling wave data of the voltage at the M end of the line; Step 2: Preprocess the acquired voltage traveling wave data; Step 3: Use Fourier Transform (FFT) to perform spectrum analysis on the preprocessed voltage traveling wave data within the sliding time window to obtain the amplitude-frequency curve with frequency on the horizontal axis and amplitude on the vertical axis. Step 4: Calibrate the local peaks of the amplitude-frequency curve and calculate the frequency difference between each peak. Step 5: Within the maximum discrimination time limit, determine whether the frequency difference between adjacent sliding time windows is equal. If they are equal, the fault still exists, and the circuit breaker is not closed. If the frequency difference is not equal, the fault is determined to have disappeared, and Step 6 is executed. Step 6: Calculate the time when the fault disappears, combine the deionization after the fault disappears and determine the reclosing time, and output the closing signal; Step 4 specifically refers to: Step 4.1: Obtain the frequencies corresponding to the peak values ​​of the amplitude-frequency curve within the i-th (i=1,2,3,…n) sliding time window, and define them as follows: ; Step 4.2: Calculate the difference between adjacent frequencies , , , The mode of the frequency difference is defined as the frequency difference within the sliding time window. ; Step 5 specifically includes: Step 5.1: Set the maximum discrimination time limit : ； In the formula, For automatic reclosing, a fixed time is set. The time when the circuit breaker trips after the fault occurs. Deionization time after the fault disappears; Step 5.2: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit: ； Then it is determined that the fault disappears within the i+2 time window, where, It is the mode of the frequency difference within the window at time i+1. It is the mode of the frequency difference within the window at time i+2; Step 5.3: If the i-th, i+1-th, and i+2-th sliding windows satisfy the following within the maximum discrimination time limit: ； Then it is determined that the fault still exists within the window at time i+2; Step 6 specifically refers to: Step 6.1: Calculate the time when the fault disappears based on the obtained fault disappearance sliding window number i+2: ； In the formula, The moment the fault disappears; Step 6.2: Combine the deionization time after the fault disappears The reclosing time is determined as follows: ； In the formula, This is the reclosing time.

2. The three-phase adaptive reclosing method for wind farm transmission lines based on frequency difference according to claim 1, characterized in that, Step 2 specifically refers to: Step 2.1: Perform phase mode transformation on the voltage traveling wave data at terminal M; Step 2.2: Perform differential transformation on the data after phase mode transformation.

3. The three-phase adaptive reclosing method for wind farm transmission lines based on frequency difference according to claim 1, characterized in that, Step 3 specifically refers to: Step 3.1: Define the length of the sliding time window as T; Step 3.2: Perform spectrum analysis on the differentially transformed voltage signal using FFT within a sliding time window; Step 3.3: Obtain the amplitude-frequency curve of the spectrum analysis.

4. A system for implementing the frequency difference-based three-phase adaptive reclosing method for wind farm transmission lines as described in claim 1, characterized in that, include: Electrical signal acquisition module, used for acquiring and processing data; The numerical calculation module is used to calculate the frequency difference of each sliding time window. ; The fault nature determination module is used to determine whether the fault has disappeared within the maximum determination time limit by combining a sliding time window, and output the determination result; The reclosing execution module is used to receive the closing execution signal or closing lockout signal output by the fault nature determination module and execute the action.

5. The system according to claim 4, characterized in that, The electrical signal acquisition module includes: The voltage measurement unit is used to acquire the analog voltage signal on the secondary side of the CVT; An analog-to-digital converter is used to convert analog signals into digital signals.

6. The system according to claim 4, characterized in that, The numerical calculation module includes: The phase-mode conversion unit is used to calculate the phase-mode components of the traveling wave of the voltage at the M terminal. The numerical calculation unit is used to calculate the difference of the data after phase mode transformation, and uses FFT to perform spectral analysis on the preprocessed data and calculate the difference between the frequency peaks of each sliding time window.

7. The system according to claim 4, characterized in that, The fault nature determination module includes: The time limit setting unit is used to set the maximum discrimination time limit; The fault nature discrimination unit is used to construct fault nature identification criteria and, within the maximum discrimination time limit, combine a sliding time window to determine the fault disappearance time. ; The closing signal unit is used to output the closing execution signal or the closing lockout signal.

8. The system according to claim 4, characterized in that, The reclosing execution module includes: The closing start unit is used to initiate the reclosing of the circuit breakers at both ends of the transmitting line; The closing interlocking unit is used to interlock the reclosing of the circuit breakers at both ends of the sending line.

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