High-resistance grounding fault longitudinal protection method and device based on double-terminal zero-sequence current ratio

Abstract

The present invention relates to a high-resistance grounding fault longitudinal protection method and device based on a double-terminal zero-sequence current ratio. The method comprises obtaining the upstream zero-sequence current and the downstream zero-sequence current of a single-phase grounding fault line in a low-resistance grounding distribution network system; if the upstream zero-sequence current is greater than the maximum unbalanced current of the low-resistance grounding distribution network system, the zero-sequence current ratio is calculated according to the upstream zero-sequence current and the downstream zero-sequence current to obtain the zero-sequence current ratio; if the zero-sequence current ratio meets the protection criterion, after a delay time T, the protection switch of the low-resistance grounding distribution network system is controlled to operate to cut off the fault line. The method obtains the upstream zero-sequence current and the downstream zero-sequence current of a single-phase grounding fault line in a low-resistance grounding distribution network system, calculates the zero-sequence current ratio under the condition that the upstream zero-sequence current is greater than the maximum unbalanced current, and controls the protection switch to operate to cut off the fault line when the zero-sequence current ratio meets the protection criterion, thereby realizing fault protection for the low-resistance grounding distribution network system.

Description

Technical Field

[0001] The present invention relates to the technical field of power system differential protection, and in particular to a high-resistance grounding fault longitudinal protection method and device based on double-terminal zero-sequence current ratio. Background Art

[0002] The distribution network with a low-resistance grounding at the neutral point needs to be equipped with zero-sequence overcurrent protection. In general, the setting calculation of the zero-sequence overcurrent protection action value needs to consider the influence of the capacitive current of the protected line and the maximum unbalanced current during normal operation. Therefore, the action value of the zero-sequence overcurrent protection is high. When a high-resistance grounding fault (HIF) occurs, the fault current is relatively small, and it is difficult for conventional zero-sequence overcurrent protection to identify high-resistance grounding faults. Although high-resistance faults do not affect the normal power supply of the system to the load, they can easily cause electric shock and electrical fire accidents. Therefore, it is of great significance to quickly and reliably detect high-resistance grounding faults in distribution networks with a low-resistance grounding at the neutral point.

[0003] The existing high-resistance grounding protection principle includes: first, the fault line is selected by using the relationship between the zero-sequence current of each outgoing line and the zero-sequence current of the neutral point during the fault; second, the zero-sequence voltage information is introduced on the basis of the existing zero-sequence current protection principle to correct the measured zero-sequence current, so that the corrected zero-sequence current measurement value is similar to the situation of the metallic grounding fault at the fault head end, thereby improving the protection sensitivity of the high-resistance grounding fault of the small resistance grounding system. The disadvantage is that the voltage quantity needs to be introduced. If the correction quantity is too large, the protection may malfunction; third, the high-resistance fault protection is realized by using the projection difference between the neutral point current and the zero-sequence current; fourth, an improved inverse time zero-sequence overcurrent protection is proposed to reduce the starting threshold value of the protection. The disadvantage is that the setting is complex, the flexibility is poor, and the synchronization and accuracy requirements of the equipment are high, which is difficult to meet the requirements on site. Therefore, if the existing zero-sequence overcurrent protection is applied to the differential protection of the high-resistance grounding fault of the distribution network, the differential protection will refuse to operate because the current of the high-resistance grounding fault is very small. Summary of the invention

[0004] The embodiment of the present invention provides a high-resistance grounding fault longitudinal protection method and device based on double-terminal zero-sequence current ratio, which is used to solve the technical problem that the existing differential protection for high-resistance grounding faults refuses to operate and cannot protect the distribution network.

[0005] In order to achieve the above purpose, the embodiment of the present invention provides the following technical solutions:

[0006] A high-resistance grounding fault pilot protection method based on double-terminal zero-sequence current ratio is applied to a low-resistance grounding distribution network system. The high-resistance grounding fault pilot protection method comprises the following steps:

[0007] Obtaining the upstream zero-sequence current and downstream zero-sequence current of a single-phase grounding fault line in a low-resistance grounding distribution network system;

[0008] If the upstream zero-sequence current is greater than the maximum unbalanced current of the low-resistance grounded distribution network system, a zero-sequence current ratio is obtained by calculation based on the upstream zero-sequence current and the downstream zero-sequence current;

[0009] If the zero-sequence current ratio meets the protection criterion, after a delay time T, the protection switch of the low-resistance grounding distribution network system is controlled to operate and cut off the fault line.

[0010] Preferably, obtaining the zero-sequence current ratio by calculation according to the upstream zero-sequence current and the downstream zero-sequence current includes: taking the absolute value of the ratio of the upstream zero-sequence current to the downstream zero-sequence current as the zero-sequence current ratio.

[0011] Preferably, the maximum unbalanced current is at least 3A, and the delay time T is the sum of the zero-sequence overcurrent action time limit and the time step of the low-resistance grounded distribution network system.

[0012] Preferably, the protection criterion is that the zero-sequence current ratio is greater than 20.

[0013] Preferably, the high-resistance grounding fault longitudinal protection method based on the two-terminal zero-sequence current ratio includes: if the upstream zero-sequence current is not greater than the maximum unbalanced current of the low-resistance grounding distribution network system, or if the zero-sequence current ratio does not meet the protection criterion, the protection switch of the low-resistance grounding distribution network system will not operate.

[0014] The present invention also provides a high-resistance grounding fault pilot protection device based on double-terminal zero-sequence current ratio, which is used in a low-resistance grounding distribution network system. The high-resistance grounding fault pilot protection device includes: a data acquisition module, a calculation module and a fault protection module;

[0015] The data acquisition module is used to obtain the upstream zero-sequence current and the downstream zero-sequence current of the line where a single-phase grounding fault occurs in the low-resistance grounding distribution network system;

[0016] The calculation module is used to calculate and obtain a zero-sequence current ratio according to the upstream zero-sequence current and the downstream zero-sequence current based on the fact that the upstream zero-sequence current is greater than the maximum unbalanced current of the low-resistance grounding distribution network system;

[0017] The fault protection module is used to control the protection switch of the low-resistance grounding distribution network system to operate and cut off the fault line after a delay time T according to the zero-sequence current ratio satisfying the protection criterion.

[0018] Preferably, the calculation module is used to take the absolute value of the ratio of the upstream zero-sequence current to the downstream zero-sequence current as the zero-sequence current ratio.

[0019] Preferably, the maximum unbalanced current is 3A, and the delay time T is the sum of the zero-sequence overcurrent action time limit and the time step of the low-resistance grounded distribution network system.

[0020] Preferably, the protection criterion is that the zero-sequence current ratio is greater than 20.

[0021] The present invention also provides a terminal device, comprising a processor and a memory;

[0022] The memory is used to store program codes and transmit the program codes to the processor;

[0023] The processor is used to execute the above-mentioned high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to the instructions in the program code.

[0024] It can be seen from the above technical scheme that the embodiment of the present invention has the following advantages: the high-resistance grounding fault longitudinal protection method and device based on the double-end zero-sequence current ratio, the method includes obtaining the upstream zero-sequence current and the downstream zero-sequence current of the single-phase grounding fault line of the small-resistance grounding distribution network system; if the upstream zero-sequence current is greater than the maximum unbalanced current of the small-resistance grounding distribution network system, the zero-sequence current ratio is calculated according to the upstream zero-sequence current and the downstream zero-sequence current to obtain; if the zero-sequence current ratio meets the protection criterion, after the delay time T, the protection switch of the small-resistance grounding distribution network system is controlled to act and the fault line is cut off. The high-resistance grounding fault longitudinal protection method based on the double-end zero-sequence current ratio obtains the upstream zero-sequence current and the downstream zero-sequence current of the single-phase grounding fault line of the small-resistance grounding distribution network system, and calculates the zero-sequence current ratio of the system based on the condition that the upstream zero-sequence current is greater than the maximum unbalanced current, and controls the protection switch to act to cut off the fault line when the zero-sequence current ratio meets the protection criterion, thereby realizing the fault protection of the small-resistance grounding distribution network system, and solves the technical problem that the existing differential protection for high-resistance grounding faults refuses to act and cannot protect the distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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 of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0026] Figure 1 A schematic diagram of the steps of a high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio according to an embodiment of the present invention;

[0027] Figure 2A schematic diagram of the steps of a high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio according to another embodiment of the present invention;

[0028] Figure 3 A schematic diagram of single-phase grounding of a low-resistance grounded distribution network system in a high-resistance grounding fault pilot protection method based on double-terminal zero-sequence current ratio according to an embodiment of the present invention;

[0029] Figure 4 A single-phase grounding zero-sequence diagram of a low-resistance grounding distribution network system in a high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio according to an embodiment of the present invention;

[0030] Figure 5 It is an electrical diagram of a single-phase high-resistance grounding model of a 100kV low-resistance grounding system in a high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio according to an embodiment of the present invention;

[0031] Figure 6 It is a framework diagram of a high-resistance grounding fault longitudinal protection device based on double-terminal zero-sequence current ratio according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The embodiments of the present application provide a method and device for longitudinal protection of high-resistance grounding faults based on a double-terminal zero-sequence current ratio, which is applied to a low-resistance grounding distribution network system to solve the technical problem that the existing differential protection for high-resistance grounding faults refuses to operate and cannot protect the distribution network.

[0034] Embodiment 1:

[0035] Figure 1 Schematic diagram of the steps of the high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to an embodiment of the present invention, Figure 2 This is a schematic diagram of the steps of a high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to another embodiment of the present invention. Figure 3 A schematic diagram of single-phase grounding of a low-resistance grounded distribution network system in a high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to an embodiment of the present invention, Figure 4A single-phase grounding zero-sequence diagram of a low-resistance grounding distribution network system in a high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio described in an embodiment of the present invention.

[0036] like Figure 1 and Figure 2 As shown, the present invention provides a high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio, which is applied to a low-resistance grounding distribution network system. The high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio comprises the following steps:

[0037] S1. Obtain the upstream zero-sequence current and downstream zero-sequence current of the line with a single-phase grounding fault in a low-resistance grounding distribution network system.

[0038] It should be noted that if Figure 3 and Figure 4 As shown, in step S1, the upstream zero-sequence current of the single-phase grounding fault line of the low-resistance grounding distribution network system can be obtained. and downstream zero sequence current

[0039] S2. If the upstream zero-sequence current is greater than the maximum unbalanced current of the low-resistance grounded distribution network system, the zero-sequence current ratio is obtained based on the upstream zero-sequence current and the downstream zero-sequence current.

[0040] It should be noted that in a low-resistance grounded distribution network system, the maximum unbalanced current in the low-resistance grounded distribution network system is The value of needs to consider the unbalanced current, line parameter imbalance and zero-sequence current transformer transmission characteristics that may occur under the asymmetric operating conditions of the low-resistance grounding distribution network system. For example: The maximum unbalanced zero-sequence current of the overhead line and cable line of the 10kV low-resistance grounding system is about 0.37A and 0.26A respectively. Considering the linear range and measurement error of the zero-sequence current transformer, the starting current should be at least 0.5% of the full scale of the zero-sequence current transformer. Then the maximum unbalanced current in the low-resistance grounding distribution network system is The value should be no less than 3A. Maximum unbalanced current The minimum value is 3A.

[0041] In the embodiment of the present invention, the absolute value of the ratio of the upstream zero-sequence current to the downstream zero-sequence current is taken as the zero-sequence current ratio K, that is:

[0042]

[0043] S3. If the zero-sequence current ratio meets the protection criterion, after the delay time T, the protection switch of the low-resistance grounding distribution network system is controlled to operate and cut off the fault line.

[0044] It should be noted that in step S3, based on the zero-sequence current ratio satisfying the protection criterion, after the delay time T, the protection switch of the low-resistance grounding distribution network system is actuated to cut off the fault line, thereby realizing the protection of the low-resistance grounding distribution network system. The protection switch may be a circuit breaker. In this embodiment, if the zero-sequence current ratio satisfies the protection criterion, an action signal is then sent to the circuit breaker, and the timing register starts timing until the timing register reaches T, and the circuit breaker cuts off the fault line according to the action signal.

[0045] In the embodiment of the present invention, the protection criterion refers to that the zero-sequence current ratio is greater than 20.

[0046] In the embodiment of the present invention, the value of the delay time T needs to consider the coordination between the various devices in the protection of the small resistance grounding distribution network system. Therefore, the action time limit of the protection switch action of the small resistance grounding distribution network system should be longer than the existing zero-sequence overcurrent action time limit T 1 One time step Δt is higher. Considering the action time, reset time of the low-resistance grounding distribution network system and the time for the zero-sequence current in the line to decrease from the fault level to below the starting current after the fault is removed, the time step Δt is generally 0.5s. Then T = T 1 +Δt.

[0047] The high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio provided by the present invention comprises: obtaining the upstream zero-sequence current and the downstream zero-sequence current of the single-phase grounding fault line of the small-resistance grounding distribution network system; if the upstream zero-sequence current is greater than the maximum unbalanced current of the small-resistance grounding distribution network system, calculating the zero-sequence current ratio according to the upstream zero-sequence current and the downstream zero-sequence current; if the zero-sequence current ratio meets the protection criterion, after a delay time T, controlling the protection switch of the small-resistance grounding distribution network system to act and cut off the fault line. The high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio obtains the upstream zero-sequence current and the downstream zero-sequence current of the single-phase grounding fault line of the small-resistance grounding distribution network system, and calculates the zero-sequence current ratio of the system based on the condition that the upstream zero-sequence current is greater than the maximum unbalanced current, and controls the protection switch to act to cut off the fault line when the zero-sequence current ratio meets the protection criterion, thereby realizing fault protection of the small-resistance grounding distribution network system, and solving the technical problem that the existing differential protection for high-resistance grounding faults refuses to act and cannot protect the distribution network.

[0048] In one embodiment of the present invention, the high-resistance grounding fault longitudinal protection method based on the two-terminal zero-sequence current ratio includes: if the upstream zero-sequence current is not greater than the maximum unbalanced current of the low-resistance grounding distribution network system, or if the zero-sequence current ratio does not meet the protection criterion, the protection switch of the low-resistance grounding distribution network system will not operate.

[0049] It should be noted that the high-resistance grounding fault longitudinal protection method based on the two-terminal zero-sequence current ratio does not start the longitudinal protection of the low-resistance grounding distribution network system when the upstream zero-sequence current is not greater than the maximum unbalanced current and the zero-sequence current ratio does not meet the protection criterion, that is, the protection switch of the low-resistance grounding distribution network system does not operate.

[0050] like Figure 3 and Figure 4 As shown, in one embodiment of the present invention, the high-resistance grounding fault longitudinal protection method based on the double-terminal zero-sequence current ratio also includes constructing a protection criterion based on the zero-sequence current ratio, and constructing the protection criterion based on the zero-sequence current ratio includes:

[0051] Based on the expressions of upstream zero-sequence current and downstream zero-sequence current, the expressions of upstream zero-sequence current and downstream zero-sequence current are processed to remove transition resistance, and the initial zero-sequence current ratio expression is obtained;

[0052] Simplify the initial zero-sequence current ratio expression based on the constraint conditions to obtain the zero-sequence current ratio expression;

[0053] The protection criterion of the zero-sequence current ratio is determined based on the upstream zero-sequence current amplitude of the fault line being more than 20 times the downstream zero-sequence current amplitude.

[0054] It should be noted that the expression of upstream zero-sequence current is:

[0055]

[0056] The expression of downstream zero-sequence current is:

[0057]

[0058] In the formula, Z 1∑ , Z 2∑ , Z 0∑ is the equivalent impedance seen from the fault point to the network; is the equivalent power source electromotive force, c 0 is the zero-sequence capacitance per unit length of the fault line or feeder, z 0 is the zero-sequence impedance per unit length of the fault line or feeder, l nu is the distance from the fault point to the beginning of the fault line, l' nd is the distance from the fault point to the busbar on the N side of the fault line, R f is the transition resistance on the fault line or feeder, Y up(0) is the equivalent admittance upstream of the fault point in the zero-sequence network, Y down(0) is the equivalent admittance downstream of the fault point in the zero-sequence network, and jω is the reactance of the fault line or feeder.

[0059] In the embodiment of the present invention, it can be known from the expression of the upstream zero-sequence current and the expression of the downstream zero-sequence current that the transition resistance R f It only exists in the denominator. By dividing the expression of the upstream zero-sequence current by the expression of the downstream zero-sequence current, the transition resistance can be eliminated. Then, its modulus is taken and set to K to obtain the initial zero-sequence current ratio expression. The initial zero-sequence current ratio expression is:

[0060]

[0061] In the embodiment of the present invention, the constraint conditions include:

[0062]

[0063] According to the constraint conditions, the initial zero-sequence current ratio expression is simplified to the zero-sequence current ratio expression, which is:

[0064]

[0065] From the zero-sequence current ratio expression, we can see that although the K value is not affected by the transition resistance R f However, it is greatly affected by the fault location. For example, taking the commonly used parameters of the domestic 10kV system as an example, that is, the neutral point grounding resistance is 10Ω, the protection criterion of the zero-sequence current ratio can be determined as:

[0066]

[0067] Therefore, the amplitude of the upstream zero-sequence current of the fault line is more than 20 times the amplitude of the downstream zero-sequence current of the fault line, and this ratio has nothing to do with the transition resistance value of the fault grounding point. In the non-fault line, this ratio is approximately equal to 1.

[0068] Figure 5 This is an electrical diagram of a single-phase high-resistance grounding model of a 100kV low-resistance grounding system in a high-resistance grounding fault longitudinal protection method based on a double-terminal zero-sequence current ratio described in an embodiment of the present invention.

[0069] In the embodiment of the present invention, the feasibility of the high-resistance grounding fault longitudinal protection method based on the double-terminal zero-sequence current ratio is illustrated by the following case: In the electromagnetic transient simulation software PSCAD / EMTDC4.6, a single-phase high-resistance grounding model of a 10kV low-resistance grounding system is established. Figure 5As shown. The 10kV low-resistance grounding system includes an infinite power supply, cable lines, a main transformer, and a grounding transformer. The cable line parameters are as follows: Positive sequence: positive sequence resistance per unit length of the cable line r1 = 0.1050Ω / km, positive sequence reactance per unit length of the cable line x1 = 0.0800Ω / km, positive sequence capacitance per unit length of the cable line to ground c1 = 0.4700μF / km. Zero sequence: zero sequence resistance per unit length of the cable line r0 = 1.0500Ω / km, zero sequence reactance per unit length of the cable line x0 = 0.3200Ω / km, zero sequence capacitance per unit length of the cable line c 0 =0.4700090μF / km. The zero-sequence impedance of the grounding transformer is 10Ω, the neutral point grounding resistance is 10Ω, the length of each circuit of the line is set to 10km, and the protection terminals are installed at the beginning, 5km and end of the line. Figure 5 As shown, a single-phase grounding fault is set between the first line BK1-BK2, and the upstream zero-sequence current at BK1 and the downstream zero-sequence current at BK2 are obtained; then the grounding fault of the 10kV low-resistance grounding system is protected by the high-resistance grounding fault longitudinal protection method based on the double-terminal zero-sequence current ratio. The grounding fault of the 10kV low-resistance grounding system is protected by the longitudinal protection process in the electromagnetic transient simulation software PSCAD / EMTDC 4.6, and the execution results of the protection switch are shown in Table 1 below.

[0070] Table 1 Simulation results of single-phase ground fault in low-resistance grounding system

[0071]

[0072] It can be seen from the above table that when the fault location and the number of non-fault lines change, the ratio of the zero-sequence current amplitude upstream of the fault line to the zero-sequence current amplitude downstream of the fault line still satisfies the relationship of being greater than 20, and the protection switch can still operate reliably. Moreover, from metallic grounding to 1000Ω high-resistance grounding, the zero-sequence current ratio K value is almost unaffected. It can be seen that the high-resistance grounding fault longitudinal protection method based on the double-end zero-sequence current ratio can improve the ability to withstand transition resistance to more than 1000Ω.

[0073] Embodiment 2:

[0074] Figure 6 It is a framework diagram of a high-resistance grounding fault longitudinal protection device based on double-terminal zero-sequence current ratio according to an embodiment of the present invention.

[0075] like Figure 6 The present invention further provides a high-resistance grounding fault longitudinal protection device based on a double-terminal zero-sequence current ratio, which is applied to a low-resistance grounding distribution network system. The high-resistance grounding fault longitudinal protection device includes a data acquisition module 10, a calculation module 20 and a fault protection module 30;

[0076] The data acquisition module 10 is used to acquire the upstream zero-sequence current and the downstream zero-sequence current of the line with a single-phase grounding fault in the low-resistance grounding distribution network system;

[0077] The calculation module 20 is used to calculate the zero-sequence current ratio according to the upstream zero-sequence current and the downstream zero-sequence current based on the fact that the upstream zero-sequence current is greater than the maximum unbalanced current of the low-resistance grounding distribution network system;

[0078] The fault protection module 30 is used to control the protection switch of the low-resistance grounding distribution network system to operate and cut off the fault line after a delay time T according to the zero-sequence current ratio meeting the protection criterion.

[0079] In the embodiment of the present invention, the calculation module is used to take the absolute value of the ratio of the upstream zero-sequence current to the downstream zero-sequence current as the zero-sequence current ratio.

[0080] In the embodiment of the present invention, the maximum unbalanced current is 3A, and the delay time T is the sum of the zero-sequence overcurrent action time limit and the time step of the low-resistance grounded distribution network system.

[0081] In an embodiment of the present invention, the protection criterion is that the zero-sequence current ratio is greater than 20.

[0082] It should be noted that the content of the module in the device of Example 2 corresponds to the step content of the method of Example 1. The step content of the method of Example 1 has been described in detail in Example 1, and the description of the content of the module will not be repeated in Example 2.

[0083] Embodiment three:

[0084] The present invention also provides a terminal device, comprising a processor and a memory;

[0085] A memory, used for storing program codes and transmitting the program codes to a processor;

[0086] The processor is used to execute the above-mentioned high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to the instructions in the program code.

[0087] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0088] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0089] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0090] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0091] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk and other media that can store program codes.

[0092] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-resistance grounding fault pilot protection method based on double-terminal zero-sequence current ratio, applied to a low-resistance grounding distribution network system, characterized in that: The high-resistance ground fault longitudinal protection method comprises the following steps: Obtaining the upstream zero-sequence current and downstream zero-sequence current of a single-phase grounding fault line in a low-resistance grounding distribution network system; If the upstream zero-sequence current is greater than the maximum unbalanced current of the low-resistance grounded distribution network system, a zero-sequence current ratio is obtained by calculation based on the upstream zero-sequence current and the downstream zero-sequence current; If the zero-sequence current ratio meets the protection criterion, after a delay time T, the protection switch of the low-resistance grounding distribution network system is controlled to operate and cut off the fault line.

2. The high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to claim 1 is characterized in that: Obtaining the zero-sequence current ratio by calculation according to the upstream zero-sequence current and the downstream zero-sequence current includes: taking the absolute value of the ratio of the upstream zero-sequence current to the downstream zero-sequence current as the zero-sequence current ratio.

3. The high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to claim 1 is characterized in that: The maximum unbalanced current is at least 3A, and the delay time T is the sum of the zero-sequence overcurrent action time limit and the time step of the small resistance grounding distribution network system.

4. The high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to claim 1 is characterized in that: The protection criterion is that the zero-sequence current ratio is greater than 20.

5. The high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio according to claim 1 is characterized in that: include: If the upstream zero-sequence current is not greater than the maximum unbalanced current of the low-resistance grounded distribution network system, or if the zero-sequence current ratio does not meet the protection criterion, the protection switch of the low-resistance grounded distribution network system will not operate.

6. A high-resistance ground fault longitudinal protection device based on double-terminal zero-sequence current ratio, characterized in that: Applied to a low-resistance grounding distribution network system, the high-resistance grounding fault longitudinal protection device comprises: a data acquisition module, a calculation module and a fault protection module; The data acquisition module is used to obtain the upstream zero-sequence current and the downstream zero-sequence current of the line where a single-phase grounding fault occurs in the low-resistance grounding distribution network system; The calculation module is used to calculate and obtain a zero-sequence current ratio according to the upstream zero-sequence current and the downstream zero-sequence current based on the fact that the upstream zero-sequence current is greater than the maximum unbalanced current of the low-resistance grounding distribution network system; The fault protection module is used to control the protection switch of the low-resistance grounding distribution network system to operate and cut off the fault line after a delay time T according to the zero-sequence current ratio satisfying the protection criterion.

7. The high-resistance grounding fault longitudinal protection device based on double-terminal zero-sequence current ratio according to claim 6 is characterized in that: The calculation module is used to take the absolute value of the ratio of the upstream zero-sequence current to the downstream zero-sequence current as the zero-sequence current ratio.

8. The high-resistance grounding fault longitudinal protection device based on double-terminal zero-sequence current ratio according to claim 6 is characterized in that: The maximum unbalanced current is 3A, and the delay time T is the sum of the zero-sequence overcurrent action time limit and the time step of the low-resistance grounded distribution network system.

9. The high-resistance grounding fault longitudinal protection device based on double-terminal zero-sequence current ratio according to claim 6, characterized in that: The protection criterion is that the zero-sequence current ratio is greater than 20.

10. A terminal device, characterized in that: including a processor and a memory; The memory is used to store program codes and transmit the program codes to the processor; The processor is used to execute the high-resistance grounding fault longitudinal protection method based on double-terminal zero-sequence current ratio as described in any one of claims 1 to 5 according to the instructions in the program code.

Images