Distance protection method and system based on fault quantity network characteristics

Abstract

The invention relates to the technical field of electric power automation, and provides a distance protection method and system based on fault quantity network characteristics, and the method comprises the steps: carrying out the analysis to obtain a fault state network equivalent circuit and a fault component network equivalent circuit of a double-end power system under an R-L model; obtaining a distance measurement equation according to the fault point current equation and the fault point voltage equation; integral taking processing is carried out on two sides of the distance measurement equation; a sliding window lists a linear equation to obtain a ranging overdetermined equation set; solving the distance measurement overdetermined equation set to obtain a single-phase system fault distance measurement result; expanding the analysis and calculation process of the single-phase system in the previous step to a three-phase system, constructing and solving a linear equation distance measurement formula when a single-phase earth fault and an inter-phase fault occur, and obtaining a fault distance measurement result of the three-phase system; and comparing the distance measurement result with the setting method, and determining whether the fault is an internal fault or an external fault. The method has high robustness, and can adapt to the parameter change of the power system and the dynamic characteristics of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power automation, and in particular to a distance protection method and system based on fault quantity network characteristics. Background Art

[0002] With the rapid development of power systems, especially the large-scale access of new energy and the widespread application of power electronic equipment, the operating characteristics of traditional power systems are undergoing significant changes. These changes have brought new challenges to existing relay protection systems, especially in fault detection, location and isolation. Compared with conventional systems, low-inertia systems with new energy as the main body have the characteristics of short transient processes, limited fault currents, controlled power supply parameters and complex laws. This is because compared with traditional power systems, low-inertia systems with new energy as the main body contain a large number of power electronic power equipment, and the structure, parameters and characteristics of the power grid have also changed significantly.

[0003] The reliability of differential protection based on two-end communication is restricted by the information transmission channel, so there is a certain risk. Therefore, the protection strategy based on single-end quantity is more suitable as an important safety barrier under extreme working conditions. At the same time, if the protection can provide fault location information, the difficulty of repairing the faulty cable will be greatly reduced. Combining the above two realities, the distance protection based on single-end quantity is the best choice for low-inertia systems as the main protection. However, the traditional distance protection based on measuring impedance has low reliability under weak fault characteristics, is greatly affected by the harmonic components of the fault current, and has a slow action speed, which is difficult to meet the protection requirements of low-inertia systems. Summary of the invention

[0004] The object of the present invention is to solve at least one technical problem in the background technology and to provide a distance protection method and system based on fault quantity network characteristics.

[0005] To achieve the above object, the present invention provides a distance protection method based on fault quantity network characteristics, comprising:

[0006] S1. Analyze and obtain the fault state network equivalent circuit and fault component network equivalent circuit of the two-terminal power supply system under the RL model;

[0007] S2. Obtaining a distance measurement equation based on the fault point current equation and the fault point voltage equation;

[0008] S3. Integrate both sides of the ranging equation;

[0009] S4. Write linear equations in sliding window to obtain the range-measuring overdetermined equations;

[0010] S5. The fault distance calculation method based on the least squares optimization algorithm is used to solve the overdetermined distance measurement equations to obtain the result of single-phase system fault distance measurement;

[0011] S6. Extend the analysis and calculation process of the single-phase system in steps S1 to S5 to the three-phase system, use the Clarke matrix to perform phase mode transformation, construct and solve the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault, and obtain the result of fault distance measurement for the three-phase system;

[0012] S7. Compare the three-phase system fault location measurement results with the setting method to determine whether the fault is an internal fault or an external fault.

[0013] According to one aspect of the present invention, the distance measurement equation is obtained according to the fault point current equation and the fault point voltage equation, including:

[0014] In the fault state network equivalent circuit, the fault point current satisfies:

[0015]

[0016] i F =i m +i n =(i mn +Δi m )+(-i mn +Δi n )=Δi m +Δi n ;

[0017] In the formula, u m and u F is the instantaneous voltage at line M and F at the time of fault, i m and i n are the instantaneous currents on the M side and the N side during the fault, i F is the instantaneous value of the current at the fault point, i mn is the instantaneous value of the load current when the system is operating normally, Δi m and Δi n are the currents flowing from the M-side and N-side busbars to the fault point during a fault, rp and Lp are the resistance and inductance per unit length of the line, respectively;

[0018] Therefore, the fault component of the opposite system current can be obtained as:

[0019]

[0020] In the formula, Δi n is the fault component of the opposite system current, R F is the transition resistance during fault;

[0021] In the fault component network equivalent circuit, the voltages of the two-end system converted to the fault point are equal, and we can get:

[0022]

[0023] In the formula, R m , R n ′ and L n ′ are the equivalent resistance and inductance values ​​of the M side and N side respectively;

[0024] From the above equations, eliminating the opposite side current and the fault point voltage and rearranging them, the distance measurement equation can be obtained as follows:

[0025]

[0026] Where x1~x5 are the coefficients of the linear differential equation.

[0027] According to one aspect of the present invention, after integrating both sides of the distance measurement equation, it is:

[0028]

[0029] In the formula, the coefficients x1~x5 of each linear differential equation are related to the fault distance p and the fault transition resistance R F and the real-time operating parameters of the system after the fault point R n ′, L n The relationship between the four unknown parameters is:

[0030]

[0031] According to one aspect of the present invention, the sliding window writes linear equations to obtain the range-finding overdetermined equation group:

[0032] After the fault, the measured values ​​of n sampling points in the fault transient process are used to establish multiple equations. The corresponding equations (n>4) form an overdetermined set of ranging equations, where each equation corresponds to a different time t.

[0033] According to one aspect of the present invention, the fault distance calculation method based on the least squares optimization algorithm solves the overdetermined distance measurement equations to obtain the single-phase system fault distance measurement result:

[0034] The fault distance calculation method based on the least squares optimization algorithm solves the overdetermined distance measurement equations to obtain the values ​​of the coefficients of the linear differential equations. After substituting them into the relationship and obtaining the four unknown parameters, the fault distance can be obtained, and then the fault distance is used to distinguish the faults inside and outside the area.

[0035] According to one aspect of the present invention, the setting method is:

[0036] The distance protection method based on parameter identification calculates the fault distance x f , the criterion of this distance protection method is:

[0037] x f <x set =k rel ·L;

[0038] In the formula, x set is the set value of the distance, L is the line length, k rel is the reliability coefficient, which is 0.8~0.85, i.e. 80%~85% of the total length of the protection line; when the fault distance x f Less than the set value x set , it is determined to be an internal fault, otherwise it is an external fault.

[0039] Furthermore, to achieve the above object, the present invention also provides a distance protection system based on fault quantity network characteristics, comprising:

[0040] The equivalent circuit analysis acquisition module is used to analyze and obtain the fault state network equivalent circuit and fault component network equivalent circuit of the two-terminal power supply system under the RL model;

[0041] A distance measurement equation acquisition module obtains a distance measurement equation according to a fault point current equation and a fault point voltage equation;

[0042] The integral processing module performs integral processing on both sides of the ranging equation;

[0043] The equation group acquisition module writes linear equations in sliding windows to obtain the range-finding overdetermined equation group;

[0044] The fault distance measurement result acquisition module solves the overdetermined distance measurement equations based on the fault distance calculation method of the least squares optimization algorithm to obtain the single-phase system fault distance measurement result;

[0045] The linear equation distance measurement formula construction module extends the analysis and calculation process of the single-phase system to the three-phase system. After using the Clarke matrix for phase model transformation, the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault is constructed and solved to obtain the fault distance measurement result of the three-phase system.

[0046] The fault determination module compares the three-phase system fault location results with the setting method to determine whether the fault is an internal fault or an external fault.

[0047] Furthermore, to achieve the above-mentioned purpose, the present invention also provides an electronic device, comprising a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the distance protection method based on fault quantity network characteristics as described above is implemented.

[0048] Furthermore, to achieve the above-mentioned purpose, the present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the distance protection method based on fault quantity network characteristics as described above is implemented.

[0049] According to the solution of the present invention, in order to solve the problem of theoretical error in positioning of single-ended faults based on the traditional non-traveling wave principle, the present invention proposes a distance protection method based on the differential equation reduction fitting solution of the fault quantity network characteristics. Based on the traditional time-domain distance protection technology, the fault component network model and its corresponding differential equation group related to various fault conditions are established by applying modal analysis, and combined with the traditional fault state network differential equation, so as to derive the time-domain distance measurement formula based on real-time sampling data. This technology regards the distance between the fault point and the protection device, the transition resistance of the fault point and the dynamic operating parameters of the opposite end system as the RL model parameters to be identified, thereby effectively eliminating the theoretical error in the single-ended measurement method and ensuring good applicability to all possible fault types.

[0050] According to the scheme of the present invention, the present invention has strong robustness: since the distance measurement equation is solved by second-order differential, directly using it to solve the fault distance will result in large errors in calculation, so integrating both sides of the equation has achieved better robustness and can adapt to changes in power system parameters and the dynamic characteristics of the system; the present invention has high accuracy: the method solves the problem of positioning theoretical errors in traditional single-ended fault positioning based on the non-traveling wave principle, and improves the accuracy of fault positioning through real-time parameter identification; the present invention has a faster response: based on time domain analysis, the method can quickly respond to faults and disturbances in the system, and has the advantages of fast action speed and being unaffected by harmonics; the present invention has strong adaptability: it is suitable for low-inertia systems including new energy power supplies and power electronic equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A flowchart schematically showing a distance protection method based on fault quantity network characteristics according to an embodiment of the present invention;

[0052] Figure 2 A schematic diagram showing a fault state network equivalent circuit diagram according to an embodiment of the present invention;

[0053] Figure 3 Schematically showing a fault component network equivalent circuit diagram according to an embodiment of the present invention;

[0054] Figure 4 A schematic diagram showing a single-phase ground short-circuit system model according to an embodiment of the present invention;

[0055] Figure 5 A schematic diagram showing a single-phase ground short circuit 0-mode fault component network equivalent circuit diagram according to an embodiment of the present invention;

[0056] Figure 6 A schematic diagram of a two-phase interphase short-circuit system model according to an embodiment of the present invention is shown;

[0057] Figure 7 The figure schematically shows an equivalent circuit diagram of a two-phase interphase short-circuit fault component according to an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The present invention will now be discussed with reference to exemplary embodiments. It should be understood that the embodiments discussed are only to enable those skilled in the art to better understand and thus implement the present invention, rather than implying any limitation on the scope of the present invention.

[0059] As used herein, the term “including” and variations thereof are to be interpreted as open-ended terms meaning “including, but not limited to.” The term “based on” is to be interpreted as “based, at least in part, on.” The terms “one embodiment” and “an embodiment” are to be interpreted as “at least one embodiment.”

[0060] Figure 1 The flowchart schematically shows a distance protection method based on fault quantity network characteristics according to an embodiment of the present invention. Figure 1 As shown, in this implementation, the distance protection method based on the fault quantity network characteristics includes:

[0061] S1. Analyze and obtain the fault state network equivalent circuit and fault component network equivalent circuit of the two-terminal power supply system under the RL model;

[0062] S2. Obtaining a distance measurement equation based on the fault point current equation and the fault point voltage equation;

[0063] S3. Integrate both sides of the ranging equation;

[0064] S4. Write linear equations in sliding window to obtain the range-measuring overdetermined equations;

[0065] S5. The fault distance calculation method based on the least squares optimization algorithm is used to solve the overdetermined distance measurement equations to obtain the result of single-phase system fault distance measurement;

[0066] S6. Extend the analysis and calculation process of the single-phase system in steps S1 to S5 to the three-phase system, use the Clarke matrix to perform phase mode transformation, construct and solve the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault, and obtain the result of fault distance measurement for the three-phase system;

[0067] S7. Compare the three-phase system fault location measurement results with the setting method to determine whether the fault is an internal fault or an external fault.

[0068] Further, according to an embodiment of the present invention, firstly, a single-terminal accurate fault location algorithm for linear differential equation parameter identification is derived under a single-phase power transmission system model. Specifically, in the above step S1, the fault state network equivalent circuit and the fault component network equivalent circuit of the two-terminal power system under the RL model are respectively as follows: Figure 2 and Figure 3 shown.

[0069] Further, according to an embodiment of the present invention, a distance measurement equation is obtained according to the fault point current equation and the fault point voltage equation, including:

[0070] like Figure 2 As shown, in the fault state network equivalent circuit, the fault point current satisfies:

[0071]

[0072] i F =i m +i n =(i mn +Δi m )+(-i mn +Δi n )=Δi m +Δi n ;

[0073] In the formula, u m and u F is the instantaneous voltage at line M and F at the time of fault, i m and i n are the instantaneous currents on the M side and the N side during the fault, i F is the instantaneous value of the current at the fault point, i mn is the instantaneous value of the load current when the system is operating normally, Δi m and Δi n are the currents flowing from the M-side and N-side busbars to the fault point during a fault, rp and Lp are the resistance and inductance per unit length of the line, respectively;

[0074] Therefore, the fault component of the opposite system current can be obtained as:

[0075]

[0076] In the formula, Δi n is the fault component of the opposite system current, R F is the transition resistance during fault;

[0077] like Figure 3As shown, in the fault component network equivalent circuit, the voltage of the two-end system is equal to the fault point voltage, which can be obtained:

[0078]

[0079] In the formula, R m , R n ′ and L n ′ are the equivalent resistance and inductance values ​​of the M side and N side respectively;

[0080] From the above equations, eliminating the opposite side current and the fault point voltage and rearranging them, the distance measurement equation can be obtained as follows:

[0081]

[0082] Where x1~x5 are the coefficients of the linear differential equation.

[0083] Further, according to an embodiment of the present invention, in order to improve the robustness of the distance measurement equation solution, the error is reduced by integrating both sides of the equation. After integrating both sides of the distance measurement equation, it is obtained as follows:

[0084]

[0085] In the formula, the coefficients x1~x5 of each linear differential equation are related to the fault distance p and the fault transition resistance R F and the real-time operating parameters of the system after the fault point R n ′, L n The relationship between the four unknown parameters is:

[0086]

[0087] Further, according to an embodiment of the present invention, the sliding window writes linear equations to obtain the range-finding overdetermined equation group:

[0088] After the fault, the measured values ​​of n sampling points in the fault transient process are used to establish multiple equations. The corresponding equations (n>4) form an overdetermined set of ranging equations, where each equation corresponds to a different time t.

[0089] In this embodiment, the overdetermined distance measurement equations composed of multiple nonlinear equations are solved to obtain the fault distance p, and the four unknown parameters p, R in the RL model can also be obtained. F , R n ′, L n 'value;

[0090]

[0091] Further, according to an embodiment of the present invention, the fault distance calculation method based on the least squares optimization algorithm is used to solve the distance measurement overdetermined equations, and the result of single-phase system fault distance measurement is obtained as follows:

[0092] The fault distance calculation method based on the least squares optimization algorithm solves the overdetermined distance measurement equations to obtain the values ​​of the coefficients of the linear differential equations. After substituting them into the relationship and obtaining the four unknown parameters, the fault distance can be obtained, and then the fault distance is used to distinguish the faults inside and outside the area.

[0093] Specifically, based on the overdetermined distance measurement equations and taking the measurement equations of all sampling points as data redundancy, nonlinear least squares estimation is performed on x1-x5 to obtain the values ​​of each coefficient.

[0094] The formula Simplified to Using the least squares method, we can get

[0095] Substitute the corresponding relationship between each coefficient and the parameter to be identified (unknown parameter) Then we can get the four unknown parameters p, R F , R n ′, L n ′, we can get the fault distance x f =p, so the fault distance can be used to distinguish the faults inside and outside the area;

[0096] The above is the processing flow of the highly robust time domain parameter identification distance protection method.

[0097] Further, according to an embodiment of the present invention, the above analysis and calculation process of the single-phase system is extended to the three-phase system. The single-phase fault and inter-phase fault of the three-phase system are specifically described below:

[0098] (I) Single-phase failure of three-phase system:

[0099] Based on the analysis of single-phase system, for three-phase system, when Clarke matrix is ​​used for phase transformation, the system model of single-phase ground short circuit is as follows: Figure 4 As shown; the equivalent circuit of the single-phase ground short circuit 0-mode fault component network is as follows Figure 5 shown.

[0100] When a single-phase ground fault occurs, the four parameters to be identified by the system become: fault distance p, transition resistance R F , the system zero mode resistance R after the fault point n '0 and 0 mode inductance L n ′0. At this time, the relationship between the 4 parameters to be identified and the coefficients x1~x5 of the linear differential equation is:

[0101]

[0102] Perform nonlinear least squares estimation on the coefficients of the equation to obtain the values ​​of x1~x5.

[0103] (II) Phase-to-phase fault in three-phase system:

[0104] Based on the above analysis of the single-phase system, for the three-phase system, when the Clarke matrix is ​​used for phase transformation, the system model of the phase-to-phase fault is as follows: Figure 6 As shown; the equivalent circuit of the two-phase short-circuit fault component is as follows Figure 7 shown.

[0105] When two phases are short-circuited, the four parameters to be identified by the system become: fault distance p, transition resistance R F , the system 1 mode resistance R after the fault point n '1 and 1 mode inductance L n ′1. By taking integrals on both sides of the equation to reduce the error and improve the robustness of the distance measurement equation solution, the linear equation distance measurement formula for two-phase short circuit is derived:

[0106]

[0107] When two phases are short-circuited, the four parameters to be identified by the system become: fault distance p, transition resistance R F , the system 1 mode resistance R after the fault point n '1 and 1 mode inductance L n ′1. At this time, the relationship between the 4 parameters to be identified and the coefficients x1 to x5 of the linear equation is as follows:

[0108]

[0109] The three-phase short circuit fault can be calculated using the linear equation distance measurement formula for two-phase short circuit, which will not be repeated here.

[0110] From the above, we can see that for a three-phase system, after the Clarke matrix is ​​used for phase mode transformation, the analysis process is similar to that of a single-phase system. Using a similar derivation idea, the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault is obtained.

[0111] Further, according to an embodiment of the present invention, the setting method is:

[0112] The distance protection method based on parameter identification calculates the fault distance x f , the criterion of this distance protection method is:

[0113] x f <x set =k rel ·L;

[0114] In the formula, xset is the set value of the distance, L is the line length, k rel is the reliability coefficient, which is 0.8~0.85, i.e. 80%~85% of the total length of the protection line; when the fault distance x f Less than the set value x set , it is determined to be an internal fault, otherwise it is an external fault. For internal faults, the protection device should determine the fault phase according to the phase selection element and immediately cut off the fault phase to prevent the fault from spreading; for external faults, the protection should not act to avoid unnecessary circuit breaker tripping.

[0115] According to the above scheme of the present invention, in order to solve the problem of theoretical error in positioning of single-ended faults based on the traditional non-traveling wave principle, the present invention proposes a distance protection method based on the differential equation reduction fitting solution of the fault quantity network characteristics. Based on the traditional time domain distance protection technology, the fault component network model and its corresponding differential equation group related to various fault conditions are established by applying modal analysis, and combined with the traditional fault state network differential equation, so as to derive the time domain distance measurement formula based on real-time sampling data. This technology regards the distance between the fault point and the protection device, the transition resistance of the fault point and the dynamic operating parameters of the opposite end system as the RL model parameters to be identified, thereby effectively eliminating the theoretical error in the single-ended measurement method and ensuring good applicability to all possible fault types.

[0116] According to the above scheme of the present invention, the present invention has strong robustness: since the distance measurement equation is solved by second-order differential, directly using it to solve the fault distance will result in large errors in calculation, so integrating both sides of the equation has achieved better robustness and can adapt to changes in power system parameters and the dynamic characteristics of the system; the present invention has high accuracy: this method solves the problem of positioning theoretical errors in traditional single-ended fault positioning based on the non-travelling wave principle, and improves the accuracy of fault positioning through real-time parameter identification; the present invention has a faster response: based on time domain analysis, this method can quickly respond to faults and disturbances in the system, and has the advantages of fast action speed and being unaffected by harmonics; the present invention has strong adaptability: it is suitable for low-inertia systems including new energy power supplies and power electronic equipment.

[0117] Furthermore, to achieve the above object, the present invention also provides a distance protection system based on fault quantity network characteristics, comprising:

[0118] The equivalent circuit analysis acquisition module is used to analyze and obtain the fault state network equivalent circuit and fault component network equivalent circuit of the two-terminal power supply system under the RL model;

[0119] A distance measurement equation acquisition module obtains a distance measurement equation according to a fault point current equation and a fault point voltage equation;

[0120] The integral processing module performs integral processing on both sides of the ranging equation;

[0121] The equation group acquisition module writes linear equations in sliding windows to obtain the range-finding overdetermined equation group;

[0122] The fault distance measurement result acquisition module solves the overdetermined distance measurement equations based on the fault distance calculation method of the least squares optimization algorithm to obtain the single-phase system fault distance measurement result;

[0123] The linear equation distance measurement formula construction module extends the analysis and calculation process of the single-phase system to the three-phase system. After using the Clarke matrix for phase model transformation, the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault is constructed and solved to obtain the fault distance measurement result of the three-phase system.

[0124] The fault determination module compares the three-phase system fault location results with the setting method to determine whether the fault is an internal fault or an external fault.

[0125] Further, according to an embodiment of the present invention, firstly, a single-terminal accurate fault location algorithm for linear differential equation parameter identification is derived under a single-phase power transmission system model. Specifically, in the above step S1, the fault state network equivalent circuit and the fault component network equivalent circuit of the two-terminal power system under the RL model are respectively as follows: Figure 2 and Figure 3 shown.

[0126] Further, according to an embodiment of the present invention, a distance measurement equation is obtained according to the fault point current equation and the fault point voltage equation, including:

[0127] like Figure 2 As shown, in the fault state network equivalent circuit, the fault point current satisfies:

[0128]

[0129] i F =i m +i n =(i mn +Δi m )+(-i mn +Δi n )=Δi m +Δi n ;

[0130] In the formula, u m and u F is the instantaneous voltage at line M and F at the time of fault, i m and i n are the instantaneous currents on the M side and the N side during the fault, i F is the instantaneous value of the current at the fault point, imn is the instantaneous value of the load current when the system is operating normally, Δi m and Δi n are the currents flowing from the M-side and N-side busbars to the fault point during a fault, rp and Lp are the resistance and inductance per unit length of the line, respectively;

[0131] Therefore, the fault component of the opposite system current can be obtained as:

[0132]

[0133] In the formula, Δi n is the fault component of the opposite system current, R F is the transition resistance during fault;

[0134] like Figure 3 As shown, in the fault component network equivalent circuit, the voltage of the two-end system is equal to the fault point voltage, which can be obtained:

[0135]

[0136] In the formula, R m , R n ′ and L n ′ are the equivalent resistance and inductance values ​​of the M side and N side respectively;

[0137] From the above equations, eliminating the opposite side current and the fault point voltage and rearranging them, the distance measurement equation can be obtained as follows:

[0138]

[0139] Where x1~x5 are the coefficients of the linear differential equation.

[0140] Further, according to an embodiment of the present invention, in order to improve the robustness of the distance measurement equation solution, the error is reduced by integrating both sides of the equation. After integrating both sides of the distance measurement equation, it is obtained as follows:

[0141]

[0142] In the formula, the coefficients x1~x5 of each linear differential equation are related to the fault distance p and the fault transition resistance R F and the real-time operating parameters of the system after the fault point R n ′, L n The relationship between the four unknown parameters is:

[0143]

[0144] Further, according to an embodiment of the present invention, the sliding window writes linear equations to obtain the range-finding overdetermined equation group:

[0145] After the fault, the measured values ​​of n sampling points in the fault transient process are used to establish multiple equations. The corresponding equations (n>4) form an overdetermined set of ranging equations, where each equation corresponds to a different time t.

[0146] In this embodiment, the overdetermined distance measurement equations composed of multiple nonlinear equations are solved to obtain the fault distance p, and the four unknown parameters p, R in the RL model can also be obtained. F , R n ′, L n 'value;

[0147]

[0148] Further, according to an embodiment of the present invention, the fault distance calculation method based on the least squares optimization algorithm is used to solve the distance measurement overdetermined equations, and the result of single-phase system fault distance measurement is obtained as follows:

[0149] The fault distance calculation method based on the least squares optimization algorithm solves the overdetermined distance measurement equations to obtain the values ​​of the coefficients of the linear differential equations. After substituting them into the relationship and obtaining the four unknown parameters, the fault distance can be obtained, and then the fault distance is used to distinguish the faults inside and outside the area.

[0150] Specifically, based on the overdetermined distance measurement equations and taking the measurement equations of all sampling points as data redundancy, nonlinear least squares estimation is performed on x1-x5 to obtain the values ​​of each coefficient.

[0151] The formula Transform Using the least squares method, we can get

[0152] Substitute the corresponding relationship between each coefficient and the parameter to be identified (unknown parameter) Then we can get the four unknown parameters p, R F , R n ′, L n ′, we can get the fault distance x f =p, so the fault distance can be used to distinguish the faults inside and outside the area;

[0153] The above is the processing flow of the highly robust time domain parameter identification distance protection method.

[0154] Further, according to an embodiment of the present invention, the above analysis and calculation process of the single-phase system is extended to the three-phase system. The single-phase fault and inter-phase fault of the three-phase system are specifically described below:

[0155] (I) Single-phase failure of three-phase system:

[0156] Based on the analysis of single-phase system, for three-phase system, when Clarke matrix is ​​used for phase transformation, the system model of single-phase ground short circuit is as follows: Figure 4 As shown; the equivalent circuit of the single-phase ground short circuit 0-mode fault component network is as follows Figure 5 shown.

[0157] When a single-phase ground fault occurs, the four parameters to be identified by the system become: fault distance p, transition resistance R F , the system zero mode resistance R after the fault point n '0 and 0 mode inductance L n ′0. At this time, the relationship between the 4 parameters to be identified and the coefficients x1~x5 of the linear differential equation is:

[0158]

[0159] Perform nonlinear least squares estimation on the coefficients of the equation to obtain the values ​​of x1~x5.

[0160] (II) Phase-to-phase fault in three-phase system:

[0161] Based on the above analysis of the single-phase system, for the three-phase system, when the Clarke matrix is ​​used for phase transformation, the system model of the phase-to-phase fault is as follows: Figure 6 As shown; the equivalent circuit of the two-phase short-circuit fault component is as follows Figure 7 shown.

[0162] When two phases are short-circuited, the four parameters to be identified by the system become: fault distance p, transition resistance R F , the system 1 mode resistance R after the fault point n '1 and 1 mode inductance L n ′1. By taking integrals on both sides of the equation to reduce the error and improve the robustness of the distance measurement equation solution, the linear equation distance measurement formula for two-phase short circuit is derived:

[0163]

[0164] When two phases are short-circuited, the four parameters to be identified by the system become: fault distance p, transition resistance R F , the system 1 mode resistance R after the fault point n '1 and 1 mode inductance L n ′1. At this time, the relationship between the 4 parameters to be identified and the coefficients x1 to x5 of the linear equation is as follows:

[0165]

[0166] The three-phase short circuit fault can be calculated using the linear equation distance measurement formula for two-phase short circuit, which will not be repeated here.

[0167] From the above, we can see that for a three-phase system, after the Clarke matrix is ​​used for phase mode transformation, the analysis process is similar to that of a single-phase system. Using a similar derivation idea, the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault is obtained.

[0168] Further, according to an embodiment of the present invention, the setting method is:

[0169] The distance protection method based on parameter identification calculates the fault distance x f , the criterion of this distance protection method is:

[0170] x f <x set =k rel ·L;

[0171] In the formula, x set is the set value of the distance, L is the line length, k rel is the reliability coefficient, which is 0.8~0.85, i.e. 80%~85% of the total length of the protection line; when the fault distance x f Less than the set value x set , it is determined to be an internal fault, otherwise it is an external fault. For internal faults, the protection device should determine the fault phase according to the phase selection element and immediately cut off the fault phase to prevent the fault from spreading; for external faults, the protection should not act to avoid unnecessary circuit breaker tripping.

[0172] According to the above scheme of the present invention, in order to solve the problem of theoretical error in positioning of single-ended faults based on the traditional non-traveling wave principle, the present invention proposes a distance protection method based on the differential equation reduction fitting solution of the fault quantity network characteristics. Based on the traditional time domain distance protection technology, the fault component network model and its corresponding differential equation group related to various fault conditions are established by applying modal analysis, and combined with the traditional fault state network differential equation, so as to derive the time domain distance measurement formula based on real-time sampling data. This technology regards the distance between the fault point and the protection device, the transition resistance of the fault point and the dynamic operating parameters of the opposite end system as the RL model parameters to be identified, thereby effectively eliminating the theoretical error in the single-ended measurement method and ensuring good applicability to all possible fault types.

[0173] According to the above scheme of the present invention, the present invention has strong robustness: since the distance measurement equation is solved by second-order differential, directly using it to solve the fault distance will result in large errors in calculation, so integrating both sides of the equation has achieved better robustness and can adapt to changes in power system parameters and the dynamic characteristics of the system; the present invention has high accuracy: this method solves the problem of positioning theoretical errors in traditional single-ended fault positioning based on the non-travelling wave principle, and improves the accuracy of fault positioning through real-time parameter identification; the present invention has a faster response: based on time domain analysis, this method can quickly respond to faults and disturbances in the system, and has the advantages of fast action speed and being unaffected by harmonics; the present invention has strong adaptability: it is suitable for low-inertia systems including new energy power supplies and power electronic equipment.

[0174] Furthermore, to achieve the above objectives, the present invention also provides an electronic device, comprising a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the distance protection method based on the fault quantity network characteristics as described above is implemented.

[0175] Furthermore, to achieve the above-mentioned purpose, the present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the distance protection method based on fault quantity network characteristics as described above is implemented.

[0176] Those skilled in the art will appreciate that the modules and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0177] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described devices and equipment can refer to the corresponding processes in the aforementioned method implementation methods, and will not be repeated here.

[0178] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the modules is only a logical function division. There may be other division methods in actual implementation, such as multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0179] The modules described as separate components may or may not be physically separated, and the components shown as modules may or may not be physical modules, that is, they may be located in one place or distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the embodiments of the present invention.

[0180] In addition, each functional module in the embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0181] If the functions are implemented in the form of software function modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention can be essentially or partly embodied in the form of a software product that contributes to the prior art. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the energy-saving signal sending / receiving method of each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, ROM, RAM, magnetic disks, or optical disks.

[0182] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with the technical features with similar functions disclosed in this application (but not limited to) by each other.

[0183] It should be understood that the size of the serial numbers of each step in the content of the invention and the implementation methods of the present invention does not absolutely mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation methods of the present invention.

Claims

1. A distance protection method based on fault volume network characteristics, characterized in that: include: S1. Analyze and obtain the fault state network equivalent circuit and fault component network equivalent circuit of the two-terminal power supply system under the RL model; S2. Obtaining a distance measurement equation based on the fault point current equation and the fault point voltage equation; S3. Integrate both sides of the ranging equation; S4. Write linear equations in sliding window to obtain the range-measuring overdetermined equations; S5. The fault distance calculation method based on the least squares optimization algorithm is used to solve the overdetermined distance measurement equations to obtain the result of single-phase system fault distance measurement; S6. Extend the analysis and calculation process of the single-phase system in steps S1 to S5 to the three-phase system, use the Clarke matrix to perform phase mode transformation, construct and solve the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault, and obtain the result of fault distance measurement for the three-phase system; S7. Compare the three-phase system fault location measurement results with the setting method to determine whether the fault is an internal fault or an external fault.

2. The distance protection method based on fault quantity network characteristics according to claim 1 is characterized in that: The distance measurement equation is obtained according to the fault point current equation and the fault point voltage equation, including: In the fault state network equivalent circuit, the fault point current satisfies: i F =i m +i n =(i mn +Δi m )+(-i mn +Δi n )=Δi m +Δi n ; In the formula, u m and u F is the instantaneous voltage at line M and F at the time of fault, i m and i n are the instantaneous currents on the M side and the N side during the fault, i F is the instantaneous value of the current at the fault point, i mn is the instantaneous value of the load current when the system is operating normally, Δi m and Δi n are the currents flowing from the M-side and N-side busbars to the fault point during a fault, rp and Lp are the resistance and inductance per unit length of the line, respectively; Therefore, the fault component of the opposite system current can be obtained as: In the formula, Δi n is the fault component of the opposite system current, R F is the transition resistance during fault; In the fault component network equivalent circuit, the voltages of the two-end system converted to the fault point are equal, and we can get: In the formula, R m , R n ′ and L n ′ are the equivalent resistance and inductance values ​​of the M side and N side respectively; From the above equations, eliminating the opposite side current and the fault point voltage and rearranging them, the distance measurement equation can be obtained as follows: Where x1~x5 are the coefficients of the linear differential equation.

3. The distance protection method based on fault quantity network characteristics according to claim 2 is characterized in that: After integrating both sides of the distance measurement equation, it is: In the formula, the coefficients x1~x5 of each linear differential equation are related to the fault distance p and the fault transition resistance R F and the real-time operating parameters of the system after the fault point R n ′, L n The relationship between the four unknown parameters is:

4. The distance protection method based on fault quantity network characteristics according to claim 3 is characterized in that: The sliding window writes linear equations to obtain the range-finding overdetermined equations: After the fault, the measured values ​​of n sampling points in the fault transient process are used to establish multiple equations. The corresponding equations form an overdetermined set of ranging equations, where each equation corresponds to a different time t; Among them, n>4.

5. The distance protection method based on fault quantity network characteristics according to claim 4 is characterized in that: The fault distance calculation method based on the least squares optimization algorithm solves the overdetermined distance measurement equations and obtains the single-phase system fault distance measurement result as follows: The fault distance calculation method based on the least squares optimization algorithm solves the overdetermined distance measurement equations to obtain the values ​​of the coefficients of the linear differential equations. After substituting them into the relationship and obtaining the four unknown parameters, the fault distance can be obtained, and then the fault distance is used to distinguish the faults inside and outside the area.

6. The distance protection method based on fault quantity network characteristics according to any one of claims 1 to 5, characterized in that: The setting method is: The distance protection method based on parameter identification calculates the fault distance x f , the criterion of this distance protection method is: x f <x set =k rel ·L; In the formula, x set is the set value of the distance, L is the line length, k rel is the reliability coefficient, which is 0.8~0.85, i.e. 80%~85% of the total length of the protection line; when the fault distance x f Less than the set value x set , it is determined to be an internal fault, otherwise it is an external fault.

7. A distance protection system based on fault volume network characteristics, characterized in that: include: The equivalent circuit analysis acquisition module is used to analyze and obtain the fault state network equivalent circuit and fault component network equivalent circuit of the two-terminal power supply system under the RL model; A distance measurement equation acquisition module obtains a distance measurement equation according to a fault point current equation and a fault point voltage equation; The integral processing module performs integral processing on both sides of the ranging equation; The equation group acquisition module writes linear equations in sliding windows to obtain the range-finding overdetermined equation group; The fault distance measurement result acquisition module solves the overdetermined distance measurement equations based on the fault distance calculation method of the least squares optimization algorithm to obtain the single-phase system fault distance measurement result; The linear equation distance measurement formula construction module extends the analysis and calculation process of the single-phase system to the three-phase system. After using the Clarke matrix for phase model transformation, the linear equation distance measurement formula for single-phase grounding fault and phase-to-phase fault is constructed and solved to obtain the fault distance measurement result of the three-phase system. The fault determination module compares the three-phase system fault location results with the setting method to determine whether the fault is an internal fault or an external fault.

8. An electronic device, characterized in that The invention comprises a processor, a memory and a computer program stored in the memory and executable on the processor, wherein when the computer program is executed by the processor, the distance protection method based on the fault quantity network characteristics as claimed in any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the distance protection method based on fault quantity network characteristics as described in any one of claims 1 to 6 is implemented.

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