A ground fault judgment method based on a data acquisition device

Abstract

The present application relates to the technical field of distribution network automation, and discloses a grounding fault judgment method based on a data acquisition device, comprising the following steps: S1: installing equipment at a line monitoring node, and collecting three-phase currents when a grounding fault occurs in the line; S2: synthesizing zero sequence currents of the monitoring node by using the collected three-phase currents; S3: calculating an effective value and an amplitude of the last cycle of the zero sequence currents; S4: slidingly calculating the effective value and the amplitude of the zero sequence currents; and S5: setting a high-resistance fault criterion, and if the criterion is met, the grounding fault is determined to be a high-resistance grounding fault, otherwise, the grounding fault is determined to be a low-resistance grounding fault. The present application provides a grounding fault judgment method based on a data acquisition device, and solves the problems of large calculation amount and inaccuracy in calculating similarity after steady-state compensation of an arc-suppression coil grounding system.

Description

Technical Field

[0001] This invention relates to the field of power distribution network automation technology, and in particular to a ground fault judgment method based on a data acquisition device. Background Technology

[0002] Some medium-voltage distribution network systems in my country use arc-suppression coil grounding systems, a type of low-current grounding system. After a ground fault occurs, the fault current is small, and especially since the fault steady-state is compensated, it is difficult to accurately locate the fault section. Although the system currently allows operation with a fault for 2 hours, if the fault is not cleared for an extended period, it may lead to overvoltage causing a two-phase-to-ground short circuit, seriously threatening the safe and stable operation of the power grid. Therefore, after a ground fault occurs, it is necessary to locate the fault section promptly and accurately to assist patrol personnel in identifying and eliminating the fault as early as possible, ensuring the safe and stable operation of the power grid.

[0003] Currently, for arc suppression coil systems, due to compensation for steady-state fault information, only transient information or high-frequency signals after filtering the steady-state data can be used. However, for high-resistance grounding faults, there is no transient information, and filtering the steady-state data involves significant computation and slow convergence. If it were possible to distinguish between high and low resistance grounding faults, and to employ a separate feature extraction algorithm for high-resistance grounding faults, the location accuracy could be greatly improved. Therefore, there is an urgent need to develop an algorithm with low computational complexity that can distinguish between high and low resistance grounding faults. Summary of the Invention

[0004] This invention addresses the shortcomings and defects of existing technologies by providing a grounding fault judgment method based on a data acquisition device. This method identifies whether a grounding fault is a high-resistance or low-resistance fault, providing a prerequisite for calculating characteristic values ​​under different transition resistances and ensuring the accuracy of locating high-resistance grounding faults.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A ground fault detection method based on a data acquisition device includes the following steps:

[0007] S1: Install sampling equipment at the line monitoring node to collect the three-phase current when a ground fault occurs on the line;

[0008] S2: Use the collected three-phase current to synthesize the zero-sequence current of the monitoring node;

[0009] S3: Calculate the effective value and amplitude of the last cycle of the zero-sequence current;

[0010] S4: Calculate the effective value and amplitude of the zero-sequence current using sliding motion;

[0011] S5: Set the high-resistance fault criterion. If the criterion is met, it is determined to be a high-resistance ground fault; otherwise, it is a low-resistance ground fault.

[0012] Furthermore, the installation equipment in step 1 is not limited to fault indicators, FTUs, or primary and secondary fusion devices.

[0013] Furthermore, the formula for calculating the effective value of the last cycle of the zero-sequence current in step 3 is as follows:

[0014]

[0015] Among them, RMS last In represents the effective value of the last cycle of the calculated zero-sequence current, and I0(n) represents the instantaneous value of the zero-sequence current at the nth point. CycPoint represents the mean value of the last cycle of the zero-sequence current, while CycPoint represents the number of sampling points within one power frequency cycle.

[0016] Furthermore, the formula for calculating the amplitude of the last cycle of the zero-sequence current in step 3 is as follows:

[0017] Amp = (Peak - Valley) / 2;

[0018] Where Amp represents the amplitude of the last cycle of the zero-sequence current, Peak represents the peak value of the last cycle of the zero-sequence current, and Valley represents the valley value of the last cycle of the zero-sequence current.

[0019] Furthermore, the formula for calculating the effective value of the zero-sequence current in step 4 is as follows:

[0020]

[0021] Among them, RMS raf (k) represents the effective value of the zero-sequence current obtained from the k-th sliding calculation, and I0(n) represents the instantaneous value of the zero-sequence current at the n-th point. represents the mean of the zero-sequence current from the m-th sampling point to the +m-1-th sampling point, where CycPoint represents the number of sampling points within one power frequency cycle, and k represents the k-th sliding.

[0022] Furthermore, the formula for calculating the zero-sequence current amplitude in step 4 is as follows:

[0023]

[0024] Among them, Amp raf(k) represents the zero-sequence current amplitude obtained by the k-th sliding calculation, Peak represents the peak value of the zero-sequence current between the integer sampling points of the 1+k*CycPoint and (k+1)*CycPoint, and Valley represents the valley value of the zero-sequence current between the integer sampling points of the 1+k*CycPoint and (k+1)*CycPoint.

[0025] Furthermore, the high and low resistance grounding fault criteria set in step 5 are as follows: if the effective value of the zero-sequence current obtained by sliding calculation is less than the effective value threshold of the zero-sequence current, and the amplitude of the zero-sequence current obtained by sliding calculation is less than the amplitude threshold of the zero-sequence current, then it is a high resistance grounding fault; otherwise, it is a low resistance grounding fault.

[0026] Furthermore, in step 5, the threshold value of the zero-sequence current effective value is set to n times the effective value of the zero-sequence current of the last cycle, and the threshold value of the zero-sequence current amplitude is set to n times the amplitude of the zero-sequence current of the last cycle, where n takes any number greater than 1.

[0027] The beneficial technical effects of this invention are as follows: It provides a ground fault judgment method based on a data acquisition device, which can identify whether the transition resistance of a ground fault is low-resistance or high-resistance, providing conditions for using a separate feature extraction algorithm for high-resistance ground faults, thereby ensuring the accuracy of high-resistance ground fault location. This method has low computational load, requiring only zero-sequence current for identification, and has good engineering applicability. Attached Figure Description

[0028] Figure 1 This is the overall flowchart of the present invention.

[0029] Figure 2 This is the zero-sequence current waveform in Example 1 of the present invention.

[0030] Figure 3 The curve of the effective value of the zero-sequence current obtained by sliding calculation in Example 1 of this invention.

[0031] Figure 4 The zero-sequence current amplitude curve is obtained by sliding calculation in Example 1 of this invention.

[0032] Figure 5 This is the zero-sequence current waveform in Example 2 of the present invention.

[0033] Figure 6 The curve of the effective value of the zero-sequence current obtained by sliding calculation in Example 2 of this invention.

[0034] Figure 7 The zero-sequence current amplitude curve obtained by sliding calculation in Example 2 of this embodiment of the invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and do not limit the scope of the invention.

[0036] Example:

[0037] A ground fault detection method based on a data acquisition device includes the following steps:

[0038] S1: Install equipment at the line monitoring node to collect the three-phase current when a ground fault occurs on the line.

[0039] S2: The zero-sequence current of the monitoring node is synthesized using the collected three-phase currents. The zero-sequence current is as follows: Figure 2 , Figure 5 As shown.

[0040] S3: Calculate the effective value and amplitude of the last cycle of the zero-sequence current. In Case 1, the effective value of the last cycle of the zero-sequence current is 2.95A and the amplitude is 4.2A. In Case 2, the effective value of the last cycle of the zero-sequence current is 8.9A and the amplitude is 12A.

[0041] S4: Calculate the effective value and amplitude of the zero-sequence current in Case 1 and Case 2 using sliding motion, such as... Figure 3 , Figure 4 As shown, the effective value and amplitude obtained by sliding calculation in Case 1 show an increasing trend. Therefore, the amplitude and effective value of the zero-sequence current in the last cycle are the largest. The maximum effective value of the zero-sequence current obtained by sliding calculation in Case 1 is 2.7A, and the maximum amplitude of the zero-sequence current obtained by sliding calculation is 3.9A.

[0042] like Figure 6 , Figure 7 As shown, the effective value and amplitude obtained by the sliding calculation in Case 2 are at their maximum at the time of the fault. The maximum effective value of the zero-sequence current obtained by the sliding calculation in Case 2 is 22A, and the maximum amplitude is 57A.

[0043] S5: Set the high resistance fault criterion. The specific criterion is: threshold setting: take n as 1.3>1, then the effective value threshold of zero-sequence current in Case 1 is 1.3*2.95A, and the amplitude threshold of zero-sequence current is 1.3*4.2A.

[0044] In Case 2, the effective value threshold of the zero-sequence current is 1.3*8.9A, and the amplitude threshold of the zero-sequence current is 1.3*12A.

[0045] In Case 1, the maximum effective value of the zero-sequence current obtained by sliding calculation is 2.7A, which is less than 1.3*2.95A. At the same time, the maximum amplitude of the zero-sequence current obtained by sliding calculation is 3.9A, which is less than 1.3*4.2A. Since 2.7 < 2.95, n can be any number greater than 1. The maximum effective value of the zero-sequence current obtained by sliding calculation, i.e., the maximum amplitude, will definitely be less than the set threshold. Therefore, all points in Case 1 obtained by sliding calculation are less than the set threshold. It is determined that the fault in Case 1 belongs to a high-resistance grounding fault.

[0046] For Case 2, the maximum effective value of the zero-sequence current of 22A obtained by sliding calculation is greater than 1.3*8.9A, and the maximum amplitude of the zero-sequence current of 60A obtained by sliding calculation is greater than 1.3*12A. Therefore, there are points in the sliding process that are greater than the set threshold, and Case 2 is determined to be a low-resistance grounding fault.

[0047] The above embodiments are descriptions of specific implementations of the present invention, and not limitations thereof. Those skilled in the art can make various modifications and changes without departing from the spirit and scope of the present invention to obtain corresponding equivalent technical solutions. Therefore, all equivalent technical solutions should be included in the patent protection scope of the present invention.

Claims

1. A grounding fault judgment method based on a data acquisition device, characterized in that, Includes the following steps: S1: Install sampling equipment at the line monitoring node to collect the three-phase current when a ground fault occurs on the line; S2: Use the collected three-phase current to synthesize the zero-sequence current of the monitoring node; S3: Calculate the effective value and amplitude of the last cycle of the zero-sequence current; S4: Calculate the effective value and amplitude of the zero-sequence current using sliding motion; S5: Set the threshold value of the zero-sequence current effective value to n times the effective value of the last cycle of the zero-sequence current, and set the threshold value of the zero-sequence current amplitude to n times the amplitude of the last cycle of the zero-sequence current. S6: If all effective values ​​of zero-sequence currents obtained by sliding calculation are less than the threshold value of effective zero-sequence currents, and all amplitude values ​​of zero-sequence currents obtained by sliding calculation are less than the threshold value of amplitude of zero-sequence currents, then it is judged as a high-resistance grounding fault; otherwise, it is judged as a low-resistance grounding fault.

2. The grounding fault judgment method based on a data acquisition device according to claim 1, characterized in that, The equipment installed in step S1 is not limited to fault indicators, FTUs, or primary and secondary fusion devices.

3. The grounding fault judgment method based on a data acquisition device according to claim 1, characterized in that, The formula for calculating the effective value of the last cycle of the zero-sequence current in step S3 is as follows: ; in, This represents the effective value of the last cycle of the calculated zero-sequence current. This represents the instantaneous value of the zero-sequence current at the nth point of the last cycle. This represents the average value of the last cycle of the zero-sequence current. This represents the number of sampling points within one power frequency cycle; The formula for calculating the amplitude of the last cycle of the zero-sequence current is: in, This represents the amplitude of the last cycle of the zero-sequence current. Represents the peak value of the last cycle of the zero-sequence current. This represents the valley value of the last cycle of the zero-sequence current.

4. The grounding fault judgment method based on a data acquisition device according to claim 1, characterized in that, The formula for calculating the effective value of the zero-sequence current in step S4 is as follows: ; in, This represents the effective value of the zero-sequence current obtained from the k-th sliding calculation. This represents the instantaneous value of the zero-sequence current at the nth point. Represents the zero-sequence current from the m-th sampling point to the... The mean of the sampling points, This represents the number of sampling points within one power frequency cycle, and k represents the kth sliding motion. The formula for calculating the zero-sequence current amplitude using sliding motion is: ; in, This represents the zero-sequence current amplitude obtained from the k-th sliding calculation. Representing the zero-sequence current in the first... To the Peak values ​​between integer sampling points Representing the zero-sequence current in the first... To the Valley values ​​between integer sampling points.

5. The grounding fault judgment method based on a data acquisition device according to claim 1, characterized in that, In step S5, n takes a number greater than 1.

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