Multi-terminal line pilot protection method and system based on time domain model identification

Abstract

The invention discloses a multi-end line pilot protection method and system based on time domain model identification, and relates to the technical field of electrical engineering, and the method comprises the steps: obtaining a three-phase voltage sampling value, a three-phase current sampling value and a switching value of each end of a multi-end line; judging whether each end of the multi-end line meets a protection starting condition or not; if yes, differential voltage variation and differential current are calculated, and correlation coefficients of the differential voltage variation and the differential current are calculated; judging whether the correlation coefficient is within a preset fault threshold range or not; if the correlation coefficient is not within the preset fault threshold range, determining that the multi-terminal line has an external fault, and enabling the protection device not to act; and if the correlation coefficient is within a preset fault threshold range, determining that the multi-terminal line has an internal fault, and enabling the protection device to act to remove the fault. According to the invention, the influence of capacitive current and a power electronic power supply on pilot protection performance is overcome, the operating characteristics of a relay protection device are improved, and safe and stable operation of a power system is ensured.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering technology, and in particular to a multi-terminal line pilot protection method and system based on time domain model identification. Background Art

[0002] Differential protection is generally used as the main protection for AC lines. When it comes to long-distance transmission lines with obvious distribution characteristics such as high voltage levels and long line lengths, the existence of distributed capacitive currents makes Kirchhoff's current law no longer satisfied, reducing the sensitivity and reliability of differential protection. In addition, the existing power system presents the new "double high" characteristics of a high proportion of new energy and a high proportion of power electronic equipment, which has caused a huge change in the fault characteristics of the power system compared with before, manifested as: the amplitude of the short-circuit current is limited, and the frequency of the short-circuit current is no longer a single industrial frequency component. These changes in the fault current characteristics of the power system further reduce the operating performance of existing relay protection devices, threatening the safe and stable operation of the power system.

[0003] The existing access to new energy represented by wind and solar usually adopts multi-terminal wiring. Compared with the original power system, the fault characteristics of the multi-terminal line system have changed dramatically, as shown in the following: (1) A fault at any location on the line will affect the normal operation of the entire line. Once a fault occurs, it is required to quickly isolate the fault; (2) Conventional backup protection (distance protection, zero-sequence protection, etc.) cannot meet the requirements of speed and selectivity due to the difficulty in setting the fixed value. This puts forward new requirements for the relay protection configuration of distributed new energy power transmission lines.

[0004] In response to the above problems, most scholars are currently studying the following solutions:

[0005] Some scholars have proposed protection principles based on waveform characteristics. These methods use mathematical correlation to characterize the difference in line current at each end after a fault in or outside the area, avoiding the impact of capacitive current on protection performance. However, when the output of the new energy system is low, the fault current change trend at each end of the line is not obvious, and the correlation of current changes at each end of the line cannot be compared. At this time, the protection performance of this type of principle is reduced and there is even a risk of refusal to operate.

[0006] Some scholars have proposed the principle of energy distribution at different frequencies. This is to construct protection criteria based on the principle that the high-frequency and low-frequency current energy distribution characteristics of the fault current are different when there is a fault inside or outside the zone, so as to avoid the influence of non-power frequency components on the protection performance. However, this type of method requires the extraction of high-frequency signals, which puts higher requirements on the hardware of the protection device.

[0007] In view of the problem that multi-terminal line systems need to quickly remove faults and the difficulty in coordinating protection setting, some domestic scholars have conducted relevant research and simulation on the principles of multi-terminal lines, but have not yet applied them to devices. Some manufacturers have studied and developed the communication and synchronization methods of multi-terminal line protection, but the protection principles have not been publicly published. Summary of the invention

[0008] The purpose of the present invention is to provide a multi-terminal line pilot protection method and system based on time domain model identification in order to solve at least one of the above technical problems.

[0009] In the first aspect, an embodiment of the present invention provides a multi-terminal line longitudinal protection method based on time domain model identification, which is applied to a protection device for a multi-terminal line; comprising: obtaining three-phase voltage sampling values, three-phase current sampling values ​​and switch quantities of each end of the multi-terminal line; judging whether each end of the multi-terminal line meets the protection start-up conditions based on the three-phase voltage sampling values, the three-phase current sampling values ​​and the switch quantities; if so, respectively calculating the differential voltage change and the differential current based on the three-phase voltage sampling values ​​and the three-phase current sampling values, and calculating the correlation coefficient between the differential voltage change and the differential current; judging whether the correlation coefficient is within a preset fault threshold range; if the correlation coefficient is not within the preset fault threshold range, determining that an out-of-zone fault occurs on the multi-terminal line, and the protection device does not operate; if the correlation coefficient is within the preset fault threshold range, determining that an in-zone fault occurs on the multi-terminal line, and the protection device operates to remove the fault.

[0010] Furthermore, the method further includes: if at least one end of the multi-terminal line does not meet the protection start condition, no longitudinal differential protection judgment is performed.

[0011] Furthermore, if the correlation coefficient is within the preset fault threshold range, the method further includes: based on the size of the correlation coefficient, determining the fault type and outputting an action message.

[0012] Further, respectively calculating the differential voltage change and the differential current based on the three-phase voltage sampling values ​​and the three-phase current sampling values ​​includes: calculating the differential current based on the three-phase current sampling values ​​includes: In the formula, N represents the number of line terminals, Φ represents the three phases A, B, and C, and i cd represents the differential current, i Sn Indicates the three-phase current sampling value of the n-th line, i G represents the grid-side current sampling value; and calculating the differential voltage based on the three-phase voltage sampling values, including: In the formula, u cd represents the differential voltage, u SnIndicates the three-phase voltage sampling value of the n-th line, u G represents a grid-side voltage sampling value; and calculating the differential voltage change based on the differential voltage, including: Where u′ cd represents the differential voltage change, T represents the sampling interval, u cd (k) represents the kth sample value, u cd (k-1) represents the k-1th sampling value.

[0013] Furthermore, the calculation formula for the correlation coefficient between the differential voltage change and the differential current includes:

[0014]

[0015] Where ρ is the correlation coefficient, N W is the data window length.

[0016] Furthermore, the preset fault threshold range includes [-1, 0.7).

[0017] In the second aspect, an embodiment of the present invention further provides a multi-terminal line longitudinal protection system based on time domain model identification, which is applied to a protection device for a multi-terminal line; it includes: a sampling module, a first judgment module, a calculation module, a second judgment module and a determination module; wherein the sampling module is used to obtain the three-phase voltage sampling value, the three-phase current sampling value and the switch quantity of each end of the multi-terminal line; the first judgment module is used to judge whether each end of the multi-terminal line meets the protection start condition based on the three-phase voltage sampling value, the three-phase current sampling value and the switch quantity; the calculation module is used to determine whether each end of the multi-terminal line meets the protection start condition if each end of the multi-terminal line meets the protection start condition If all the terminals meet the protection start-up conditions, the differential voltage change and the differential current are calculated based on the three-phase voltage sampling values ​​and the three-phase current sampling values, and the correlation coefficient between the differential voltage change and the differential current is calculated; the second judgment module is used to judge whether the correlation coefficient is within the preset fault threshold range; the determination module is used to determine that an out-of-zone fault occurs in the multi-terminal line if the correlation coefficient is not within the preset fault threshold range, and the protection device does not operate; if the correlation coefficient is within the preset fault threshold range, it is determined that an in-zone fault occurs in the multi-terminal line, and the protection device operates to remove the fault.

[0018] Furthermore, the determination module is further configured to, if the correlation coefficient is within the preset fault threshold range, determine the fault type based on the size of the correlation coefficient and output an action message.

[0019] An embodiment of the present invention further provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method provided in the embodiment of the present invention when executing the computer program.

[0020] An embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and when the computer instructions are executed by a processor, the method provided by the embodiment of the present invention is implemented.

[0021] The present invention provides a multi-terminal line pilot protection method and system based on time domain model identification, which converts the identification of unstable electrical quantities into the identification of determined topological structure changes, solves the restriction of capacitive current on pilot protection performance, and avoids the influence of power electronic power supply on fault characteristics, thereby ensuring the safe and reliable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A flowchart of a multi-terminal line pilot protection method based on time domain model identification provided by an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of a four-terminal single-phase line fault model provided by an embodiment of the present invention;

[0025] Figure 3 A schematic diagram of an out-of-area fault model of a four-terminal single-phase line provided in an embodiment of the present invention;

[0026] Figure 4 A phase A ground fault circuit diagram in a double-terminal three-phase line area provided by an embodiment of the present invention;

[0027] Figure 5 A circuit diagram of a BC phase grounding fault in a double-terminal three-phase line area provided by an embodiment of the present invention;

[0028] Figure 6 A schematic diagram of a multi-terminal line pilot protection system based on time domain model identification provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Embodiment 1

[0031] Figure 1 1 is a flow chart of a multi-terminal line pilot protection method based on time domain model identification provided according to an embodiment of the present invention, and the method is applied to a protection device of a multi-terminal line. Figure 1 As shown, the method specifically comprises the following steps:

[0032] Step S102, obtaining three-phase voltage sampling values, three-phase current sampling values ​​and switching values ​​of each end of the multi-terminal line.

[0033] Step S104, based on the three-phase voltage sampling values, the three-phase current sampling values ​​and the switch quantity, determine whether each end of the multi-terminal line meets the protection start condition; if yes, execute step S106; if not, execute step S114.

[0034] Step S106, respectively calculating the differential voltage variation and the differential current based on the three-phase voltage sampling values ​​and the three-phase current sampling values, and calculating the correlation coefficient between the differential voltage variation and the differential current.

[0035] Step S108, determining whether the correlation coefficient is within a preset fault threshold range; if not, executing step S110; if yes, executing step S112.

[0036] Step S110, determining that an out-of-area fault occurs in the multi-terminal line and the protection device does not operate.

[0037] Step S112, determining that a multi-terminal line has an in-area fault, and the protection device operates to remove the fault.

[0038] Step S114: No longitudinal differential protection determination is performed.

[0039] Figure 2 is a schematic diagram of a four-terminal single-phase line fault model provided according to an embodiment of the present invention. Figure 3 FIG. 1 is a schematic diagram of a four-terminal single-phase line out-of-area fault model provided according to an embodiment of the present invention. Figure 2 and Figure 3 As shown, the embodiment of the present invention takes a four-terminal single-phase line as an example to illustrate the sampling value in step S102. S1 、E S2 、E S3 、EG are the equivalent electromotive force of power source 1, power source 2, power source 3 and grid side, u S1 、u S2 、u S3 、u G are the three-phase voltage sampling values ​​of power source 1, power source 2, power source 3 and the grid side, i S1 、i S2 、i S3 、i G They are the three-phase current sampling values ​​of power source 1, power source 2, power source 3 and the grid side; i SC1 ~i SC9 、i GC is the capacitive current to ground, i F Inject current into the fault point; Z L1 ~Z L5 is the equivalent impedance of the line, C is the equivalent capacitance of the line to ground, "S" represents the electrical quantity on the source side, and "G" represents the electrical quantity on the grid side. The device collects the three-phase voltage sampling values ​​and three-phase current sampling values ​​u at each end of the line in real time. S1 、u S2 、u S3 、u G 、i S1 、i S2 、i S3 、i G And switch quantity.

[0040] Specifically, in step S104, according to the obtained three-phase voltage sampling values ​​and three-phase current sampling values ​​and switching values ​​of each end, it is judged whether the line protection device at each end meets the starting conditions of the current mutation starting element, the zero-sequence current and phase current starting element, the static stability damage detection element, the weak feed starting element and the TWJ starting element. Since the starting of the protection device is not the focus of the present invention, it will not be elaborated in detail.

[0041] Specifically, if none of the above five starting modes works, the longitudinal differential protection judgment will no longer be performed.

[0042] In an optional implementation provided in an embodiment of the present invention, Figure 2 Taking the fault circuit diagram of the four-terminal single-phase line area as an example, the differential current and differential voltage are calculated as follows:

[0043]

[0044] Where N represents the number of line terminals, i cd represents the differential current, i Sn Indicates the three-phase current sampling value of the n-th line, i G Indicates the grid-side current sampling value.

[0045] Among them, Φ represents the three phases A, B, and C. For example, when Φ represents the A phase, i cdΦ represents the differential current of phase A, i SnΦ Indicates the A-phase current sampling value of the n-th line, i GΦ Indicates the grid-side A phase current sampling value; and so on.

[0046]

[0047] In the formula, u cd represents the differential voltage, u Sn Indicates the three-phase voltage sampling value of the n-th line, u G represents the grid-side voltage sampling value; then, the differential voltage change is calculated based on the differential voltage, including:

[0048]

[0049] In the formula, u′ cd represents the differential voltage change, T represents the sampling interval, u cd (k) represents the kth sample value, u cd (k-1) represents the k-1th sampling value.

[0050] Specifically, the calculation formula for the correlation coefficient between the differential voltage change and the differential current includes:

[0051]

[0052] In the formula, ρ is the correlation coefficient, N W is the data window length.

[0053] Among them, Φ represents the three phases A, B, and C, and the correlation coefficient ρ includes ρ A , B , C , respectively represent the correlation coefficient between the A-phase differential voltage change and the A-phase differential current, the correlation coefficient between the B-phase differential voltage change and the B-phase differential current, and the correlation coefficient between the C-phase differential voltage change and the C-phase differential current.

[0054] Preferably, the preset fault threshold range includes [-1, 0.7).

[0055] In an optional implementation provided in an embodiment of the present invention, when p A , B , C When any value is between [-1,0.7), it is judged that a fault occurs in the multi-terminal line, and the protection device is activated to remove the fault; when ρ A , B , CWhen the values ​​are not between [-1,0.7), it is judged that an out-of-area fault occurs in the multi-terminal line and the protection device does not operate.

[0056] Taking a single-phase system as an example, the theoretical derivation of the criterion is as follows:

[0057] (1) Single-phase system out-of-zone fault:

[0058] The circuit diagram of the fault outside the area is as follows Figure 3 As shown. According to Kirchhoff's current law, the differential current is the sum of the capacitive currents:

[0059]

[0060] because Figure 3 It is a four-terminal circuit, so N is 4. Substituting into equation (5), we get:

[0061] i cd =i S1 +i S2 +i S3 +i G =i SC1 +i SC2 +i SC3 +i SC4 +i SC5 +i SC6 +i SC7 +i SC8 +i SC9 +i GC (6)

[0062] The voltage-current characteristics of the capacitor are:

[0063]

[0064] Substituting formula (7) into formula (12), we can obtain:

[0065]

[0066] It can be concluded that when an out-of-zone fault occurs, the first-order derivative of the differential voltage is proportional to the differential current, that is, the differential current and differential voltage satisfy the capacitor model and are independent of the properties of the power supplies on both sides.

[0067] (2) Single-phase system fault:

[0068] The fault circuit diagram in the area is as follows Figure 2 As shown, the differential current also includes the fault point injection current:

[0069]

[0070] The calculation formula of the capacitance current on both sides to ground is:

[0071]

[0072] Substituting formula (10) into formula (9) yields:

[0073]

[0074] It can be seen that when the fault occurs within the zone, the differential current and differential voltage do not satisfy the capacitor model due to the asymmetry of the capacitors on both sides and the existence of the injected current at the fault point; when the fault occurs outside the zone, the differential current and differential voltage satisfy the capacitor model.

[0075] The method provided in the embodiment of the present invention is also applicable to a three-phase system. Figure 4 A phase A grounding fault circuit diagram in a double-terminal three-phase line area provided according to an embodiment of the present invention. Figure 5 1 is a circuit diagram of a BC phase grounding fault in a double-terminal three-phase line area provided according to an embodiment of the present invention. Figure 4 and Figure 5 Taking the double-terminal three-phase line shown in the figure as an example, the model that the differential voltage and differential current conform to when internal and external faults occur in the three-phase system is analyzed.

[0076] (3) Single-phase fault in three-phase system area:

[0077] Figure 4 In, C Sg , C Gg are the capacitance to ground on the source side and the grid side respectively; C Sm , C Gm are the phase capacitances on the source side and the grid side respectively. G,A is the measured current of phase A at the grid-side busbar, i GAB is the grid-side AB phase capacitance current, i GAg is the capacitance current of phase A on the grid side, and the capacitance currents on the source side and other phases are similar.

[0078] For the A-phase differential current, the source-side and grid-side capacitance currents, compared with the single-phase line, include the phase-to-phase capacitance current in addition to the ground capacitance current:

[0079]

[0080] Taking the grid side as an example, the calculation formulas for phase-to-phase capacitance current and ground capacitance current are:

[0081]

[0082] Zero-sequence compensation can be used to eliminate the BC phase voltage. The calculation formula for positive-sequence capacitance and zero-sequence capacitance is:

[0083]

[0084] Define the zero-sequence compensation coefficient:

[0085] k 01 =C0 / C1-1 (15)

[0086] Substituting equations (13), (14) and (15) into the grid-side capacitor current term in equation (12), we can obtain:

[0087]

[0088] In the formula, u mGA is the grid-side phase A voltage after zero-sequence compensation, C G1 is the grid-side equivalent capacitance. Similarly, zero-sequence compensation is performed on the source side and other phase voltages, and the calculation formula for the capacitance current on both sides can be written as:

[0089]

[0090] In the formula, C S1 is the equivalent capacitance on the source side. Substituting equation (17) into equation (12), we can obtain:

[0091]

[0092] In formula (18), the main component of the differential current is i F , the specific form of the capacitor current expression does not affect the properties of the differential current. It can be seen that the differential current of phase A and the differential voltage after zero-sequence compensation do not conform to the capacitor model. For the other two-phase differential current, take phase B as an example:

[0093]

[0094] Similarly, zero-sequence compensation is performed on the voltages on both sides, and since phase B is not the fault phase, the capacitances on both sides are considered equal, so the calculation formula for the capacitance currents on both sides can be written as:

[0095]

[0096] Substituting formula (20) into formula (19) yields:

[0097]

[0098] Similar to the fault outside the single-phase line area, the differential current of phase B and the differential voltage after zero-sequence compensation conform to the capacitor model, and the same conclusion is reached for phase C.

[0099] (4) Phase-to-phase fault within a three-phase system:

[0100] The circuit diagram of BC phase grounding fault in the area is as follows Figure 5 As shown, FB ,i FC The fault current injected into the BC phase, R gis the fault-to-ground branch resistance. Taking phase B as an example, the fault phase differential current calculation formula is:

[0101]

[0102] Similar to the A phase when the A phase is grounded in the area, the BC phase differential current and the differential voltage after zero-sequence compensation do not conform to the capacitor model, while the differential current calculation formula of the non-fault phase A phase is:

[0103]

[0104] It can be seen that the differential current of phase A and the differential voltage after zero-sequence compensation conform to the capacitor model. For phase-to-phase short circuit and three-phase short circuit, the analysis results are also consistent with the single-phase line, that is, the fault phase does not satisfy the capacitor model when the fault occurs within the zone, while the three phases satisfy the capacitor model when the fault occurs outside the zone. Therefore, the method provided by the present invention transforms the identification of unstable electrical quantities into the identification of the change in the determined topological structure.

[0105] Specifically, in step S112, if the correlation coefficient is within the preset fault threshold range, the method further includes: based on the size of the correlation coefficient, determining the fault type and outputting an action message.

[0106] Table 1 is a fault type discrimination table provided according to an embodiment of the present invention. As shown in Table 1, the fault type is judged to be a single-phase grounding fault or a phase-to-phase fault according to the correlation coefficient of the three-phase differential current and differential voltage changes. In the table, "+" indicates that the correlation coefficient is between [-1, 0.7), and "-" indicates that the correlation coefficient is outside [-1, 0.7).

[0107] Table 1 Fault type identification

[0108]

[0109] From the above description, it can be seen that the present invention provides a multi-terminal line longitudinal protection method based on time domain model identification, which converts the judgment of unstable electrical quantities into the identification of certain topological structure changes, solves the restriction of capacitive current on the performance of longitudinal protection, and avoids the influence of power electronic power supply on fault characteristics, thereby ensuring the safe and reliable operation of the power system.

[0110] Embodiment 2

[0111] Figure 6 is a schematic diagram of a multi-terminal line pilot protection system based on time domain model recognition provided according to an embodiment of the present invention, the system is applied to a protection device of a multi-terminal line. Figure 6 As shown, the system includes: a sampling module 10 , a first judgment module 20 , a calculation module 30 , a second judgment module 40 and a determination module 50 .

[0112] Specifically, the sampling module 10 is used to obtain three-phase voltage sampling values, three-phase current sampling values ​​and switching values ​​at each end of the multi-terminal line.

[0113] The first judgment module 20 is used to judge whether each end of the multi-terminal line meets the protection start condition based on the three-phase voltage sampling value, the three-phase current sampling value and the switch value.

[0114] The calculation module 30 is used to calculate the differential voltage change and the differential current based on the three-phase voltage sampling values ​​and the three-phase current sampling values ​​respectively if each end of the multi-terminal line meets the protection start condition, and calculate the correlation coefficient between the differential voltage change and the differential current.

[0115] The second judgment module 40 is used to judge whether the correlation coefficient is within a preset fault threshold range.

[0116] The determination module 50 is used to determine that an out-of-area fault occurs in the multi-terminal line if the correlation coefficient is not within the preset fault threshold range, and the protection device does not operate; if the correlation coefficient is within the preset fault threshold range, it is determined that an in-area fault occurs in the multi-terminal line, and the protection device operates to remove the fault.

[0117] Specifically, the determination module 50 is further configured to, if the correlation coefficient is within a preset fault threshold range, determine the fault type based on the size of the correlation coefficient and output an action message.

[0118] The present invention further provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method provided in the embodiment of the present invention when executing the computer program.

[0119] The present invention also provides a computer-readable storage medium, which stores computer instructions. When the computer instructions are executed by a processor, the method provided in the embodiment of the present invention is implemented.

[0120] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0121] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A multi-terminal line pilot protection method based on time domain model identification, characterized in that: A protection device for multi-terminal lines; comprising: Obtaining three-phase voltage sampling values, three-phase current sampling values ​​and switching quantities at each end of the multi-terminal line; Based on the three-phase voltage sampling value, the three-phase current sampling value and the switch value, judging whether each end of the multi-terminal line meets the protection start condition; If yes, then respectively calculating the differential voltage variation and the differential current based on the three-phase voltage sampling values ​​and the three-phase current sampling values, and calculating the correlation coefficient between the differential voltage variation and the differential current; Determining whether the correlation coefficient is within a preset fault threshold range; If the correlation coefficient is not within the preset fault threshold range, it is determined that an out-of-area fault occurs in the multi-terminal line, and the protection device does not operate; If the correlation coefficient is within the preset fault threshold range, it is determined that an in-area fault occurs in the multi-terminal line, and the protection device is activated to remove the fault.

2. The method according to claim 1, characterized in that: The method further includes: if at least one end of the multi-end line does not meet the protection start condition, then no longitudinal differential protection judgment is performed.

3. The method according to claim 1, characterized in that: If the correlation coefficient is within the preset fault threshold range, the method further includes: based on the size of the correlation coefficient, determining the fault type and outputting an action message.

4. The method according to claim 1, characterized in that: Calculating the differential voltage change and the differential current based on the three-phase voltage sampling values ​​and the three-phase current sampling values ​​respectively, including: Calculating the differential current based on the three-phase current sampling values ​​includes: In the formula, N represents the number of line terminals, Φ represents the three phases A, B, and C, and i cd represents the differential current, i Sn Indicates the three-phase current sampling value of the n-th line, i G Indicates the grid-side current sampling value; Calculating the differential voltage based on the three-phase voltage sampling values ​​includes: In the formula, u cd represents the differential voltage, u Sn Indicates the three-phase voltage sampling value of the n-th line, u G Indicates the grid-side voltage sampling value; Calculating the differential voltage change based on the differential voltage includes: In the formula, u ′ cd represents the differential voltage change, T represents the sampling interval, u cd (k) represents the kth sample value, u cd (k-1) represents the k-1th sampling value.

5. The method according to claim 4, characterized in that: The calculation formula of the correlation coefficient between the differential voltage change and the differential current includes: Where ρ is the correlation coefficient, N W is the data window length.

6. The method according to claim 1, characterized in that: The preset fault threshold range includes [-1, 0.7).

7. A multi-terminal line pilot protection system based on time domain model identification, characterized in that: A protection device applied to a multi-terminal line; comprising: a sampling module, a first judgment module, a calculation module, a second judgment module and a determination module; wherein, The sampling module is used to obtain the three-phase voltage sampling value, the three-phase current sampling value and the switching value of each end of the multi-terminal line; The first judgment module is used to judge whether each end of the multi-terminal line meets the protection start condition based on the three-phase voltage sampling value, the three-phase current sampling value and the switch value; The calculation module is used to calculate the differential voltage change and the differential current respectively based on the three-phase voltage sampling values ​​and the three-phase current sampling values ​​if each end of the multi-terminal line meets the protection start condition, and calculate the correlation coefficient between the differential voltage change and the differential current; The second judgment module is used to judge whether the correlation coefficient is within a preset fault threshold range; The determination module is used to determine that an out-of-area fault occurs in the multi-terminal line if the correlation coefficient is not within the preset fault threshold range, and the protection device does not operate; if the correlation coefficient is within the preset fault threshold range, it is determined that an in-area fault occurs in the multi-terminal line, and the protection device operates to remove the fault.

8. The system according to claim 7, characterized in that: The determination module is further configured to, if the correlation coefficient is within the preset fault threshold range, determine the fault type based on the size of the correlation coefficient and output an action message.

9. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the method according to any one of claims 1 to 6 when executing the computer program.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and when the computer instructions are executed by a processor, the method according to any one of claims 1 to 6 is implemented.

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