Distance protection method and device based on positive and negative sequence impedance difference of converter and medium

Abstract

The invention relates to the technical field of relay protection, in particular to a distance protection method and device based on the positive and negative sequence impedance difference of a current converter, and aims at a single-phase earth fault and an inter-phase fault to firstly construct a fault loop equation; then calculating the equivalent positive-sequence impedance of an opposite-end system by using the characteristics that the equivalent positive-sequence impedance and the equivalent negative-sequence impedance of a converter are large in difference, the positive-sequence impedance and the negative-sequence impedance of non-rotating elements such as a line and a transformer are equal, and the equivalent positive-sequence impedance and the equivalent negative-sequence impedance of an opposite-end synchronous machine are approximately equal in combination with a fault boundary condition and a line Bergeron model; substituting into a fault loop equation, and solving a fault distance; and combining a direction element, a phase selection element and the fault distance algorithm to construct a distance protection device suitable for the converter access system. According to the method, the influence of the uncertainty of transition resistance and opposite-end system parameters on distance measurement can be reduced, and the accuracy and reliability of distance protection under the conditions of long-line and high-resistance faults in the converter access system are improved.

Description

Technical Field

[0001] This invention relates to the field of relay protection technology, and in particular to a distance protection method, device and medium based on the difference between positive and negative sequence impedances of a converter. Background Technology

[0002] The high penetration rate of power electronic devices into the power grid has led to increasingly complex system fault characteristics and a deterioration in the adaptability of traditional protection systems. In particular, for distance protection, the weak feedback characteristics exhibited by power electronic devices during faults exacerbate the auxiliary effect on the system at the other end, making the problem of traditional distance protection failing to operate more prominent when non-metallic faults occur on the line.

[0003] Existing research on distance protection improvement methods mainly falls into three categories: impedance complex plane methods, parameter identification methods, and control-protection coordination methods. Among them, impedance complex plane-based methods are mostly based on the assumption that the impedance phases on both sides of the fault point are the same. When a high-resistance ground fault occurs, distance protection algorithms based on impedance complex plane are prone to large errors. Distance protection algorithms based on parameter identification rely on the line RL model and do not fully consider the frequency variation effect of line parameters. They also assume that the transition resistance is constant during the fault transient, which has certain deviations in actual engineering. Distance protection algorithms based on converter control-protection coordination rely on converter control strategies, which are difficult to implement in current engineering.

[0004] In conclusion, it is necessary to further study the distance protection principle and related devices applicable to converter access systems to ensure the safe operation of the power system. Summary of the Invention

[0005] This invention provides a distance protection method, device, and medium based on the difference between positive and negative sequence impedances of a converter, which can effectively solve the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A distance protection method based on the difference between positive and negative sequence impedances of a converter includes the following steps: After detecting an asymmetrical fault, based on the measured electrical quantities and line parameters of the station side, fault loop equations are constructed for single-phase grounding faults and phase-to-phase faults respectively. By taking advantage of the characteristics that the equivalent positive and negative sequence impedances of the converter are not equal, the positive and negative sequence impedances of the non-rotating components of the line and transformer are equal, and the equivalent positive and negative sequence impedances of the synchronous machine at the opposite end are approximately equal, and combined with the boundary conditions corresponding to the fault type, the equivalent positive sequence impedance of the system at the opposite end can be solved from the electrical quantities measured at the protection installation point. Substitute the equivalent positive sequence impedance of the peer system into the fault loop equation, and transform the fault loop equation to eliminate the unknown transition resistance parameter, to obtain a quadratic equation with only the fault distance proportionality coefficient d as an unknown. Solving the quadratic equation yields two candidate solutions for d. Substituting each candidate solution back into the fault loop equation, the corresponding transition resistance R is obtained. f And the true solution is selected based on the constraints of fault distance and transition resistance; The selected fault distance proportional coefficient d is compared with the setting values ​​d of the directional element, phase selection element, and distance protection stage I. set The system performs linkage detection, and when a fault is determined to be within the positive direction zone, the protection device activates.

[0007] Furthermore, the boundary conditions corresponding to the fault types include: for a single-phase ground fault, the positive-sequence current and the negative-sequence current at the fault point are equal; for a phase-to-phase fault, the positive-sequence current and the negative-sequence current at the fault point have equal amplitudes but opposite phases, as specifically stated below: ; in, and These are the positive-sequence current and negative-sequence current at the fault point, respectively.

[0008] Furthermore, for AG faults in single-phase ground faults, the equivalent positive sequence impedance of the opposite end system is shown in equation (1): (1) And the mutation difference satisfies: ; in, The positive sequence impedance of the opposite system. , , and These represent the sudden changes in voltage and current in phases B and C before and after the fault. The propagation coefficient of the transmission line. For line length, Line impedance; For the BC fault in phase-to-phase faults, the equivalent positive sequence impedance of the opposite end system is shown in equation (2): (2) in, The positive sequence impedance of the opposite system. and The voltage and current changes in phase A before and after the fault are represented. This is the line wave impedance.

[0009] Furthermore, for the AG fault in a single-phase ground fault, the fault loop equation is expressed as shown in equation (3): (3) in, and These are the voltage and current of phase A, respectively. This is the zero-sequence current compensation coefficient. This is the positive sequence impedance of the line. and These represent the abrupt changes in positive-sequence voltage and positive-sequence current before and after the fault on the station side, respectively; d is the ratio of the calculated fault distance to the actual fault distance; R f For transition resistance; For the BC fault in the phase-to-phase fault, the fault loop equation is expressed as shown in equation (4): (4) in, and These are the voltage and current of phase B, respectively. and These are the C-phase voltage and current, respectively. This represents the apparent impedance measured at the protection installation location for a phase-to-phase fault (BC). It represents the proportionality coefficient for complex numbers.

[0010] Furthermore, for AG faults within single-phase ground faults, the default transition resistance R... f With the phase at 0, a tan transform is taken on both sides of equation (3) to eliminate R. f It is represented as shown in equation (5): (5) Expanding equation (5) constructs a quadratic equation with the unknown d, and the solution for d is shown in equation (6): (6) in, This represents the apparent impedance measured at the protection installation location. This represents an intermediate complex number introduced during the transformation process. A1, B1, and C1 are real coefficients composed of the known impedance magnitude and phase angle. Indicates the positive sequence impedance of the line phase angle, Indicates the measurement of apparent impedance phase angle, Z represents the equivalent positive-sequence impedance of the opposite system. n1 The phase angle.

[0011] Furthermore, for the BC fault in phase-to-phase faults, the default transition resistance R is... fWith the phase at 0, a tan transform is taken on both sides of equation (4) to eliminate R. f The transformed expression is expanded to construct a quadratic equation with only the fault distance d as the unknown, as shown in equation (7): (7) Among them, A2, B2, and C2 are real coefficients composed of the known impedance magnitude and phase angle. This indicates the phase angle of the apparent impedance measured between phases BC.

[0012] Furthermore, based on the constraints of fault distance and transition resistance, the true solution is selected according to the discrimination logic shown in equation (8): (8) Where d is the fault distance, R f This is the transition resistance.

[0013] Furthermore, the criteria for determining faults within and outside the distance protection zone I satisfy equation (9): (9) Where, d set The protection settings are for section I of the line.

[0014] A distance protection device based on the difference between positive and negative sequence impedances of a converter, comprising: The loop construction module is used to construct fault loop equations for single-phase grounding faults and phase-to-phase faults respectively, based on the three-phase voltage, current and line parameter information collected at the protection installation location after detecting an asymmetrical fault. The impedance calculation module is used to establish the calculation relationship of the equivalent positive sequence impedance of the counterpart system based on the sequence component equivalent modeling, and to calculate the equivalent positive sequence impedance of the counterpart system by combining the fault boundary conditions and the line equivalent model parameters, using the voltage and current sequence components or their abrupt changes before and after the fault at the protection installation location. The equation transformation and solution module is used to substitute the equivalent positive sequence impedance of the peer system into the fault loop equation, and to perform an equivalent transformation on the fault loop equation by utilizing the characteristic that the transition resistance is a purely resistive element to eliminate or weaken the influence of the transition resistance term, thereby obtaining the solution equation for the fault distance proportionality coefficient d and outputting one or more candidate solutions. The filtering module is used to substitute candidate solutions back into the solution to obtain the transition resistance R. f And based on d and R f Filter true solutions within a reasonable range; Phase selection unit, used to identify the faulty phase based on voltage sequence components; Direction unit, used to determine the direction of the fault; The criterion output unit is used to determine the fault as a positive directional fault on the station side when the directional unit determines it, based on d and the I-segment set value d.set The comparison results output the fault criteria within / outside the zone.

[0015] Furthermore, the impedance calculation module is configured to: construct and solve an equation for the equivalent positive sequence impedance of the opposite end system based on a distributed parameter line model or an equivalent line model, using the abrupt changes in the voltage and current sequence components of the healthy or non-faulty phases before and after the fault. The equation transformation and solution module is configured to perform a tangent function tan transformation on both sides of the fault loop equation to achieve the equivalent transformation. The equation transformation and solution module is configured to construct the solution equation into a quadratic algebraic equation in one variable about the fault distance proportionality coefficient d and solve it to obtain two candidate solutions. The filtering module is configured to substitute candidate solutions back into the fault loop equation to calculate the transition resistance and filter true solutions based on a preset effective range and non-negative constraints.

[0016] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method.

[0017] The technical solution of this invention can achieve the following technical effects: This invention utilizes the characteristic that the transition resistance phase is 0 to perform a tan transformation on both sides of the fault loop equation, thereby eliminating the influence related to the transition resistance in the equation. This allows the ranging equation to retain only the fault distance proportional coefficient d as an unknown quantity, thus weakening the under-distance or failure to operate effect of high-resistance grounding or non-metallic faults on distance protection from a mechanistic perspective.

[0018] First, the equivalent positive-sequence impedance of the peer system is calculated based on the characteristics of the positive and negative sequence impedance differences of the converter, the fault boundary conditions, and the Bergeron model of the line. Then, the impedance is substituted into the fault loop equation to complete the distance measurement, thereby reducing the disturbance of the apparent impedance and distance measurement results caused by the auxiliary and parameter changes of the peer system.

[0019] The transition resistance R is obtained by substituting the two candidate d values ​​obtained from the quadratic equation back into the equation. f Then, based on the reasonable range of d and R f Non-negative constraint screening can effectively eliminate mathematical pseudo-solutions and improve the stability and usability of ranging output.

[0020] The ranging results are linked with the phase selection element, direction element, and I-segment setting dset to form a complete action chain of "phase selection - direction - ranging - intra-zone / outside-zone discrimination". The logic is clear, the modular design is easy to implement, and it is suitable for distance protection configuration of converter access system. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 Circuit diagram of the converter grid-connected system; Figure 2 This is a schematic diagram of the process of the present invention; Figure 3 This is a logic diagram of the corresponding protection device of the present invention; Figure 4 This is the fault distance measurement result of the distance protection algorithm corresponding to this invention. Detailed Implementation

[0023] 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.

[0024] In the description of this invention, it should be understood that 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.

[0025] 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.

[0026] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0027] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0028] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0029] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0030] This invention provides a distance protection method and device based on the difference between positive and negative sequence impedances of a converter. For single-phase grounding faults and phase-to-phase faults, a fault loop equation is first constructed. Then, combining the characteristics of large difference between the equivalent positive and negative sequence impedances of the converter and the fault boundary conditions, the equivalent positive sequence impedance of the opposite system is derived. Substituting this into the fault loop equation, the fault distance is solved. Combining the directional element, the phase selection element and the proposed fault distance algorithm, a distance protection device suitable for converter-connected systems is constructed.

[0031] This invention is applicable to converter grid-connected scenarios, with the distance protection device installed at the line end on the station side. The device can collect three-phase voltage, current, and zero-sequence current at the protection installation location, and perform distance measurement and in-zone / out-zone discrimination based on line parameters.

[0032] During asymmetrical faults, converter-connected systems exhibit characteristics such as weak feed and significant differences in equivalent sequence impedance. Traditional distance protection is susceptible to failure to operate or increased error due to the influence of transition resistance and equivalent parameters of the peer system. This invention utilizes the characteristic of "large differences in equivalent positive and negative sequence impedances of the converter" to significantly improve the distance measurement adaptability and operational reliability under high-resistance faults and long-line conditions by calculating the equivalent positive sequence impedance of the peer system and introducing subsequent processing to eliminate transition resistance.

[0033] During asymmetrical faults, converter-connected systems exhibit characteristics such as weak feed and significant differences in equivalent sequence impedance. Traditional distance protection is susceptible to failure to operate or increased error due to the influence of transition resistance and equivalent parameters of the peer system. This invention utilizes the characteristic of "large differences in equivalent positive and negative sequence impedances of the converter" to significantly improve the distance measurement adaptability and operational reliability under high-resistance faults and long-line conditions by calculating the equivalent positive sequence impedance of the peer system and introducing subsequent processing to eliminate transition resistance.

[0034] In this embodiment, as Figure 2 As shown, a distance protection method based on the difference between the positive and negative sequence impedances of a converter includes the following steps: After detecting an asymmetrical fault, based on the measured electrical quantities and line parameters of the station side, fault loop equations are constructed for single-phase grounding faults and phase-to-phase faults respectively. The detection of asymmetrical faults can be completed by starting elements. The electrical quantities of the station side are usually the fundamental phasors before and after the fault or their abrupt changes. The abrupt changes can be obtained by subtracting the steady-state phasor of one cycle before the fault from the phasor of several sampling points / half-cycles after the fault.

[0035] By taking advantage of the large difference in equivalent positive and negative sequence impedances of the converter, the equal positive and negative sequence impedances of non-rotating components such as lines and transformers, and the approximately equal equivalent positive and negative sequence impedances of the synchronous machine at the opposite end, and in combination with the corresponding fault boundary conditions and the Bergeron model of the line, the equivalent positive sequence impedance of the system at the opposite end is calculated.

[0036] The boundary conditions corresponding to the fault types include: for a single-phase ground fault, the positive-sequence current and the negative-sequence current at the fault point are equal; for a phase-to-phase fault, the positive-sequence current and the negative-sequence current at the fault point have equal amplitudes but opposite phases, as specifically stated below: ; in, and These are the positive-sequence current and negative-sequence current at the fault point, respectively.

[0037] Furthermore, the Bergeron model is used to consider the effects of line distributed parameters, which better reflects the characteristics of long lines and transient propagation compared to the simplified RL model. Based on the differentiated response with large differences in positive and negative sequence impedances of the converter, the equivalent positive sequence impedance of the opposite end system is calculated.

[0038] See Figure 1 As shown, for an AG fault in a single-phase ground fault, the equivalent positive sequence impedance of the system at the other end is as shown in equation (1): (1) And the mutation difference satisfies: ; in, The positive sequence impedance of the opposite system. , , and These represent the sudden changes in voltage and current in phases B and C before and after the fault. The propagation coefficient of the transmission line. For line length, Line impedance; For the BC fault in phase-to-phase faults, the equivalent positive sequence impedance of the opposite end system is shown in equation (2): (2) in, The positive sequence impedance of the opposite system. and The voltage and current changes in phase A before and after the fault are represented. This is the line wave impedance.

[0039] By first calculating the equivalent positive sequence impedance of the peer system, the uncertainty of the peer system parameters in traditional distance protection is explicitly absorbed into the equivalent parameters, so that subsequent ranging is mainly determined by the measured quantities and line parameters at this end, thereby reducing the impact of unknown and changing peer system parameters on ranging accuracy and operational reliability from the source.

[0040] Furthermore, the equivalent positive sequence impedance of the opposite system is substituted into the fault loop equation. Taking advantage of the characteristic that the phase of the transition resistance is 0, a tan transformation is performed on both sides of the fault loop equation to eliminate the transition resistance, forming a quadratic equation with only the fault distance proportionality coefficient d as the unique unknown. Specifically, for the AG fault in a single-phase ground fault, the fault loop equation is expressed as shown in equation (3): (3) in, and These are the voltage and current of phase A, respectively. This is the zero-sequence current compensation coefficient. This is the positive sequence impedance of the line. and These represent the abrupt changes in positive-sequence voltage and positive-sequence current before and after the fault on the station side, respectively; d is the ratio of the calculated fault distance to the actual fault distance; R f For transition resistance; For the BC fault in the phase-to-phase fault, the fault loop equation is expressed as shown in equation (4): (4) in, and These are the voltage and current of phase B, respectively. and These are the C-phase voltage and current, respectively. This represents the apparent impedance measured at the protection installation location for a phase-to-phase fault (BC). It represents the proportionality coefficient for complex numbers.

[0041] Furthermore, for AG faults within single-phase ground faults, the default transition resistance R... f With the phase at 0, a tan transform is taken on both sides of equation (3) to eliminate R. f It is represented as shown in equation (5): (5) Expanding equation (5) constructs a quadratic equation with the unknown d, and the solution for d is shown in equation (6): (6) in, This represents the apparent impedance measured at the protection installation location. This represents an intermediate complex number introduced during the transformation process. A1, B1, and C1 are real coefficients composed of the known impedance magnitude and phase angle. Indicates the positive sequence impedance of the line phase angle, Indicates the measurement of apparent impedance phase angle, Z represents the equivalent positive-sequence impedance of the opposite system. n1 The phase angle.

[0042] For the BC fault in phase-to-phase faults, the default transition resistance R is... f With the phase at 0, a tan transform is taken on both sides of equation (4) to eliminate R. f The transformed expression is expanded to construct a quadratic equation with only the fault distance d as the unknown, as shown in equation (7): (7) Among them, A2, B2, and C2 are real coefficients composed of the known impedance magnitude and phase angle. This indicates the phase angle of the apparent impedance measured between phases BC.

[0043] The above steps weaken or eliminate the influence of transition resistance during high-resistance faults from the key criteria, avoiding large errors caused by the phase assumption not being valid in the traditional impedance complex plane method when grounding at high resistance. At the same time, the solution is in the form of a quadratic equation, which facilitates engineering implementation and real-time calculation.

[0044] Solving the quadratic equation yields two candidate solutions for d. Substituting each candidate solution back into the fault loop equation, the corresponding transition resistance R is obtained. f The true solution is selected based on the constraints of fault distance and transition resistance.

[0045] Specifically, the true solution is selected based on the constraints of fault distance and transition resistance, according to the discrimination logic shown in equation (8): (8) Where d is the fault distance, R f This is the transition resistance.

[0046] Find R by back substitution f By combining reasonable interval screening, mathematical pseudo-solutions can be effectively eliminated, improving the usability and consistency of ranging results; especially in long lines, weak feeds, significant boosting, or large sampling disturbances, the risk of misjudgment can be reduced.

[0047] See Figure 3 As shown, the fault distance proportional coefficient d obtained by screening is compared with the setting values ​​d of the directional element, the phase selection element, and the distance protection I section. set Perform linkage judgment and execute distance protection logic: When a fault is determined to be within the positive direction zone, the protection device will activate.

[0048] Specifically, the criteria for determining faults within and outside the distance protection zone I satisfy equation (9): (9) Where, d set This is the protection setting for section I of the line. By connecting the ranging result with the direction, phase selection, and setting value in series, a complete and implementable protection link can be formed: ensuring both selectivity and speed of action, and utilizing the robustness of the ranging method of this invention under high-resistance faults to reduce failure to operate.

[0049] This invention further discloses a distance protection device based on the difference between positive and negative sequence impedances of a converter, characterized in that it includes: The loop construction module is used to construct fault loop equations for single-phase grounding faults and phase-to-phase faults respectively, based on the three-phase voltage, current and line parameter information collected at the protection installation location after detecting an asymmetrical fault. The impedance calculation module is used to establish the calculation relationship of the equivalent positive sequence impedance of the counterpart system based on the sequence component equivalent modeling, and to calculate the equivalent positive sequence impedance of the counterpart system by combining the fault boundary conditions and the line equivalent model parameters, using the voltage and current sequence components or their abrupt changes before and after the fault at the protection installation location. The equation transformation and solution module is used to substitute the equivalent positive sequence impedance of the peer system into the fault loop equation, and to perform an equivalent transformation on the fault loop equation by utilizing the characteristic that the transition resistance is a purely resistive element to eliminate or weaken the influence of the transition resistance term, thereby obtaining the solution equation for the fault distance proportionality coefficient d and outputting one or more candidate solutions. The filtering module is used to substitute candidate solutions back into the solution to obtain the transition resistance R. f And based on d and R fFilter true solutions within a reasonable range; Phase selection unit, used to identify the faulty phase based on voltage sequence components; Direction unit, used to determine the direction of the fault; The criterion output unit is used to determine the fault as a positive directional fault on the station side when the directional unit determines it, based on d and the I-segment set value d. set The comparison results output the fault criteria within / outside the zone.

[0050] The impedance calculation module is configured to: construct and solve an equation for the equivalent positive sequence impedance of the system at the opposite end based on the distributed parameter line model or equivalent line model, using the abrupt changes in voltage and current sequence components of the healthy or non-faulty phases before and after the fault; the equation transformation and solution module is configured to perform a tangent function tan transformation on both sides of the fault loop equation to achieve an equivalent transformation; the equation transformation and solution module is configured to construct the solution equation into a quadratic algebraic equation in one variable about the fault distance proportionality coefficient d and solve it to obtain two candidate solutions; the screening module is configured to substitute the candidate solutions back into the fault loop equation to calculate the transition resistance and screen the true solution based on the preset effective interval and non-negative constraints.

[0051] This invention also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the above-described method. The storage medium can be in the form of a USB flash drive, external hard drive, ROM, RAM, Flash, disk, etc. Through software embedding, the algorithm of this invention can be quickly deployed in protection devices on different hardware platforms, improving the portability of the solution and the efficiency of engineering deployment.

[0052] Simulation verification A multi-module converter grid-connected system with a voltage level of 500kV, a transmission power of 400MW, and a system frequency of 50Hz was constructed using PSCAD / EMTDC software, with a line length of 200km. Table 1 shows the R-value at different locations. f The calculation results of the proposed fault distance algorithm for an AG fault with a current of 100Ω, where d true d represents the actual fault distance. c The correct solution selected by equation (8); d wrong This is an incorrect solution.

[0053] Table 1. Calculation results of fault distance when AG fault occurs at different fault locations. As shown in Table 1, the proposed method still has good accuracy in a 200km line and can distinguish between incorrect and correct solutions through the logic shown in Equation (8).

[0054] In summary, this invention provides a distance protection principle and related device based on the difference characteristics of positive and negative sequence impedance of converters. This invention can improve the problem of failure to operate in traditional distance protection under high impedance faults and ensure the safe and stable operation of the power grid.

[0055] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments 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. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0056] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0057] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. 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 this invention.

[0058] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0059] Although this application has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made thereto without departing from the spirit and scope of this application. Accordingly, this specification and drawings are merely exemplary illustrations of the application as defined herein, and are to be considered as covering any and all modifications, variations, combinations, or equivalents within the scope of this application. Clearly, those skilled in the art can make various alterations and modifications to this application without departing from its scope. Thus, if such modifications and modifications fall within the scope of this application and its equivalents, this application intends to include such modifications and modifications.

Claims

1. A distance protection method based on the difference between positive and negative sequence impedances of a converter, characterized in that, Includes the following steps: After detecting an asymmetrical fault, based on the measured electrical quantities and line parameters of the station side, fault loop equations are constructed for single-phase grounding faults and phase-to-phase faults respectively. By taking advantage of the characteristics that the equivalent positive and negative sequence impedances of the converter are not equal, the positive and negative sequence impedances of the non-rotating components of the line and transformer are equal, and the equivalent positive and negative sequence impedances of the synchronous machine at the opposite end are approximately equal, and combined with the boundary conditions corresponding to the fault type, the equivalent positive sequence impedance of the system at the opposite end can be solved from the electrical quantities measured at the protection installation point. Substitute the equivalent positive sequence impedance of the peer system into the fault loop equation, and transform the fault loop equation to eliminate the unknown transition resistance parameter, to obtain an equation that only contains the fault distance proportionality coefficient d as an unknown quantity. Solving the equation yields two candidate solutions for d. Substituting each candidate solution back into the fault loop equation, the corresponding transition resistance R is obtained. f And the true solution is selected based on the constraints of fault distance and transition resistance; The selected fault distance proportional coefficient d is compared with the setting values ​​d of the directional element, phase selection element, and distance protection stage I. set The system performs linkage detection, and when a fault is determined to be within the positive direction zone, the protection device activates.

2. The distance protection method based on the difference in positive and negative sequence impedance of the converter according to claim 1, characterized in that, The boundary conditions corresponding to the fault types include: for a single-phase ground fault, the positive-sequence current and the negative-sequence current at the fault point are equal; for a phase-to-phase fault, the positive-sequence current and the negative-sequence current at the fault point have equal amplitudes but opposite phases, as specifically stated below: ； in, and These are the positive-sequence current and negative-sequence current at the fault point, respectively.

3. The distance protection method based on the difference in positive and negative sequence impedance of the converter according to claim 2, characterized in that, For the AG fault in a single-phase ground fault, the equivalent positive sequence impedance of the system at the other end is shown in equation (1): ； (1) And the mutation difference satisfies: ； in, The positive sequence impedance of the opposite system. , , and These represent the sudden changes in voltage and current in phases B and C before and after the fault. The propagation coefficient of the transmission line. For line length, Line impedance; For the BC fault in phase-to-phase faults, the equivalent positive sequence impedance of the opposite end system is shown in equation (2): ；(2) in, The positive sequence impedance of the opposite system. and The voltage and current changes in phase A before and after the fault are represented. This is the line wave impedance.

4. The distance protection method based on the difference in positive and negative sequence impedance of the converter according to claim 3, characterized in that, For the AG fault in a single-phase ground fault, the fault loop equation is expressed as shown in equation (3): ；(3) in, and These are the voltage and current of phase A, respectively. This is the zero-sequence current compensation coefficient. This is the positive sequence impedance of the line. and These represent the abrupt changes in positive-sequence voltage and positive-sequence current before and after the fault on the station side, respectively; d is the ratio of the calculated fault distance to the actual fault distance; R f For transition resistance; For the BC fault in the phase-to-phase fault, the fault loop equation is expressed as shown in equation (4): ；(4) in, and These are the voltage and current of phase B, respectively. and These are the C-phase voltage and current, respectively. This represents the apparent impedance measured at the protection installation location for a phase-to-phase fault (BC). It represents the proportionality coefficient for complex numbers.

5. The distance protection method based on the difference between positive and negative sequence impedances of the converter according to claim 4, characterized in that, For AG faults in single-phase ground faults, the default transition resistance R f With the phase at 0, a tan transform is taken on both sides of equation (3) to eliminate R. f It is represented as shown in equation (5): ；(5) Expanding equation (5) constructs a quadratic equation with the unknown d, and the solution for d is shown in equation (6): ；(6) in, This represents the apparent impedance measured at the protection installation location. This represents an intermediate complex number introduced during the transformation process. A1, B1, and C1 are real coefficients composed of the known impedance magnitude and phase angle. Indicates the positive sequence impedance of the line phase angle, Indicates the measurement of apparent impedance phase angle, Z represents the equivalent positive-sequence impedance of the opposite system. n1 The phase angle.

6. The distance protection method based on the difference between positive and negative sequence impedances of the converter according to claim 5, characterized in that, For the BC fault in phase-to-phase faults, the default transition resistance R is... f With the phase at 0, a tan transform is taken on both sides of equation (4) to eliminate R. f The transformed expression is expanded to construct a quadratic equation with only the fault distance d as the unknown, as shown in equation (7): ；(7) Among them, A2, B2, and C2 are real coefficients composed of the known impedance magnitude and phase angle. This indicates the phase angle of the apparent impedance measured between phases BC.

7. The distance protection method based on the difference between positive and negative sequence impedances of the converter according to claim 1, characterized in that, Based on the constraints of fault distance and transition resistance, the true solution is selected according to the discrimination logic shown in equation (8): ；(8) Where d is the fault distance, R f This is the transition resistance.

8. The distance protection method based on the difference between positive and negative sequence impedances of the converter according to claim 1, characterized in that, The criteria for determining faults within and outside the distance protection zone I satisfy equation (9): ；(9) Where, d set The protection settings are for section I of the line.

9. A distance protection device based on the difference between positive and negative sequence impedances of a converter, characterized in that, include: The loop construction module is used to construct fault loop equations for single-phase grounding faults and phase-to-phase faults respectively, based on the three-phase voltage, current and line parameter information collected at the protection installation location after detecting an asymmetrical fault. The impedance calculation module is used to establish the calculation relationship of the equivalent positive sequence impedance of the counterpart system based on the sequence component equivalent modeling, and to calculate the equivalent positive sequence impedance of the counterpart system by combining the fault boundary conditions and the line equivalent model parameters, using the voltage and current sequence components or their abrupt changes before and after the fault at the protection installation location. The equation transformation and solution module is used to substitute the equivalent positive sequence impedance of the peer system into the fault loop equation, and to perform an equivalent transformation on the fault loop equation by utilizing the characteristic that the transition resistance is a purely resistive element to eliminate or weaken the influence of the transition resistance term, thereby obtaining the solution equation for the fault distance proportionality coefficient d and outputting one or more candidate solutions. The filtering module is used to substitute candidate solutions back into the solution to obtain the transition resistance R. f And based on d and R f Filter true solutions within a reasonable range; Phase selection unit, used to identify the faulty phase based on voltage sequence components; Direction unit, used to determine the direction of the fault; The criterion output unit is used to determine the fault as a positive directional fault on the station side when the directional unit determines it, based on d and the I-segment set value d. set The comparison results output the fault criteria within / outside the zone.

10. The distance protection device based on the difference between positive and negative sequence impedances of the converter according to claim 9, characterized in that, The impedance calculation module is configured to: construct and solve an equation for the equivalent positive sequence impedance of the opposite end system based on a distributed parameter line model or an equivalent line model, using the abrupt changes in voltage and current sequence components of the healthy or non-faulty phases before and after the fault. The equation transformation and solution module is configured to perform a tangent function tan transformation on both sides of the fault loop equation to achieve the equivalent transformation. The equation transformation and solution module is configured to construct the solution equation into a quadratic algebraic equation in one variable about the fault distance proportionality coefficient d and solve it to obtain two candidate solutions. The filtering module is configured to substitute candidate solutions back into the fault loop equation to calculate the transition resistance and filter true solutions based on a preset effective range and non-negative constraints.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, it implements the method described in any one of claims 1 to 8.

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