Line pilot protection method and system based on short-circuit current two-dimensional distribution trajectory characteristics

Abstract

A line pilot protection method and system based on time-domain short-circuit current two-dimensional distribution trajectory characteristics. By constructing a time-domain line-mode current matrix that is not affected by calculation errors, the two-dimensional distribution plane characteristics of time-domain current are analyzed, and the distribution principal / secondary axis vectors that quantify the characteristics are extracted, including two characteristic functions of vector direction angle and modulus length. Based on this, a fault recognition criterion based on the amplitude-phase information fusion of the distribution principal axis direction angle is constructed, and a fault phase selection criterion based on the modulus current cumulative sum function is constructed, so that the protection can still reliably act when the short-circuit current change characteristics caused by high-resistance faults are not significant. The sensitivity of the present application is superior to that of conventional pilot protection, and the tolerance to transformation error and signal synchronization error is strong, so that the present application can be effectively applied to new power systems containing a high proportion of new energy.

Description

Technical Field

[0001] This invention belongs to the field of relay protection technology, and more specifically, relates to a line longitudinal protection method and system based on the two-dimensional distribution trajectory characteristics of time-domain short-circuit current. Background Technology

[0002] my country's new power system construction has entered a period of accelerated transformation. By 2025, wind and solar power installed capacity will surpass that of thermal power, making new energy the largest installed power source in my country. Large-scale new energy is mainly connected to the grid via high-voltage AC transmission lines. Compared to traditional synchronous power sources, the fault characteristics of new energy power sources are deeply coupled with converter control, resulting in limited short-circuit current amplitude, controlled phase, and a high proportion of harmonic components. Consequently, power frequency phasor differential protection, as the main protection for transmission lines, faces problems such as difficulty in extracting power frequency quantities, reduced operating quantities, and increased braking quantities, leading to decreased sensitivity or even failure to operate.

[0003] To achieve reliable and fast-acting line protection in scenarios with a high proportion of new energy access, scholars have conducted extensive research on time-domain main protection, proposing (1) an improved differential protection scheme; (2) time-domain current waveform correlation protection; and (3) protection based on line model identification. However, the above-mentioned typical new principles of time-domain main protection have the following three limitations: (1) the improved differential protection scheme is difficult to balance sensitivity and speed in double-ended weak feeder systems or high-resistance faults. (2) time-domain waveform correlation protection is based on waveform change trend comparison, which makes it difficult to identify high-resistance faults where the current waveform change trend before and after the fault is not significant. (3) for model identification-based protection, protection based on lumped parameter models is difficult to apply to long lines; the reliability of protection based on distributed parameter models is easily affected by the distortion of non-fault phase current. Therefore, it is urgent to study new methods and systems for line longitudinal protection that can be effectively applied to new power systems with a high proportion and large scale of new energy. Summary of the Invention

[0004] To address the technical challenges in the protection of transmission lines in new power systems with high proportions and large-scale renewable energy, such as difficulties in extracting power frequency quantities, reduced action quantities, and increased braking quantities leading to decreased sensitivity, this invention proposes a longitudinal protection method and system for transmission lines based on the two-dimensional distribution trajectory characteristics of time-domain short-circuit current.

[0005] Therefore, the technical solution of the present invention provides a line longitudinal protection method and system based on the two-dimensional distribution trajectory characteristics of time-domain short-circuit current, so as to solve the problem of insufficient protection adaptability of existing line protection principles under the conditions of new energy access to strong / weak systems, different fault types, and high-resistance faults.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: The first aspect of the present invention provides a line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of time-domain short-circuit current, comprising: Step 1: Real-time acquisition of voltage and current sampling sequences on both the local and opposite sides of the transmission line; Step 2: Extract the three-phase current sampling sequence of this side into the actual line-mode current sequence through phase mode transformation. Based on the pre-constructed Berylon distributed parameter model, the line-mode current sequence extrapolated from the opposite side to this side is calculated using the voltage and current sampling sequences from the opposite side. ; Step 3: Calculate the minimum error energy between the actual current and the calculated current of the line model on this side, and obtain the corrected calculated current sequence of the line model through adaptive synchronous correction. ; Step 4: Construct a second-order real symmetric matrix based on the current sequence calculated from the corrected line model. The principal axis direction angle, which reflects the two-dimensional trajectory distribution characteristics of time-domain current, is extracted through feature decomposition. and eigenvalues , ; Step 5: Construct an action function using the spindle direction angle, and combine it with an adaptive braking function based on eigenvalues ​​and current-energy ratios to identify faults; Step 6: If the fault is identified as non-fault or external to the zone, no protection action signal will be issued; if the fault is identified as internal to the zone, the fault type and fault phase will be identified using the zero-sequence current condition and the modulus current accumulation function, and a protection action signal will be issued.

[0007] More preferably, In step 2, the instantaneous current value is calculated by constructing the line model on side M according to the following formula. :

[0008] in, , , These are respectively deduced to the M side. α mold, β Model and γ The instantaneous value of the current is calculated using the modulus. , , The instantaneous current values ​​of j are calculated by extrapolating the line-mode voltage and current sampling values ​​from the opposite side N to the a, b, and c phases of the local side M, based on the Berylon line model.

[0009] More preferably, In step 3, the adaptive synchronization correction process includes: Calculate the error energy function ,in, For this side M side in The actual current value of the line model at time [time]. The time interval is used to extrapolate from the contralateral N side to this side. The current value is calculated for the line model. The potential synchronization error offset is expressed in terms of the number of sampling points. W For the length of the data window, For sampling points within the data window, The sampling interval; Search The smallest synchronization error offset Calculate the current after adaptive synchronization correction. Thus, the corrected line-mode calculated current sequence is obtained. .

[0010] More preferably, In step 4, based on the actual current sequence of the local line mode... and the corrected line model calculated current sequence Construct a second-order real symmetric matrix for:

[0011] in, , , , , , By examining second-order real symmetric matrices Feature decomposition extracts the principal axis direction angles that reflect the characteristics of the two-dimensional trajectory distribution of the time-domain current plane. and eigenvalues , ;in, It is a second-order real symmetric matrix Maximum eigenvalue, It is a second-order real symmetric matrix Minimum eigenvalue; and These are the transposes of the corresponding sequences; cov is for covariance calculation.

[0012] More preferably, In step 4, the main axis direction angle Solve using the following formula:

[0013] Eigenvalues , Solve using the following formula: .

[0014] More preferably, In step 5, the constructed action function is: ; for At any given moment, the principal axis direction angle; Construct the adaptive braking function as follows , Basic braking coefficient, For adaptive braking operators; Fault identification criteria are ,when When, it is identified as no fault or an external fault. At that time, it was identified as a fault within the area.

[0015] More preferably, Adaptive braking operator Calculate as follows:

[0016]

[0017]

[0018]

[0019] , They are respectively Second-order real symmetric matrix at time step Two orthogonal eigenvalues, Basic braking coefficient The value range is 3.5-4.5.

[0020] More preferably, In step 6, the fault type and fault phase are identified using the zero-sequence current condition and the modulus current accumulation function, specifically as follows: Condition 1: ,in, This is the instantaneous value of the zero-sequence current. This is the system's rated current; Condition 2: , Simultaneously satisfying; among which, This represents the cumulative current sum function corresponding to the modulus of the two non-faulty phases. This represents the cumulative current sum function corresponding to the moduli of the faulty phase and the first healthy phase. This represents the cumulative current sum function corresponding to the moduli of the faulty phase and the second healthy phase; Condition 3: A modulus relationship exists. and Simultaneously satisfying; among which, This represents the modulus-corresponding current cumulative sum function containing two fault phases; If condition 1 is met, condition 2 is met, and condition 3 is not met, then it is determined to be a single-phase ground fault, and the faulty phase is the faulty phase described in condition 2. If condition 1 is not met, condition 2 is not met, and condition 3 is met, then it is determined to be a phase-to-phase fault, and the faulty phase is the faulty phase described in condition 3; If condition 1 is met, condition 2 is not met, and condition 3 is met, then it is determined to be a two-phase ground fault, and the faulty phase is the faulty phase described in condition 3.

[0021] More preferably, Modulus current cumulative sum function Calculate using the following formula: ,in, W For the length of the data window, For sampling points within the data window, The sampling interval is... This is the adaptive synchronization correction for side M. The instantaneous value of the current is calculated using the line-model at a given time. This is the instantaneous value of the actual current of the line model on side M.

[0022] Secondly, the present invention provides a line longitudinal protection system based on the two-dimensional distribution trajectory characteristics of short-circuit current, comprising: The electrical quantity acquisition module is used to collect voltage and current values ​​on both the local and opposite sides of the transmission line. The line-mode current calculation module is used to calculate the actual current sequence of the line-mode on this side. And the current sequence calculated using the voltage and current on the opposite side to extrapolate to this side from the line model. ; The adaptive synchronous correction module is used to adaptively and synchronously correct the calculated current sequence of the line model based on the minimum error energy between the actual current and the calculated current of the line model on this side, thereby obtaining the corrected calculated current sequence of the line model. ; The time-domain current two-dimensional distribution trajectory feature calculation module constructs a second-order real symmetric matrix based on the corrected line model current sequence. The principal axis direction angle, which reflects the two-dimensional trajectory distribution characteristics of time-domain current, is extracted through feature decomposition. and eigenvalues , ; The fault identification module uses the spindle direction angle to construct an action function and combines it with an adaptive braking function based on eigenvalues ​​and current-energy ratio to identify the presence or absence of faults and fault areas. The fault type identification module uses zero-sequence current conditions and modulus current accumulation function to identify fault types and fault phases.

[0023] Thirdly, the present invention provides a computing device, comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, they implement the steps of the line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of short-circuit current.

[0024] Fourthly, the present invention provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the steps of the line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of short-circuit current.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: under the conditions of new energy access to strong / weak systems, different fault types and high resistance faults, the proposed protection can reliably identify faults in the area and accurately select the faulty phase, with an action time of less than 10ms, and has a strong ability to withstand CT transmission error and signal synchronization error. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a flowchart of the line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of time-domain short-circuit current according to the present invention; Figure 2 This is a schematic diagram of the Berylon circuit model; Figure 3 A schematic diagram of the two-dimensional plane characteristics of time-domain current under different system states; Figure 4 This is a schematic diagram of the test function results; Figure 5 A model for large-scale photovoltaic-storage grid integration systems; Figure 6 This is a schematic diagram of the fault identification function waveform; Figure 7 This is a schematic diagram of a routine protection sensitivity analysis. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0028] 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 those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] This invention is described in detail with reference to the schematic diagrams. When detailing the embodiments of this invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not be construed as limiting the scope of protection of this invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0031] Furthermore, in the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used solely for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" in this invention should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; similarly, they can refer to mechanical connections, electrical connections, or direct connections, or indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] This invention discloses a longitudinal protection method for lines based on the two-dimensional distribution trajectory characteristics of short-circuit current, comprising: Step 1: Real-time acquisition of voltage and current sampling sequences on both the local and opposite sides of the transmission line; Step 2: Extract the three-phase current sampling sequence of this side into the actual line-mode current sequence through phase mode transformation. Based on the pre-constructed Berylon distributed parameter model, the line-mode current sequence extrapolated from the opposite side to this side is calculated using the voltage and current sampling sequences from the opposite side. ; Using the line-mode voltage and current sampling values ​​from the N-side, based on the Berylon line model considering distributed parameters and lumped resistance parameters, and combining the line-mode voltage and current sampling values ​​from the N-side with the line surge impedance... Traveling wave propagation delay Calculate and extrapolate the line-mode current to the M side of this side. .

[0034] The calculated three-phase line-mode currents are combined to construct the line-mode current matrix on the M side as follows. :

[0035] in, , , These are respectively deduced to the M side. α mold, β Model and γ Calculate the current value using the modulus; , , The current values ​​are calculated for phases a, b, and c on the M side, respectively.

[0036] The actual current sequence of the line mode is composed of the actual currents of the line mode acquired within the sampling window on side M. Within the sampling window, the line-mode calculation current sequence is formed by calculating the line-mode calculation current derived from the voltage and current sampling sequence on the opposite side to this side. .

[0037] Step 3: Calculate the minimum error energy between the actual current and the calculated current of the line model on this side, and obtain the corrected calculated current sequence of the line model through adaptive synchronous correction. ; The adaptive synchronization correction process includes: Calculate the error energy function ,in, For this side M side in The actual current sampling value of the line mode at time t. The time interval is used to extrapolate from the contralateral N side to this side. The current value is calculated for the line model. The potential synchronization error offset is expressed in terms of the number of sampling points. W For the length of the data window, For sampling points within the data window, The sampling interval; Search The smallest synchronization error offset Calculate the current after adaptive synchronization correction. Thus, the corrected line-mode calculated current sequence is obtained. Step 4: Construct a second-order real symmetric matrix based on the current sequence calculated from the corrected line model. The principal axis direction angle, which reflects the two-dimensional trajectory distribution characteristics of time-domain current, is extracted through feature decomposition. and eigenvalues , ; Based on the actual current sequence of this side-line model and the corrected line model calculated current sequence Construct a second-order real symmetric matrix for:

[0038] in, , , , , , , ; The principal axis direction angle, which reflects the two-dimensional trajectory distribution characteristics of the time-domain current plane, is extracted through feature decomposition. and eigenvalues , .in, The largest eigenvalue of the matrix. It is the smallest eigenvalue of the matrix. Calculate the instantaneous current value for the unsynchronized line model. The instantaneous current value is calculated for the line model after adaptive synchronization correction. It is a sequence composed of the instantaneous values ​​of the actual current of the local line mode within the data window. This is a sequence of instantaneous current values ​​calculated from the corrected line model within the data window. and These are the transposes of the corresponding sequences, and cov is the covariance calculation.

[0039] Main spindle orientation angle Solve using the following formula:

[0040]

[0041] Eigenvalues , Solve using the following formula: .

[0042] Step 5: Construct an action function using the spindle direction angle, and combine it with an adaptive braking function based on eigenvalues ​​and current-energy ratios to identify faults; Action function for ; The principal axis direction angle of the time-domain current plane trajectory is used to characterize the difference in amplitude and phase deflection between the measured current vector and the calculated current vector. , Each is a matrix The two orthogonal eigenvalues, representing the magnitudes of the principal and secondary axes of the planar trajectory distribution, are used to characterize the intensity of the time-domain current energy change; the adaptive braking function is... , The basic braking coefficient takes into account synchronization error, transmission error, and noise interference. For adaptive braking operators;

[0043]

[0044]

[0045] Fault identification criteria are ,when When, it is identified as no fault or an external fault. At that time, it was identified as a fault within the area.

[0046] Step 6: If the fault is identified as non-fault or external to the zone, no protection action signal will be issued; if the fault is identified as internal to the zone, the fault type and fault phase will be identified using the zero-sequence current condition and the modulus current accumulation function, and a protection action signal will be issued.

[0047] The modulus current cumulative sum function is ,in, W For the length of the data window, For sampling points within the data window, The sampling interval is... The instantaneous current value is calculated for the line model on this side (M side) after adaptive synchronization correction. The fault type and fault phase are identified using the actual instantaneous value of the line current on this side (M side) as follows: Condition 1: ,in, This is the instantaneous value of the zero-sequence current. This is the system's rated current; Condition 2: , Simultaneously satisfying; among which, This represents the cumulative current sum function corresponding to the modulus of the two non-faulty phases. This represents the cumulative current sum function corresponding to the moduli of the faulty phase and the first healthy phase. This represents the cumulative current sum function corresponding to the moduli of the faulty phase and the second healthy phase; Condition 3: A modulus relationship exists. and Simultaneously satisfying; among which, This represents the modulus-corresponding current cumulative sum function containing two fault phases; If condition 1 is met, condition 2 is met, and condition 3 is not met, then it is determined to be a single-phase ground fault, and the faulty phase is the faulty phase described in condition 2. If condition 1 is not met, condition 2 is not met, and condition 3 is met, then it is determined to be a phase-to-phase fault, and the faulty phase is the faulty phase described in condition 3; If condition 1 is met, condition 2 is not met, and condition 3 is met, then it is determined to be a two-phase ground fault, and the faulty phase is the faulty phase described in condition 3.

[0048] This invention also discloses a line longitudinal protection system based on the two-dimensional distribution trajectory characteristics of short-circuit current, comprising: The electrical quantity acquisition module is used to collect voltage and current values ​​on both the local and opposite sides of the transmission line. The line-mode current calculation module is used to calculate the actual current sequence of the line-mode on this side. And the current sequence calculated using the voltage and current on the opposite side to extrapolate to this side from the line model. ; The adaptive synchronous correction module is used to adaptively and synchronously correct the calculated current sequence of the line model based on the minimum error energy between the actual current and the calculated current of the line model on this side, thereby obtaining the corrected calculated current sequence of the line model. ; The time-domain current two-dimensional distribution trajectory feature calculation module constructs a second-order real symmetric matrix based on the corrected line model current sequence. The principal axis direction angle, which reflects the two-dimensional trajectory distribution characteristics of time-domain current, is extracted through feature decomposition. and eigenvalues , ; The fault identification module uses the spindle direction angle to construct an action function and combines it with an adaptive braking function based on eigenvalues ​​and current-energy ratio to identify the presence or absence of faults and fault areas. The fault type identification module uses zero-sequence current conditions and modulus current accumulation function to identify fault types and fault phases.

[0049] Example 1 Reference Figure 1 As one embodiment of the present invention, this embodiment provides a line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of time-domain short-circuit current, including: S100: Real-time acquisition of voltage and current sampling sequences on both the local and opposite sides of the transmission line.

[0050] S200: Extracts three-phase current into line-mode current through phase-mode transformation, such as... Figure 2 Based on the pre-constructed Berylon distributed parameter model, the line model current derived from the opposite end to this side (M side) is calculated using the voltage and current sampling sequence of the opposite side (N side).

[0051] Specifically, firstly, the actual three-phase current sampling values ​​on this side (M side) are... , , Converted into the actual linear modulus current matrix by phase subtraction. Actual three-phase current sampling values ​​on this side (M side) , , Converted into the actual linear modulus current matrix by phase subtraction. The actual three-phase current sampling values ​​on the opposite side (N side) will be used. , , Converted into the actual linear modulus current matrix by phase subtraction. Actual three-phase current sampling values ​​on the opposite side (N side) , , Converted into the actual linear modulus current matrix by phase subtraction. .

[0052]

[0053]

[0054] in, , , M side respectively α mold, β Model and γ Modular actual current sequence; , , These are the actual current sequences of phases a, b, and c on the M side, respectively. , , M side respectively α mold, β Model and γ Modular actual voltage sequence; , , These are the actual voltage sequences of phases a, b, and c on side M, respectively. , , N sides respectively α mold, β Model and γ Modular actual current sequence; , , These are the actual current sequences for phases a, b, and c on the N-side, respectively. , , N sides respectively α mold, β Model and γ Modular actual voltage sequence; , , These are the actual voltage sequences for phases a, b, and c on the N side, respectively. The subscript M indicates this side, and the subscript N indicates the opposite side.

[0055] Then, based on the Berylon line model with distributed inductive-capacitive reactance parameters and lumped resistance parameters, the analytical relationship between the time-domain electrical quantities at both ends of the line is established. The positive direction of the current is defined as the direction from the busbar to the line. Using the actual voltage and current of the line model on the opposite side (N side), the calculated current on this side (M side) is derived. The time-domain calculation formula is as follows:

[0056]

[0057] In the formula, Line impedance; For traveling wave propagation delay, For line length, For traveling wave speed, and These are inductance per unit length and capacitance per unit length, respectively. This is the delay for traveling wave transmission. Let be the time shift factor, which satisfies the following equation:

[0058] Representing the actual voltage or current, based on the Berylon model, it utilizes the sampled line-mode voltage value from the opposite side (N side). , , and current sampling value , , Calculate the line model current extrapolated to this side (M side). , , And construct the computational value line modulus current matrix .

[0059]

[0060] S300: Adaptive synchronous correction algorithm is adopted. By calculating the minimum error energy between the actual current of the line mode on this side and the calculated current of the line mode, the waveforms of the actual current sequence of the line mode on this side and the calculated current sequence of the line mode are adaptively aligned when there is no fault or a fault outside the zone.

[0061] In this application embodiment, the adaptive synchronization correction algorithm includes: Calculate the error energy function ,in, For this side (M side) in The actual current sampling value of the line mode at time t. The time interval is used to extrapolate from the opposite side (N side) to this side. The current value is calculated for the line model. The potential synchronization error offset is expressed in terms of the number of sampling points. W This refers to the data window length, which ranges from 10ms to 30ms. For sampling points within the data window, The sampling interval corresponds to a sampling frequency range of 1200Hz-4800Hz; Search The smallest synchronization error offset Calculate the local current after adaptive synchronization correction. Thus, the corrected line-mode calculated current sequence is obtained. .

[0062] S400: Based on the actual current sequence of this side-line model and the corrected line model calculated current sequence Construct a second-order real symmetric matrix The principal axis direction angle, which reflects the characteristics of the two-dimensional trajectory distribution, is extracted through feature decomposition. and eigenvalues , .

[0063] In this embodiment of the application, for a second-order real symmetric matrix principal axis direction angle and eigenvalues , ,include: Second-order real symmetric matrix Solve using the following formula:

[0064] in, , , , , , , .

[0065] in, The largest eigenvalue of the matrix. It is the smallest eigenvalue of the matrix. Calculate the instantaneous current value for the unsynchronized line model. The instantaneous current value is calculated for the line model after adaptive synchronization correction. It is a sequence composed of the instantaneous values ​​of the actual current of the local line mode within the data window. This is a sequence of instantaneous current values ​​calculated from the corrected line model within the data window. and These are the transposes of the corresponding sequences.

[0066] Main spindle orientation angle Solve using the following formula:

[0067]

[0068] in, , The phase angle difference between the actual modulus current and the calculated modulus current after correction.

[0069] With uncorrected direction angle For example, it also has the ability to characterize current amplitude and phase features. Figure 3 As shown, when there is no fault or a fault outside the fault zone, the amplitudes and phases of the time-domain currents are similar. Approaching 45° or 225°. In case of a fault within the area, if on this side... and same direction , or ;like and Reverse, , or .also, and The greater the difference in amplitude, the better. The smaller, The smaller the angle between it and the horizontal axis, the better.

[0070] Eigenvalues , Solve using the following formula:

[0071] S500: The action function is constructed using the spindle direction angle, and combined with the adaptive braking function based on the eigenvalue and current-energy ratio, fault identification is performed.

[0072] In this application embodiment, the action function, adaptive braking function, and fault identification criterion include: Action function for .

[0073] The adaptive braking function is . The recommended value range for the basic braking coefficient, taking into account synchronization error, transmission error, and noise interference, is 3.5-4.5. It is an adaptive braking operator.

[0074]

[0075]

[0076]

[0077] Fault identification criteria are ,when When, it is identified as no fault or an external fault. At that time, it was identified as a fault within the area. The action verification results are as follows: Figure 4 As shown.

[0078] S600: If the fault is identified as non-fault or external to the zone, no protection action signal will be issued; if the fault is identified as internal to the zone, the fault type and fault phase will be identified using the zero-sequence current condition and the modulus current accumulation function, and a protection action signal will be issued.

[0079] In the embodiments of this application, the methods for identifying the modulus current accumulation function, fault type, and fault phase include: The modulus current cumulative sum function is ,in, W For the length of the data window, For sampling points within the data window, The sampling interval is... The instantaneous current value is calculated for the line model on this side (M side) after adaptive synchronization correction. The fault type and fault phase are identified using the actual instantaneous value of the line current on this side (M side) as follows: Condition 1 (Zero-sequence current condition): ,in, This is the instantaneous value of the zero-sequence current. This is the system's rated current.

[0080] Condition 2: A modulus relationship exists. , Both conditions must be met. This represents the modulus corresponding to two non-faulty phases. function. This represents the modulus corresponding to both the faulty phase and the first healthy phase. function, This indicates the modulus corresponding to both the faulty phase and the second healthy phase. function.

[0081] Condition 3: A modulus relationship exists. and Both conditions must be met. This represents the modulus-corresponding cumulative sum function containing two fault phases.

[0082] If condition 1 is met, condition 2 is met, and condition 3 is not met, it is a single-phase ground fault, and the faulty phase is the faulty phase described in condition 2. If condition 1 is not met, condition 2 is not met, and condition 3 is met, it is a phase-to-phase fault, and the faulty phase is the faulty phase described in condition 3. If condition 1 is met, condition 2 is not met, and condition 3 is met, it is a two-phase ground fault, and the faulty phase is the faulty phase described in condition 3.

[0083] It should be noted that this method can reliably identify faults within the area and accurately select the faulty phase under conditions of new energy access to strong / weak systems, different fault types, and high-resistance faults, with an action time of less than 10 ms, and has strong tolerance to CT transmission error and signal synchronization error.

[0084] Based on the above description of the implementation methods, those skilled in the art can clearly understand that the present invention can be implemented using software and necessary general-purpose hardware, and of course, it can also be implemented using hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as a computer floppy disk, read-only memory (ROM), random access memory (RAM), flash memory, hard disk, or optical disk, etc., including several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods of the various embodiments of the present invention.

[0085] Example 2 (Simulation Analysis Version) Reference Figure 5 This is one embodiment of the present invention. Unlike the first embodiment, this embodiment uses a large-scale optical energy storage and transmission system model built on the PSCAD platform as an example to verify the feasibility of the line longitudinal protection based on the two-dimensional distribution trajectory characteristics of time-domain short-circuit current of the present invention.

[0086] The system model uses a 200 km transmission line as the protected object to verify the performance of the proposed protection system. The sampling frequency used by the protection system is 2500 Hz, the data window length is 20 ms, and it contains 50 sampling points. The system parameters are shown in Table 1.

[0087] Table 1 Simulation System Parameters

[0088] For faults within the zone, the grid-connected system impedance is 5 Ω (strong system), with a time of 1.0 s. Figure 5 Taking grounding and phase-to-phase faults occurring at the beginning (F1), middle (F2), and end (F3) of a line as examples, the protection performance is verified. The fault section identification results are shown in Table 2, and the fault phase selection results are shown in Table 3.

[0089] Table 2 Fault Identification Results within the Zone

[0090] Table 3. Fault Phase Selection Results within the Zone

[0091] For faults outside the zone, the time is 1.0 s. Figure 5 Taking ground faults and phase-to-phase faults in F4 and F5 as examples, the protection performance is verified. The fault section identification results are shown in Table 4.

[0092] Table 4. Fault Identification Results Outside the Zone

[0093] For faults within the zone, taking a short circuit to ground via a 450 Ω resistor in phase A of F1 as an example, the fault zone identification function waveform is as follows: Figure 6 As shown in (a); for an external short circuit, taking a metallic short circuit in phase CA at F5 as an example, the waveform of the fault zone identification function is as follows. Figure 6 As shown in (b) of the diagram.

[0094] As shown in Tables 1-3, in scenarios where new energy sources are connected to a strong system, the proposed protection can accurately identify fault zones and select fault phases, with an action time of less than 10 ms.

[0095] The proposed protection system was compared with ratio-controlled differential protection and cosine similarity-based correlation protection. It should be noted that due to errors in the Berylone current of the non-faulty phase, the proposed modulus current was also used for comparative analysis, and the comparison focused on the ability to withstand transition resistance, i.e., sensitivity.

[0096] Taking a short circuit to ground via a 330 Ω resistor in phase A of F2 in zone F2 as an example, the α-mode current waveform, and The waveforms are as follows: Figure 7 As shown in (a), (b) and (c).

[0097] It can be seen that in the case of a high-resistance fault, and The difference is extremely weak, leading to a decrease in the sensitivity of conventional protection. Specifically, for differential protection, Typical braking coefficients less than 0.5~0.8 result in protection failure; for correlated protection, Greater than 0.8 indicates and Strong correlation exists, and protection cannot identify faults within the affected area. It is worth noting that the above analysis applies to scenarios where new energy sources are connected to a strong system. If new energy sources are connected to a weak system, the sensitivity of conventional protection will be further reduced.

[0098] In comparison, the verification results in Sections 3.1 and 3.2 show that when new energy sources are connected to a weak system, the proposed protection can identify high-resistance faults with a transition resistance of 450 Ω, which is more sensitive than conventional protection. The simulation results are consistent with the theoretical analysis in Section 2.2.3.

[0099] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of short-circuit current, characterized in that, include: Step 1: Real-time acquisition of voltage and current sampling sequences on both the local and opposite sides of the transmission line; Step 2: Extract the three-phase current sampling sequence of this side into the actual line-mode current sequence through phase mode transformation. Based on the pre-constructed Berylon distributed parameter model, the line-mode current sequence extrapolated from the opposite side to this side is calculated using the voltage and current sampling sequences from the opposite side. ; Step 3: Calculate the minimum error energy between the actual current and the calculated current of the line model on this side, and obtain the corrected calculated current sequence of the line model through adaptive synchronous correction. ; Step 4: Construct a second-order real symmetric matrix based on the current sequence calculated from the corrected line model. The principal axis direction angle, which reflects the two-dimensional trajectory distribution characteristics of time-domain current, is extracted through feature decomposition. and eigenvalues , ; Step 5: Construct an action function using the spindle direction angle, and combine it with an adaptive braking function based on eigenvalues ​​and current-energy ratios to identify faults; Step 6: If the fault is identified as no fault or an external fault, no protection action signal will be issued; If the fault is identified as an intra-zone fault, the fault type and fault phase are identified using the zero-sequence current condition and the modulus current accumulation function, and the output protection action signal is activated.

2. The longitudinal protection method for lines according to claim 1, characterized in that, In step 2, the instantaneous current value is calculated by constructing the line model on side M according to the following formula. : in, , , These are respectively deduced to the M side. α mold, β Model and γ The instantaneous value of the current is calculated using the modulus. , , The instantaneous current values ​​of j are calculated by extrapolating the line-mode voltage and current sampling values ​​from the opposite side N to the a, b, and c phases of the local side M, based on the Berylon line model.

3. The longitudinal protection method for lines according to claim 1, characterized in that, In step 3, the adaptive synchronization correction process includes: Calculate the error energy function , in, For this side M side in The actual current value of the line model at time [time]. The time interval is used to extrapolate from the contralateral N side to this side. The current value is calculated for the line model. The potential synchronization error offset is expressed in terms of the number of sampling points. W For the length of the data window, For sampling points within the data window, The sampling interval; Search The smallest synchronization error offset Calculate the current after adaptive synchronization correction. Thus, the corrected line-mode calculated current sequence is obtained. .

4. The longitudinal protection method for lines according to claim 1, characterized in that, In step 4, based on the actual current sequence of the local line mode... and the corrected line model calculated current sequence Construct a second-order real symmetric matrix for: in, , , , , ， By examining second-order real symmetric matrices Feature decomposition extracts the principal axis direction angles that reflect the characteristics of the two-dimensional trajectory distribution of the time-domain current plane. and eigenvalues , ;in, It is a second-order real symmetric matrix Maximum eigenvalue, It is a second-order real symmetric matrix Minimum eigenvalue; and These are the transposes of the corresponding sequences; cov is for covariance calculation.

5. The longitudinal protection method for lines according to claim 4, characterized in that, In step 4, the main axis direction angle Solve using the following formula: Eigenvalues , Solve using the following formula: 。 6. The longitudinal protection method for lines according to claim 1, characterized in that, In step 5, the constructed action function is: ; for At any given moment, the principal axis direction angle; Construct the adaptive braking function as follows , Basic braking coefficient, For adaptive braking operators; Fault identification criteria are ,when When, it is identified as no fault or an external fault. At that time, it was identified as a fault within the area.

7. The longitudinal protection method for lines according to claim 6, characterized in that, Adaptive braking operator Calculate as follows: , They are respectively Second-order real symmetric matrix at time step Two orthogonal eigenvalues, Basic braking coefficient The value range is 3.5-4.

5.

8. The longitudinal protection method for lines according to claim 1 or 7, characterized in that, In step 6, the fault type and fault phase are identified using the zero-sequence current condition and the modulus current accumulation function, specifically as follows: Condition 1: ,in, This is the instantaneous value of the zero-sequence current. This is the system's rated current; Condition 2: , Simultaneously satisfying; among which, This represents the cumulative current sum function corresponding to the modulus of the two non-faulty phases. This represents the cumulative current sum function corresponding to the moduli of the faulty phase and the first healthy phase. This represents the cumulative current sum function corresponding to the moduli of the faulty phase and the second healthy phase; Condition 3: A modulus relationship exists. and Simultaneously satisfying; among which, This represents the modulus-corresponding current cumulative sum function containing two fault phases; If condition 1 is met, condition 2 is met, and condition 3 is not met, then it is determined to be a single-phase ground fault, and the faulty phase is the faulty phase described in condition 2. If condition 1 is not met, condition 2 is not met, and condition 3 is met, then it is determined to be a phase-to-phase fault, and the faulty phase is the faulty phase described in condition 3; If condition 1 is met, condition 2 is not met, and condition 3 is met, then it is determined to be a two-phase ground fault, and the faulty phase is the faulty phase described in condition 3.

9. The longitudinal protection method for lines according to claim 8, characterized in that, Modulus current cumulative sum function Calculate using the following formula: ,in, W For the length of the data window, For sampling points within the data window, The sampling interval is... This is the adaptive synchronization correction for side M. The instantaneous value of the current is calculated using the line-model at a given time. This is the instantaneous value of the actual current of the line model on side M.

10. A line longitudinal protection system based on the method of any one of claims 1-9, characterized in that, include: The electrical quantity acquisition module is used to collect voltage and current values ​​on both the local and opposite sides of the transmission line. The line-mode current calculation module is used to calculate the actual current sequence of the line-mode on this side. And the current sequence calculated using the voltage and current on the opposite side to extrapolate to this side from the line model. ; The adaptive synchronous correction module is used to adaptively and synchronously correct the calculated current sequence of the line model based on the minimum error energy between the actual current and the calculated current of the line model on this side, thereby obtaining the corrected calculated current sequence of the line model. ; The time-domain current two-dimensional distribution trajectory feature calculation module constructs a second-order real symmetric matrix based on the corrected line model current sequence. The principal axis direction angle, which reflects the two-dimensional trajectory distribution characteristics of time-domain current, is extracted through feature decomposition. and eigenvalues , ; The fault identification module uses the spindle direction angle to construct an action function and combines it with an adaptive braking function based on eigenvalues ​​and current-energy ratio to identify the presence or absence of faults and fault areas. The fault type identification module uses zero-sequence current conditions and modulus current accumulation function to identify fault types and fault phases.

11. An electronic device, comprising: Memory and processor; The memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions. When the computer-executable instructions are executed by the processor, they implement the steps of the line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of short-circuit current as described in any one of claims 1 to 9.

12. A computer-readable storage medium storing computer-executable instructions that, when executed by a processor, implement the steps of the line longitudinal protection method based on the two-dimensional distribution trajectory characteristics of short-circuit current as described in any one of claims 1 to 9.

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