Distance protection method and device based on transient state identification of converter, and medium
By adopting a distance protection method based on converter transient state identification, multiple sets of fault loop equations are constructed within a short time window using low-pass filtering and fast phasor extraction. Combined with the zero-sequence network invariant characteristics for elimination, the problems of non-operation and poor adaptability of traditional distance protection in converter grid-connected systems are solved, and accurate distance measurement and fast action are achieved for high-resistance grounding and non-metallic faults.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- STATE GRID JIANGSU ELECTRIC POWER CO LTD RESEARCH INSTITUTE
- Filing Date
- 2026-03-05
- Publication Date
- 2026-04-28
AI Technical Summary
Traditional distance protection is prone to failure to operate and has poor adaptability in converter grid-connected systems. Especially after the connection of power electronic devices, the fault characteristics are complex, resulting in a prominent failure to operate during non-metallic faults. Furthermore, bidirectional power flow fluctuations affect the setting coordination and directionality.
A distance protection method based on converter transient state identification is adopted. Multiple sets of unrelated fault loop equations are constructed within a short time window through low-pass filtering and fast phasor extraction. Combined with the zero-sequence network invariant characteristics, the influence of transition resistance and the electrical quantity terms at the other end is eliminated, and the fault distance is quickly calculated.
It improves the ranging accuracy and protection reliability in high-resistance grounding and non-metallic fault scenarios, adapts to bidirectional power flow and changes in operating mode, and enables rapid action and differentiation between inside and outside the fault zone.
Smart Images
Figure CN121939320A_ABST
Abstract
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 converter transient state identification. Background Technology
[0002] Distance protection, as an important component of transmission line protection, is widely used as backup protection for 220kV and above systems, as well as main protection for some 110kV systems. Traditional distance protection is mostly based on impedance measurement under steady-state or quasi-steady-state fault conditions. It calculates the fault impedance by measuring the voltage and current at the protection installation point and converts it into the fault distance to achieve the distinction between inside and outside the fault zone and the corresponding action.
[0003] As the penetration rate of converters in the power grid continues to increase, the high penetration rate of power electronic devices in the grid leads to more complex system fault characteristics and deteriorates the adaptability of traditional protection systems. This is particularly true for distance protection, where the integration of power electronic devices fundamentally alters the system fault characteristics. The weak feedback characteristics exhibited during faults exacerbate the reinforcing effect on the peer system, making the problem of traditional distance protection failing to operate more prominent when non-metallic faults occur on lines. Simultaneously, the integration of power electronic devices makes the power grid system operation more complex and variable, with increased bidirectional power flow and random fluctuations, which affects the setting coordination and directionality of distance protection.
[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 converter transient state identification, 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 converter transient state identification, applicable to distance protection of converter grid-connected systems during single-phase ground faults and / or phase-to-phase ground faults, includes the following steps: Fault transient electrical quantity data is obtained at the protection installation location, and the fault transient electrical quantity data is subjected to low-pass filtering to filter out high-frequency attenuation components, thereby obtaining filtered fault transient data. The filtered fault transient data is processed by fast phasor extraction to extract the power frequency phasors under different short time windows, and obtain the real and imaginary parts of the voltage and current power frequency phasors under each short time window. During the transient phase of the fault, at least two non-overlapping short time windows are selected, and the real and imaginary parts of the power frequency phasors corresponding to each short time window are used as electrical quantities under different fault states to construct multiple sets of fault loop equations including the fault distance. Based on the zero-sequence network invariance of the system, the fault loop equation is eliminated by eliminating the transition resistance term and the electrical quantity term at the other end, and an equation containing only the fault distance d is constructed and solved to obtain the fault distance d. The faulty phase is determined by the phase selection element, and the fault direction is determined by the direction element. When the fault is determined to be a positive direction fault on the station side, the fault distance d is compared with the protection setting d within section I of the line. set Comparison: If d < d set If the fault is detected, it is determined to be an internal fault and a trip command is output; otherwise, it is determined to be an external fault.
[0007] Furthermore, a fourth-order low-pass Butterworth filter is used for the low-pass filtering, with a cutoff frequency set to 100Hz.
[0008] Furthermore, within the short time window selected during the transient phase of the fault, the data 40-60ms after the fault, after low-pass filtering, is used as the data for state "1", and the data 60-80ms after the fault is used as the data for state "2", in order to construct at least two sets of equations for unrelated fault states to solve for the fault distance.
[0009] Furthermore, the fast phasor extraction employs a two-sampling-point orthogonal phasor extraction algorithm, which includes the following steps: Set the sampling value i of two consecutive points k i k +1, then at the base frequency i k i k +1 can be expressed as equation (1): (1) The instantaneous values of the real and imaginary parts of the current phasor in equation (1) can be expressed as equation (2): (2) Where I is the amplitude of the fundamental frequency component; Ψ is the initial phase angle; τ is the phase angle corresponding to the sampling interval; i ck and i sk These represent the real and imaginary parts of the current phasor, respectively; c c1 c c2 c s1 c s2 These are the filter coefficients; The filter function obtained by performing Z-transform on equation (2) can be expressed as equation (3): (3) Based on the characteristics of orthogonal filters having consistent amplitude-frequency characteristics and phase-frequency characteristics that differ by 90°, the coefficients of the orthogonal filters can be obtained as shown in equation (4): (4) Where, φ c (z), φ s (z) are the filter functions corresponding to the real and imaginary parts, respectively; z is the Z-transform variable.
[0010] Furthermore, the orthogonal filter function of two sampling points that satisfies the orthogonality condition is expressed as Equation (5), and based on Equation (5), the transfer function of the two-point orthogonal phasor filter can be derived as shown in Equation (6): (5) (6) Among them, Y c (z), Y s (z) is the transfer function of a two-point orthogonal phasor filter.
[0011] Furthermore, for the AG fault in a single-phase ground fault, the fault loop equation is established as shown in equation (7): (7) Among them, u ma_re u ma_im i ma_re i ma_im i m0_re i m0_im Let i represent the real and imaginary parts of the phase A voltage, phase A current, and zero-sequence current phasors at the protection installation location, respectively, extracted after processing by the transfer function of a two-point orthogonal phasor filter. f0_re i f0_im Let r1 and l1 represent the real and imaginary parts of the zero-sequence current phasor at the fault point, respectively; r1 represents the positive-sequence resistance per unit length of the line; and l1 represents the voltage drop across the line. r It means that k l It means that R f This indicates the transition resistance.
[0012] Furthermore, based on the invariant characteristics of the zero-sequence network of the system, the relationship between zero-sequence electrical quantities under different fault states is established to satisfy equation (8): (8) Differentiating the terms in the numerator and denominator of equation (8) yields equation (9): (9) The derivative is approximated using the difference method: ; Among them, i m0_re_1 i m0_im_1Let i represent the real and imaginary parts of the zero-sequence current at the protection installation location under the first time window, respectively. m0_re_2 i m0_im_2 Let i represent the real and imaginary parts of the zero-sequence current at the protection installation location under the second time window, respectively. f0_re_1 i f0_im_1 Under the first time window, the real and imaginary parts of the zero-sequence current at the fault point, i f0_re_2 i f0_im_2 In the second time window, the real and imaginary parts of the zero-sequence current at the fault point, f s This represents the sampling frequency, and t is the sampling point number.
[0013] Furthermore, the fault circuit equation is differentiated and substituted into equation (9) to eliminate the transition resistance R. f And the electrical quantity terms at the other end, the calculation expression for d during AG fault satisfies equation (10): (10) Among them, Г AG_1 This represents the dynamic impedance voltage drop per unit length in the first state, Γ. AG_1 This represents the dynamic impedance voltage drop per unit length in the second state.
[0014] Furthermore, for the BCG fault in a two-phase ground fault, the calculation expression of d for the BCG fault is obtained by the same elimination method as for the AG fault, satisfying equation (11). (11) Among them, electrical quantities with subscripts containing "bc" represent the superposition of electrical quantities in phase B and phase C, u mbc i mbc U represents the sum of voltage and current in phase B and phase C, respectively. mbc_re_1 u mbc_im_1 These represent u under the first time window. mbc The real and imaginary parts, i mbc_re_1 i mbc_re_1 These represent i under the first time window. mbc The real and imaginary parts, u mbc_re_2 u mbc_im_2 These represent u under the second time window. mbc The real and imaginary parts, i mbc_re_2 i mbc_re_2 These represent i under the second time window. mbc The real and imaginary parts.
[0015] A distance protection device based on converter transient state identification includes: The data acquisition module collects three-phase voltage, three-phase current, and zero-sequence current at the protection installation location; The filtering module performs low-pass filtering on the sampled data; The phasor extraction module extracts the real and imaginary parts of the power frequency phasors of voltage and current within multiple short time windows; The state construction and equation generation module is used to select at least two non-overlapping short time windows during the transient phase of the fault, and use the real and imaginary parts of the power frequency phasors corresponding to each short time window as electrical quantities under different fault states, and construct multiple sets of fault loop equations including the fault distance accordingly. The elimination and solution module is used to process the multiple sets of fault loop equations based on the invariant characteristics of the zero-sequence network of the system, so as to weaken or eliminate the influence of unknown quantities related to the transition resistance and the opposite end system, obtain the solution equation for the fault distance d, and solve for the fault distance d. The phase selection module identifies the faulty phase based on voltage sequence components; The direction module determines the direction of the fault; The execution module, when a fault occurs in the forward direction, compares the fault distance d with the protection setting value within section I of the line, outputs the result of inside / outside the section, and executes the action.
[0016] Furthermore, the filtering module employs a fourth-order low-pass Butterworth filter with a cutoff frequency of 100Hz; The phasor extraction module employs a two-sampling-point orthogonal phasor extraction algorithm to extract the real and imaginary parts of the power frequency phasor within a short time window. The state construction and equation generation module takes the low-pass filtered data 40-60ms after the fault as state 1 and the data 60-80ms after the fault as state 2, so as to form at least two sets of fault loop equations corresponding to the multiple sets of fault states that are unrelated to each other. The state construction and equation generation module constructs a fault loop equation based on the power frequency phasor of the fault phase voltage, the power frequency phasor of the fault phase current, and the power frequency phasor of the zero-sequence current during a single-phase ground fault, and constructs a fault loop equation based on the superposition of the power frequency phasors of the two fault phase voltages and the power frequency phasors of the two fault phases during a two-phase ground fault. The elimination and solution module is configured to: establish constraint relationships between zero-sequence electrical quantities under different fault states that satisfy the zero-sequence network invariance characteristics, and use these constraint relationships to perform elimination processing on the multiple sets of fault loop equations.
[0017] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method.
[0018] The technical solution of this invention can achieve the following technical effects: This invention constructs a fault loop equation and introduces differentiation processing, and combines the zero-sequence network invariance to eliminate variables in the equation. This can eliminate the influence of the transition resistance term Rf in the process of solving the fault distance, thereby improving the ranging accuracy and protection reliability in high-resistance grounding / non-metallic fault scenarios.
[0019] By utilizing multiple sets of unrelated fault states formed by different short time windows and using the zero-sequence network invariant relationship as a constraint for elimination, the influence of the electrical quantities and system parameters at the other end can be weakened or eliminated, thereby improving the adaptability under bidirectional power flow and changing operating conditions.
[0020] Low-pass filtering is used to suppress high-frequency attenuation components, and a two-sampling-point orthogonal phasor extraction algorithm is used to quickly obtain the real / imaginary parts of the power frequency phasor within a short time window. Furthermore, at least two non-overlapping short time windows are selected to construct a set of equations, so that sufficient independent information can be generated during the fault transient stage to calculate the fault distance and meet the requirements of rapid action in stage I.
[0021] This invention is applicable to both single-phase grounding faults and phase-to-phase grounding faults. It achieves unified phasor extraction, state construction, elimination distance calculation, and internal / external region discrimination logic within the same framework, which facilitates engineering implementation and promotion. Attached Figure Description
[0022] 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.
[0023] 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 The fault distance calculation trajectory of the proposed protection algorithm under different fault locations; Figure 4 The fault distance calculation trajectory of the proposed protection algorithm under different transition resistances; Figure 5 This is a logic diagram of the corresponding protection device of the present invention. Detailed Implementation
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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)."
[0030] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn 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.
[0031] This invention provides a distance protection method, device, and medium based on converter transient state identification, applicable to distance protection in converter-connected grid systems during single-phase ground faults and / or phase-to-phase ground faults. First, a low-pass filter is used to process the fault transient data, and a fast vector extraction algorithm is employed to extract fault transient data of the converter-connected grid system under different small time windows. Using the extracted electrical quantities under different small time windows, multiple sets of uncorrelated fault loop equations are constructed. Then, leveraging the characteristics of the zero-sequence impedance network in asymmetrical ground fault scenarios—which remains unchanged with converter control characteristics while the positive and negative sequence equivalent impedances fluctuate with converter control characteristics—the zero-sequence electrical quantities, peer system parameters, and transition resistance in the equations are eliminated, constructing a linear equation containing only the fault distance as an unknown quantity, enabling rapid solution of the fault distance. Finally, combining directional elements, phase selection elements, and the proposed distance protection principle, a distance protection device is constructed.
[0032] In this embodiment, as Figure 2 As shown, the distance protection method based on converter transient state identification includes the following steps: Fault transient electrical quantity data is acquired at the protection installation location. This data includes at least three-phase voltage, three-phase current, and zero-sequence current. The fault transient electrical quantity data is then low-pass filtered to remove high-frequency attenuation components, resulting in filtered fault transient data. Preferably, a fourth-order low-pass Butterworth filter is used for low-pass filtering, with a cutoff frequency set to 100Hz.
[0033] The transient state of converter grid connection faults is usually accompanied by high-frequency attenuation components and switching harmonics. Directly using these components for short-window phasor extraction will introduce bias. Low-pass filtering first can ensure that subsequent phasor extraction mainly reflects the power frequency components. By using a low-pass filter with a cutoff frequency of 100 Hz, the influence of high-frequency attenuation components and harmonics on short-window phasors can be significantly suppressed, improving the stability and consistency of subsequent multi-state equation construction and elimination distance calculation.
[0034] The filtered fault transient data is processed by fast phasor extraction to extract the power frequency phasors under different short time windows, and obtain the real and imaginary parts of the voltage and current power frequency phasors under each short time window.
[0035] Specifically, the fast phasor extraction uses a two-sampling-point orthogonal phasor extraction algorithm, which includes the following steps: Set the sampling value i of two consecutive points k i k +1, then at the base frequency i k i k +1 can be expressed as equation (1): (1) The instantaneous values of the real and imaginary parts of the current phasor in equation (1) can be expressed as equation (2): (2) Where I is the amplitude of the fundamental frequency component; Ψ is the initial phase angle; τ is the phase angle corresponding to the sampling interval; i ck and i sk These represent the real and imaginary parts of the current phasor, respectively; c c1 c c2 c s1 c s2 These are the filter coefficients; The filter function obtained by performing Z-transform on equation (2) can be expressed as equation (3): (3) Based on the characteristics of orthogonal filters having consistent amplitude-frequency characteristics and phase-frequency characteristics that differ by 90°, the coefficients of the orthogonal filters can be obtained as shown in equation (4): (4) Where, φ c (z), φ s (z) are the filter functions corresponding to the real and imaginary parts, respectively; z is the Z-transform variable.
[0036] Combining equations (3) and (4), the orthogonal filter function of two sampling points that satisfies the orthogonality condition is expressed as equation (5), and based on equation (5), the transfer function of the two-point orthogonal phasor filter can be derived as shown in equation (6): (5) (6) Among them, Y c (z), Y s (z) is the transfer function of a two-point orthogonal phasor filter.
[0037] The core of the two-point orthogonal phasor extraction algorithm is to construct the real / imaginary parts of the power frequency phasor within an extremely short data window using a pair of orthogonal filters with consistent amplitude-frequency characteristics and phase-frequency characteristics differing by 90°. This satisfies the measurement requirements of "fast and short window" in the transient stage. The extraction objects include not only current, but also voltage and zero-sequence current, which facilitates the subsequent establishment of fault loop equations and zero-sequence constraint relationships.
[0038] Compared to traditional long-window phasor algorithms, the short-window extraction of this invention can enter the distance calculation faster, improving the speed of distance protection action; at the same time, it retains the "state changes" brought about by converter control during the transient period, providing usable information for the subsequent construction of "unrelated fault states".
[0039] Selecting windows forms "State 1 / State 2", constructing unrelated fault state equations. During the fault transient phase, at least two non-overlapping short time windows are selected, and the electrical quantities corresponding to different short time windows are used as multiple sets of unrelated fault states formed by the dynamic adjustment of the converter, and multiple sets of fault loop equations including fault distance are constructed.
[0040] In the short time window selected during the transient phase of the fault, the data 40-60ms after the fault after low-pass filtering is used as the data for state "1", and the data 60-80ms after the fault is used as the data for state "2", so as to construct at least two sets of equations for unrelated fault states to solve the fault distance.
[0041] Furthermore, based on the zero-sequence network invariance of the system, the fault loop equation is eliminated by eliminating the transition resistance term and the electrical quantity term at the other end, and an equation containing only the fault distance d is constructed and solved to obtain the fault distance d.
[0042] This invention utilizes the dynamic adjustment characteristics of the converter during fault transients: within different short time windows, the power frequency phasor of its output electrical quantities exhibits distinguishable changes, thus forming multiple sets of unrelated fault states such as State 1 / State 2. These state quantities form the basis for subsequent elimination: only when the two sets of states exhibit different characteristics in the unknown terms can effective elimination be achieved through simultaneous equations.
[0043] The uncorrelated states formed by non-overlapping short windows can provide redundancy and independence for the subsequent elimination of transition resistance terms and opposite-end electrical quantity terms, making the final equation containing only the fault distance d easier to solve stably.
[0044] In this embodiment, for the AG fault in a single-phase ground fault, the fault loop equation is established as shown in equation (7): (7) Among them, u ma_re u ma_im i ma_re i ma_im i m0_re i m0_im Let i represent the real and imaginary parts of the phase A voltage, phase A current, and zero-sequence current phasors at the protection installation location, respectively, extracted after processing by the transfer function of a two-point orthogonal phasor filter. f0_re i f0_imLet r1 and l1 represent the real and imaginary parts of the zero-sequence current phasor at the fault point, respectively; r1 represents the positive-sequence resistance per unit length of the line; and l1 represents the voltage drop across the line. r It means that k l It means that R f This indicates the transition resistance.
[0045] Furthermore, based on the invariant characteristics of the zero-sequence network of the system, the relationship between zero-sequence electrical quantities under different fault states is established to satisfy equation (8): (8) Differentiating the terms in the numerator and denominator of equation (8) yields equation (9): (9) The derivative is approximated using the difference method: ; Among them, i m0_re_1 i m0_im_1 Let i represent the real and imaginary parts of the zero-sequence current at the protection installation location under the first time window, respectively. m0_re_2 i m0_im_2 Let i represent the real and imaginary parts of the zero-sequence current at the protection installation location under the second time window, respectively. f0_re_1 i f0_im_1 Under the first time window, the real and imaginary parts of the zero-sequence current at the fault point, i f0_re_2 i f0_im_2 In the second time window, the real and imaginary parts of the zero-sequence current at the fault point, f s This represents the sampling frequency, and t is the sampling point number.
[0046] Differentiate the fault loop equation and substitute it into equation (9) to eliminate the transition resistance R. f And the electrical quantities at the opposite end, the calculation expression for the fault distance d during AG fault is obtained, which satisfies equation (10): (10) Among them, Г AG_1 This represents the dynamic impedance voltage drop per unit length in the first state, Γ. AG_1 This represents the dynamic impedance voltage drop per unit length in the second state.
[0047] In this embodiment, for the BCG fault in a two-phase ground fault, the calculation expression of the fault distance d when the BCG fault is obtained by the same elimination method as the AG fault, which satisfies equation (11); (11) Among them, electrical quantities with subscripts containing "bc" represent the superposition of electrical quantities in phase B and phase C, u mbc i mbc U represents the sum of voltage and current in phase B and phase C, respectively.mbc_re_1 u mbc_im_1 These represent u under the first time window. mbc The real and imaginary parts, i mbc_re_1 i mbc_re_1 These represent i under the first time window. mbc The real and imaginary parts, u mbc_re_2 u mbc_im_2 These represent u under the second time window. mbc The real and imaginary parts, i mbc_re_2 i mbc_re_2 These represent i under the second time window. mbc The real and imaginary parts.
[0048] Finally, the faulty phase is determined by the phase selection element, and the fault direction is determined by the direction element. When the fault is determined to be a positive fault on the station side, the fault distance d is compared with the protection setting d within section I of the line. set Comparison: If d < d set If the fault is detected, it is determined to be an internal fault and a trip command is output; otherwise, it is determined to be an external fault.
[0049] The distance protection device implements the following logic: 1) First, the fault phase is identified using the voltage sequence component phase selection element; 2) Then, the fault direction is identified using the direction element; 3) For a fault in the positive direction on the station side, the fault distance is identified using the invented distance protection principle; when the calculated fault distance is less than the protection section I setting value, it is determined to be an in-zone fault, otherwise it is determined to be an out-of-zone fault, as shown in equation (12): (12) Where, d set These are the protection settings for section I of the line. Due to the significant time delays in actual engineering projects for protection sections II and III, they will not be discussed here.
[0050] The present invention also provides a distance protection device based on converter transient state identification, comprising: The data acquisition module collects three-phase voltage, three-phase current, and zero-sequence current at the protection installation location; The filtering module performs low-pass filtering on the sampled data; The phasor extraction module extracts the real and imaginary parts of the power frequency phasors of voltage and current within multiple short time windows; The state construction and equation generation module is used to select at least two non-overlapping short time windows during the transient phase of the fault, and use the real and imaginary parts of the power frequency phasors corresponding to each short time window as electrical quantities under different fault states, and construct multiple sets of fault loop equations including the fault distance accordingly. The elimination and solution module is used to process the multiple sets of fault loop equations based on the invariant characteristics of the zero-sequence network of the system, so as to weaken or eliminate the influence of unknown quantities related to the transition resistance and the opposite end system, obtain the solution equation for the fault distance d, and solve for the fault distance d. The phase selection module identifies the faulty phase based on voltage sequence components; The direction module determines the direction of the fault; The execution module, when a fault occurs in the forward direction, compares the fault distance d with the protection setting value within section I of the line, outputs the result of inside / outside the section, and executes the action.
[0051] The filtering module uses a fourth-order low-pass Butterworth filter with a cutoff frequency of 100Hz; The phasor extraction module uses a two-sampling-point orthogonal phasor extraction algorithm to extract the real and imaginary parts of the power frequency phasor within a short time window; The state construction and equation generation module uses the low-pass filtered data 40-60ms after the fault as state 1 and the data 60-80ms after the fault as state 2 to form multiple sets of fault loop equations corresponding to at least two sets of unrelated fault states. The state construction and equation generation module constructs fault loop equations based on the power frequency phasor of fault phase voltage, power frequency phasor of fault phase current, and power frequency phasor of zero sequence current during single-phase ground fault, and constructs fault loop equations based on the superposition of the power frequency phasors of two fault phase voltage and power frequency phasors of two fault phases during two-phase ground fault. The elimination and solution module is configured to: establish constraint relationships between zero-sequence electrical quantities under different fault states that satisfy the zero-sequence network invariance characteristics, and use these constraint relationships to perform elimination processing on multiple sets of fault loop equations.
[0052] The present invention further discloses a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method.
[0053] In this embodiment, as Figures 3 to 5 As shown, to verify the effectiveness of the proposed distance protection, a system was built in PSCAD / EMTDC software. Figure 1 The simulation parameters of the grid model with inverter power supply shown are shown in Table 1, and the sampling frequency is set to 4 kHz.
[0054] Table 1 Simulation Model Parameters 1) Fault location This section verifies the influence of fault location on the proposed method. Table 2 lists the average real part of the fault distance calculation results when high-resistance faults occur at different locations. The simulation results show that the proposed method has good accuracy when faults occur at different locations.
[0055] Table 2. Average values of fault distance calculation results at different fault locations. 2) Transition resistance Subsequently, R was verified. f Table 3 lists the impact of different R values on the proposed method. f The average real part of the fault distance calculated using the proposed method under fault conditions is shown in the simulation results, indicating that the proposed method has good resistance to transition resistance.
[0056] Table 3. Average values of fault distance calculation results under different fault resistances. 3) System parameters Then, in this subsection, the positive sequence impedance Z of the opposite end system in the model was adjusted. n1 The values of Z were selected to verify the impact of system parameters on the proposed method. Table 4 lists the values for different Z values. n1 The calculation results of the proposed method under different Z values show that the proposed protection is effective in different Z values. n1 It has high accuracy across all possible values.
[0057] Table 4. Calculation results of the proposed method under different Zn1 values. In summary, this invention provides a distance protection principle and related device based on converter transient state identification. Compared with previous studies, the distance protection proposed in this invention does not rely on assumptions about the system sequence impedance phase, nor does it rely on the control and protection coordination strategy of the converter. It can effectively overcome the influence of system parameters and transition resistance, quickly calculate the fault distance, and achieve the correct operation of distance protection.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.
[0063] 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.
[0064] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.
Claims
1. A distance protection method based on converter transient state identification, characterized in that, Includes the following steps: Fault transient electrical quantity data is acquired at the protection installation location, and the fault transient electrical quantity data is subjected to low-pass filtering to obtain filtered fault transient data. The filtered fault transient data is processed by fast phasor extraction to extract the power frequency phasors under different short time windows, and obtain the real and imaginary parts of the voltage and current power frequency phasors under each short time window. During the transient phase of the fault, at least two non-overlapping short time windows are selected, and the real and imaginary parts of the power frequency phasors corresponding to each short time window are used as electrical quantities under different fault states to construct multiple sets of fault loop equations including the fault distance. The fault loop equation is processed based on the zero-order network invariance property of the system to obtain an equation containing only the fault distance d, and the fault distance d is obtained by solving it. The faulty phase is determined by the phase selection element, and the fault direction is determined by the direction element. When the fault is determined to be a positive direction fault on the station side, the fault distance d is compared with the protection setting d within section I of the line. set Comparison: If d < d set If the fault is detected, it is determined to be an internal fault and a trip command is output; otherwise, it is determined to be an external fault.
2. The distance protection method based on converter transient state identification as described in claim 1, characterized in that, The low-pass filter uses a fourth-order low-pass Butterworth filter with a cutoff frequency of 100Hz.
3. The distance protection method based on converter transient state identification as described in claim 1, characterized in that, In the short time window selected during the transient phase of the fault, the data 40-60ms after the fault after low-pass filtering is used as the data for state "1", and the data 60-80ms after the fault is used as the data for state "2", so as to construct at least two sets of equations for unrelated fault states to solve the fault distance.
4. The distance protection method based on converter transient state identification according to claim 1, characterized in that, Fast phasor extraction employs a two-sampling-point orthogonal phasor extraction algorithm, including the following steps: Set the sampling value i of two consecutive points k i k +1, then at the base frequency i k i k +1 can be expressed as equation (1): ；(1) The instantaneous values of the real and imaginary parts of the current phasor in equation (1) can be expressed as equation (2): ；(2) Where I is the amplitude of the fundamental frequency component; Ψ is the initial phase angle; τ is the phase angle corresponding to the sampling interval; i ck and i sk These represent the real and imaginary parts of the current phasor, respectively; c c1 c c2 c s1 c s2 These are the filter coefficients; The filter function obtained by performing Z-transform on equation (2) can be expressed as equation (3): ；(3) Based on the characteristics of orthogonal filters having consistent amplitude-frequency characteristics and phase-frequency characteristics that differ by 90°, the coefficients of the orthogonal filters can be obtained as shown in equation (4): ；(4) Where, φ c (z), φ s (z) are the filter functions corresponding to the real and imaginary parts, respectively; z is the Z-transform variable.
5. The distance protection method based on converter transient state identification according to claim 4, characterized in that, The orthogonal filter function of two sampling points that satisfies the orthogonality condition is expressed as Equation (5), and the transfer function of the two-point orthogonal phasor filter can be derived from Equation (5) as shown in Equation (6): ；(5) ；(6) Among them, Y c (z), Y s (z) is the transfer function of a two-point orthogonal phasor filter.
6. The distance protection method based on converter transient state identification as described in claim 5, characterized in that, For the AG fault in a single-phase ground fault, the fault loop equation is established as shown in equation (7): ；(7) Among them, u ma_re u ma_im i ma_re i ma_im i m0_re i m0_im Let i represent the real and imaginary parts of the phase A voltage, phase A current, and zero-sequence current phasors at the protection installation location, respectively, extracted after processing by the transfer function of a two-point orthogonal phasor filter. f0_re i f0_im Let r1 and l1 represent the real and imaginary parts of the zero-sequence current phasor at the fault point, respectively; r1 represents the positive-sequence resistance per unit length of the line; and l1 represents the voltage drop across the line. r It means that k l It means that R f This indicates the transition resistance.
7. The distance protection method based on converter transient state identification as described in claim 6, characterized in that, Based on the invariant properties of the zero-sequence network of the system, the relationship between zero-sequence electrical quantities under different fault states is established, satisfying equation (8): ；(8) Differentiating the terms in the numerator and denominator of equation (8) yields equation (9): ；(9) The derivative is approximated using the difference method: ； Among them, i m0_re_1 i m0_im_1 Let i represent the real and imaginary parts of the zero-sequence current at the protection installation location under the first time window, respectively. m0_re_2 i m0_im_2 Let i represent the real and imaginary parts of the zero-sequence current at the protection installation location under the second time window, respectively. f0_re_1 i f0_im_1 Under the first time window, the real and imaginary parts of the zero-sequence current at the fault point, i f0_re_2 i f0_im_2 In the second time window, the real and imaginary parts of the zero-sequence current at the fault point, f s This represents the sampling frequency, and t is the sampling point number.
8. The distance protection method based on converter transient state identification according to claim 7, characterized in that, Differentiate the fault loop equation and substitute it into equation (9) to eliminate the transition resistance R. f And the electrical quantities at the opposite end, the calculation expression for the fault distance d of the AG fault is obtained, which satisfies equation (10): ；(10) Among them, Г AG_1 This represents the dynamic impedance voltage drop per unit length in the first state, Γ. AG_1 This represents the dynamic impedance voltage drop per unit length in the second state.
9. The distance protection method based on converter transient state identification as described in claim 8, characterized in that, For the BCG fault in a two-phase ground fault, the calculation expression of d for the BCG fault is obtained by the same elimination method as the AG fault, which satisfies equation (11). ；(11) Among them, electrical quantities with subscripts containing "bc" represent the superposition of electrical quantities in phase B and phase C, u mbc i mbc U represents the sum of voltage and current in phase B and phase C, respectively. mbc_re_1 u mbc_im_1 These represent u under the first time window. mbc The real and imaginary parts, i mbc_re_1 i mbc_re_1 These represent i under the first time window. mbc The real and imaginary parts, u mbc_re_2 u mbc_im_2 These represent u under the second time window. mbc The real and imaginary parts, i mbc_re_2 i mbc_re_2 These represent i under the second time window. mbc The real and imaginary parts.
10. A distance protection device based on converter transient state identification, characterized in that, include: The data acquisition module collects three-phase voltage, three-phase current, and zero-sequence current at the protection installation location; The filtering module performs low-pass filtering on the sampled data; The phasor extraction module extracts the real and imaginary parts of the power frequency phasors of voltage and current within multiple short time windows; The state construction and equation generation module is used to select at least two non-overlapping short time windows during the transient phase of the fault, and use the real and imaginary parts of the power frequency phasors corresponding to each short time window as electrical quantities under different fault states, and construct multiple sets of fault loop equations including the fault distance accordingly. The elimination and solution module is used to process the multiple sets of fault loop equations based on the invariant characteristics of the zero-sequence network of the system, so as to weaken or eliminate the influence of unknown quantities related to the transition resistance and the opposite end system, obtain the solution equation for the fault distance d, and solve for the fault distance d. The phase selection module identifies the faulty phase based on voltage sequence components; The direction module determines the direction of the fault; The execution module, when a fault occurs in the forward direction, compares the fault distance d with the protection setting value within section I of the line, outputs the result of inside / outside the section, and executes the action.
11. The distance protection device based on converter transient state identification according to claim 10, characterized in that, The filtering module uses a fourth-order low-pass Butterworth filter with a cutoff frequency of 100Hz. The phasor extraction module employs a two-sampling-point orthogonal phasor extraction algorithm to extract the real and imaginary parts of the power frequency phasor within a short time window. The state construction and equation generation module uses the low-pass filtered data 40-60ms after the fault as state 1 and the data 60-80ms after the fault as state 2 to form at least two sets of fault loop equations corresponding to the multiple sets of fault states that are unrelated to each other. The state construction and equation generation module constructs a fault loop equation based on the power frequency phasor of the fault phase voltage, the power frequency phasor of the fault phase current, and the power frequency phasor of the zero-sequence current during a single-phase ground fault, and constructs a fault loop equation based on the superposition of the power frequency phasors of the two fault phase voltages and the power frequency phasors of the two fault phases during a two-phase ground fault. The elimination and solution module is configured to: establish constraint relationships between zero-sequence electrical quantities under different fault states that satisfy the zero-sequence network invariance characteristics, and use these constraint relationships to perform elimination processing on the multiple sets of fault loop equations.
12. 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 9.