Double-ended weak system single-phase grounding fault distance protection method, device, equipment and medium

Abstract

The present invention relates to the technical field of relay protection in power systems, and particularly to a single-phase ground fault distance protection method, device, equipment and medium for a double-ended weak system. The method includes: setting a protection startup criterion when a single-phase ground fault occurs in a transmission line; when the protection startup criterion is satisfied, obtaining a composite sequence network diagram of the single-phase ground fault, and constructing a closed curve in the composite sequence network diagram; based on Kirchhoff's current law, using the negative sequence current and zero sequence current on the system side to calculate the zero sequence current on the new energy side; calculating the fault location through the current relationship between the system side and the new energy power source; performing fault identification on the fault location, and performing fault protection according to the set conditions. The present invention can accurately eliminate the influence of the transition resistance on the distance protection only by relying on the comprehensive sequence current on its own side when a single-phase ground fault occurs, accurately calculate the fault distance, thereby significantly improving the performance of the distance protection and ensuring the reliable and rapid operation of the distance protection during in-zone faults.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection in power systems, and in particular to a single-phase grounding fault distance protection method, device, equipment and medium for a double-ended weak system. Background Art

[0002] Single-phase grounding faults are the most common faults in the power grid, mostly occurring in humid and rainy weather. Single-phase grounding faults may generate overvoltages, burn out equipment, and even cause phase-to-phase short circuits, expanding accidents. Therefore, quickly identifying and removing faults is of great significance for ensuring system stability.

[0003] As an important part of transmission line protection, distance protection has been widely used in ultra-high voltage power grids. With the development of power electronics technology and new energy power generation technology, the scenario of double-ended weak systems has gradually increased. The access of new energy power sources to weak power grids is a typical double-ended weak system. After a fault occurs in the AC transmission line, different from the access of new energy power sources to strong power grids, the short-circuit current amplitudes on the system side and the new energy side are similar, and the zero-sequence current does not dominate. During a single-phase grounding fault, the influence of the transition resistance on the performance of the distance protection on the system side increases. Especially in the case of a large transition resistance, the performance of the distance protection on the system side deteriorates. Therefore, it is urgent to study the single-phase grounding fault distance protection method for the system side of double-ended weak systems to improve the line fault identification ability of double-ended weak systems.

[0004] The information disclosed in this background art section is only intended to deepen the understanding of the overall background art of the present invention, and should not be regarded as an admission or any form of implication that this information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The present invention provides a single-phase grounding fault distance protection method, device, equipment and medium for a double-ended weak system, thereby effectively solving the problems in the background art.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a single-phase grounding fault distance protection method for a double-ended weak system, including the following steps:

[0007] Set the protection start criterion when a single-phase grounding fault occurs in the transmission line;

[0008] When a single-phase grounding fault occurs in the transmission line where a new energy power source is connected to a weak power grid and the protection start criterion is satisfied, obtain the composite sequence network diagram of the single-phase grounding fault, and construct a closed curve in the composite sequence network diagram;

[0009] Based on Kirchhoff's current law, use the negative-sequence current and zero-sequence current on the system side to calculate the zero-sequence current on the new energy side;

[0010] Calculate the fault distance based on the current relationship between the system side and the new energy power source;

[0011] Perform fault identification on the fault distance and carry out fault protection according to the set conditions.

[0012] Furthermore, the protection startup criterion includes:

[0013]

[0014] In the formula, is the relative ground voltage of the system side. When the voltage of a certain phase drops below 0.9 pu, the protection starts.

[0015] Furthermore, constructing a closed curve in the composite sequence network diagram includes:

[0016] Set the new energy power source side of the negative sequence network in the composite sequence network diagram to be open;

[0017] Let the zero-sequence current of the new energy power source side and the zero-sequence current of the system side flow into the closed curve, and the negative-sequence current of the system side flow out of the closed curve.

[0018] Furthermore, calculating the zero-sequence current of the new energy side by using the negative-sequence current and zero-sequence current of the system side includes:

[0019]

[0020] Furthermore, calculating the fault distance includes the following steps:

[0021] Obtain an equation about the fault distance α by making the voltage division of the zero-sequence currents on the impedance of the system side and the new energy power source side equal;

[0022] Eliminate the current of the new energy power source side, and calculate the fault distance α based on the negative-sequence and zero-sequence currents flowing through the protection on the system side.

[0023] Furthermore, the equation of the fault distance α is:

[0024]

[0025] In the formula, is the zero-sequence current of the new energy power source side, is the zero-sequence current of the system side, Z Inv-T 0 is the zero-sequence impedance of the step-up transformer on the new energy power source side, Z L 0 is the zero-sequence impedance of the AC transmission line, Z G 0is the equivalent zero-sequence impedance of the weak power grid.

[0026] Further, the calculated fault distance α includes:

[0027] Based on the equation of the fault distance α, solve for the fault distance to obtain:

[0028]

[0029] Eliminate the current on the new energy power supply side, and the fault distance α calculated by the system side based on the negative-sequence and zero-sequence currents flowing through the local protection is:

[0030]

[0031] Further, the fault protection according to the set conditions includes:

[0032] When the fault distance α is less than α set.1 , the protection trips without delay; when α is less than α set.2 but greater than α set.1 , the protection trips with a delay of Δt, where α set.1 and α set.2 are respectively the set first fault distance value and the second fault distance value, and α set.1 is less than α set.2 .

[0033] The present invention also includes a single-phase ground fault distance protection device for a double-ended weak system, which uses the method as described above. The device includes:

[0034] A protection start criterion unit for setting the protection start criterion when a single-phase ground fault occurs on the transmission line;

[0035] A closed curve unit for obtaining a single-phase ground fault composite sequence network diagram and constructing a closed curve in the composite sequence network diagram when a single-phase ground fault occurs on the transmission line where the new energy power supply is connected to the weak power grid and the protection start criterion is satisfied;

[0036] A zero-sequence current calculation unit for calculating the zero-sequence current on the new energy side by using the negative-sequence current and zero-sequence current on the system side based on Kirchhoff's current law;

[0037] A fault distance calculation unit for eliminating the current on the new energy power supply side through the current relationship between the system side and the new energy power supply, and calculating the fault distance based on the negative-sequence current and zero-sequence current flowing through the system side protection;

[0038] A fault protection unit for fault identification of the fault distance and performing fault protection according to the set conditions.

[0039] The present invention further includes a computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the above-mentioned method is implemented.

[0040] The present invention further includes a storage medium, on which a computer program is stored. When the computer program is executed by a processor, the above-mentioned method is implemented.

[0041] The beneficial effects of the present invention are as follows: When a single-phase grounding fault occurs, the present invention can accurately eliminate the influence of the transition resistance on the distance protection only relying on the comprehensive sequence current on its own side, accurately calculate the fault distance, thereby significantly improving the performance of the distance protection and ensuring the reliable and rapid operation of the distance protection in the event of an in-zone fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0043] Figure 1 It is a flowchart of the method in Embodiment 1;

[0044] Figure 2 It is a structural schematic diagram of the device in Embodiment 1;

[0045] Figure 3 It is a transmission line system diagram of a new energy power source accessing a weak power grid in Embodiment 2;

[0046] Figure 4 It is a flowchart of the single-phase grounding fault distance protection method for a double-ended weak system in Embodiment 2;

[0047] Figure 5 It is a composite sequence network diagram during single-phase grounding in Embodiment 2;

[0048] Figure 6 It is a closed curve in the composite sequence network diagram in Embodiment 2;

[0049] Figure 7 It is the calculation results of the fault distance of the method of the present invention when an A-phase grounding fault occurs at 20%, 50%, and 90% through a 1Ω transition resistance;

[0050] Figure 8 It is the calculation results of the fault distance of the traditional method when an A-phase grounding fault occurs at 20%, 50%, and 90% through a 1Ω transition resistance;

[0051] Figure 9The fault distance calculation results of the method of the present invention when a phase A ground fault occurs through a 10Ω transition resistance at 20%, 50%, and 90%;

[0052] Figure 10 The fault distance calculation results of the traditional method when a phase A ground fault occurs through a 10Ω transition resistance at 20%, 50%, and 90%;

[0053] Figure 11 The fault distance calculation results of the method of the present invention when a phase A ground fault occurs through a 100Ω transition resistance at 20%, 50%, and 90%;

[0054] Figure 12 The fault distance calculation results of the traditional method when a phase A ground fault occurs through a 100Ω transition resistance at 20%, 50%, and 90%;

[0055] Figure 13 The fault distance calculation results of the method of the present invention when a phase A ground fault occurs through a 100Ω transition resistance at 20%, 50%, and 90% (the output power of the new energy power source becomes 0.1 pu);

[0056] Figure 14 The fault distance calculation results of the traditional method when a phase A ground fault occurs through a 100Ω transition resistance at 20%, 50%, and 90% (the output power of the new energy power source becomes 0.1 pu);

[0057] Figure 15 The structural schematic diagram of the computer device of the present invention. Specific embodiments

[0058] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0059] Embodiment 1:

[0060] As Figure 1 shown: A single-phase ground fault distance protection method for a double-ended weak system includes the following steps:

[0061] Set the protection start criterion when a single-phase ground fault occurs on the transmission line;

[0062] When a single-phase ground fault occurs on the transmission line where the new energy power source is connected to the weak power grid and the protection start criterion is met, obtain the composite sequence network diagram of the single-phase ground fault, and construct a closed curve in the composite sequence network diagram;

[0063] Based on Kirchhoff's current law, use the negative sequence current and zero sequence current on the system side to calculate the zero sequence current on the new energy side;

[0064] Calculate the fault distance based on the current relationship between the system side and the new energy power source;

[0065] Conduct fault identification on the fault distance and perform fault protection according to the set conditions.

[0066] Utilize the characteristic of the open - circuit negative - sequence current on the new energy power source side. Based on the negative - sequence current and zero - sequence current flowing through the protection installation on the system side (this side), deduce the zero - sequence current on the new energy power source side (the opposite side), and then calculate the fault distance. Finally, conduct fault identification based on the calculated fault distance. The method in this embodiment enables the protection to accurately calculate the fault distance when a single - phase grounding fault occurs on the double - ended weak system line where the new energy power source is connected to a weak power grid, ensures the reliable and rapid operation of the distance protection during in - zone faults, significantly improves the fault - identification ability of the double - ended weak system line, and has strong practical engineering application value.

[0067] In this embodiment, the protection startup criterion includes:

[0068]

[0069] In the formula, is the relative - to - ground voltage on the system side. When the voltage of a certain phase drops below 0.9 pu, the protection starts.

[0070] Construct a closed curve in the composite sequence network diagram, including:

[0071] Set the new energy power source side of the negative - sequence network in the composite sequence network diagram to be open - circuit;

[0072] Let the zero - sequence current on the new energy power source side and the zero - sequence current on the system side flow into the closed curve, and the negative - sequence current on the system side flow out of the closed curve.

[0073] Among them, deducing the zero - sequence current on the new energy side using the negative - sequence current and zero - sequence current on the system side includes:

[0074]

[0075] As an optimization of the above - mentioned embodiment, calculating the fault distance includes the following steps:

[0076] Obtain an equation about the fault distance α using the equal voltage division of the zero - sequence current on the system side and the new energy power source side in impedance;

[0077] Eliminate the current on the new energy power source side, and calculate the fault distance α on the system side based on the negative - sequence and zero - sequence currents flowing through the protection on this side.

[0078] In this embodiment, the equation of the fault distance α is:

[0079]

[0080] In the formula, is the zero-sequence current on the new energy power source side, is the zero-sequence current on the system side, and Z Inv-T 0 is the zero-sequence impedance of the step-up transformer on the new energy power source side, and Z L 0 is the zero-sequence impedance of the AC transmission line, and Z G 0 is the equivalent zero-sequence impedance of the weak power grid.

[0081] Among them, the calculated fault distance α includes:

[0082] Based on the equation of the fault distance α, solve the fault distance to obtain:

[0083]

[0084] Eliminate the current on the new energy power source side, and the fault distance α calculated by the system side based on the negative-sequence and zero-sequence currents flowing through the local protection is:

[0085]

[0086] As a preference of the above embodiment, perform fault protection according to the set conditions, including:

[0087] When the fault distance α is less than α set.1 , the protection trips without delay; when α is less than α set.2 but greater than α set.1 , the protection trips with a delay of Δt. α set.1 and α set.2 are respectively the set first fault distance value and second fault distance value, and α set.1 is less than α set.2 .

[0088] As Figure 2 shown, this embodiment also includes a single-phase grounding fault distance protection device for a double-ended weak system. Using the method as described above, the device includes:

[0089] A protection startup criterion unit for setting the protection startup criterion when a single-phase grounding fault occurs on the transmission line;

[0090] A closed curve unit for obtaining the composite sequence network diagram of the single-phase grounding fault and constructing a closed curve in the composite sequence network diagram when a single-phase grounding fault occurs on the transmission line where the new energy power source is connected to the weak power grid and the protection startup criterion is met;

[0091] The zero-sequence current calculation unit, based on Kirchhoff's current law, calculates the zero-sequence current on the new energy side by using the negative-sequence current and zero-sequence current on the system side;

[0092] The fault distance calculation unit is used to eliminate the current on the new energy power source side through the current relationship between the system side and the new energy power source, and calculates the fault distance based on the negative-sequence current and zero-sequence current flowing through the system side protection;

[0093] The fault protection unit is used to identify faults for the fault distance and perform fault protection according to the set conditions.

[0094] Embodiment 2:

[0095] In order to overcome the problem of incorrect operation of the in-zone fault during a single-phase ground fault in the traditional transmission line distance protection in a double-ended weak system where a new energy power source is connected to a weak power grid, this embodiment proposes a single-phase ground fault distance protection method for a double-ended weak system based on comprehensive sequence current. The system diagram of the new energy power source connected to the weak power grid is as Figure 3 shown. Generally, the new energy power source is connected to the power grid through a transformer step-up and then through an extra-high voltage AC transmission line. At this time, the weak power grid provides a small short-circuit current, and the short-circuit current provided by the new energy power source is only 1-2 times its rated current, and a negative-sequence current suppression strategy is adopted during the fault. When a single-phase ground fault occurs on the transmission line, the short-circuit current amplitudes on the system side and the new energy power source side are similar. The phase-controlled characteristic of the short-circuit current on the new energy power source side has a great impact on the system side distance protection under a single-phase ground fault through a transition resistance, resulting in a decrease in the sensitivity of the system side distance protection or even refusal to operate.

[0096] As Figure 4 shown, a single-phase ground fault distance protection method for a double-ended weak system based on comprehensive sequence current is as follows:

[0097] (1) When a single-phase ground fault occurs on the transmission line where the new energy power source is connected to the weak power grid, the voltage of the fault phase drops, and the protection starts. The starting criterion is as follows:

[0098]

[0099] In the formula, is the relative ground voltage on the system side. When the voltage of a certain phase drops below 0.9 pu, the protection starts.

[0100] (2) When a single-phase ground fault (taking phase A grounding as an example) occurs on the transmission line where the new energy power source is connected to the weak power grid, the composite sequence network diagram is as Figure 5 shown.

[0101] In the figure, α is the fault distance, R g is the grounding transition resistance, is the A-phase equivalent voltage source of the weak power grid, is the positive-sequence current of phase A flowing into the ground at the fault point, is the negative-sequence current of phase A at the protection installation location on the new energy power source side, is the negative-sequence current of phase A at the protection installation location on the system side, is the zero-sequence current of phase A at the protection installation location on the new energy power source side, is the zero-sequence current of phase A at the protection installation location on the system side, Z Inv-T + , Z Inv-T - and Z Inv-T 0 are respectively the positive-sequence impedance, negative-sequence impedance and zero-sequence impedance of the step-up transformer on the new energy power source side, Z L + , Z L - and Z L 0 are respectively the positive-sequence impedance, negative-sequence impedance and zero-sequence impedance of the AC transmission line, Z G + , Z G - and Z G 0 are respectively the equivalent positive-sequence impedance, negative-sequence impedance and zero-sequence impedance of the weak power grid.

[0102] (3) The measured impedance of the traditional ground distance protection on the system side is shown in the following formula:

[0103]

[0104] In the formula, Z AG is the measured impedance of the phase A ground distance protection, is the phase A voltage on the system side, is the phase A current on the system side, is the phase A current on the new energy power source side, Z L is the transmission line impedance, is the zero-sequence current on the system side, K is the zero-sequence compensation coefficient (K = (z0 - z1) / (3z1), z1 is the positive-sequence impedance per unit length of the AC transmission line, z0 is the zero-sequence impedance per unit length of the AC transmission line), Z add is the additional impedance caused by the transition resistance.

[0105] When the new energy power source is connected to a strong power grid, will be much larger than Therefore, Z add the numerator and denominator of will be mainly composed of Even if shows the characteristics of phase control, it will be affected by is submerged, so Z add The amplitude will not be very large and the phase will be close to zero degrees.

[0106] However, when a new energy power source is connected to a weak power grid, and have similar amplitudes, showing the characteristics of phase control, Z add it will show a situation where the phase seriously deviates from zero degrees, resulting in the measured impedance seriously deviating from the actual impedance and causing the distance protection to fail. The following presents a solution to this problem.

[0107] (4) Based on Figure 5 the shown composite sequence network diagram, since the new energy power source usually adopts a control strategy to suppress negative sequence current, the new energy power source side in the negative sequence network is open. Construct a closed curve in the composite sequence network diagram, as Figure 6 shown, and flow into the closed curve, flow out of the closed curve.

[0108] Based on Kirchhoff's current law, the following formula can be obtained, that is, the zero-sequence current on the new energy power source side is deduced using the negative-sequence current and zero-sequence current on the system side.

[0109]

[0110] (5) Use the equal voltage division of the zero-sequence current on the system side and the new energy power source side on the impedance to obtain an equation about α.

[0111]

[0112] (6) By solving α in formula (4), we can get:

[0113]

[0114] Combined with the current relationship between the system side and the new energy power source side in formula (3), the current on the new energy power source side can be further eliminated. The fault distance α calculated by the system side based on the negative-sequence and zero-sequence currents flowing through the local protection is:

[0115]

[0116] According to the fault distance obtained in (6) for fault identification, when α is less than α set.1 , the protection trips without delay; when α is less than α set.2 but greater than α set.1 , the protection trips with a delay of Δt.

[0117] The following is a further description of the present embodiment in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present embodiment, and cannot be used to limit the protection scope of the present embodiment.

[0118] The system diagram of new energy power supply connected to weak power grid is as follows Figure 3 As shown. The short-circuit current provided by the power grid is low and the system equivalent impedance is large. The short-circuit current amplitude provided by the new energy power source is only 1-2 times of its rated current. In this specific embodiment, the new energy power source takes the photovoltaic station as an example. After the photovoltaic power generation units are collected, they are stepped up and connected to the 220kV AC transmission line through two transformers with a capacity of 240MVA. set.1 Take 0.8, α set.2 Take 1.2, Δt take 0.5s, and the other system parameters are shown in the following table.

[0119] Table 1 Main parameters of new energy power sources and weak power grids

[0120]

[0121]

[0122] The sequence impedance and admittance parameters of the 220kV AC transmission line are shown in Table 2. The line length is 80km.

[0123] Table 2 Main parameters of 220kV AC transmission line

[0124]

[0125] In this embodiment, the subsequent conventional distance protection fault distance is calculated by dividing the imaginary part of the measured impedance calculated by equation (2) by the line unit reactance.

[0126] (1) Figure 3 When the new energy power source is connected to the weak grid transmission line at 20%, 50% and 90% and a phase A grounding fault occurs through a 1Ω transition resistor, the fault distance calculation result of the method in this embodiment is as follows: Figure 7 As shown in the figure, the fault distance calculation results of traditional distance protection are as follows Figure 8 shown.

[0127] Depend on Figure 7 - Figure 8It can be seen that when an A-phase ground fault occurs at 20%, 50%, and 90% of the transmission line of the new energy power source connected to the weak power grid through a 1Ω transition resistance, the calculated fault distances in this embodiment are 19.5%, 49.9%, and 90.3% respectively, and the relative errors are 2.5%, 0.2%, and 0.33% respectively, accurately reflecting the actual fault distance. Although the traditional method operates correctly, the calculated fault distances are 0.65%, 16.7%, and 58.5% respectively, and the relative errors are 96.8%, 66.6%, and 35.0% respectively. When the fault is 90%, the first section of the distance protection operates, there is a risk of misoperation. It should be noted that the calculated fault distance in this embodiment and the calculated fault distance of the traditional distance protection mentioned here are both the steady-state values after the fault.

[0128] (2) Figure 3 When an A-phase ground fault occurs at 20%, 50%, and 90% of the transmission line of the new energy power source connected to the weak power grid through a 10Ω transition resistance in Figure 9 as shown, the calculated results of the fault distance of the traditional distance protection are as Figure 10 shown.

[0129] From Figure 9 - Figure 10 It can be seen that when an A-phase ground fault occurs at 20%, 50%, and 90% of the transmission line of the new energy power source connected to the weak power grid through a 10Ω transition resistance, the calculated fault distances in this embodiment are 20.3%, 50.3%, and 90.4% respectively, and the relative errors are 1.5%, 0.5%, and 0.44% respectively, accurately reflecting the actual fault distance. The calculated fault distances of the traditional method are -172.7%, -192.0%, and -224.7% respectively, and the relative errors are all greater than 100%. The error is much larger than that of the method in this embodiment, and the distance protection action criterion is not satisfied, so the distance protection does not operate.

[0130] (3) Figure 3 When an A-phase ground fault occurs at 20%, 50%, and 90% of the transmission line of the new energy power source connected to the weak power grid through a 100Ω transition resistance in Figure 11 as shown, the calculated results of the fault distance of the traditional distance protection are as Figure 12 shown.

[0131] From Figure 11 - Figure 12It can be seen that when an A-phase ground fault occurs through a 100Ω transition resistance at the 20%, 50%, and 90% positions of the transmission line where the new energy power source is connected to the weak power grid, the calculated fault distances in this embodiment are 20.0%, 50.1%, and 90.2% respectively, and the relative errors are 0%, 0.2%, and 0.22% respectively, accurately reflecting the actual fault distance. The fault distances calculated by the traditional method are -2247.3%, -2756.0%, and -3885.8% respectively, and the relative errors are all greater than 100%. The error is much larger than that of the method in this embodiment, and the distance protection action criterion is not satisfied, so the distance protection does not operate.

[0132] (1) to (3) The test results are summarized in the following table.

[0133] Table 3 Comparison of the performance of the method in this embodiment and traditional distance protection

[0134]

[0135] As can be seen from the above table, as the transition resistance increases, the calculation error of the fault distance of the traditional distance protection gradually increases. This is because the increase in the transition resistance leads to an increase in the additional impedance. Therefore, it is difficult for the traditional distance protection to correctly reflect the fault distance. However, since the method in this embodiment eliminates the influence of the transition resistance at the theoretical level, the calculation error of the fault distance is hardly affected by the increase in the transition resistance, and the error can be maintained at a low level.

[0136] (4) Next, test the performance of the method in this embodiment when the output power of the new energy power source changes. When the output power of the new energy power source becomes 0.1 pu, Figure 3 When an A-phase ground fault occurs through a 100Ω transition resistance at the 20%, 50%, and 90% positions of the transmission line where the new energy power source is connected to the weak power grid, the calculated results of the fault distance by the method in this embodiment are as Figure 13 shown, and the calculated results of the fault distance of the traditional distance protection are as Figure 14 shown.

[0137] From Figure 13 - Figure 14 it can be seen that when the output power of the new energy power source becomes 0.1 pu and an A-phase ground fault occurs through a 100Ω transition resistance at the 20%, 50%, and 90% positions of the transmission line where the new energy power source is connected to the weak power grid, the calculated fault distances in this embodiment are 20.0%, 50.1%, and 90.2% respectively, and the relative errors are 0%, 0.2%, and 0.22% respectively, accurately reflecting the actual fault distance and not being affected by the change in the operation mode of the new energy power source. The fault distances calculated by the traditional method are -178.8%, -188.8%, and -206.2% respectively, and the relative errors are all greater than 100%. The error is much larger than that of the method in this embodiment, and the distance protection action criterion is not satisfied, so the distance protection does not operate.

[0138] Utilize the characteristic of open - circuit negative - sequence current on the new - energy power - source side. Based on the negative - sequence current and zero - sequence current flowing through the protection installation location on the system side (this side), calculate the zero - sequence current on the new - energy power - source side (the opposite side), and then calculate the fault distance. Finally, perform fault identification according to the calculated fault distance. The method of this embodiment enables the protection to accurately calculate the fault distance when a single - phase grounding fault occurs in a double - ended weak - system line where a new - energy power source is connected to a weak power grid, ensures the reliable and rapid operation of the distance protection for in - zone faults, significantly improves the fault - identification ability of the double - ended weak - system line, and has strong practical engineering application value.

[0139] Please refer to Figure 15 The structural schematic diagram of the computer device provided by the embodiment of the present application shown in. A computer device 400 provided by the embodiment of the present application includes: a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410. When the computer program is executed by the processor 410, it executes the above - mentioned method.

[0140] The embodiment of the present application also provides a storage medium 430. A computer program is stored on the storage medium 430. When the computer program is run by the processor 410, it executes the above - mentioned method.

[0141] Among them, the storage medium 430 can be implemented by any type of volatile or non - volatile storage device or a combination thereof, such as static random - access memory (SRAM for short), electrically erasable programmable read - only memory (EEPROM for short), erasable programmable read - only memory (EPROM for short), programmable read - only memory (PROM for short), read - only memory (ROM for short), magnetic memory, flash memory, a magnetic disk or an optical disc.

[0142] In the description of the present invention, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. The meaning of "a plurality" is two or more, unless otherwise clearly and specifically defined.

[0143] In the present invention, unless otherwise clearly defined and limited, the terms "installed", "connected", "coupled", "fixed", etc. shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral one; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0144] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without conflict, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0145] Any process or method description shown in a flowchart or described in other ways herein can be understood to represent a module, segment, or portion of code including one or more executable instructions for implementing a specific logical function or process. The scope of the preferred embodiments of the present invention includes additional implementations, where the functions may be executed in a substantially simultaneous manner or in a reverse order according to the functions involved, rather than in the order shown or discussed, which should be understood by those skilled in the art to which the embodiments of the present invention pertain.

[0146] The logic and / or steps represented in the flowchart or otherwise described herein can, for example, be considered as a definitional sequence of executable instructions for implementing logical functions and can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, a system including a processor, or other systems that can fetch and execute instructions from the instruction execution system, apparatus, or device. As used in this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples of the computer-readable medium (a non-exhaustive list) include the following: an electrical connection portion with one or more wirings (electronic device), a portable computer diskette (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium can even be paper or other suitable medium on which the program can be printed, as the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpretation, or otherwise processing as appropriate, and then storing it in a computer memory.

[0147] It should be understood that various parts of the present invention can be implemented by hardware, software, firmware, or a combination thereof. In the above-described embodiments, multiple steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, any one or a combination of the following techniques well known in the art can be used: discrete logic circuits having logic gate circuits for implementing logical functions on data signals, application specific integrated circuits having appropriate combinational logic gate circuits, programmable gate arrays (PGAs), field programmable gate arrays (FPGAs), etc.

[0148] Those of ordinary skill in the art of this technology can understand that all or part of the steps carried by the method of implementing the above embodiments can be completed by a program instructing relevant hardware, and the program can be stored in a computer-readable storage medium. When the program is executed, it includes one or a combination of the steps of the method embodiments.

[0149] The above-mentioned storage medium can be a read-only memory, a magnetic disk, an optical disc, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A double-terminal weak system single-phase grounding fault distance protection method, characterized in that: The steps include: Set the protection start-up criteria when a single-phase grounding fault occurs on the transmission line; When a single-phase grounding fault occurs in a transmission line where a new energy power source is connected to a weak power grid and the protection start criterion is met, a composite sequence network diagram of the single-phase grounding fault is obtained, and a closed curve is constructed in the composite sequence network diagram; Based on Kirchhoff's current law, the zero-sequence current on the renewable energy side is calculated using the negative-sequence current and zero-sequence current on the system side. Calculate the fault distance through the current relationship between the system side and the new energy power supply; Identify faults based on the fault distance and perform fault protection according to the set conditions; The calculating of the fault distance comprises the following steps: The equation about the fault distance α is obtained by using the equal partial pressure of the zero-sequence current on the system side and the new energy power supply side on the impedance; Eliminate the current on the renewable energy power supply side, and calculate the fault distance α based on the negative-sequence and zero-sequence currents flowing through the protection on this side; The equation for the fault distance α is: In the formula, is the zero-sequence current on the renewable energy power supply side, is the zero sequence current on the system side, Z Inv-T 0 is the zero-sequence impedance of the step-up transformer on the new energy power supply side, Z L 0 is the zero-sequence impedance of the AC transmission line, Z G 0 is the equivalent zero-sequence impedance of the weak power grid; The calculated fault distance α includes: Based on the equation of the fault distance α, the fault distance is solved to obtain: Eliminate the current on the renewable energy power supply side, and the fault distance α calculated by the system side based on the negative-sequence and zero-sequence currents flowing through the protection on this side is: The fault protection according to the set conditions includes: When the fault distance α is less than α set.1 , the protection trips without delay; when α is less than α set.2 But greater than α set.1 , protection delay △t tripping, α set.1 and α set.2 are the first fault distance value and the second fault distance value set respectively, and α set.1 Less than α set.2 .

2. The double-terminal weak system single-phase grounding fault distance protection method according to claim 1 is characterized in that: The protection start criteria include: In the formula, It is the voltage relative to the ground on the system side. When the voltage of one phase drops below 0.9pu, the protection starts.

3. The double-terminal weak system single-phase grounding fault distance protection method according to claim 1 is characterized in that: The constructing a closed curve in the composite sequence network graph comprises: The zero-sequence current on the new energy power supply side and system side zero sequence current Flow into the closed curve, the negative sequence current on the system side Flow out of the closed curve.

4. The double-terminal weak system single-phase grounding fault distance protection method according to claim 3 is characterized in that: The method of calculating the zero-sequence current on the renewable energy side by using the negative-sequence current and the zero-sequence current on the system side includes:

5. A double-terminal weak system single-phase grounding fault distance protection device, characterized in that: Using the method according to any one of claims 1 to 4, the device comprises: A protection start criterion unit is used to set the protection start criterion when a single-phase grounding fault occurs in the transmission line; A closed curve unit is used to obtain a composite sequence network diagram of a single-phase grounding fault when a single-phase grounding fault occurs in a transmission line of a new energy power source connected to a weak power grid and the protection start criterion is met, and to construct a closed curve in the composite sequence network diagram; The zero-sequence current calculation unit uses the negative-sequence current and zero-sequence current on the system side to calculate the zero-sequence current on the renewable energy side based on Kirchhoff's current law; A fault distance calculation unit is used to eliminate the current on the new energy power supply side through the current relationship between the system side and the new energy power supply, and calculate the fault distance based on the negative sequence current and zero sequence current flowing through the system side protection; The fault protection unit is used to identify the fault distance and perform fault protection according to the set conditions.

6. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 4 is implemented.

7. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 4 is implemented.

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