Double-end weak system single-phase earth fault distance protection method, device, equipment and medium

Abstract

The invention relates to the technical field of power system relay protection, in particular to a double-end weak system single-phase earth fault distance protection method, device and equipment and a medium, and the method comprises the steps: setting a protection starting criterion when a power transmission line has a single-phase earth fault; when the protection starting criterion is met, a single-phase earth fault composite sequence network diagram is obtained, and a closed curve is constructed in the composite sequence network diagram; on the basis of the Kirchhoff's current law, calculating the zero-sequence current of the new energy side by using the negative-sequence current and the zero-sequence current of the system side; the fault position is calculated through the current relation between the system side and the new energy power supply; fault identification is carried out on the fault position, and fault protection is carried out according to set conditions. According to the method, when a single-phase earth fault occurs, the influence of transition resistance on distance protection can be accurately eliminated only through the comprehensive sequence current on the side, and the fault distance is accurately calculated, so that the performance of distance protection is remarkably improved, and reliable and rapid action of distance protection in case of an internal fault is ensured.

Description

Technical Field

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

[0002] Single-phase grounding fault is the most common fault in the power grid, which often occurs in humid and rainy weather. Single-phase grounding fault may generate overvoltage, burn equipment, and even cause phase-to-phase short circuit and expand the accident. Rapid identification and removal of faults are of great significance to ensure 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, two-terminal weak system scenarios have gradually increased. The access of new energy power sources to weak power grids is a typical two-terminal weak system. After the AC transmission line fails, unlike 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 is not dominant. As a result, during single-phase grounding faults, the distance protection performance on the system side is more affected by the transition resistance, especially in the case of large transition resistance, the distance protection performance on the system side decreases. Therefore, it is urgent to study the distance protection method for single-phase grounding faults on the system side of the two-terminal weak system to improve the fault identification capability of the two-terminal weak system line.

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

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

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

[0007] Set the protection start-up criteria when a single-phase grounding fault occurs on the transmission line;

[0008] 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;

[0009] 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.

[0010] Calculate the fault distance through the current relationship between the system side and the new energy power supply;

[0011] Fault identification is performed based on the fault distance, and fault protection is performed according to the set conditions.

[0012] Furthermore, the protection start criterion includes:

[0013]

[0014] 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.

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

[0016] Set the negative-sequence network new energy power supply side in the composite sequence network diagram to be open circuit;

[0017] 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.

[0018] Furthermore, 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:

[0019]

[0020] Further, the calculating of the fault distance comprises the following steps:

[0021] 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;

[0022] 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.

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

[0024]

[0025] 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 0is the equivalent zero-sequence impedance of the weak power grid.

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

[0027] Based on the equation of the fault distance α, the fault distance is solved to obtain:

[0028]

[0029] 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:

[0030]

[0031] Further, the performing 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 , protection delay Δt 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 .

[0033] The present invention also includes a double-terminal weak system single-phase grounding fault distance protection device, using the above method, the device includes:

[0034] A protection start criterion unit is used to set the protection start criterion when a single-phase grounding fault occurs in the transmission line;

[0035] 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;

[0036] 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;

[0037] 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;

[0038] The fault protection unit is used to identify the fault distance and perform fault protection according to the set conditions.

[0039] The present invention also includes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method described above is implemented.

[0040] The present invention also includes a storage medium on which a computer program is stored. When the computer program is executed by a processor, the method described above 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 transition resistance on distance protection by relying only on the comprehensive sequence current on this side, accurately calculate the fault distance, thereby significantly improving the performance of distance protection and ensuring reliable and rapid operation of distance protection when faults occur in the area. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 is a flow chart of the method in Example 1;

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

[0045] Figure 3 A transmission line system diagram of the new energy power source connected to the weak power grid in Example 2;

[0046] Figure 4 This is a flow chart of the double-terminal weak system single-phase grounding fault distance protection method in Example 2;

[0047] Figure 5 This is the composite sequence network diagram when the single-phase is grounded in Example 2;

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

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

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

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

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

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

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

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

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

[0057] Fig.15 It is a structural schematic diagram of the computer device of the present invention. DETAILED DESCRIPTION

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

[0059] Embodiment 1:

[0060] like Figure 1 As shown: A double-terminal weak system single-phase grounding fault distance protection method includes the following steps:

[0061] Set the protection start-up criteria when a single-phase grounding fault occurs on the transmission line;

[0062] When a single-phase grounding fault occurs in the transmission line where the new energy power source is connected to the weak power grid and the protection start-up 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;

[0063] 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.

[0064] Calculate the fault distance through the current relationship between the system side and the new energy power supply;

[0065] Fault identification is performed based on the fault distance, and fault protection is performed according to the set conditions.

[0066] By utilizing the characteristics of the negative sequence current open circuit on the new energy power supply side, the zero sequence current on the new energy power supply side (opposite side) is calculated based on the negative sequence current and zero sequence current flowing through the protection installation on the system side (this side), and then the fault distance is calculated, and finally the fault identification is performed according to 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 in a two-terminal weak system line such as a new energy power supply connected to a weak power grid, so as to ensure reliable and rapid action of the distance protection in the event of an in-area fault, significantly improve the fault identification capability of the two-terminal weak system line, and has a strong practical engineering application value.

[0067] In this embodiment, the protection start criteria include:

[0068]

[0069] 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.

[0070] Construct closed curves in a composite sequence network graph, including:

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

[0072] 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.

[0073] Among them, the zero-sequence current on the renewable energy side is calculated using the negative-sequence current and zero-sequence current on the system side, including:

[0074]

[0075] As a preferred embodiment of the above, calculating the fault distance includes the following steps:

[0076] 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;

[0077] 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.

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

[0079]

[0080] 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.

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

[0082] Based on the equation of fault distance α, the fault distance is solved and obtained:

[0083]

[0084] 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:

[0085]

[0086] As a preferred embodiment of the above, performing fault protection according to set conditions includes:

[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 , protection delay Δt 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 .

[0088] like Figure 2 As shown, this embodiment also includes a double-terminal weak system single-phase grounding fault distance protection device, using the above method, the device includes:

[0089] A protection start criterion unit is used to set the protection start criterion when a single-phase grounding fault occurs in the transmission line;

[0090] The closed curve unit is used to obtain a composite sequence network diagram of the single-phase grounding fault when a single-phase grounding fault occurs in the transmission line of the new energy power source connected to the weak power grid and the protection start criterion is met, and a closed curve is constructed in the composite sequence network diagram;

[0091] 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;

[0092] 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;

[0093] The fault protection unit is used to identify 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 traditional transmission line distance protection during single-phase grounding faults in two-terminal weak systems such as new energy power sources connected to weak power grids, this embodiment proposes a two-terminal weak system single-phase grounding fault distance protection method based on comprehensive sequence current. Figure 3 As shown in the figure, new energy power sources are generally connected to the power grid through ultra-high voltage AC transmission lines after being stepped up by transformers. At this time, the short-circuit current provided by the weak power grid is small, and the short-circuit current provided by the new energy power source is only 1-2 times of its rated current, and a negative sequence current suppression strategy is adopted during the fault. When a single-phase grounding fault occurs in the transmission line, the short-circuit current amplitudes on the system side and the new energy power source side are similar. The phase-controlled characteristics of the short-circuit current on the new energy power source side have a greater impact on the distance protection on the system side under a single-phase grounding fault through a transition resistor, thereby reducing the sensitivity of the distance protection on the system side or even causing it to refuse to operate.

[0096] like Figure 4 As shown in FIG. 1 , a distance protection method for single-phase grounding fault in a two-terminal weak system based on comprehensive sequence current is provided. The specific steps are as follows:

[0097] (1) When a single-phase grounding fault occurs in the transmission line of a new energy power source connected to a weak power grid, the voltage of the fault phase drops and the protection is activated. The activation criteria are as follows:

[0098]

[0099] In the formula, It is the voltage between the system side and the ground. When the voltage of a phase drops below 0.9pu, the protection starts.

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

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

[0102] (3) The measurement impedance of the traditional ground distance protection on the system side is as follows:

[0103]

[0104] In the formula, Z AG The impedance of the A phase ground distance protection is measured. is the system side A phase voltage, is the phase A current on the system side, is the phase A current on the new energy power supply 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=(z 0 -z 1 ) / (3z 1 ), z 1 is the positive sequence impedance per unit length of the AC transmission line, z 0 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 new energy sources are connected to the strong power grid, will be much greater than Therefore Z add The numerator and denominator of constitute, even if Showing phase-controlled characteristics, it will also be Flooded, so Z add The amplitude will not be very large and the phase will be close to zero.

[0106] However, when new energy sources are connected to weak power grids, and The amplitude is similar, It shows phase-controlled characteristics, Z add The phase will deviate seriously from zero, causing the measured impedance to deviate seriously from the actual impedance, resulting in the failure of distance protection. The following is a solution to this problem.

[0107] (4) Based on Figure 5 As shown in the composite sequence network diagram, since the new energy power supply usually adopts the control strategy of suppressing the negative sequence current, the new energy power supply side in the negative sequence network is open circuit, and a closed curve is constructed in the composite sequence network diagram, such as Figure 6 As 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 renewable energy power supply side is calculated using the negative-sequence current and zero-sequence current on the system side.

[0109]

[0110] (5) The equation about α is obtained by using the equal voltage division of the zero-sequence current on the system side and the new energy power supply side on the impedance.

[0111]

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

[0113]

[0114] Combined with the current relationship between the system side and the new energy power supply in formula (3), the current on the new energy power supply 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 protection on this side is:

[0115]

[0116] Fault identification is performed based on the fault distance obtained by (6). 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 delay Δt trips.

[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 a phase A grounding fault occurs at 20%, 50% and 90% of the new energy power supply connected to the weak power grid transmission line through a 1Ω transition resistor, the fault distances calculated by this embodiment are 19.5%, 49.9% and 90.3%, respectively, and the relative errors are 2.5%, 0.2% and 0.33%, respectively, which accurately reflect the actual fault distance. Although the traditional method works 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 distance protection stage I is activated, and there is a risk of false operation. It should be pointed out that the fault distance calculated by this embodiment and the fault distance calculated by the traditional distance protection mentioned here are both steady-state values ​​after the fault.

[0128] (2) 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 10Ω transition resistor, the fault distance calculation result of the method in this embodiment is as follows: Fig. 9 As shown in the figure, the fault distance calculation results of traditional distance protection are as follows Fig.10 shown.

[0129] Depend on Figure 9-10 It can be seen that when the A-phase grounding fault occurs at 20%, 50% and 90% of the new energy power supply connected to the weak power grid transmission line through the 10Ω transition resistor, the fault distances calculated by this embodiment are 20.3%, 50.3% and 90.4% respectively, and the relative errors are 1.5%, 0.5% and 0.44% respectively, which accurately reflects the actual fault distance. The fault distances calculated by the traditional method are -172.7%, -192.0% and -224.7% respectively, and the relative errors are all greater than 100%, which is much greater than the method of this embodiment, and the distance protection action criterion is not met, so the distance protection does not act.

[0130] (3) 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 100Ω transition resistor, the fault distance calculation result of the method in this embodiment is as follows: Fig.11 As shown in the figure, the fault distance calculation results of traditional distance protection are as follows Fig.12 shown.

[0131] Depend on Figure 11-Figure 12It can be seen that when the A-phase grounding fault occurs at 20%, 50% and 90% of the new energy power supply connected to the weak power grid transmission line through a 100Ω transition resistor, the fault distances calculated by this embodiment are 20.0%, 50.1% and 90.2% respectively, and the relative errors are 0%, 0.2% and 0.22% respectively, which accurately reflects 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%, which is much greater than the method of this embodiment, and the distance protection action criterion is not met, so the distance protection does not act.

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

[0133] Table 3 Comparison of performance between 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 fault distance calculation error of the traditional distance protection gradually increases. This is because the increase in transition resistance leads to an increase in additional impedance, so it is difficult for the traditional distance protection to correctly reflect the fault distance. However, since the method of this embodiment eliminates the influence of the transition resistance at the theoretical level, the fault distance calculation error is almost unaffected by the increase in transition resistance, and the error can be kept at a low level.

[0136] (4) Next, the performance of the method of this embodiment is tested when the output power of the new energy power source changes. When the output power of the new energy power source changes to 0.1 pu, Figure 3 When the A phase grounding fault occurs at 20%, 50% and 90% of the weak grid transmission line connected to the new energy power source through a 100Ω transition resistor, the fault distance calculation result of the method in this embodiment is as follows: Fig.13 As shown in the figure, the fault distance calculation results of traditional distance protection are as follows Fig.14 shown.

[0137] Depend on Figure 13-14 It can be seen that when the output power of the new energy power source becomes 0.1pu, and the A-phase grounding fault occurs at 20%, 50% and 90% of the new energy power source connected to the weak power grid transmission line through a 100Ω transition resistor, the fault distances calculated by this embodiment are 20.0%, 50.1% and 90.2%, respectively, and the relative errors are 0%, 0.2% and 0.22%, respectively, which accurately reflect the actual fault distance and are not 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%, which is much greater than the method of this embodiment, and the distance protection action criterion is not met, so the distance protection does not act.

[0138] By utilizing the open-circuit characteristics of the negative-sequence current on the new energy power supply side, the zero-sequence current on the new energy power supply side (opposite side) is calculated based on the negative-sequence current and zero-sequence current flowing through the protection installation on the system side (this side), and then the fault distance is calculated, and finally the fault is identified based on 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 two-terminal weak system line such as a new energy power supply connected to a weak power grid, ensuring reliable and rapid action of the distance protection in the event of an in-area fault, significantly improving the fault identification capability of the two-terminal weak system line, and having a strong practical engineering application value.

[0139] See also Fig.15 A computer device 400 provided in an embodiment of the present application includes: a processor 410 and a memory 420, wherein the memory 420 stores a computer program executable by the processor 410, and when the computer program is executed by the processor 410, the above method is executed.

[0140] The embodiment of the present application further provides a storage medium 430 on which a computer program is stored. When the computer program is run by the processor 410, the above method is executed.

[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), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable red-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, disk or optical disk.

[0142] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0143] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, 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 conjunction 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 do not necessarily refer 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, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0145] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention belong.

[0146] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic devices), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0147] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0148] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0149] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, 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 cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify 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; Fault identification is performed based on the fault distance, and fault protection is performed according to the set conditions.

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. The double-terminal weak system single-phase grounding fault distance protection method according to claim 1 is characterized in that: 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.

6. The double-terminal weak system single-phase grounding fault distance protection method according to claim 5 is characterized in that: 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.

7. The double-terminal weak system single-phase grounding fault distance protection method according to claim 6 is characterized in that: 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:

8. The double-terminal weak system single-phase grounding fault distance protection method according to claim 1 is characterized in that: 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 Δt 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 .

9. A double-terminal weak system single-phase ground fault distance protection device, characterized in that: Using the method according to any one of claims 1 to 8, 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.

10. 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 8 is implemented.

11. 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 8 is implemented.

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