A high resistance grounding protection method for a small resistance grounding system

Abstract

This invention relates to a high-resistance grounding protection method for a low-resistance grounding system, comprising: (1) collecting and calculating the zero-sequence voltage and zero-sequence current of the line; (2) shifting the zero-sequence voltage to the left by one-quarter of the power frequency cycle within one power frequency cycle, and then normalizing the sampled values ​​of the left-shifted zero-sequence voltage and zero-sequence current; when the zero-sequence voltage of the line is greater than the zero-sequence voltage start-up setting value, calculating the waveform comparison coefficient Kr of the processed zero-sequence voltage and zero-sequence current; (3) comparing the waveform comparison coefficient Kr. r Comparison coefficient constant K set The size of K r >K set When the fault occurs, the line is identified as having a ground fault. This method is simple and easy to implement, and can improve the sensitivity of high-resistance ground fault detection in low-resistance grounding systems.

Description

Technical Field

[0001] This invention belongs to the field of power distribution network relay protection technology, specifically relating to a high-resistance grounding protection method for a low-resistance grounding system. Background Technology

[0002] Low-resistance grounding systems are increasingly widely used in distribution networks of large and medium-sized cities in my country due to their advantages such as effectively limiting arc grounding overvoltages, timely disconnection of faulty lines, and reduction of equipment insulation levels. Single-phase grounding faults account for over 80% of distribution network faults, making them one of the main fault types. However, due to the complex environment of distribution network feeders, single-phase high-resistance grounding faults are prone to occur. Although the fault current of high-resistance grounding faults is small, the high temperature generated by the fallen high-voltage line and the fault arc can cause significant harm to nearby people and the surrounding environment, even leading to personal injury accidents. Furthermore, if the fault current is allowed to persist, it will further damage the insulation, causing more serious faults and expanding the fault range. Therefore, grounding fault protection systems with high-resistance fault identification capabilities are of great significance for ensuring the safe and stable operation of low-resistance grounding systems.

[0003] Currently, the main ground fault protection scheme for low-resistance grounding systems is staged zero-sequence current protection. However, under high-resistance conditions, due to the very small fault current, the sensitivity of existing zero-sequence current protection is poor. Taking the zero-sequence stage II as an example, its withstand transition resistance value is approximately 100Ω, which obviously cannot meet the requirements for high-resistance ground fault detection. Some substations also use zero-sequence directional protection schemes, but the polarity verification of the instrument transformers is difficult, and the effect is not ideal. Summary of the Invention

[0004] The purpose of this invention is to provide a method for protecting high-resistance grounding in a low-resistance grounding system. This method is simple and easy to implement, and can improve the sensitivity of high-resistance grounding fault detection in a low-resistance grounding system.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: a high-resistance grounding protection method for a low-resistance grounding system, comprising:

[0006] (1) Collect and calculate the zero-sequence voltage and zero-sequence current of the line;

[0007] (2) Shift the zero-sequence voltage to the left by one-quarter of the power frequency cycle, and then normalize the sampled values ​​of the zero-sequence voltage and zero-sequence current after the left shift; when the zero-sequence voltage of the line is greater than the zero-sequence voltage start-up setting, calculate the waveform comparison coefficient Kr of the processed zero-sequence voltage and zero-sequence current.

[0008] (3) Compare waveforms, comparison coefficient K r Comparison coefficient constant K set The size of Kr >K set When the fault occurs, the line is identified as having a grounding fault.

[0009] Furthermore, in step (1), the zero-sequence voltage of a single-phase grounding is:

[0010]

[0011] The zero-sequence current of a normal circuit is:

[0012]

[0013] The zero-sequence current of the faulty outgoing line is:

[0014]

[0015] in, R is the voltage of the faulty phase before the fault. f R is the short-circuit grounding resistance. g For grounding resistance, C 0∑ This is the sum of the zero-sequence capacitances of all lines to ground.

[0016] Furthermore, in step (1), a protection device is used to collect zero-sequence current and zero-sequence voltage, and the number of sampling points for each power frequency cycle is N.

[0017] Furthermore, in step (2), the formula for the zero-sequence voltage normalization process is:

[0018]

[0019] The formula for normalizing zero-sequence current is:

[0020]

[0021] The waveform comparison coefficient K is calculated by dividing the sum of the absolute values ​​of the differences between all zero-sequence voltage and zero-sequence current samples within a power frequency cycle by the sum of the absolute values ​​of all zero-sequence voltage and zero-sequence current samples within a power frequency cycle. r The calculation formula is as follows:

[0022]

[0023] Where k is the current sampling point, i is the time shift value, U0 is the zero-sequence voltage sampling value, and I0 is the zero-sequence current sampling value. It is the normalized zero-sequence voltage sample value. It is the normalized zero-sequence current sample value.

[0024] Furthermore, in step (2), the zero-sequence voltage start-up setting U setThe value range is 3 to 5V.

[0025] Furthermore, in step (3), when K r >K set When the line is identified as having a ground fault, and after a set delay value t... set The subsequent action is to trip or alarm.

[0026] Furthermore, the comparison coefficient constant K set The value range is 0.3 to 0.4.

[0027] Furthermore, the delay setpoint t set The value range is 0.3 to 1s.

[0028] Compared with existing technologies, this invention has the following advantages: By analyzing the waveform relationship between zero-sequence current and zero-sequence voltage in faulty and non-faulty lines, this invention enables the detection of high-resistance grounding faults in low-resistance grounding systems. This method is not only simple and easy to implement, but also significantly improves the sensitivity of high-resistance grounding fault detection in low-resistance grounding systems. Therefore, this invention has strong practicality and broad application prospects. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the implementation of a high-resistance grounding protection method for a low-resistance grounding system according to an embodiment of the present invention.

[0030] Figure 2 This is a MATLAB model diagram corresponding to the high-resistance grounding protection method for a low-resistance grounding system in this embodiment of the invention.

[0031] Figure 3 In this embodiment of the invention, under a grounding resistance of 1000Ω, the zero-sequence voltage and current diagram of the faulted line after conversion is compared with that of the faulted line K. r1 The graph shows the changes in i (time shift).

[0032] Figure 4 In this embodiment of the invention, under a grounding resistance of 1000Ω, the calculated zero-sequence voltage and current diagram of the normal line is compared with the K of the normal line. r2 As the i (time shift) changes, the first cycle is a transient process (within 0.02s). The delay of high-resistance grounding protection is generally more than 0.3s. Therefore, this transient process has no impact on the protection criterion.

[0033] Figure 5 This is a comparison diagram of the zero-sequence current of the three feeders under a grounding resistance of 1000Ω in an embodiment of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0036] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0037] like Figure 1 As shown, this embodiment provides a high-resistance grounding protection method for a low-resistance grounding system, including the following steps:

[0038] (1) Collect and calculate the zero-sequence voltage and zero-sequence current of the line.

[0039] The zero-sequence voltage for a single-phase ground fault is:

[0040]

[0041] The zero-sequence current of a normal circuit is:

[0042]

[0043] The zero-sequence current of the faulty outgoing line is:

[0044]

[0045] in, R is the voltage of the faulty phase before the fault. f R is the short-circuit grounding resistance. g For grounding resistance, C 0∑ This is the sum of the zero-sequence capacitances of all lines to ground.

[0046] A protection device is used to collect zero-sequence current and zero-sequence voltage, with N sampling points per power frequency cycle.

[0047] (2) Shift the zero-sequence voltage to the left by one-quarter of the power frequency cycle, and then normalize the sampled values ​​of the shifted zero-sequence voltage and zero-sequence current. When the zero-sequence voltage of the line is greater than the zero-sequence voltage start-up setting, calculate the waveform comparison coefficient Kr of the processed zero-sequence voltage and zero-sequence current.

[0048] The formula for normalizing the zero-sequence voltage is as follows:

[0049]

[0050] The formula for normalizing zero-sequence current is:

[0051]

[0052] The waveform comparison coefficient K is calculated by dividing the sum of the absolute values ​​of the differences between all zero-sequence voltage and zero-sequence current samples within a power frequency cycle by the sum of the absolute values ​​of all zero-sequence voltage and zero-sequence current samples within a power frequency cycle. r The calculation formula is as follows:

[0053]

[0054] Where k is the current sampling point, i is the time shift value, U0 is the zero-sequence voltage sampling value, and I0 is the zero-sequence current sampling value. It is the normalized zero-sequence voltage sample value. It is the normalized zero-sequence current sample value.

[0055] In this embodiment, the zero-sequence voltage start-up setting U set Use 3-5V.

[0056] (3) Compare waveforms, comparison coefficient K r Comparison coefficient constant K set The size of K r >K set When the line is identified as having a ground fault, and after a set delay value t... est The subsequent action is to trip or alarm.

[0057] In this embodiment, the comparison coefficient is set to K. set Take a value of 0.3 to 0.4; delay setpoint t est Take a time of 0.3 to 1 second.

[0058] This embodiment uses MATLAB / Simulink to simulate the system, and the system model is as follows: Figure 2 As shown in the figure. The system power supply voltage is set to 10kV, the frequency to 50Hz, and the lengths of the three feeders are 13km, 20km, and 25km, respectively. The ground fault is a single-phase ground fault of phase A, and the grounding resistance at the short-circuit point is 100Ω, 500Ω, 1000Ω, and 2000Ω, respectively. The calculation results of this method are shown in the table below:

[0059] Table 1. K values ​​for fault lines with different grounding resistances r1

[0060]

[0061] Table 2 K for normal lines with different grounding resistances r2

[0062]

[0063] As can be seen from Tables 1 and 2, when the grounding resistance in a low-resistance grounding system ranges from 100 to 2000 Ω, the method used to calculate the fault location K... r1 K of non-faulty lines r2 The difference is obvious, K set A value of 0.3-0.4 can reliably identify lines with grounding faults.

[0064] In summary, this invention proposes a new protection criterion based on the relationship between zero-sequence voltage and zero-sequence current. This criterion can sensitively detect high-resistance grounding faults of 2kΩ in low-resistance grounding systems. Furthermore, it requires little computation and is easy to implement on microcomputer protection devices.

[0065] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0066] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0067] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0068] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for high resistance grounding protection of a low resistance grounding system, characterized in that, include: (1) Collect and calculate the zero-sequence voltage and zero-sequence current of the line; (2) Shift the zero-sequence voltage to the left by one-quarter of the power frequency cycle, and then normalize the sampled values ​​of the zero-sequence voltage and zero-sequence current after the left shift; when the zero-sequence voltage of the line is greater than the zero-sequence voltage start-up setting, calculate the waveform comparison coefficient Kr of the processed zero-sequence voltage and zero-sequence current. (3) Compare waveforms using comparison coefficient K r Comparison coefficient constant K set The size of K r >K set When the fault occurs, the line is identified as having a ground fault. In step (2), the formula for normalizing the zero-sequence voltage is: The formula for normalizing zero-sequence current is: The waveform comparison coefficient K is calculated by dividing the sum of the absolute values ​​of the differences between all zero-sequence voltage and zero-sequence current samples within a power frequency cycle by the sum of the absolute values ​​of all zero-sequence voltage and zero-sequence current samples within a power frequency cycle. r The calculation formula is as follows: wherein k is the current sampling point, i is the time shift value, U0 is the zero sequence voltage sampling value, I0 is the zero sequence current sampling value, is the normalized zero sequence voltage sampling value, is the normalized zero sequence current sampling value.

2. The method of claim 1, wherein, In step (1), the zero-sequence voltage of a single-phase ground fault is: The zero-sequence current of a normal circuit is: The zero-sequence current of the faulty outgoing line is: in, The voltage of the faulty phase before the fault occurred. For short-circuit grounding resistance, For grounding resistance, This is the sum of the zero-sequence capacitances of all lines to ground.

3. The method of claim 1, wherein, In step (1), a protection device is used to collect zero-sequence current and zero-sequence voltage, and the number of sampling points for each power frequency cycle is N.

4. The method of claim 1, wherein, In step (2), the zero-sequence voltage starting value U set is in the range of 3-5 V.

5. The method of claim 1, wherein, In step (3), when a ground fault line is judged, and after a set delay time the breaker is tripped or an alarm is given.

6. The method of claim 5, wherein, Comparative coefficient constant value is in the range of 0.3 to 0.

4.

7. A high-resistance grounding protection method for a low-resistance grounding system according to claim 5, characterized in that, Delay constant value The value range of the delay constant value is 0.3-1s.

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