A power distribution network t-connected multi-terminal line pilot protection method and system

Abstract

The application discloses a power distribution network T-connection multi-terminal line pilot protection method and system, relates to the technical field of power system relay protection technology, and solves the problem of insufficient reliability caused by insufficient fault feature extraction of traditional pilot protection under the conditions of high-resistance grounding and strong noise interference of T-connection multi-terminal line in the prior art. The application firstly obtains three-phase current fault components after fault starting of each switch in the protection area and voltage before fault starting, then decouples the three-phase coupled electrical quantities into independent modulus components, subsequently performs S transformation on the modulus of each switch current fault component and the modulus of the voltage before fault starting, utilizes the high resolution characteristic of S transformation in the time-frequency domain, and based on the relative entropy calculation of the S transformation energy spectrum of each switch, constructs an energy relative entropy difference criterion, thereby still maintaining stable discrimination ability under the conditions of strong noise and high-resistance grounding, and realizing reliable identification and rapid action of internal and external faults of the T-connection multi-terminal line.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and in particular to a method and system for longitudinal protection of T-connected multi-terminal lines in a distribution network. Background Technology

[0002] With the large-scale integration of distributed power sources and the continuous increase in urban power distribution network load density, the distribution network topology has evolved from the traditional single-source radial network to a complex multi-terminal network with multiple power sources. Among these, T-connected multi-terminal lines, as a common branch topology in distribution networks, are widely used in scenarios where substations supply power to multiple load areas. The boundary of their protection zone involves the main switch on the substation side and multiple branch switches connecting various loads. Longitudinal protection, due to its ability to utilize electrical quantity information at both ends or multiple ends of the line for fault identification, possesses inherent selectivity and speed, making it an important development direction for the main protection of T-connected multi-terminal lines. In existing technologies, longitudinal protection for multi-terminal lines mainly relies on methods such as amplitude comparison of fault component currents, phase relationship analysis, or impedance calculation, distinguishing between intra-zone and extra-zone faults by detecting the abrupt changes in electrical quantities at each end during a fault. However, in the actual operation environment of the distribution network, the length of each branch of the T-connection line varies greatly, the load types are complex, and high-resistance grounding faults occur frequently, resulting in the fault characteristics exhibiting significant dispersion and non-stationarity in the time and frequency domain. Traditional discrimination methods based on amplitude or phase within a single time window are difficult to fully capture the subtle distribution differences of fault transient energy.

[0003] Existing technologies suffer from the problem that traditional longitudinal protection systems, under conditions of high-resistance grounding and strong noise interference in T-connected multi-terminal lines, cannot effectively extract the time-frequency domain distribution differences of fault transient energy because they rely solely on the amplitude or phase information of the fault component current. This leads to insufficient reliability in fault identification between internal and external zones. Specifically, traditional methods typically perform time-domain comparisons or simple frequency-domain transformations on the three-phase current fault components, failing to effectively decouple the three-phase coupled components to highlight fault mode characteristics. They also fail to fully utilize the relative entropy differences in electrical quantities before and after fault initiation to quantify the asymmetry of energy distribution at each switch. When a grounding fault occurs via a transition resistor or a high-resistance fault at the line end, the amplitude of the fault component current attenuates significantly and is affected by the load current. Traditional amplitude criteria are prone to sensitivity reduction or even failure to operate. Simultaneously, the integration of inverter-type distributed power sources in the distribution network makes the fault current controlled and its characteristics more complex, further weakening the adaptability of longitudinal protection based on fixed phase thresholds and making it difficult to meet the stringent requirements for protection selectivity and reliability in T-connected multi-terminal lines.

[0004] Therefore, a longitudinal protection method and system for T-connected multi-terminal lines in a power distribution network is needed. Summary of the Invention

[0005] To address the problem of insufficient fault feature extraction and thus low reliability in traditional longitudinal protection methods for T-connected multi-terminal lines under conditions of high-resistance grounding and strong noise interference, this invention provides a longitudinal protection method and system for T-connected multi-terminal lines in distribution networks. This method decouples three-phase fault components through phase-mode transformation to highlight independent mode characteristics and introduces S-transform to characterize the transient energy distribution of the fault in the time-frequency domain at high resolution. Furthermore, it utilizes the energy relative entropy difference to quantify the asymmetry of energy distribution at the multi-terminal switches, constructing a longitudinal protection criterion independent of amplitude and phase thresholds. This effectively solves the problems of insufficient sensitivity and decreased reliability of traditional methods under high-resistance grounding and noise interference, significantly improving the robustness and speed of fault identification inside and outside the T-connected multi-terminal line area. The specific technical solution is as follows: A method for longitudinal protection of multi-terminal T-connected lines in a distribution network includes the following steps: The three-phase current fault components after fault initiation and the voltage before fault initiation at each switch in the T-connected multi-terminal line protection area of ​​the distribution network within a time window are obtained; wherein, the switch includes a first switch on the substation side and a second switch connected to each load respectively. The current fault component and the voltage before fault initiation are subjected to phase-mode transformation to obtain the modulus of each switch current fault component and the modulus of the voltage before fault initiation. Based on the modulus of the fault current component of each switch and the modulus of the voltage before the fault starts, calculate the relative entropy of the S-transform energy of each switch. Based on the relative entropy of the S-transform energy of each switch, the difference between the relative entropy of the S-transform energy of the first switch and each of the second switches is obtained, and then the sum of the relative entropy differences is obtained. The sum of the relative entropy differences of energy is compared with the protection setting value. When the sum of the relative entropy differences of energy is greater than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the distribution network, the longitudinal protection is activated, and the switch in the area is tripped.

[0006] Preferably, the method for determining the fault start time is as follows: The three-phase current at each switch is compared with the overcurrent element judgment set value. If the three-phase current at at least one switch is greater than the overcurrent element judgment set value, the current moment is the fault start moment. The overcurrent element judgment setting is set to the maximum load current of the distribution network line.

[0007] Preferably, the current fault component is the current at the current moment minus the current at the previous two wave moments, and the specific calculation formula is as follows: In the formula: t At the current sampling time, T For power frequency cycle, , , These are the instantaneous values ​​of the A-phase, B-phase, and C-phase currents of the k-th switch at the current sampling time t, respectively. , , These are the instantaneous current values ​​of phase A, phase B, and phase C of the k-th switch at the two power frequency cycles preceding the current sampling time. , , These are the fault components of phase A, phase B, and phase C currents of the k-th switch at the current sampling time t; The modulus of the current fault component is calculated as follows: In the formula, This is the modulus of the current fault component.

[0008] Preferably, the modulus of the voltage before fault initiation The calculation method is as follows: In the formula, , , These are the instantaneous voltage values ​​of phase A, phase B, and phase C before the start of the faulty k-th switch.

[0009] Preferably, the S-transform is represented as follows: In the formula, For signal At any moment ,frequency The complex-valued spectrum of the S-transform at the location; The time-domain signal to be transformed corresponds to the current fault component modulus of each switch. or voltage modulus before fault start ; This is the time shift factor; For frequency variables; This is the time variable for integration.

[0010] Preferably, the S-transform energy of each switch is relative to its entropy. H k The calculation method is as follows: In the formula, This is the time shift factor; For frequency variables; For the first Modulus of individual switching current fault components Normalized energy spectral density after S-transformation; For the first Voltage modulus before startup due to switch failure Normalized energy spectral density after S-transformation.

[0011] The preferred method for obtaining the sum of the energy relative entropy differences is as follows: In the formula, It is the sum of the relative entropy differences of energy. For the first switch and the second The S-transform energy relative entropy difference of the second switch The total number of switches within the protected area.

[0012] A longitudinal protection system for multi-terminal T-connected lines in a distribution network, applied to any of the methods described above, includes: The electrical quantity acquisition module is configured to acquire the three-phase current fault components and the voltage before fault initiation at each switch in the protection area of ​​the T-connected multi-terminal line of the distribution network within a certain time window; wherein, the switch includes a first switch on the substation side and a second switch connected to each load respectively; The modulus acquisition module is configured to perform Clark phase-mode transformation on the three-phase current fault components and the voltage before fault initiation, respectively, to obtain the modulus of each switch current fault component and the modulus of the voltage before fault initiation; the energy relative entropy calculation module is configured to calculate the S-transform energy relative entropy of each switch based on the modulus of the current fault components and the modulus of the voltage before fault initiation of each switch. The difference sum acquisition module is configured to obtain the difference between the S-transform energy relative entropy of the first switch and each of the second switches based on the S-transform energy relative entropy of each switch, and then obtain the sum of the energy relative entropy differences; The fault judgment and processing module is configured to compare the sum of the relative entropy differences of energy with the protection setting value. When the sum of the relative entropy differences of energy is greater than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the distribution network, the longitudinal protection is activated, and the switch in the area is tripped.

[0013] A computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device where the computer-readable storage medium is located to perform the longitudinal protection method for T-connected multi-terminal lines in a power distribution network as described above.

[0014] A processor for running a program, wherein the program executes the longitudinal protection method for T-connected multi-terminal lines in a distribution network as described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first obtains the three-phase current fault components after fault initiation and the voltage before fault initiation at each switch in the protected area. Then, it decouples the three-phase coupled electrical quantities into independent modulus components through phase-mode transformation, effectively separating the line-mode and zero-mode fault characteristics and avoiding feature annihilation caused by component coupling under three-phase asymmetrical faults. Subsequently, it performs S-transformation on the modulus of the fault current components and the modulus of the voltage before fault initiation at each switch. Utilizing the high-resolution characteristics of S-transformation in the time-frequency domain, it accurately characterizes the distribution law of fault transient energy at different frequency scales. Based on the relative entropy calculation of the S-transform energy spectrum at each switch, it constructs a criterion for the energy relative entropy difference. By comparing the sum of the energy relative entropy differences between the first switch on the substation side and the second switches on each load side with the protection setting value, this method can use the asymmetric difference in energy distribution as the essential feature for fault identification, rather than relying on amplitude or phase information that is easily affected by attenuation. Thus, it maintains stable discrimination capability under strong noise and high-resistance grounding conditions, realizing reliable identification and rapid action of faults inside and outside the T-connected multi-terminal line area. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0017] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a schematic diagram of a T-connected multi-terminal line topology in a power distribution network provided in an embodiment of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0020] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0021] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0022] Example 1 like Figure 1 As shown, this embodiment provides a longitudinal protection method for multi-terminal T-connected lines in a distribution network, including the following steps: Step S1: Obtain the three-phase current fault component and the voltage before fault initiation at each switch in the T-connected multi-terminal line protection area of ​​the distribution network within the time window.

[0023] like Figure 2 As shown, the T-connected multi-terminal line protection area of ​​the distribution network includes the first switch (denoted as switch 1) on the substation side and the second switches (denoted as switches q, q=2,3,…,n, where n is the total number of switches) connected to each load respectively. Each switch is equipped with a current transformer and a voltage transformer for real-time acquisition of three-phase current and three-phase voltage.

[0024] The method for determining the fault initiation time is as follows: the three-phase current at each switch is compared with the overcurrent element's judgment setting value. When the three-phase current at at least one switch is greater than the overcurrent element's judgment setting value, the current time is the fault initiation time. The overcurrent element's judgment setting value is set to the maximum load current of the distribution network line to avoid misjudgment caused by load fluctuations during normal operation.

[0025] Step S2: Perform phase-mode transformation on the current fault component and the voltage before fault initiation to obtain the modulus of each switch current fault component and the modulus of the voltage before fault initiation.

[0026] The current fault component is the current at the current moment minus the current at the previous two wave moments. The specific calculation formula is as follows: In the formula: t At the current sampling time, T For power frequency cycle, , , These are the instantaneous values ​​of the A-phase, B-phase, and C-phase currents of the k-th switch at the current sampling time t, respectively. , , These are the instantaneous current values ​​of phase A, phase B, and phase C of the k-th switch at the two power frequency cycles preceding the current sampling time. , , These are the fault components of phase A, phase B, and phase C currents of the k-th switch at the current sampling time t.

[0027] Modulus of current fault component The calculation method is as follows: Modulus of voltage before fault start The calculation method is as follows: In the formula, , , These are the instantaneous voltage values ​​of phase A, phase B, and phase C before the start of the faulty k-th switch.

[0028] The aforementioned phase-mode transformation adopts a simplified form of the Clark transformation, which decouples the three-phase coupled electrical quantities into independent modulus components through linear combination, effectively separating the fault characteristics of the linear mode and zero mode, and avoiding the feature annihilation caused by component coupling under three-phase asymmetrical faults.

[0029] Step S3: Calculate the relative entropy of S-transform energy for each switch based on the modulus of the fault current component and the modulus of the voltage before the fault starts.

[0030] The S-transform is represented as follows: In the formula, For signal At any moment ,frequency The complex-valued spectrum of the S-transform at the location; The time-domain signal to be transformed corresponds to the current fault component modulus of each switch. or voltage modulus before fault start ; This is the time shift factor; For frequency variables; This is the time variable for integration.

[0031] S-transform energy relative entropy of each switch The calculation method is as follows: In the formula, This is the time shift factor; For frequency variables; For the first Modulus of individual switching current fault components Normalized energy spectral density after S-transformation; For the first Voltage modulus before startup due to switch failure Normalized energy spectral density after S-transformation.

[0032] S-transform energy relative entropy Essentially, it quantifies the degree of deviation of the transient current energy distribution after a fault from the voltage energy distribution under normal operating conditions. When a fault occurs within the protected area, the switches near the fault point will exhibit significant abrupt changes in energy distribution, with a relatively large S-transform energy entropy value; while during faults outside the protected area or normal operation, the energy distribution of each switch is relatively balanced, with a relatively small S-transform energy entropy value.

[0033] Step S4: Based on the relative entropy of the S-transformation energy of each switch, obtain the difference between the relative entropy of the S-transformation energy of the first switch and each of the second switches, and then obtain the sum of the relative entropy differences.

[0034] The sum of the relative entropy differences in energy is obtained as follows: In the formula, It is the sum of the relative entropy differences of energy. For the first switch and the second The S-transform energy relative entropy difference of the second switch The total number of switches within the protected area.

[0035] Sum of relative entropy differences in energy This comprehensively reflects the cumulative degree of energy asymmetry between the substation side and all load sides. When a fault occurs within the protection zone, the energy surge caused by the fault is unevenly distributed at each switch, and the relative entropy difference between the substation side and the load side is significant, with the sum of the differences increasing significantly. However, for faults outside the protection zone, the energy distribution at each switch shows a consistent trend, and the sum of the differences is close to zero.

[0036] Step S5: Compare the sum of the relative entropy differences of energy with the protection setting value. When the sum of the relative entropy differences of energy is greater than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the distribution network, the longitudinal protection is activated, and the switch in the area is tripped.

[0037] The setting of protection settings needs to take into account the influence of line parameters, load characteristics and transition resistance. The minimum energy relative entropy difference under various fault conditions in the area is calculated through offline simulation, and a certain margin is reserved to ensure the sensitivity and reliability of the protection.

[0038] The following specific example further illustrates the implementation effect of this embodiment: A simulation model of a 10kV distribution network with T-connected multi-terminal lines was built using PSCAD / EMTDC. The system is powered by 35kV / 10kV distribution transformers. The lines include a mixed structure of overhead lines and cables (main line length 11km, branch line lengths 7km, 2km, and 4km respectively), and the load capacity covers the light to heavy load range (0.8~1.2 times the rated load). Simulation parameter settings: sampling frequency 4kHz, data window length 5ms (including 20 sampling points), S-transform frequency range 0~1kHz (covering the main frequency components of distribution network fault transients), overcurrent component judgment setting set to 1.2 times the maximum load current, and protection setting value ΣΔH set=1.6. Fault setting scheme: fault occurrence time is 0.6s, duration is 0.1s, and fault point is defined as follows: Fault points within the zone: f2 (middle section of the main line), f3 (middle section of the first branch line); Fault points outside the zone: f1 (substation outlet side, outside the protection zone), f4 (end of the second branch line), f5 (end of the third branch line); Fault types include BC phase-to-phase short circuit and ABC three-phase short circuit (also taking into account typical phase-to-phase fault scenarios), and transition resistance covers 0~200Ω (covering common low-resistance faults and high-resistance fault conditions in distribution networks).

[0039] Table 1: Simulation Results The following key conclusions can be drawn from the simulation data in Table 1: 1) Accuracy of fault identification within the zone: Under all fault conditions within the zone (points f2 and f3), regardless of whether the fault type is a BC phase-to-phase short circuit or an ABC three-phase short circuit, as the transition resistance increases from 0Ω to 200Ω, the total energy relative entropy difference... All values ​​were greater than or equal to the protection setting value of 1.6, with the minimum value being 1.651 (200Ω high-resistance BC phase-to-phase fault at point f3) and the maximum value being 2.184 (ABC three-phase short-circuit fault at point f3), and the protection operated reliably. This indicates that the method proposed in this invention can effectively capture the time-frequency energy distribution consistency characteristics of multi-terminal switch fault signals during faults within the region through S-transform energy relative entropy. Even in a 200Ω high-resistance fault scenario, it can still maintain sufficient discrimination margin, solving the problem of insufficient sensitivity of traditional protection for high-resistance faults.

[0040] 2) Reliability of interlocking for external faults: Under all external fault conditions (points f1, f4, and f5), All values ​​are less than 1.6, with the maximum value being 1.410 (three-phase short circuit at point f4, ABC) and the minimum value being 0.613 (phase-to-phase fault at point f5, BC). All protections reliably block out faults. During faults outside the protection zone, the fault points (f1, f4, f5) are located outside the protection zone. The time-frequency energy distribution of the fault signals from some switches differs significantly from that of the first switch on the substation side, causing the sum of the differences to fall short of the set value. This demonstrates the excellent fault section selectivity of this method and effectively avoids maloperation during faults outside the protection zone.

[0041] 3) Adaptability to different fault conditions: Whether it is a phase-to-phase short circuit (BC) or a three-phase short circuit (ABC), whether it is a main line fault (f2) or a branch line fault (f3), this method can accurately identify the fault, indicating that it has good adaptability to common phase-to-phase fault types and fault locations in different zones. When the transition resistance increases from 0Ω to 200Ω, the SigmaDelta H of the fault in the zone only gradually decreases from 1.820 to 1.651 without significant fluctuations, indicating that the method has strong anti-high impedance interference capability and can adapt to the complex fault grounding conditions of the distribution network.

[0042] Engineering application feasibility: In the simulation, the sampling frequency is 4kHz and the data window is 5ms. Combined with R-GOOSE lightweight communication (data length ≤ 4 bytes), the entire protection action process can be completed within 10ms, which is much faster than the action time of traditional overcurrent protection in distribution networks (usually hundreds of milliseconds), enabling rapid fault isolation. At the same time, the method does not require the transmission of high sampling rate analog data and has low bandwidth requirements for communication channels (only small byte message transmission needs to be supported), reducing engineering deployment costs and making it suitable for large-scale promotion and application.

[0043] Example 2 This embodiment provides a longitudinal protection system for multi-terminal T-connected lines in a distribution network, applied to the method described in Embodiment 1, including: The electrical quantity acquisition module is configured to acquire the three-phase current fault components and the voltage before fault initiation at each switch in the protection zone of the T-connected multi-terminal line of the distribution network within a certain time window. The switches include a first switch on the substation side and second switches connected to each corresponding load.

[0044] The modulus acquisition module is configured to perform Clark phase-mode transformation on the three-phase current fault components and the voltage before fault initiation, respectively, to obtain the modulus of each switch current fault component and the modulus of the voltage before fault initiation.

[0045] The energy relative entropy calculation module is configured to calculate the S-transform energy relative entropy of each switch based on the modulus of the current fault component of each switch and the modulus of the voltage before the fault starts.

[0046] The difference sum acquisition module is configured to obtain the difference between the relative entropy of the S-transformation energy of the first switch and each of the second switches based on the relative entropy of the S-transformation energy of each switch, and then obtain the sum of the relative entropy differences.

[0047] The fault judgment and processing module is configured to compare the sum of the relative entropy differences of energy with the protection setting value. When the sum of the relative entropy differences of energy is greater than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the distribution network, the longitudinal protection is activated, and the switch in the area is tripped.

[0048] In summary, this invention first obtains the three-phase current fault components after fault initiation and the voltage before fault initiation at each switch in the protected area. Then, it decouples the three-phase coupled electrical quantities into independent modulus components through phase-mode transformation, effectively separating the line-mode and zero-mode fault characteristics and avoiding feature annihilation caused by component coupling under three-phase asymmetrical faults. Subsequently, it performs S-transformation on the modulus of the fault current components of each switch and the modulus of the voltage before fault initiation. Utilizing the high-resolution characteristics of S-transformation in the time-frequency domain, it accurately characterizes the distribution law of fault transient energy at different frequency scales. Based on the relative entropy calculation of the S-transform energy spectrum at each switch, it constructs a criterion for the energy relative entropy difference. By comparing the sum of the energy relative entropy differences between the first switch on the substation side and the second switches on each load side with the protection setting value, this method can use the asymmetric difference in energy distribution as the essential feature for fault identification, rather than relying on amplitude or phase information that is easily affected by attenuation. Thus, it maintains stable discrimination capability under strong noise and high-resistance grounding conditions, realizing reliable identification and rapid action of faults inside and outside the T-connected multi-terminal line area.

[0049] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0050] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical functional division. In actual implementation, there may be other division methods, such as multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored.

[0051] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0052] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for longitudinal protection of multi-terminal T-connected lines in a distribution network, characterized in that, Includes the following steps: The three-phase current fault components after fault initiation and the voltage before fault initiation at each switch in the T-connected multi-terminal line protection area of ​​the distribution network within a time window are obtained; wherein, the switch includes a first switch on the substation side and a second switch connected to each load respectively. The current fault component and the voltage before fault initiation are subjected to phase-mode transformation to obtain the modulus of each switch current fault component and the modulus of the voltage before fault initiation. Based on the modulus of the current fault component of each switch and the modulus of the voltage before fault initiation, calculate the relative entropy of the S-transform energy of each switch. Based on the relative entropy of the S-transformation energy of each switch, the difference between the relative entropy of the S-transformation energy of the first switch and each of the second switches is obtained, and then the sum of the relative entropy differences is obtained. The sum of the relative entropy differences of energy is compared with the protection setting value. When the sum of the relative entropy differences of energy is greater than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the distribution network, the longitudinal protection is activated, and the switch in the area is tripped.

2. The longitudinal protection method for multi-terminal T-connected lines in a distribution network according to claim 1, characterized in that, The method for determining the fault start time is as follows: The three-phase current at each switch is compared with the overcurrent element judgment set value. If the three-phase current at at least one switch is greater than the overcurrent element judgment set value, the current moment is the fault start moment. The overcurrent element judgment setting is set to the maximum load current of the distribution network line.

3. The longitudinal protection method for multi-terminal T-connected lines in a distribution network according to claim 1, characterized in that, The current fault component is the current at the current moment minus the current at the previous two wave moments. The specific calculation formula is as follows: In the formula, t At the current sampling time, T For power frequency cycle, , , These are the instantaneous values ​​of the A-phase, B-phase, and C-phase currents of the k-th switch at the current sampling time t, respectively. , , These are the instantaneous current values ​​of phase A, phase B, and phase C of the k-th switch at the two power frequency cycles preceding the current sampling time. , , These are the fault components of phase A, phase B, and phase C currents of the k-th switch at the current sampling time t; The modulus of the current fault component is calculated as follows: In the formula, This is the modulus of the current fault component.

4. The longitudinal protection method for multi-terminal T-connected lines in a distribution network according to claim 1, characterized in that, Modulus of voltage before fault start The calculation method is as follows: In the formula, , , These are the instantaneous voltage values ​​of phase A, phase B, and phase C before the start of the faulty k-th switch.

5. A method for longitudinal protection of multi-terminal T-connected lines in a distribution network according to claim 1, characterized in that, The S-transform is represented as follows: In the formula, For signal At any moment ,frequency The complex-valued spectrum of the S-transform at the location; The time-domain signal to be transformed corresponds to the current fault component modulus of each switch. or voltage modulus before fault start ; This is the time shift factor; For frequency variables; This is the time variable for integration.

6. The longitudinal protection method for multi-terminal T-connected lines in a distribution network according to claim 1, characterized in that, S-transform energy relative entropy of each switch H k The calculation method is as follows: In the formula, This is the time shift factor; For frequency variables; For the first Modulus of individual switching current fault component Normalized energy spectral density after S-transformation; For the first Voltage modulus before startup due to switch failure Normalized energy spectral density after S-transformation.

7. A method for longitudinal protection of multi-terminal T-connected lines in a distribution network according to claim 1, characterized in that, The sum of the relative entropy differences in energy is obtained as follows: In the formula, It is the sum of the relative entropy differences of energy. For the first switch and the second The S-transform energy relative entropy difference of the second switch The total number of switches within the protected area.

8. A longitudinal protection system for multi-terminal T-connected lines in a power distribution network, characterized in that, The method applied to any one of claims 1 to 7 includes: The electrical quantity acquisition module is configured to acquire the three-phase current fault components and the voltage before fault initiation at each switch in the protection area of ​​the T-connected multi-terminal line of the distribution network within a certain time window; wherein, the switch includes a first switch on the substation side and a second switch connected to each load respectively; The modulus acquisition module is configured to perform Clark phase-mode transformation on the three-phase current fault components and the voltage before fault initiation, respectively, to obtain the modulus of each switch current fault component and the modulus of the voltage before fault initiation; the energy relative entropy calculation module is configured to calculate the S-transform energy relative entropy of each switch based on the modulus of the current fault components and the modulus of the voltage before fault initiation of each switch. The difference sum acquisition module is configured to obtain the difference between the S-transform energy relative entropy of the first switch and each of the second switches based on the S-transform energy relative entropy of each switch, and then obtain the sum of the energy relative entropy differences; The fault judgment and processing module is configured to compare the sum of the relative entropy differences of energy with the protection setting value. When the sum of the relative entropy differences of energy is greater than or equal to the protection setting value, it is determined that a fault has occurred in the protection area of ​​the T-connected multi-terminal line of the distribution network, the longitudinal protection is activated, and the switch in the area is tripped.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the computer-readable storage medium to perform the longitudinal protection method for T-connected multi-terminal lines in a distribution network as described in any one of claims 1 to 7.

10. A processor, characterized in that, The processor is used to run a program, wherein the program executes the longitudinal protection method for T-connected multi-terminal lines in a distribution network according to any one of claims 1 to 7.

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