A power transmission line pilot protection method based on double-ended differential current transient energy frequency decomposition

Abstract

The application relates to a power transmission line pilot protection method based on double-terminal differential current instantaneous energy frequency decomposition, a criterion is constructed based on a double-terminal current difference value, high and low frequency energy separation is realized based on wavelet packet decomposition, and the contribution of a high frequency component is strengthened according to an instantaneous energy formula to improve sensitivity under high resistance fault. Through real-time calculation of transient energy, a high and low frequency energy ratio characteristic quantity is formed, an energy ratio change rate is taken as a discrimination basis for internal and external faults, and a reasonable threshold value is set, so that rapid and reliable discrimination of internal / external faults is realized. The application does not need complex synchronization and is not affected by load and operation mode, has speediness, sensitivity and stability, can solve the problems that traditional single-terminal / double-terminal protection is easily affected by new energy control switching strategies and amplitude limiting under external faults, leading to insufficient protection sensitivity, and can be effectively applied to rapid boundary protection of power transmission lines of a multi-outline line and a new energy through flexible transmission sending-out system.

Description

Technical Field

[0001] This invention relates to a longitudinal protection method for transmission lines, and more particularly to a longitudinal protection method for transmission lines based on the instantaneous energy frequency decomposition of dual-terminal differential current, belonging to the field of power system relay protection. Background Technology

[0002] In power systems with a high proportion of renewable energy penetration, longitudinal protection of transmission lines is the core protection method for achieving rapid fault response across the entire line. Transient longitudinal protection, due to its advantages of fast action and independence from system steady-state parameters, has become one of the mainstream technologies for protecting renewable energy transmission lines. Existing transient longitudinal protection mainly relies on the energy ratio characteristics of high and low frequency components on both sides of the line to distinguish between internal and external faults. However, its principle construction and characteristic calculation methods have inherent defects: First, the protection sensitivity is severely insufficient under high-resistance faults. Traditional energy is calculated using the square of the signal amplitude within the frequency band, failing to enhance the contribution of high-frequency transient components. This results in weak high-frequency energy and low identification of characteristic quantities on both sides during high-resistance faults, making longitudinal collaborative judgment prone to failure. Second, the time-frequency extraction accuracy of fault characteristics is limited. In renewable energy grid-connected systems, strong AC / DC coupling causes severe distortion of the short-circuit current waveform. Traditional Fourier transform and conventional S-transform methods lack sufficient frequency resolution, making it difficult to accurately separate high and low frequency components and obtain stable and reliable dual-end synchronous characteristic quantities. Due to these problems, it is difficult to adapt to the complex fault characteristics brought about by renewable energy grid connection via power electronic devices.

[0003] Therefore, there is an urgent need to develop a new method for transient longitudinal protection that is highly sensitive and accurate, adaptable to complex fault conditions, in order to improve the reliability and adaptability of transmission line protection in new energy transmission systems. Summary of the Invention

[0004] To address the issues of insufficient protection sensitivity and limited accuracy of time-frequency extraction of fault characteristics under high-resistance faults, this invention proposes a longitudinal protection method for transmission lines based on the frequency decomposition of instantaneous energy of dual-terminal differential current. The technical solution is as follows:

[0005] A longitudinal protection method for transmission lines based on the instantaneous energy frequency decomposition of dual-terminal differential current includes the following steps:

[0006] Simultaneous acquisition of signals from both ends;

[0007] Preprocess the acquired signals;

[0008] The preprocessed signal is decomposed using wavelet packet decomposition to filter high-frequency and low-frequency signals.

[0009] Instantaneous energy calculations are performed on high-frequency and low-frequency signals to obtain the high-frequency instantaneous energy and the low-frequency instantaneous energy.

[0010] The high-frequency instantaneous energy and low-frequency instantaneous energy are calculated to obtain the high-frequency-to-low-frequency energy ratio;

[0011] The energy ratio of high and low frequencies is calculated to obtain the rate of change of the energy ratio, which is used as the basis for longitudinal protection judgment. A threshold value is set. When the rate of change of the energy ratio is greater than the threshold value, it is judged as an internal fault; otherwise, it is an external fault.

[0012] Furthermore, the synchronous acquisition of dual-end signals specifically includes:

[0013] Collect three-phase currents on the M and N sides of the transmission line. , , where φ represents the three phases A, B, and C.

[0014] Furthermore, the preprocessing of the acquired signal specifically includes:

[0015] The expression for calculating the differential current at both ends of a transmission line is as follows:

[0016] (1);

[0017] Ignoring CT transmission error and transmission line signal transmission delay, under normal operation and external fault conditions, i d (t)≈0; when there is a fault within the region, i d (t) increased significantly.

[0018] Furthermore, the step of performing wavelet packet decomposition on the preprocessed signal to filter high-frequency and low-frequency signals includes the following steps:

[0019] Using the Daubechies4 wavelet as a compactly supported, orthogonal, second-order vanishing moment wavelet, its scaling function φ(t) and wavelet function ψ(t) satisfy a dual-scale relationship, expressed as follows:

[0020] (2);

[0021] In the formula, h k For the low-pass filter coefficients, g k These are the coefficients of the high-pass filter. ;

[0022] Perform L-level wavelet packet decomposition on signal x(n), and the decomposition coefficients of the k-th node in the j-th level are... The expression is as follows:

[0023] (3);

[0024] Each layer divides the frequency band into two equal parts, and the L-layer decomposition yields 2ᴸ equal-width sub-bands;

[0025] The instantaneous amplitude expressions for each frequency band are obtained by reconstructing the nodal coefficients as follows:

[0026] (4);

[0027] In the formula, This is the reconstructed signal of the j-th layer and the k-th node, i.e., the time-domain waveform of a specific frequency band;

[0028] Subband width, expressed as follows:

[0029] (5);

[0030] In the formula, B is the sub-bandwidth, f s Given the sampling frequency, the number of decomposition layers L=4;

[0031] The frequency interval f of the kth node is expressed as follows:

[0032] (6);

[0033] Furthermore, the instantaneous energy calculation of the high-frequency and low-frequency signals to obtain the high-frequency instantaneous energy and the low-frequency instantaneous energy includes the following steps:

[0034] Based on the concept of instantaneous energy in the Teager energy operator, the instantaneous energy of the short-circuit current in the ω-frequency band at time t is defined as the product of the instantaneous amplitude of the signal and the square of the instantaneous frequency, as shown in the following expression:

[0035] (7);

[0036] In the formula, Let be the instantaneous energy of the initial short-circuit current signal in the ω-frequency band at time t. Let f be the instantaneous amplitude of the short-circuit current in the ω-frequency band at time t, where ω is the angular frequency and ω = 2πf.

[0037] Define the low-frequency band range [f L1 ,f L2 ]=[1,300]Hz, high-frequency band range [f H1 ,f H2 ]=[301,1000]Hz, in length T w Within a sliding window of 10ms, for the low-frequency band [f] L1 ,f L2 ] and high frequency band [f H1 ,f H2 Integrating each component separately, the expression is as follows:

[0038] (8);

[0039] In the formula, E L E represents the total instantaneous energy of the low-frequency band differential current at both ends of the transmission line.H This refers to the total instantaneous energy of the high-frequency band differential current at both ends of the transmission line.

[0040] Furthermore, the calculation of the high-frequency instantaneous energy and the low-frequency instantaneous energy to obtain the high-low frequency energy ratio is specifically as follows:

[0041] Define the high-frequency and low-frequency instantaneous energy ratio λ of the differential current in a transmission line as the total instantaneous energy E at low frequency. L With high-frequency total instantaneous energy E H The ratio, as the core feature quantity for protection discrimination, is expressed as follows:

[0042] (9);

[0043] The energy ratio of high and low frequencies is calculated to obtain the rate of change of the energy ratio, which serves as the basis for longitudinal protection judgment. A threshold value is set; when the rate of change of the energy ratio is greater than the threshold value, it is judged as an intra-zone fault; otherwise, it is an extra-zone fault. Specifically:

[0044] The rate of change of λ is calculated by integrating the gradient of the instantaneous energy ratio λ between high and low frequencies of the differential current in the transmission line.

[0045] When operating normally or during an external fault, the rate of change of λ is close to 0; when an internal fault occurs, the rate of change of λ for the fault phase increases significantly. The protection system determines the fault to be internal or external when the following conditions are met:

[0046] (10);

[0047] In the formula, dλ / dt is the rate of change of the energy ratio λ with time; λ th To protect the startup threshold value.

[0048] The transmission line longitudinal protection device based on the frequency decomposition of instantaneous energy of dual-terminal differential current includes:

[0049] The acquisition module is used to synchronously acquire signals from both ends;

[0050] The preprocessing module is used to preprocess the acquired signals;

[0051] The wavelet packet module is used to perform wavelet packet decomposition on the preprocessed signal and filter high-frequency and low-frequency signals.

[0052] The instantaneous energy module is used to calculate the instantaneous energy of high-frequency and low-frequency signals, and to obtain the high-frequency instantaneous energy and the low-frequency instantaneous energy.

[0053] The high-frequency and low-frequency energy module is used to calculate the high-frequency instantaneous energy and low-frequency instantaneous energy to obtain the high-frequency and low-frequency energy ratio;

[0054] The judgment module is used to calculate the energy ratio of high and low frequencies and obtain the energy ratio change rate, which serves as the basis for longitudinal protection judgment. A threshold value is set. When the energy ratio change rate is greater than the threshold value, it is judged as an internal fault; otherwise, it is an external fault.

[0055] Furthermore, the acquisition module, used for synchronous acquisition of dual-end signals, refers to acquiring the three-phase currents on the M and N sides of the transmission line. , , where φ represents the three phases A, B, and C.

[0056] Collect three-phase currents on the M and N sides of the transmission line. , Where φ represents phases A, B, and C;

[0057] The preprocessing module is used to preprocess the acquired signal, which means performing differential current calculation at both ends of the transmission line on the acquired signal, as shown in the following expression:

[0058] (11);

[0059] Ignoring CT transmission error and transmission line signal transmission delay, under normal operation and external fault conditions, i d (t)≈0; when there is a fault within the region, i d (t) increased significantly.

[0060] A computer device includes a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor. When the processor executes the computer program, it implements the steps of any of the methods for longitudinal protection of transmission lines based on the instantaneous energy frequency decomposition of dual-end differential current.

[0061] A computer storage medium storing a computer program, wherein when the computer program is executed by a processor, it implements the steps of any of the above-described methods for longitudinal protection of transmission lines based on the instantaneous energy frequency decomposition of dual-end differential current.

[0062] Compared with existing technologies, its advantages are as follows:

[0063] This invention constructs a criterion based on the difference between the two-terminal currents as the basic signal, achieves high- and low-frequency energy separation based on wavelet packet decomposition, and enhances the contribution of high-frequency components according to the instantaneous energy formula to improve sensitivity under high-impedance faults. Through real-time calculation of state energy, a high- and low-frequency energy ratio characteristic quantity is formed. The energy ratio change rate is used as the basis for distinguishing between faults within and outside the fault zone, and a reasonable threshold value is set to achieve fast and reliable identification of faults within and outside the fault zone. This invention does not require complex synchronization, is not affected by load and operating mode, and has the advantages of speed, sensitivity and stability. It can solve the problems of insufficient protection sensitivity caused by the switching strategy of new energy control and amplitude limiting when traditional single-ended / double-ended protection is affected by faults outside the fault zone. It can be effectively applied to the fast boundary protection of transmission lines with multiple outgoing lines and new energy transmission systems via flexible direct transmission. Attached Figure Description

[0064] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0065] Figure 1 The fault waveform is AG+0Ω within the zone;

[0066] Figure 2 The fault waveform is ABG+0Ω within the zone;

[0067] Figure 3 The fault waveform is ABCG+0Ω within the zone;

[0068] Figure 4 The fault waveform is AB+20Ω within the zone;

[0069] Figure 5 The fault waveform is for AG+100Ω within the zone;

[0070] Figure 6 The fault waveform outside the zone is ABCG+0Ω;

[0071] Figure 7 The fault waveform is for AB+0Ω outside the zone. Detailed Implementation

[0072] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0073] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0074] The following reference Figures 1-7 The technical solutions of some embodiments of the present invention are described below.

[0075] Example 1

[0076] This invention provides an embodiment of a longitudinal protection method for transmission lines based on the frequency decomposition of instantaneous energy of dual-terminal differential current, comprising the following steps:

[0077] Simultaneous acquisition of signals from both ends;

[0078] Preprocess the acquired signals;

[0079] The preprocessed signal is decomposed by wavelet packet decomposition to filter high-frequency and low-frequency signals and achieve high- and low-frequency energy separation.

[0080] Instantaneous energy calculations are performed on high-frequency and low-frequency signals to obtain high-frequency instantaneous energy and low-frequency instantaneous energy. The signal energy value is amplified to enhance the contribution of high-frequency components and improve sensitivity under high-impedance faults.

[0081] By combining wavelet packet decomposition and high- and low-frequency instantaneous energy calculation, the protection device can identify high-impedance faults that were originally ignored due to their small amplitude, thereby solving the problem of insufficient protection sensitivity under high-impedance faults.

[0082] The high-frequency instantaneous energy and low-frequency instantaneous energy are calculated to obtain the high-low frequency energy ratio, which serves as the core characteristic quantity for protection discrimination.

[0083] The energy ratio of high and low frequencies is calculated to obtain the energy ratio change rate, which is used as the basis for longitudinal protection judgment. A reasonable threshold value is set. When the energy ratio change rate is greater than the threshold value, it is judged as an internal fault; otherwise, it is an external fault.

[0084] Example 2

[0085] This invention provides another embodiment: a transmission line longitudinal protection device based on the instantaneous energy frequency decomposition of double-ended differential current, used to implement the transmission line longitudinal protection method based on the instantaneous energy frequency decomposition of double-ended differential current described in Embodiment 1. The device specifically includes:

[0086] The acquisition module is used to synchronously acquire signals from both ends;

[0087] The preprocessing module is used to preprocess the acquired signals;

[0088] The wavelet packet module is used to filter high-frequency and low-frequency signals to achieve high- and low-frequency energy separation;

[0089] The instantaneous energy module is used to obtain high-frequency and low-frequency instantaneous energy, and to enhance the contribution of high-frequency components to improve sensitivity under high-resistivity faults.

[0090] High and low frequency energy modules are used to determine the high and low frequency energy ratio;

[0091] The judgment module is used to distinguish between faults within and outside the zone.

[0092] The acquisition module is used to synchronously acquire dual-end signals, which means it acquires the three-phase currents on the M and N sides of the transmission line. , Where φ represents phases A, B, and C; the preprocessing module is used to preprocess the acquired signal, which refers to calculating the differential current at both ends of the transmission line from the acquired signal, as shown in the following expression:

[0093] (1);

[0094] In the formula, The differential current value at both ends of the transmission line is given, ignoring CT transmission error and signal transmission delay. This value is used during normal operation and under external fault conditions. d (t)≈0; when there is a fault within the region, i d (t) increased significantly.

[0095] Example 3

[0096] The present invention provides another embodiment, Figures 1-3 The figures show the protection operation curves for phase A, two-phase AB, and three-phase ABC metallic faults occurring within the transmission line area, respectively. As can be seen from the figures, due to the rapid increase in the high-frequency component of the differential current after the fault, the energy ratio of the differential current in the fault phase decreases rapidly, and its rate of change exceeds the protection activation threshold value λ. th The protection device operates reliably.

[0097] Example 4

[0098] The present invention provides another embodiment, Figure 4-5 The figures show the protection operation curves for a phase-to-phase (AB) fault with a 20Ω transition resistance and a phase-A ground fault with a 100Ω transition resistance within the transmission line zone, respectively. As can be seen from the figures, after a high-resistance fault within the transmission line zone, the high-frequency component of the differential current increases rapidly, and the energy ratio of the differential current in the fault phase decreases rapidly. The rate of change of this energy ratio exceeds the protection activation threshold λ. th The protection device operates reliably. Its performance is unaffected by transition resistance and it exhibits good high-resistance withstand capability.

[0099] Example 5

[0100] The present invention provides another embodiment, Figure 6-7 These are the protection operation curves for a metallic fault between phases AB outside the transmission line zone and a metallic ground fault ABCG outside the zone, respectively. As shown in the figure, the rate of change of the fault phase differential current energy ratio is less than the protection activation threshold value λ. thThe protection device is reliable and does not activate.

[0101] Example 6

[0102] Based on the same inventive concept, this invention also provides a computer device, including a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor. When the processor executes the computer program, it implements the steps of the transmission line longitudinal protection method based on the instantaneous energy frequency decomposition of dual-end differential current described in Embodiment 1.

[0103] Example 7

[0104] Based on the same inventive concept, this embodiment of the invention also provides a computer storage medium storing a computer program. When the computer program is executed by a processor, it implements the steps of the transmission line longitudinal protection method based on dual-end differential current instantaneous energy frequency decomposition described in Embodiment 1.

[0105] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0106] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0107] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0108] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0109] In the description of this specification, the terms "one embodiment," "some embodiments," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0110] Finally, it should be noted that:

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A longitudinal protection method for transmission lines based on the instantaneous energy frequency decomposition of dual-terminal differential current, characterized in that, Includes the following steps: Simultaneous acquisition of signals from both ends; Preprocess the acquired signals; The preprocessed signal is decomposed using wavelet packet decomposition to filter high-frequency and low-frequency signals. Instantaneous energy calculations are performed on high-frequency and low-frequency signals to obtain the high-frequency instantaneous energy and the low-frequency instantaneous energy. The high-frequency instantaneous energy and low-frequency instantaneous energy are calculated to obtain the high-frequency-to-low-frequency energy ratio; The energy ratio of high and low frequencies is calculated to obtain the rate of change of the energy ratio, which is used as the basis for longitudinal protection judgment. A threshold value is set. When the rate of change of the energy ratio is greater than the threshold value, it is judged as an internal fault; otherwise, it is an external fault.

2. The method for longitudinal protection of transmission lines based on instantaneous energy frequency decomposition of dual-end differential current according to claim 1, characterized in that, The synchronous acquisition of dual-end signals specifically refers to: Collect three-phase currents on the M and N sides of the transmission line. , , where φ represents the three phases A, B, and C.

3. The method for longitudinal protection of transmission lines based on instantaneous energy frequency decomposition of dual-end differential current according to claim 1, characterized in that, The preprocessing of the acquired signals specifically includes: The expression for calculating the differential current at both ends of a transmission line is as follows: （1）； In the formula, The differential current value at both ends of the transmission line is given, ignoring CT transmission error and signal transmission delay. This value is used during normal operation and under external fault conditions. d (t)≈0; when there is a fault within the region, i d (t) increased significantly.

4. The method for longitudinal protection of transmission lines based on instantaneous energy frequency decomposition of dual-end differential current according to claim 1, characterized in that, The step of performing wavelet packet decomposition on the preprocessed signal to filter high-frequency and low-frequency signals includes the following steps: Using the Daubechies4 wavelet as a compactly supported, orthogonal, second-order vanishing moment wavelet, its scaling function φ(t) and wavelet function ψ(t) satisfy a dual-scale relationship, expressed as follows: （2）； In the formula, h k For the low-pass filter coefficients, g k These are the coefficients of the high-pass filter. ; Perform L-level wavelet packet decomposition on signal x(n), and the decomposition coefficients of the k-th node in the j-th level are... The expression is as follows: （3）； Each layer divides the frequency band into two equal parts, and the L-layer decomposition yields 2ᴸ equal-width sub-bands; The instantaneous amplitude expressions for each frequency band are obtained by reconstructing the nodal coefficients as follows: （4）； In the formula, This represents the reconstruction signal of the j-th layer and the k-th node; Subband width, expressed as follows: （5）； In the formula, B is the sub-bandwidth, f s Given the sampling frequency, the number of decomposition layers L=4; The frequency interval f of the kth node is expressed as follows: （6）。 5. The method for longitudinal protection of transmission lines based on instantaneous energy frequency decomposition of dual-end differential current according to claim 1, characterized in that, The instantaneous energy calculation of high-frequency and low-frequency signals to obtain the high-frequency instantaneous energy and low-frequency instantaneous energy includes the following steps: Based on the concept of instantaneous energy in the Teager energy operator, the instantaneous energy of the short-circuit current in the ω-frequency band at time t is defined as the product of the instantaneous amplitude of the signal and the square of the instantaneous frequency, as shown in the following expression: （7）； In the formula, Let be the instantaneous energy of the initial short-circuit current signal in the ω-frequency band at time t. Let f be the instantaneous amplitude of the short-circuit current in the ω-frequency band at time t, where ω is the angular frequency and ω = 2πf. Define the low-frequency band range [f L1 ,f L2 ]=[1,300]Hz, high-frequency band range [f H1 ,f H2 ]=[301,1000]Hz, in length T w Within a sliding window of 10ms, for the low-frequency band [f] L1 ,f L2 ] and high frequency band [f H1 ,f H2 Integrating each component separately, the expression is as follows: （8）； In the formula, E L E represents the total instantaneous energy of the low-frequency band differential current at both ends of the transmission line. H This refers to the total instantaneous energy of the high-frequency band differential current at both ends of the transmission line.

6. The method for longitudinal protection of transmission lines based on instantaneous energy frequency decomposition of dual-end differential current according to claim 1, characterized in that, The calculation of high-frequency instantaneous energy and low-frequency instantaneous energy to obtain the high-low frequency energy ratio is as follows: Define the high-frequency and low-frequency instantaneous energy ratio λ of the differential current in a transmission line as the total instantaneous energy E at low frequency. L With high-frequency total instantaneous energy E H The ratio, as the core feature quantity for protection discrimination, is expressed as follows: （9）； The energy ratio of high and low frequencies is calculated to obtain the rate of change of the energy ratio, which serves as the basis for longitudinal protection judgment. A threshold value is set; when the rate of change of the energy ratio is greater than the threshold value, it is judged as an intra-zone fault; otherwise, it is an extra-zone fault. Specifically: The rate of change of λ is calculated by integrating the gradient of the instantaneous energy ratio λ between high and low frequencies of the differential current in the transmission line. When operating normally or during an external fault, the rate of change of λ is close to 0; when an internal fault occurs, the rate of change of λ for the fault phase increases significantly. The protection system determines the fault to be internal or external when the following conditions are met: （10）； In the formula, dλ / dt is the rate of change of the energy ratio λ with time; λ th To protect the startup threshold value.

7. A transmission line longitudinal protection device based on the frequency decomposition of instantaneous energy of dual-end differential current, characterized in that, include: The acquisition module is used to synchronously acquire signals from both ends; The preprocessing module is used to preprocess the acquired signals; The wavelet packet module is used to perform wavelet packet decomposition on the preprocessed signal and filter high-frequency and low-frequency signals. The instantaneous energy module is used to calculate the instantaneous energy of high-frequency and low-frequency signals, and to obtain the high-frequency instantaneous energy and the low-frequency instantaneous energy. The high-frequency and low-frequency energy module is used to calculate the high-frequency instantaneous energy and low-frequency instantaneous energy to obtain the high-frequency and low-frequency energy ratio; The judgment module is used to calculate the energy ratio of high and low frequencies and obtain the energy ratio change rate, which serves as the basis for longitudinal protection judgment. A threshold value is set. When the energy ratio change rate is greater than the threshold value, it is judged as an internal fault; otherwise, it is an external fault.

8. A transmission line longitudinal protection device based on the instantaneous energy frequency decomposition of double-ended differential current according to claim 7, characterized in that, The acquisition module is used to synchronously acquire dual-end signals, which means it acquires the three-phase currents on the M and N sides of the transmission line. , Where φ represents phases A, B, and C; the preprocessing module is used to preprocess the acquired signal, which refers to calculating the differential current at both ends of the transmission line from the acquired signal, as shown in the following expression: （1）； In the formula, The differential current value at both ends of the transmission line is given, ignoring CT transmission error and signal transmission delay. This value is used during normal operation and under external fault conditions. d (t)≈0; when there is a fault within the region, i d (t) increased significantly.

9. A computer device, comprising a storage medium, a processor, and a computer program stored on the storage medium and executable on the processor, wherein the processor executes the computer program to implement the steps of the transmission line longitudinal protection method based on the instantaneous energy frequency decomposition of dual-end differential current as described in any one of claims 1-6.

10. A computer storage medium storing a computer program, wherein when the computer program is executed by a processor, it implements the steps of the transmission line longitudinal protection method based on the instantaneous energy frequency decomposition of dual-end differential current as described in any one of claims 1-6.

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