Transient zero sequence distance track small current grounding system line selection method and system

Abstract

The invention relates to the technical field of power system relay protection, and discloses a transient zero-sequence distance track small current grounding system line selection method and system, and the method comprises the steps: obtaining a zero-sequence component of a system node; calculating a characteristic variable quantity according to the zero-sequence component to obtain a first result; and obtaining a transient zero-sequence distance trajectory based on the characteristic variable quantity, and judging a line selection result. According to the method, a theory that a single-phase earth fault of a single-interval small-current grounding system accords with a transient zero-state second-order system step response is taken as a basic theory assumption, and fault features supported by the theory are extracted only by calculating zero-sequence distance impedance of a fault transient process and judging a track of the zero-sequence distance impedance; the invention provides a transient zero-sequence distance track small-current grounding system line selection method, which is small in calculation amount, is concentrated at the fault occurrence moment, can be integrated in various medium and low voltage relay protection devices under the condition of not needing additional primary wiring or chip computing power improvement cost, and realizes single-phase grounding fault line selection of a medium and low voltage non-effective grounding system.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection for electric power systems, and in particular to a line selection method and system for a transient zero-sequence distance track small current grounding system. Background Art

[0002] At present, the neutral point non-effective grounding operation mode is widely used in my country's medium-voltage distribution network, mainly including the neutral point ungrounded mode and the neutral point grounding mode through the arc suppression coil. Compared with the high-voltage transmission network, the probability of failure in the medium-voltage distribution network is higher, and the single-phase grounding fault is one of the most important types of faults. When a single-phase grounding fault occurs in the medium-voltage distribution network under the neutral point non-effective grounding operation mode, since the zero-sequence current loop cannot be formed between the system neutral point and the fault grounding point, the three-phase line voltage of the system still maintains a symmetrical relationship, does not affect the normal power supply of the load, and the system can continue to operate for a period of time, with high power supply reliability. However, due to the single-phase grounding of the system, the voltage of the non-fault phase to the ground increases to 1.732 times the rated voltage, which poses a serious threat to the insulation capacity of the system, and may induce another point grounding fault to cause two-point grounding, two-phase short circuit or even three-phase short circuit, threatening personal safety and equipment safety. Therefore, in order to ensure the safe operation of the system, when a single-phase grounding fault occurs in the system, it is very necessary to quickly detect and eliminate the fault.

[0003] The current single-bay relay protection device mainly uses steady-state zero-sequence overcurrent protection to detect single-phase grounding faults. When the system adopts a neutral point non-effective grounding operation mode, the current of a single-phase grounding fault is weak and unstable, making it difficult for the steady-state zero-sequence overcurrent protection to detect the fault, and it does not play a good protective role in practical applications.

[0004] At present, some single-bay relay protection devices use transient zero-sequence overcurrent protection to detect single-phase grounding faults. The transient method generally uses a high-frequency sampling rate of not less than 6000Hz to intercept the transient zero-sequence voltage and current waveforms in a short period of time before and after the fault to calculate and detect the system single-phase grounding fault. Since the neutral point non-effective grounding system mainly has two different types, the neutral point ungrounded system and the arc suppression coil grounding system, and the neutral point arc suppression coil grounding system has the problem of unfixed resonant frequency band and unfixed initial phase angle of fault phase voltage, if the characteristics of transient zero-sequence voltage and current, especially the characteristics of resonant grounding, are not further calculated and judged, it will lead to the identification deviation and error of fault characteristics, and cause inevitable interference to the detection and judgment results of single-phase grounding faults. Summary of the invention

[0005] In view of the above-mentioned problems, the present invention is proposed.

[0006] Therefore, the technical problem solved by the present invention is: the problem of single-phase grounding fault line selection applicability of a single-bay relay protection device to two different types of systems: a neutral point ungrounded system and an arc suppression coil grounded system.

[0007] To solve the above technical problems, the present invention provides the following technical solutions: a transient zero-sequence distance trajectory small current grounding system line selection method, comprising: obtaining the zero-sequence component of the system node; calculating the characteristic change amount according to the zero-sequence component to obtain a first result; obtaining the transient zero-sequence distance trajectory based on the characteristic change amount, and judging the line selection result.

[0008] As a preferred solution of the transient zero-sequence distance trajectory small current grounding system line selection method described in the present invention, wherein: the acquisition of the zero-sequence component of the system node includes acquiring the zero-sequence component by direct acquisition or calculation based on the three-phase electrical data of the bus.

[0009] As a preferred scheme of the transient zero-sequence distance trajectory small current grounding system line selection method described in the present invention, after calculating the characteristic change amount according to the zero-sequence component, it also includes comparing the characteristic change amount with a preset characteristic change amount threshold to obtain a first result, and judging whether a grounding fault occurs according to the first result.

[0010] As a preferred scheme of the transient zero-sequence distance trajectory small current grounding system line selection method described in the present invention, wherein: the transient zero-sequence distance trajectory obtained based on the characteristic change includes calculating the transient zero-sequence distance from the startup moment and recording the moving trajectory of the transient zero-sequence distance on the real and imaginary axis.

[0011] As a preferred solution of the transient zero-sequence distance trajectory small current grounding system line selection method described in the present invention, wherein: the judging of the line selection result includes judging the line selection result according to the transient zero-sequence distance trajectory and the order in which the trajectory passes through the detection circle in sequence.

[0012] As a preferred solution of the transient zero-sequence distance trajectory small current grounding system line selection method described in the present invention, wherein: the zero-sequence component includes but is not limited to zero-sequence current and zero-sequence voltage; the characteristic variation includes but is not limited to zero-sequence voltage phasor, zero-sequence current phasor and zero-sequence voltage mutation; the zero-sequence voltage phasor and zero-sequence current phasor are obtained through a phasor calculation model, including analog low-pass filtering, synchronous sampling, DFT calculation and digital filtering links, and the calculation model is expressed as:

[0013]

[0014] Where X(i) represents the phasor calculation result of the i-th sampling point; Gain represents the gain coefficient; N represents the low-pass filter window length; k represents all sampling points within N; x(i+k) represents the original signal value of the i+k-th sampling point; W (k)represents the filter window function; j represents the imaginary unit; Δt represents the sampling interval; ω0 represents the basic frequency of the signal.

[0015] As a preferred solution of the transient zero-sequence distance trajectory small current grounding system line selection method described in the present invention, wherein: the transient zero-sequence distance includes but is not limited to being calculated using the normalized transient zero-sequence distance, expressed as:

[0016]

[0017] in, The transient zero-sequence distance of the k-th sampling point; U0(k) represents the zero-sequence voltage of the k-th sampling point; I0(k) represents the zero-sequence current of the k-th sampling point; Indicates the phase difference between zero-sequence voltage and zero-sequence current; Z 0-r (k) represents the real part of the transient zero-sequence distance of the kth sampling point; Z 0-i (k) represents the imaginary part of the transient zero-sequence distance of the kth sampling point.

[0018] A transient zero-sequence distance trajectory low-current grounding system line selection system adopting any of the methods described in the present invention, wherein: an acquisition module obtains a zero-sequence component by directly collecting or calculating based on three-phase electrical data of a bus; a judgment module calculates a characteristic change amount based on the zero-sequence component, obtains a first result, and judges whether a fault occurs; a line selection module obtains a transient zero-sequence distance trajectory based on the characteristic change amount, and judges the line selection result in the order in which the trajectory passes through detection circles.

[0019] A computer device comprises: a memory and a processor; the memory stores a computer program, comprising: the steps of implementing any one of the methods of the present invention when the processor executes the computer program.

[0020] A computer-readable storage medium stores a computer program, comprising: when the computer program is executed by a processor, the steps of implementing any one of the methods of the present invention are implemented.

[0021] Beneficial effects of the present invention: The method of the present invention is based on the theoretical assumption that the single-phase grounding fault in a single-interval small current grounding system conforms to the transient zero-state second-order system step response. The fault characteristics based on the theoretical support are extracted only by calculating the zero-sequence distance impedance of the fault transient process and judging its trajectory. A transient zero-sequence distance trajectory small current grounding system line selection method is given. The calculation amount is small and concentrated at the moment of fault occurrence. It can be integrated in various medium and low voltage relay protection devices without the need for additional primary wiring or chip computing power to increase costs, so as to realize single-phase grounding fault line selection in medium and low voltage non-effective grounding systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0023] Figure 1 An overall flow chart of a transient zero-sequence distance trajectory small current grounding system line selection method provided by an embodiment of the present invention;

[0024] Figure 2 A schematic diagram of a neutral point ungrounded operation line of a transient zero-sequence distance trajectory small current grounding system line selection method provided by an embodiment of the present invention;

[0025] Figure 3 A schematic diagram of a neutral point grounding operation line through an arc suppression coil of a transient zero-sequence distance trajectory small current grounding system line selection method provided by an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of a phasor acquisition calculation model for a transient zero-sequence distance trajectory small current grounding system line selection method provided by an embodiment of the present invention;

[0027] Figure 5 A fault characteristic trajectory diagram in a neutral point ungrounded system area of ​​a transient zero-sequence distance trajectory small current grounding system line selection method provided by the second embodiment of the present invention;

[0028] Figure 6 A fault characteristic trajectory diagram outside the neutral point ungrounded system area of ​​a transient zero-sequence distance trajectory small current grounding system line selection method provided by the second embodiment of the present invention;

[0029] Figure 7 A fault characteristic trajectory diagram in a neutral point grounding system area through an arc suppression coil of a transient zero-sequence distance trajectory small current grounding system line selection method provided by the second embodiment of the present invention;

[0030] Figure 8 A fault characteristic trajectory diagram outside the neutral point grounding system area through an arc suppression coil of a transient zero-sequence distance trajectory small current grounding system line selection method provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0032] Example 1, reference Figure 1-4 , which is an embodiment of the present invention, provides a transient zero-sequence distance trajectory small current grounding system line selection method, comprising:

[0033] S1: Get the zero-sequence component of the system node.

[0034] Furthermore, system nodes include but are not limited to the current interval, bus or line, and zero-sequence components include but are not limited to zero-sequence current and zero-sequence voltage. In one embodiment of the present invention, the zero-sequence current and zero-sequence voltage can be directly collected in the current interval (i.e., the electrical section where the fault area or equipment is located).

[0035] Specifically, in this bay area, a zero-sequence current transformer and a zero-sequence voltage transformer are installed, and measurement data is directly obtained from the configured zero-sequence current and zero-sequence voltage transformers.

[0036] It should be noted that the zero-sequence current and zero-sequence voltage are sampled synchronously to ensure that the collected signals are consistent in time. The sampling rate of the voltage and current analog quantities of this interval should be coordinated with the passband of the hardware low-pass filter to avoid sampling distortion.

[0037] In another embodiment of the present invention, the system node may also be a bus node, and the zero-sequence voltage and the zero-sequence current are calculated and generated by the three-phase voltage of the bus and the three-phase current of the line.

[0038] Specifically, the three-phase voltage (V a , V b , V c ) and three-phase current (I a , I b , I c ) to calculate the zero-sequence voltage and current:

[0039]

[0040] Among them, U0 represents the zero-sequence voltage; I0 represents the zero-sequence current.

[0041] It should be noted that the two calculation methods are applicable to different scenarios. This interval acquisition directly obtains the zero-sequence voltage and zero-sequence current, which is suitable for scenarios with zero-sequence transformer configuration and has higher accuracy.

[0042] The bus and line self-generated zero-sequence signals are generated by calculating the three-phase quantities. This is suitable for scenarios without zero-sequence transformers and has lower costs, but the calculation accuracy may be affected by the symmetry of the three-phase voltage and current signals.

[0043] S2: Calculate the characteristic change amount according to the zero-sequence component to obtain a first result.

[0044] Furthermore, the characteristic variation includes but is not limited to the zero-sequence voltage phasor, the zero-sequence current phasor and the zero-sequence voltage mutation.

[0045] Specifically, phasor calculation requires analog low-pass filtering, synchronous sampling, DFT calculation, digital filtering and other links. The calculation model is as follows: Figure 2 As shown, it is expressed as:

[0046]

[0047] Where X(i) represents the phasor calculation result of the i-th sampling point; Gain represents the gain coefficient; N represents the low-pass filter window length; k represents all sampling points within N; x(i+k) represents the original signal value of the i+k-th sampling point; W (k) represents the filter window function; j represents the imaginary unit; Δt represents the sampling interval; ω0 represents the basic frequency of the signal.

[0048] Among them, the DFT calculation uses the sine and cosine factors synchronized with time for calculation, and the high-frequency interference signal in the DFT result is filtered out by the Hamming window low-pass filter, and the zero-sequence voltage phasor is obtained by calculation. and zero sequence current phasor

[0049] The calculation of zero-sequence voltage mutation is expressed as:

[0050] ΔU0(n)=||U0(n)+U0(nN / 2)|-|U0(nN / 2)+U0(nN)||

[0051] Among them, ΔU0(n) represents the zero-sequence voltage mutation; U0(n) represents the zero-sequence voltage; n represents the number of sampling points; and N represents the number of sampling period points.

[0052] Furthermore, the characteristic change amount is compared with a preset characteristic change amount threshold to obtain a first result, and whether a ground fault occurs is determined according to the first result.

[0053] The first result is mainly used to confirm whether there is a ground fault at the current system node. In one embodiment of the present invention, the first result is a binary judgment: a ground fault occurs or a ground fault does not occur. If the first result is judged as "a ground fault occurs", the system will proceed to the next step, that is, calculate the transient zero-sequence distance for further analysis and fault line selection. If the first result is judged as "no ground fault occurs", the system will continue to collect data and will not perform other operations.

[0054] The judgment basis includes but is not limited to the zero-sequence voltage mutation amount and the zero-sequence voltage amplitude. When the zero-sequence voltage mutation amount reaches the transient zero-sequence voltage mutation amount fixed value or the zero-sequence voltage amplitude reaches the transient zero-sequence voltage starting value, it is judged that a ground fault has occurred and the transient zero-sequence distance is calculated; otherwise, it is judged that no ground fault has occurred, no action is performed, and the zero-sequence components of the system nodes continue to be collected.

[0055] In another embodiment of the present invention, the mutation amount of the zero-sequence current can be added as an auxiliary judgment condition. Specifically, if the zero-sequence current changes significantly in a short period of time, the zero-sequence voltage mutation amount can be combined to determine whether a ground fault has occurred. The mutation amount of the zero-sequence current can further improve the accuracy of fault judgment when the voltage change is not obvious.

[0056] S3: Obtain the transient zero-sequence distance trajectory based on the characteristic change and determine the line selection result.

[0057] Furthermore, the transient zero-sequence distance is calculated from the start-up time, and its trajectory is recorded on the real and imaginary axes. The calculation methods of the transient zero-sequence distance include but are not limited to the normalized transient zero-sequence distance, the amplitude-phase decomposition method, the relative change rate analysis method and the difference method. In one embodiment of the present invention, the normalized transient zero-sequence distance can be used, which is expressed as:

[0058]

[0059] in, The transient zero-sequence distance of the k-th sampling point; U0(k) represents the zero-sequence voltage of the k-th sampling point; I0(k) represents the zero-sequence current of the k-th sampling point; Indicates the phase difference between zero-sequence voltage and zero-sequence current; Z 0-r (k) represents the real part of the transient zero-sequence distance of the kth sampling point; Z 0-i (k) represents the imaginary part of the transient zero-sequence distance of the kth sampling point.

[0060] In another embodiment of the present invention, the transient zero-sequence distance can also be calculated by the amplitude-phase decomposition method. The transient zero-sequence distance is decomposed into two parts, the amplitude and the phase, and the fault characteristics are identified by analyzing the changes of these two characteristics. Specifically, assuming that the transient zero-sequence distance The complex form at the kth sampling point is:

[0061]

[0062] Amplitude Indicates the size of the zero-sequence distance, which can be calculated by the following formula:

[0063]

[0064] Phase θ(k) represents the phase relationship between zero-sequence current and zero-sequence voltage and can be calculated by the following formula:

[0065]

[0066] Among them, the amplitude It represents the combined strength of zero-sequence current and zero-sequence voltage, and is a sensitive feature to signal changes. When a fault occurs, the amplitude usually changes significantly. Phase θ(k) reflects the relative phase position of zero-sequence current and zero-sequence voltage. When a fault occurs, the phase may shift or change significantly.

[0067] Furthermore, considering that the small current grounding system can continue to operate for 2 hours under a single-phase grounding fault, and that it has the highest requirements for the correctness of fault line selection, but has a lower requirement for line selection speed, this step can last long enough to ensure that the transient process is basically completed under different system parameters, and it may be appropriate to take 100ms. In the formula, k is the order of the zero-sequence distance calculated from the start time, that is, the subscript of the trajectory of the transient zero-sequence distance.

[0068] After obtaining the transient zero-sequence distance trajectory, the line selection result is determined in the order that the trajectory passes through the detection circles in sequence. Specifically, the trajectory starts from the origin, and the transient zero-sequence distance trajectory directly enters the positive imaginary axis inductive detection circle, which is the fault characteristic of the neutral point ungrounded system area; the transient zero-sequence distance trajectory directly enters the negative imaginary axis capacitive detection circle, which is the fault characteristic of the neutral point ungrounded system area outside the system area; the transient zero-sequence distance trajectory enters the negative imaginary axis capacitive detection circle after passing through the negative real axis imaginary resistance detection circle, which is the fault characteristic of the neutral point grounded through the arc suppression coil system area; the transient zero-sequence distance trajectory does not pass through the negative real axis imaginary resistance detection circle and enters the negative imaginary axis capacitive detection circle, which is the fault characteristic of the neutral point grounded through the arc suppression coil system area outside the system area; according to the trajectory, the transient zero-sequence distance trajectory small current grounding system line selection is realized.

[0069] Example 2, reference Figure 5-8 , which is an embodiment of the present invention, provides a transient zero-sequence distance trajectory small current grounding system line selection method. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through simulation experiments.

[0070] The data processed in this embodiment are derived from the measured data of the State Grid 10kV real-type test field and the RTDS simulation data of major electric power research institutes. They have been verified on a large scale, and only typical verification results are given here.

[0071] The transient zero-sequence distance trajectory is completely obtained by the method of the present invention, and the line selection result is determined according to the order in which the trajectory passes through the detection circle. The trajectory starts from the origin and is classified as follows: Figure 5-8 shown.

[0072] The three detection circles are respectively the positive imaginary axis inductive detection circle, the negative imaginary axis capacitive detection circle and the negative real axis imaginary resistive detection circle. The centers of the circles are respectively (0, 1), (0, -1) and (-1, 0). The radius is a settable parameter, which is flexible to select and has little effect on the algorithm. In this embodiment, 0.2 is selected.

[0073] like Figure 5 As shown in the figure, the transient zero-sequence distance trajectory directly enters the positive imaginary axis inductive detection circle, which is the fault characteristic in the neutral point ungrounded system area, and the line selection result is obtained.

[0074] like Figure 6 As shown in the figure, the transient zero-sequence distance trajectory directly enters the negative imaginary shaft capacitive detection circle, which is the fault characteristic outside the neutral point ungrounded system area, and the line selection result is obtained.

[0075] like Figure 7 As shown in the figure, the transient zero-sequence distance trajectory passes through the negative real axis imaginary resistive detection circle and enters the negative imaginary axis capacitive detection circle. This is the fault characteristic in the neutral point arc suppression coil grounding system area, and the line selection result is obtained.

[0076] like Figure 8 As shown in the figure, the transient zero-sequence distance trajectory does not enter the negative imaginary axis capacitive detection circle through the negative real axis imaginary resistive detection circle, which is the fault characteristic outside the neutral point grounding system area through the arc suppression coil, and the line selection result is obtained.

[0077] Embodiment 3: In an exemplary embodiment, a transient zero-sequence distance trajectory small current grounding system line selection system is also provided, including an acquisition module, a judgment module and a line selection module.

[0078] Among them, the acquisition module obtains the zero-sequence component by directly collecting or calculating according to the three-phase electrical data of the bus; the judgment module calculates the characteristic change according to the zero-sequence component, obtains the first result, and judges whether a fault occurs; the line selection module obtains the transient zero-sequence distance trajectory based on the characteristic change, and judges the line selection result according to the order of the trajectory through the detection circle.

[0079] If the above functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0080] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in conjunction with such instruction execution systems, devices or apparatuses. For the purposes of this specification, "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in conjunction with such instruction execution systems, devices or apparatuses.

[0081] More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic device), a portable computer disk case (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be a paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, deciphering or, if necessary, processing in another suitable manner, and then stored in a computer memory.

[0082] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0083] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A transient zero-sequence distance trajectory small current grounding system line selection method, characterized in that: include: Obtain the zero-sequence components of the system nodes; Calculate the characteristic variation according to the zero-sequence component to obtain a first result; The transient zero-sequence distance trajectory is obtained based on the characteristic variation to determine the line selection result.

2. The transient zero-sequence distance trajectory small current grounding system line selection method according to claim 1 is characterized in that: The obtaining of the zero-sequence component of the system node includes obtaining the zero-sequence component by directly collecting or calculating according to the three-phase electrical data of the bus.

3. The transient zero-sequence distance trajectory small current grounding system line selection method according to claim 2 is characterized in that: After calculating the characteristic variation according to the zero-sequence component, the method further includes: The characteristic change amount is compared with a preset characteristic change amount threshold to obtain a first result, and whether a ground fault occurs is determined according to the first result.

4. The transient zero-sequence distance trajectory small current grounding system line selection method according to claim 3 is characterized in that: The method of acquiring the transient zero-sequence distance trajectory based on the characteristic variation includes calculating the transient zero-sequence distance from the start-up moment and recording the moving trajectory of the transient zero-sequence distance on the real and imaginary axes.

5. The transient zero-sequence distance trajectory small current grounding system line selection method according to claim 4 is characterized in that: The determining of the line selection result includes determining the line selection result according to the transient zero-sequence distance trajectory and the order in which the trajectory passes through the detection circle in sequence.

6. The transient zero-sequence distance trajectory small current grounding system line selection method according to claim 3 is characterized in that: The zero-sequence components include but are not limited to zero-sequence current and zero-sequence voltage; The characteristic variation includes but is not limited to zero-sequence voltage phasor, zero-sequence current phasor and zero-sequence voltage mutation; The zero-sequence voltage phasor and the zero-sequence current phasor are obtained through a phasor calculation model, including analog low-pass filtering, synchronous sampling, DFT calculation and digital filtering. The calculation model is expressed as: Where X(i) represents the phasor calculation result of the i-th sampling point; Gain represents the gain coefficient; N represents the low-pass filter window length; k represents all sampling points within N; x(i+k) represents the original signal value of the i+k-th sampling point; W (k) represents the filter window function; j represents the imaginary unit; Δt represents the sampling interval; ω0 represents the basic frequency of the signal.

7. The transient zero-sequence distance trajectory small current grounding system line selection method according to claim 6 is characterized in that: The transient zero-sequence distance includes but is not limited to being calculated using the normalized transient zero-sequence distance, which is expressed as: in, The transient zero-sequence distance of the k-th sampling point; U0(k) represents the zero-sequence voltage of the k-th sampling point; I0(k) represents the zero-sequence current of the k-th sampling point; Indicates the phase difference between zero-sequence voltage and zero-sequence current; Z 0-r (k) represents the real part of the transient zero-sequence distance of the kth sampling point; Z 0-i (k) represents the imaginary part of the transient zero-sequence distance of the kth sampling point.

8. A transient zero-sequence distance trajectory small current grounding system line selection system using any of the methods of claims 1 to 7, characterized in that: include, An acquisition module acquires the zero-sequence component by directly collecting or calculating the three-phase electrical data of the bus; A judgment module, calculating a characteristic variation according to a zero-sequence component, obtaining a first result, and judging whether a fault occurs; The line selection module obtains the transient zero-sequence distance trajectory based on the characteristic variation, and determines the line selection result according to the order in which the trajectory passes through the detection circle.

9. A computer device comprising: Memory and processor; The memory stores a computer program, characterized in that: when the processor executes the computer program, the steps of the transient zero-sequence distance trajectory small current grounding system line selection method as described in any one of claims 1-7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the transient zero-sequence distance trajectory small current grounding system line selection method as described in any one of claims 1-7 are implemented.

Images