A method and apparatus for detecting ground faults in a low resistance grounded system

Abstract

The application discloses a kind of small resistance grounding system grounding fault detection method and device in the technical field of power distribution network, method includes: using sensor to collect the zero sequence current I0 and zero sequence voltage U0 of line;When the zero sequence voltage U0 of line U set , the waveform comparison coefficient K of zero sequence voltage U0 and zero sequence current I0 is calculated r , that is, the ratio of the point number of the sign opposite of zero sequence voltage U0 left shift quarter cycle and zero sequence current I0 sampling value with the sampling point number N of each power frequency cycle;When the zero sequence voltage U0 of line U set , line is normal line;The size of K r With protection starting value K set , when K r >K set , it is judged as grounding fault line, and sends out fault signal after the set delay value t set ;When K r ≤K set , line is normal line.The method is simple and easy to operate, improves the sensitivity of small resistance grounding system grounding fault detection, reduces the time consumption of judgment, improves efficiency.

Description

Technical Field

[0001] This invention relates to a method and device for detecting grounding faults in a low-resistance grounding system, belonging to the field of power distribution network technology. Background Technology

[0002] The development of the social economy has placed higher demands on power supply safety and quality, and the issue of grounding protection in distribution networks has attracted great attention from the industry. Single-phase grounding faults are the most common type of fault in distribution networks. my country's conventional medium-voltage distribution networks mainly use two methods: low-current grounding and low-resistance grounding. With low-current grounding, the line does not need to trip and can continue operating due to the small current, improving power supply reliability. Regulations stipulate that it can continue operating for 1-2 hours, but this presents challenges such as difficult line selection and high requirements for equipment insulation levels. Compared to low-current grounding systems, low-resistance grounding systems have a larger zero-sequence current during grounding faults, allowing for timely fault clearing through overcurrent protection, and offer significant advantages in overvoltage suppression and fault elimination. Statistics show that single-phase grounding faults account for over 80% of distribution network faults in low-resistance grounding systems. Furthermore, low-resistance grounding faults have the highest frequency among single-phase faults.

[0003] In fault location within low-current grounding systems, methods such as the zero-sequence current amplitude-phase comparison method and the zero-sequence admittance method are used, employing the relationship between zero-sequence voltage and current as a criterion. Low-resistance grounding distribution networks commonly use zero-sequence overcurrent protection to clear single-phase ground faults. The setting calculation for this protection needs to consider the influence of the protected line's capacitive current and the maximum unbalanced current during normal operation. Therefore, relying on zero-sequence overcurrent protection results in very low sensitivity, generally not exceeding 300Ω. In the past, fault location in low-resistance grounding systems has also involved using the relationship between the zero-sequence current of the fault line and the zero-sequence voltage of the busbar, then applying correlation analysis to calculate the correlation coefficient between the derivatives of the zero-sequence current of each outgoing line and the zero-sequence voltage of the busbar. However, in practice, determining the correlation is time-consuming, and the range of correlation at the time of a fault is ambiguous.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for detecting grounding faults in a low-resistance grounding system, thereby improving the sensitivity of grounding fault detection, reducing judgment time, and increasing efficiency.

[0006] To achieve the above objectives, the present invention is implemented using the following technical solution.

[0007] On one hand, the present invention provides a grounding fault detection method for a low-resistance grounding system, comprising:

[0008] Collect the zero-sequence current I0 and zero-sequence voltage U0 of the line;

[0009] When the zero-sequence voltage U0 of the line is greater than the starting value U set Calculate the waveform comparison coefficient K for zero-sequence voltage U0 and zero-sequence current I0. r ;

[0010] Compare the K r With protection start setting K set Size, when K r >K set The line was identified as having a ground fault, and after a set delay value t... set A fault signal was then issued.

[0011] In one embodiment, when the zero-sequence voltage U0 of the line is less than or equal to the starting value U... set The line is a normal line.

[0012] In one embodiment, the K is compared r With protection start setting K set Size, when K r ≤K set The line is a normal line.

[0013] In one embodiment, during the acquisition of zero-sequence current I0 and zero-sequence voltage U0, the number of sampling points per power frequency cycle is N.

[0014] In one embodiment, R(k) is defined as the number of points in each cycle where the zero-sequence voltage U0 is shifted to the left by a quarter cycle and the zero-sequence current I0 sample values ​​have opposite signs, as expressed below:

[0015]

[0016] Where U0 is the zero-sequence voltage sample value and I0 is the zero-sequence current sample value.

[0017] In one embodiment, the K r R(k) is the ratio of the number of sampling points N in each power frequency cycle. The formula for calculating its variation with time within the sampling period is as follows:

[0018]

[0019] Where k is the current sampling point and i is the time shift value.

[0020] In one embodiment, the start-up voltage U set The value range is 3~5V, and the protection start setting value K is...set The value ranges from 0.4 to 0.6, and the delay setpoint t set The value ranges from 0.3 to 1s.

[0021] In one embodiment, the system response after issuing a fault signal includes tripping or outputting an alarm signal.

[0022] In one embodiment, the acquisition tool for the zero-sequence current I0 and zero-sequence voltage U0 of the acquisition line is a protection device.

[0023] Secondly, the present invention provides a grounding fault detection device for a low-resistance grounding system, characterized in that it comprises:

[0024] The acquisition module is configured to: acquire the zero-sequence current I0 and the zero-sequence voltage U0 of the line;

[0025] The calculation module is configured to: when the zero-sequence voltage U0 of the line is greater than the start-up value U set Calculate the waveform comparison coefficient K for zero-sequence voltage U0 and zero-sequence current I0. r ;

[0026] The judgment module is configured to: compare the K r With protection start setting K set Size, when K r >K set The line was identified as having a ground fault, and after a set delay value t... set A fault signal was then issued.

[0027] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0028] 1. By collecting zero-sequence voltage and zero-sequence current, and performing simple comparisons and calculations, ground fault lines can be reliably identified. The process is concise and time-saving.

[0029] 2. By comparing the waveforms of zero-sequence voltage and zero-sequence current, the comparison coefficient K is used. r and protection start setting K set It proposes new protection criteria and can sensitively detect grounding faults generated in the line. Attached Figure Description

[0030] Figure 1 The diagram shown is a flowchart of the present invention;

[0031] Figure 2 The figure shown is a schematic diagram of the MATLAB model of the present invention.

[0032] Figure 3 The figure shows the comparison coefficient K between the zero-sequence voltage and current diagram of the faulted line after conversion and the waveform of the faulted line under the condition of 1000Ω grounding resistance.r1 The graph shows the changes in i (time shift).

[0033] Figure 4 This invention provides a comparison coefficient K between the zero-sequence voltage and current diagram of a normal line and the waveform of a normal line under a grounding resistance of 1000Ω. r2 The graph shows the changes in i (time shift).

[0034] Figure 5 This is a comparison diagram of the zero-sequence current of the three feeders under a grounding resistance of 1000Ω. Detailed Implementation

[0035] It should be noted that:

[0036] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations thereof. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0037] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0038] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0039] The term "and / or" simply describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. Additionally, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0040] Example 1

[0041] This embodiment describes a grounding fault detection method for a low-resistance grounding system, including:

[0042] Use sensors to collect the zero-sequence current I0 and zero-sequence voltage U0 of the line;

[0043] When the zero-sequence voltage U0 of the line is greater than the starting value U setCalculate the waveform comparison coefficient K for zero-sequence voltage U0 and zero-sequence current I0. r ;

[0044] Compare the K r With protection start setting K set Size, when K r >K set The line was identified as having a ground fault, and after a set delay value t... set A fault signal was then issued.

[0045] Example 2

[0046] Based on the same inventive concept as Embodiment 1, this embodiment also incorporates the following design:

[0047] When the zero-sequence voltage U0 of the line is less than or equal to the starting value U set The line is a normal line.

[0048] Compare the K r With protection start setting K set Size, when K r ≤K set The line is a normal line.

[0049] During the acquisition of zero-sequence current I0 and zero-sequence voltage U0, the number of sampling points per power frequency cycle is N.

[0050] Define R(k) as the number of points in each cycle where the zero-sequence voltage U0 is shifted to the left by a quarter cycle and the zero-sequence current I0 sample values ​​have opposite signs, as expressed below:

[0051]

[0052] Where U0 is the zero-sequence voltage sample value and I0 is the zero-sequence current sample value.

[0053] In one embodiment, the K r R(k) is the ratio of the number of sampling points N in each power frequency cycle. The formula for calculating its variation with time within the sampling period is as follows:

[0054]

[0055] Where k is the current sampling point and i is the time shift value.

[0056] By comparing the waveforms of zero-sequence voltage and zero-sequence current, the comparison coefficient K is used. r and protection start setting K set It proposes new protection criteria and can sensitively detect grounding faults generated in the line.

[0057] Start-up voltage U setThe value range is 3~5V, and the protection start setting value K is... set The value ranges from 0.4 to 0.6, and the delay setpoint t set The value ranges from 0.3 to 1s.

[0058] The system response after issuing a fault signal includes tripping or outputting an alarm signal. The response is not limited to these limitations; the selection criteria are based on the ability to notify of the fault, serve as a warning, and protect the system.

[0059] The acquisition tool for the zero-sequence current I0 and zero-sequence voltage U0 of the acquisition line is a protection device. It is not limited to the acquisition tool, but is selected based on the ability to acquire the zero-sequence current I0 and zero-sequence voltage U0 without affecting the circuit.

[0060] By collecting zero-sequence voltage and zero-sequence current, and performing simple comparisons and calculations, ground fault lines can be reliably identified. The process is concise and time-saving.

[0061] Example 3

[0062] Based on the same inventive concept as other embodiments, this embodiment introduces a grounding fault detection device for a low-resistance grounding system, comprising:

[0063] The acquisition module is configured to: acquire the zero-sequence current I0 and the zero-sequence voltage U0 of the line;

[0064] The calculation module is configured to: when the zero-sequence voltage U0 of the line is greater than the start-up value U set Calculate the waveform comparison coefficient K for zero-sequence voltage U0 and zero-sequence current I0. r ;

[0065] The judgment module is configured to: compare the K r With protection start setting K set Size, when K r >K set The line was identified as having a ground fault, and after a set delay value t... set A fault signal was then issued.

[0066] Example 4

[0067] This embodiment uses MATLAB / Simulink to simulate the system and build a simulation model, as detailed below. Figure 2 As shown. The simulation model has three feeders with lengths of 13km, 20km, and 18km respectively. Other parameters are set as follows: system power supply voltage is 10kV, frequency is 50Hz, power supply grounding resistance is 10Ω, grounding fault is a single-phase grounding fault of phase A, and short-circuit point grounding resistance R... f The corresponding values ​​are 300, 500, 1000, and 2000Ω.

[0068] After simulation, as Figure 3 and Figure 4 As shown, comparing the differences in Kr calculation results for faulty and non-faulty lines, it can be seen that after 0.02s, the Kr of the faulty line... r1 K remains around 1, rather than on faulty lines. r2 The value then dropped rapidly and remained around 0.05. The comparison revealed a significant difference between the two curves, which verified the feasibility of the detection method.

[0069] The results of the algorithm calculation are shown in the table below:

[0070] Table 1. K values ​​for fault lines with different grounding resistances r1

[0071]

[0072] Table 2 K for normal lines with different grounding resistances r2

[0073]

[0074] As can be seen from Tables 1 and 2, when the grounding resistance in a low-resistance grounding system ranges from 300Ω to 2000Ω, the algorithm calculates the fault location K. r1 K of non-faulty lines r2 The difference is obvious, K set A value of 0.4-0.6 can reliably identify faulty circuits.

[0075] In summary, this invention proposes a new protection criterion based on the relationship between zero-sequence voltage U0 and zero-sequence current I0. This criterion can sensitively detect high-resistance grounding faults of 2kΩ in low-resistance grounding systems, and it requires little computation and is easy to implement on microcomputer protection devices.

[0076] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. 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 illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0077] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for detecting grounding faults in a low-resistance grounding system, characterized in that, include: The zero-sequence current I0 and zero-sequence voltage U0 of the line are collected; during the process of collecting the zero-sequence current I0 and zero-sequence voltage U0 of the line, the number of sampling points in each power frequency cycle is N; When the zero sequence voltage U0 of the line > starting value U set , the waveform comparison coefficient K of the zero sequence voltage U0 and the zero sequence current I0 is calculated r ; Comparing the K r With the protection starting value K set Size, when K r > K set , it is judged that the ground fault line, and after the set delay value t set Fault signal is sent out; Defined as the number of points in each cycle where the zero-sequence voltage U0 is shifted to the left by a quarter cycle and the zero-sequence current I0 sample values ​​have opposite signs, the expression is as follows: ， Where U0 is the zero-sequence voltage sample value and I0 is the zero-sequence current sample value; The K r R(k) is the ratio of the number of sampling points N in each power frequency cycle. The formula for calculating its variation with time within the sampling period is as follows: ， Where k is the current sampling point and i is the time shift value.

2. The grounding fault detection method for a low-resistance grounding system according to claim 1, characterized in that, When the zero-sequence voltage U0 of the line is less than or equal to the starting value U set The line is a normal line.

3. The grounding fault detection method for a low-resistance grounding system according to claim 1, characterized in that, Compare the K r With protection start setting K set Size, when K r ≤K set The line is a normal line.

4. The grounding fault detection method for a low-resistance grounding system according to claim 1, characterized in that, Start-up voltage U set The value range is 3~5V, and the protection start setting value K is... set The value ranges from 0.4 to 0.6, and the delay setpoint is t. set The value range is 0.3~1s.

5. The grounding fault detection method for a low-resistance grounding system according to claim 1, characterized in that, The system's response after issuing a fault signal includes tripping or outputting an alarm signal.

6. The grounding fault detection method for a low-resistance grounding system according to claim 1, characterized in that, The acquisition tool for the zero-sequence current I0 and zero-sequence voltage U0 of the acquisition line is a protection device.

7. A grounding fault detection device for a low-resistance grounding system, characterized in that, The apparatus for performing the ground fault detection method for a low-resistance grounding system according to any one of claims 1-6, the apparatus comprising: The acquisition module is configured to: acquire the zero-sequence current I0 and the zero-sequence voltage U0 of the line; The calculation module is configured to: when the zero-sequence voltage U0 of the line is greater than the start-up value U set Calculate the waveform comparison coefficient K for zero-sequence voltage U0 and zero-sequence current I0. r ; The judgment module is configured to: compare the K r With protection start setting K set Size, when K r >K set The line was identified as having a ground fault, and after a set delay value t... set A fault signal was then issued.

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