A single-phase ground fault section selection method suitable for electronic feeder terminals

Abstract

The present invention provides a single-phase grounding fault selection method suitable for an electronic feeder terminal, comprising: when the zero-sequence voltage data meets the preset initial start condition, the initial start flag is set; when the time delay corresponding to the initial start flag being true meets the preset period, the zero-sequence voltage and zero-sequence current of N cycles before and after the initial start flag are extracted and pre-processed; at least one fault start point is obtained to determine the validity of each fault start point; the first half-wave zero-sequence voltage and the first half-wave zero-sequence current are extracted after the effective fault start, and when the flow direction is the load side, the first half-wave zero-sequence current is reversely processed; the derivative of the first half-wave zero-sequence voltage is compared with the polarity of the first half-wave zero-sequence current, and the fault selection interval is output according to the polarity comparison result. Beneficial effects: the fault section can be selected quickly and accurately, and the anti-interference ability is strong; at the same time, there is no need to distinguish the system grounding mode, which further improves the accuracy and processing efficiency of the fault selection.

Description

Technical Field

[0001] The invention relates to the technical field of fault location of power distribution lines in an electric power system, and in particular to a single-phase grounding fault section selection method applicable to an electronic feeder terminal. Background Art

[0002] Feeder Terminal Unit (FTU) is installed on 10kV feeder lines to monitor pole switches, complete remote control, telemetry, telesignaling, and fault detection functions, and communicate with the distribution automation master station to provide distribution system operation status and various parameters, i.e., information required for monitoring and control, including switch status, power parameters, phase-to-phase faults, ground faults, and parameters at the time of faults. It also executes commands issued by the distribution master station to adjust and control distribution equipment, and realizes fault location, fault isolation, and rapid power supply restoration in non-fault areas.

[0003] Feeder terminals mainly include electromagnetic feeder terminals and electronic feeder terminals. Compared with electromagnetic feeder terminals, electronic feeder terminals have a larger measurement range, higher accuracy, lower power consumption, and wider frequency response. However, due to the use of small signal transmission, their anti-interference requirements are higher.

[0004] Single-phase grounding is a single-phase grounding of a 10kV (35kV) low-current grounding system. Single-phase grounding fault is the most common fault in the distribution system and often occurs in humid and rainy weather. It is caused by many factors such as tree barriers, single-phase breakdown of insulators on distribution lines, single-phase line breaks, and harm from small animals. Single-phase grounding not only affects the normal power supply of users, but may also generate overvoltage, burn equipment, and even cause phase-to-phase short circuits to expand accidents. Due to the overhead lines, complex structures, and multiple branch lines of the distribution network, the difficulty of locating and isolating after a single-phase grounding fault occurs is further increased.

[0005] At present, there are various methods for selecting single-phase grounding faults, including steady-state method, phase current method, transient power method, and the improved first half-wave method is one of the most widely used methods with many application cases. It mainly uses the characteristics that the derivative of zero-sequence voltage and the polarity of zero-sequence current are always opposite to each other to achieve fault selection. However, for electronic feeder terminals with high anti-interference requirements, this method is difficult to implement. In addition, most of the existing single-phase grounding fault selection methods need to adjust or switch the algorithm according to different grounding methods, and are not compatible with different grounding methods. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a single-phase grounding fault section selection method applicable to an electronic feeder terminal.

[0007] The technical problem solved by the present invention can be achieved by adopting the following technical solutions:

[0008] A single-phase ground fault section selection method applicable to an electronic feeder terminal, comprising:

[0009] When the zero-sequence voltage data meets the preset initial start condition, an initial start flag is set;

[0010] Determine whether the time delay corresponding to the initial start flag being true satisfies a preset period, and when the time delay satisfies the preset period, extract the zero-sequence voltage and zero-sequence current of N cycles before and after the initial start flag for preprocessing, where N is a positive integer greater than 1;

[0011] Obtaining at least one fault starting point according to the preprocessed zero-sequence voltage and the zero-sequence current, and determining the validity of each of the fault starting points;

[0012] Extracting the first half-wave zero-sequence voltage and the first half-wave zero-sequence current after the effective fault is started, and performing reverse processing on the first half-wave zero-sequence current when the power flow direction is the load side;

[0013] The derivative of the first half-wave zero-sequence voltage is compared with the polarity of the first half-wave zero-sequence current, and a fault selection interval is output according to the polarity comparison result.

[0014] Preferably, the electronic feeder terminal is configured with: a zero-sequence voltage acquisition channel for acquiring the zero-sequence voltage data; and zero-sequence current acquisition channels of different ranges for acquiring zero-sequence current data.

[0015] Preferably, the initial start condition is that the zero-sequence voltage differential amplitude of the zero-sequence voltage data exceeds a preset first threshold and reaches a first preset number of points in total.

[0016] Preferably, after setting an initial startup flag, the method further includes: performing a stretching process on the initial startup flag.

[0017] Preferably, the preprocessing specifically includes:

[0018] Performing wavelet decomposition on the extracted zero-sequence voltage and the zero-sequence current, and extracting low-frequency zero-sequence voltage and low-frequency zero-sequence current;

[0019] The method for obtaining the fault starting point includes:

[0020] When the low-frequency zero-sequence voltage is greater than a preset second threshold, or the low-frequency zero-sequence current is greater than a preset third threshold, the fault starting point is extracted.

[0021] Preferably, the determining the validity of each of the fault starting points specifically includes:

[0022] If the fault starting point is located within the first half of the N cycles, or within the last quarter of the N cycles, then the fault starting point is determined to be invalid; otherwise, the fault starting point is valid.

[0023] Preferably, the method for determining the tidal current direction includes:

[0024] Collect three-phase voltage and three-phase current;

[0025] Active power is calculated according to the three-phase voltage and the three-phase current, and the power flow direction is determined according to the direction of the active power.

[0026] Preferably, when the power flow direction is the power supply side, the direction of the first half-wave zero-sequence current is not processed.

[0027] Preferably, the comparing the derivative of the first half-wave zero-sequence voltage with the polarity of the first half-wave zero-sequence current specifically includes:

[0028] If the derivative of the first half-wave zero-sequence voltage is opposite to the polarity of the first half-wave zero-sequence current, it is negative polarity; otherwise, it is positive polarity.

[0029] Preferably, outputting the fault selection interval according to the polarity comparison result specifically includes:

[0030] If the accumulated number of points with opposite polarities is greater than a second preset number of points, it is determined to be an in-zone grounding fault; otherwise, it is determined to be an out-of-zone fault.

[0031] The advantages or beneficial effects of the technical solution of the present invention are:

[0032] The present invention proposes a single-phase grounding section selection method suitable for electronic feeder terminals, which can quickly and accurately select the fault section and effectively cut off the fault, with fast response speed and strong anti-interference ability; at the same time, the method can be used in small current systems with various grounding methods, without the need to distinguish the system grounding methods and without algorithm switching, further improving the accuracy and processing efficiency of single-phase grounding fault section selection in small current systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flow chart of a single-phase ground fault section selection method applicable to an electronic feeder terminal in a preferred embodiment of the present invention;

[0034] Figure 2 The figure is a flowchart of a specific implementation of a single-phase ground fault section selection method applicable to an electronic feeder terminal in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments 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.

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0038] See also Figure 1-2 In a preferred embodiment of the present invention, based on the above problems existing in the prior art, a single-phase grounding fault section selection method applicable to an electronic feeder terminal is provided, comprising:

[0039] S1: When the zero-sequence voltage data meets the preset initial start condition, an initial start flag is set;

[0040] S2: Determine whether the time delay corresponding to the initial start flag being true satisfies a preset period, and when the time delay satisfies the preset period, extract the zero-sequence voltage and zero-sequence current of N cycles before and after the initial start flag for preprocessing, where N is a positive integer greater than 1;

[0041] S3: obtaining at least one fault starting point according to the preprocessed zero-sequence voltage and zero-sequence current, and determining the validity of each fault starting point;

[0042] S4: extract the first half-wave zero-sequence voltage and the first half-wave zero-sequence current after the effective fault start, and reversely process the first half-wave zero-sequence current when the power flow direction is the load side;

[0043] S5: Compare the derivative of the first half-wave zero-sequence voltage with the polarity of the first half-wave zero-sequence current, and output the fault selection interval according to the polarity comparison result.

[0044] Specifically, in view of the difficulty in extracting fault characteristics of the improved first half-wave method itself, and the problem that the electronic feeder terminal is a small signal transmission with poor anti-interference ability, in order to realize that the currently widely promoted electronic feeder terminals can quickly and accurately select the fault section and effectively cut off the fault, the present application proposes a single-phase grounding fault selection method suitable for electronic feeder terminals. First, the transient characteristics when a single-phase grounding fault occurs are used, and the zero-sequence voltage suddenly crosses the threshold as the initial starting condition. The sampling data of the zero-sequence voltage and zero-sequence current of N cycles before and after the initial starting moment are cached, and then the accurate fault starting point is found. The sampling data of the zero-sequence voltage and zero-sequence current in the first half-wave after the effective fault starting point are extracted, and the zero-sequence voltage derivative and the zero-sequence current polarity are calculated in combination with the flow direction, so as to obtain the fault section selection interval, and the alarm is reported or exported according to the grounding alarm or tripping. This application comprehensively considers the characteristics of a single-phase grounding fault in a small current grounding system, and the characteristics that the electronic feeder terminal is relatively susceptible to interference. It can effectively solve the above two problems and, to a certain extent, solve the grounding misjudgment caused by actual power grid current changes. In addition, after testing, this method can be applied to small current systems with various grounding methods, without the need to distinguish the system grounding methods, and without algorithm switching, further improving the accuracy and processing efficiency of the single-phase grounding fault selection in the small current system, and has the characteristics of high acquisition accuracy, fast response speed, strong anti-interference ability, good compatibility, and high accuracy.

[0045] Furthermore, in the above S1, before judging whether the zero-sequence voltage data meets the preset initial start-up condition, the following steps are included:

[0046] S11: Collect zero-sequence voltage data and zero-sequence current data and scale them proportionally.

[0047] Specifically, in this embodiment, since the electronic feeder terminal itself is a small signal, the collected data needs to be scaled according to the transmission ratio.

[0048] As a preferred embodiment, the electronic feeder terminal is configured with: a zero-sequence voltage acquisition channel for acquiring zero-sequence voltage data; and zero-sequence current acquisition channels of different ranges for acquiring zero-sequence current data.

[0049] Specifically, in this embodiment, the electronic feeder terminals are all equipped with direct zero-sequence voltage and zero-sequence current acquisition channels, and high-precision voltage sensors and current sensors are used to synchronously and real-timely acquire zero-sequence voltage and zero-sequence current sampling data (i.e., zero-sequence voltage data and zero-sequence current data), eliminating the synthesis calculation time. Further, the zero-sequence voltage and zero-sequence current are directly acquired through the actual mutual inductor channel, and the total number of sampling points is k as an example but not a limitation, and the total number of sampling points k=264, with high acquisition accuracy and less calculation time.

[0050] Furthermore, two sampling channels with different ranges are used to collect zero-sequence current, which greatly improves the measurement width and accuracy.

[0051] After the above S11, the following further includes: S12: reading the mutation threshold and determining the delay.

[0052] Specifically, in this embodiment, the mutation threshold of zero-sequence voltage and zero-sequence current and the setting value of judgment delay are obtained in real time. The mutation threshold includes the first threshold preset in S13 below, the second threshold and the third threshold preset in S31; the judgment delay is specifically the preset period in S21 below.

[0053] Furthermore, the mutation thresholds and the setting values ​​of the judgment delay of the above-mentioned zero-sequence voltage and zero-sequence current can be stored in the same storage unit or in their respective corresponding storage units for real-time reading.

[0054] As an example and not a limitation, the mutation thresholds and judgment delay setting values ​​of the zero-sequence voltage and zero-sequence current pre-stored in the storage unit can be fixed values; they can also be variable values, and their specific values ​​are related to the grounding method and grounding parameters, etc. Different single-phase grounding methods may correspond to different values; the values ​​corresponding to the same single-phase grounding method but different grounding parameters may also change.

[0055] As a preferred implementation, the initial start condition is that the zero-sequence voltage differential amplitude of the zero-sequence voltage data exceeds a preset first threshold value and reaches a first preset number of points in total.

[0056] Specifically, the process of judging whether the zero-sequence voltage data meets the preset initial start-up condition specifically includes: S13: judging whether the zero-sequence voltage differential amplitude exceeds the preset first threshold value and reaches the first preset number of points cumulatively: if so, enter S14; if not, return to S11; S14: set the initial start-up flag. In this embodiment, the zero-sequence voltage differential effective value is calculated by fast Fourier transform, and the zero-sequence voltage differential amplitude crossing the mutation threshold is used as the initial start-up condition. The above-mentioned first preset number of points can be set according to the actual application, and is not limited here.

[0057] As a preferred implementation, after setting an initial startup flag, the method further includes: performing a stretching process on the initial startup flag.

[0058] Specifically, in this embodiment, S14 also includes stretching the initial start flag after setting it, which can prevent multiple starts caused by data fluctuations or line oscillations. As an example but not a limitation, the initial start flag is stretched by 200ms.

[0059] As a preferred embodiment, the pretreatment specifically includes:

[0060] The extracted zero-sequence voltage and zero-sequence current are decomposed by wavelet, and low-frequency zero-sequence voltage and low-frequency zero-sequence current are extracted.

[0061] Specifically, in this embodiment, noise reduction processing is performed through wavelet decomposition to obtain 0-250 Hz components of zero-sequence voltage and zero-sequence current, and high-frequency components are removed, which to some extent makes up for the disadvantage that the electronic feeder terminal is susceptible to interference.

[0062] Furthermore, the above S2 specifically includes the following steps: S21: Determine whether the time delay corresponding to the initial start mark being true satisfies a preset period: if so, enter S22; if not, return to S11; S22: Extract the zero-sequence voltage and zero-sequence current of N cycles before and after the initial start mark, where N is a positive integer greater than 1; S23: Wavelet decomposition and extraction of low-frequency zero-sequence voltage and low-frequency zero-sequence current.

[0063] As a preferred implementation, the method for obtaining the fault starting point includes:

[0064] When the low-frequency zero-sequence voltage is greater than a preset second threshold, or the low-frequency zero-sequence current is greater than a preset third threshold, the fault starting point is extracted.

[0065] Specifically, in this embodiment, the zero-sequence current is replayed and analyzed to capture the earliest point in the line where the instantaneous value of the zero-sequence current is greater than the second threshold or the zero-sequence voltage is greater than the third threshold as the accurate fault initiation point.

[0066] As a preferred implementation, in order to reduce the misjudgment rate, the effectiveness of each fault starting point is judged, specifically including:

[0067] If the fault starting point is located within the first half of the N cycles, or within the last quarter of the N cycles, the fault starting point is judged to be invalid; otherwise, the fault starting point is valid.

[0068] Furthermore, the above S3 specifically includes the following steps: S31: determine whether the low-frequency zero-sequence voltage is greater than a preset second threshold, or whether the low-frequency zero-sequence current is greater than a preset third threshold: if so, enter S32; if not, return to S11; S32: extract the fault starting point;

[0069] S33: Determine whether the fault starting point is located within the first half of the N cycles, or within the last quarter of the N cycles: If so, determine that the fault starting point is invalid; if not, determine that the fault starting point is valid, and return to S11.

[0070] As a preferred embodiment, the method for determining the tidal current direction includes:

[0071] A1: collect three-phase voltage and three-phase current;

[0072] A2: Calculate the active power based on the three-phase voltage and three-phase current, and determine the power flow direction based on the direction of the active power.

[0073] Specifically, in this embodiment, by collecting three-phase voltage and three-phase current and calculating active power, it is determined in real time whether the power flow direction is the power supply side or the load side according to the direction of the active power.

[0074] As a preferred implementation, when the power flow direction is on the power supply side, the direction of the first half-wave zero-sequence current is not processed.

[0075] Furthermore, the above S4 specifically includes the following steps: S41: extracting the first half-wave zero-sequence voltage and the first half-wave zero-sequence current after the effective fault is started; S42: judging whether the flow direction is the load side, if so, entering S43; if not, entering S51; S43: performing reverse processing on the first half-wave zero-sequence current.

[0076] Specifically, in this embodiment, the direction of the zero-sequence current in the first half-wave is preprocessed in combination with the current flow direction judgment, which can further eliminate the grounding misjudgment caused by the change of the flow direction of the complex power grid. If the current flow direction is judged to be the power supply side, the direction of the current zero-sequence current does not need to be changed; if the current flow direction is judged to be the load side, the zero-sequence current needs to be reversed by 180°.

[0077] As a preferred implementation, S51: comparing the derivative of the first half-wave zero-sequence voltage with the polarity of the first half-wave zero-sequence current, specifically includes:

[0078] If the derivative of the first half-wave zero-sequence voltage is opposite to the polarity of the first half-wave zero-sequence current, it is negative polarity; otherwise it is positive polarity.

[0079] Specifically, in this embodiment, after the zero-sequence current direction is preprocessed, the polarity of the zero-sequence voltage derivative and the zero-sequence current is calculated using transient characteristics, and opposite polarities are negative polarity, and the same polarity is positive polarity. By using the characteristic that the derivative of the zero-sequence voltage and the zero-sequence current polarity are always opposite when single-phase grounding occurs, the effective time of the characteristic can be extended.

[0080] As a preferred implementation, the fault selection interval is output according to the polarity comparison result, specifically including:

[0081] S52: If the accumulated number of points with opposite polarities is greater than a second preset number of points, it is determined to be an in-zone grounding fault; otherwise, it is determined to be an out-of-zone fault.

[0082] Specifically, in this embodiment, if the number of points with negative polarity is greater than the second preset number of points F, it is determined that an internal ground fault occurs; otherwise, it is an external fault. Further, the second preset number of points F can be one eighth of the total number of sampling points k in the above sampling process.

[0083] In the above preferred embodiment, in the above S21-S23, S31-S33, and S52, the accurate or compatible processing of data features can make the method not need to judge the grounding method of the current grounding system, and can be compatible with the judgment of single-phase grounding faults under various grounding methods.

[0084] The advantages or beneficial effects of adopting the above technical solution are: the present invention is based on the practical application of electronic feeder terminals, uses wavelet decomposition to reduce noise, judges the effectiveness of the fault starting point, and performs direction preprocessing on the target data in combination with the currently judged flow direction, and then combines the principle of the improved first half-wave method to extract the single-phase grounding fault characteristics, and finally obtains a reliable single-phase grounding section selection result, which has the characteristics of high acquisition accuracy, fast response speed, strong anti-interference ability, good compatibility, and high accuracy.

[0085] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of this specification and illustrations should be included in the protection scope of the present invention.

Claims

1. A single-phase ground fault section selection method applicable to an electronic feeder terminal, characterized in that: include: When the zero-sequence voltage data meets the preset initial start condition, an initial start flag is set; The initial start condition is that the zero-sequence voltage differential amplitude of the zero-sequence voltage data exceeds a preset first threshold value and reaches a first preset number of points in total; Determine whether the time delay corresponding to the initial start flag being true satisfies a preset period, and when the time delay satisfies the preset period, extract the zero-sequence voltage and zero-sequence current of N cycles before and after the initial start flag for preprocessing, where N is a positive integer greater than 1; Obtaining at least one fault starting point according to the preprocessed zero-sequence voltage and the zero-sequence current, and determining the validity of each of the fault starting points; Extracting the first half-wave zero-sequence voltage and the first half-wave zero-sequence current after the effective fault starting point, and performing reverse processing on the first half-wave zero-sequence current when the power flow direction is the load side; Comparing the derivative of the first half-wave zero-sequence voltage with the polarity of the first half-wave zero-sequence current, and outputting a fault selection interval according to the polarity comparison result; The pre-processing comprises: Performing wavelet decomposition on the extracted zero-sequence voltage and the zero-sequence current, and extracting low-frequency zero-sequence voltage and low-frequency zero-sequence current; The method for obtaining the fault starting point includes: When the low-frequency zero-sequence voltage is greater than a preset second threshold, or the low-frequency zero-sequence current is greater than a preset third threshold, extracting the fault starting point; The determining of the validity of each of the fault starting points includes: If the fault starting point is located within the first half of the N cycles, or within the last quarter of the N cycles, then the fault starting point is determined to be invalid; otherwise, the fault starting point is valid.

2. The single-phase grounding fault section selection method applicable to an electronic feeder terminal according to claim 1 is characterized in that: The electronic feeder terminal is configured with: a zero-sequence voltage acquisition channel for acquiring the zero-sequence voltage data; and zero-sequence current acquisition channels of different ranges for acquiring zero-sequence current data.

3. The single-phase grounding fault section selection method applicable to an electronic feeder terminal according to claim 1 is characterized in that: After setting an initial startup flag, the method further includes: performing a stretching process on the initial startup flag.

4. The single-phase grounding fault section selection method applicable to an electronic feeder terminal according to claim 1, characterized in that: The method for determining the tidal current direction includes: Collect three-phase voltage and three-phase current; Active power is calculated according to the three-phase voltage and the three-phase current, and the power flow direction is determined according to the direction of the active power.

5. The single-phase grounding fault section selection method applicable to an electronic feeder terminal according to claim 1, characterized in that: When the power flow direction is the power supply side, the direction of the first half-wave zero-sequence current is not processed.

6. The single-phase ground fault section selection method applicable to an electronic feeder terminal according to claim 1, characterized in that: The comparing the derivative of the first half-wave zero-sequence voltage with the polarity of the first half-wave zero-sequence current specifically includes: If the derivative of the first half-wave zero-sequence voltage is opposite to the polarity of the first half-wave zero-sequence current, it is negative polarity; otherwise, it is positive polarity.

7. The single-phase grounding fault section selection method applicable to an electronic feeder terminal according to claim 1, characterized in that: Outputting the fault selection interval according to the polarity comparison result specifically includes: If the accumulated number of points with opposite polarities is greater than a second preset number of points, it is determined to be an in-zone grounding fault; otherwise, it is determined to be an out-of-zone fault.

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