A partial discharge test method for ring network cabinet in ring network distribution system

Abstract

The present application relates to the field of discharge test technology, and specifically to a partial discharge test method for a ring network cabinet in a ring network distribution system, the method comprising: respectively collecting ultra-high frequency electromagnetic signals and transient ground voltage signals of the ring network cabinet at each moment, and forming a high frequency sequence and a voltage sequence in time sequence; obtaining all peaks in the high frequency sequence, and determining the group index of each peak; obtaining the peak consistency index of the high frequency sequence; dividing the voltage sequence into subsequences, performing threshold segmentation based on the discreteness of all subsequences, and obtaining each fluctuating subsequence and each stable subsequence; analyzing the average level of the group index of the peak at the same moment as the elements in all fluctuating subsequences, and the difference in the discreteness of all fluctuating subsequences and all stable subsequences, to determine the stability index of the ring network cabinet; judging the partial discharge of the ring network cabinet based on the stability index. The present application improves the accuracy of the partial discharge test of the ring network cabinet.

Description

Technical Field

[0001] The present application relates to the technical field of discharge testing, and in particular to a method for testing partial discharge of a ring network cabinet in a ring network power distribution system. Background Art

[0002] Ring main unit refers to a high-voltage switchgear used in the ring main distribution system, and its insulating medium can use environmentally friendly gas. As an important equipment in the ring main distribution system, the ring main unit can not only distribute according to different load requirements to ensure the stability and reliability of the power supply in the system; it can also provide overload protection, short circuit protection, and leakage protection. Therefore, it is necessary to test the function of the ring main unit, detect the safety of the ring main unit, and ensure safe operation. The partial discharge phenomenon of the ring main unit will gradually destroy the insulating medium, and eventually lead to insulation failure, causing serious electrical failures.

[0003] According to the characteristics of partial discharge, the UHF detection method is currently the most widely used partial discharge test method. However, when the partial discharge test of the ring main unit is performed using the existing UHF detection method, only a single UHF electromagnetic signal is often analyzed, resulting in low accuracy in the partial discharge test of the ring main unit. Summary of the invention

[0004] In order to solve the above technical problems, the present application provides a partial discharge testing method for a ring network cabinet in a ring network distribution system to solve the existing problems.

[0005] A partial discharge test method for a ring network cabinet in a ring network distribution system of the present application adopts the following technical solution:

[0006] An embodiment of the present application provides a partial discharge test method for a ring main unit in a ring main power distribution system, the method comprising the following steps:

[0007] Collect the ultra-high frequency electromagnetic signals and transient grounding voltage signals of the ring main unit at each moment, and form high frequency sequences and voltage sequences according to the time sequence;

[0008] Obtain all peaks in the high-frequency sequence, analyze the changing trend of each peak over time, the difference between each peak and the adjacent peak, and the size and order relationship between the peaks, and determine the sociability index of each peak;

[0009] Perform threshold segmentation based on the group index of all peaks to obtain each suspected significant peak and each regular peak; analyze the difference in change trend between all suspected significant peaks and all regular peaks, as well as the difference in average level, to determine the peak consistency index of the high-frequency sequence;

[0010] The voltage sequence is divided into subsequences, and threshold segmentation is performed based on the discreteness of all subsequences to obtain each fluctuating subsequence and each stable subsequence; the average level of the group index of the peak value at the same time as the elements in all fluctuating subsequences, and the difference in the discreteness of all fluctuating subsequences and all stable subsequences are analyzed, and the stability index of the ring main unit is determined in combination with the peak consistency index;

[0011] The partial discharge condition of the ring main unit is determined based on the stability index.

[0012] In one embodiment, the process of determining the sociability index is as follows:

[0013] Obtaining a fitting straight line for all peaks in the high-frequency sequence in time sequence, and determining a distance difference index for each peak based on a positional relationship between each peak and the fitting straight line;

[0014] Calculate the mean of the difference between each peak and its adjacent peak in time sequence, and use the product of the mean and each peak as the peak mutation index of each peak; arrange all peaks in descending order, and record the sequence number of each peak after arrangement as the relative ranking of each peak;

[0015] The multiplication result of the distance difference index of each peak value and the peak mutation index is calculated, and the sum of the multiplication result and a preset value greater than 0 is calculated, and the ratio of the relative ranking of each peak value to the sum is used as the sociability index.

[0016] In one embodiment, the distance difference index is the vertical distance between each peak and the fitting straight line.

[0017] In one embodiment, obtaining each suspected significant peak and each regular peak includes:

[0018] The suspected significant peak is the peak whose sociability index is less than or equal to the segmentation threshold, and the regular peak is the peak whose sociability index is greater than the segmentation threshold.

[0019] In one embodiment, the peak coincidence index is determined as follows:

[0020] Arrange the group indexes of all suspected significant peaks and all regular peaks in descending order to obtain suspected sequences and regular sequences; record the difference in the slope of the fitted straight line between the suspected sequence and the regular sequence as the trend difference; record the difference in the mean of the suspected sequence and the regular sequence as the mean difference;

[0021] A hypothesis test is performed on the suspected sequence and the regular sequence to obtain a test value; and the peak consistency index is obtained by combining the trend difference, the mean difference and the test value.

[0022] In one embodiment, the peak consistency index is calculated as follows: ; In the formula, F is the peak consistency index of the high-frequency sequence, P is the test value, G is the trend difference between the suspected sequence and the regular sequence, H is the mean difference between the suspected sequence and the regular sequence, The default value is greater than 0.

[0023] In one embodiment, the obtaining of each fluctuating subsequence and each stationary subsequence includes:

[0024] Calculate the discrete degree of all elements of each subsequence. The fluctuating subsequence is a subsequence whose discrete degree is greater than or equal to the segmentation threshold, and the stationary subsequence is a subsequence whose discrete degree is less than the segmentation threshold.

[0025] In one embodiment, the stability index is determined by:

[0026] The average level of the sociability index is recorded as the fluctuation mean; the difference between the mean of the discrete degrees of all fluctuating subsequences and all stable subsequences is calculated and recorded as the average fluctuation difference; the stability index is obtained by combining the fluctuation mean, the average fluctuation difference and the peak consistency index.

[0027] In one embodiment, the stability index is calculated as follows: ; Wherein, K is the stability index of the ring main unit, F is the peak consistency index of the high-frequency sequence, L is the fluctuation mean, and M is the average fluctuation difference.

[0028] In one embodiment, determining the partial discharge condition of the ring main unit based on the stability index includes:

[0029] If the normalized value of the stability index is greater than or equal to a preset threshold, it is determined that no partial discharge occurs in the ring main unit; otherwise, it is determined that partial discharge occurs in the ring main unit.

[0030] This application has at least the following beneficial effects:

[0031] The present application collects ultra-high frequency electromagnetic signals and transient grounding voltage signals of the ring network cabinet at each moment, and composes high-frequency sequences and voltage sequences in time sequence; obtains all peaks in the high-frequency sequence, analyzes the changing trend of each peak with time sequence, the difference between each peak and the adjacent peaks, and the size sequence relationship between the peaks, and determines the group index of each peak. The group index reflects the degree of abnormality of each peak compared with the other peaks, and improves the accuracy of determining suspected significant peaks; performs threshold segmentation based on the group index of all peaks, and obtains each suspected significant peak and each regular peak; analyzes the difference in changing trends between all suspected significant peaks and all regular peaks, as well as the difference in average levels, and determines the peak consistency index of the high-frequency sequence; the peak consistency index reflects the consistency of the overall distribution of all peaks, and reflects the difference in the average level among all peaks. The possibility of abnormal peaks improves the reliability of local discharge judgment of the ring network cabinet; finally, the voltage sequence is divided into subsequences, and threshold segmentation is performed based on the discreteness of all subsequences to obtain each fluctuating subsequence and each stable subsequence; the average level of the group index of the peak at the same time as the elements in all fluctuating subsequences, as well as the difference in the discreteness of all fluctuating subsequences and all stable subsequences are analyzed, and the stability index of the ring network cabinet is determined in combination with the peak consistency index; the stability index takes into account the correlation between the ultra-high frequency electromagnetic signal and the transient grounding voltage signal, improves the comprehensiveness of the local discharge test on the ring network cabinet, and deeply analyzes the local discharge characteristics of the ring network cabinet; the local discharge situation of the ring network cabinet is determined based on the stability index, which improves the accuracy of the local discharge test of the ring network cabinet. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 A flowchart of the steps of a partial discharge testing method for a ring main unit in a ring main power distribution system provided in an embodiment of the present application;

[0034] Figure 2 A schematic diagram of data collection for partial discharge testing of a ring main unit provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of an ultra-high frequency electromagnetic signal when no partial discharge occurs in the ring main unit provided in an embodiment of the present application;

[0036] Figure 4 A schematic diagram of an ultra-high frequency electromagnetic signal when partial discharge occurs in a ring main unit provided in an embodiment of the present application;

[0037] Figure 5 A flow chart for constructing a stability index provided in an embodiment of the present application. DETAILED DESCRIPTION

[0038] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the following, in combination with the accompanying drawings and preferred embodiments, describes in detail the specific implementation method, structure, features and effects of a partial discharge test method for a ring network cabinet in a ring network distribution system proposed by the present application. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0039] Unless defined otherwise, 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 belongs.

[0040] The following is a detailed description of a specific scheme of a partial discharge testing method for a ring main unit in a ring main power distribution system provided by the present application in conjunction with the accompanying drawings.

[0041] An embodiment of the present application provides a partial discharge test method for a ring network cabinet in a ring network distribution system. Specifically, the following partial discharge test method for a ring network cabinet in a ring network distribution system is provided. Please refer to Figure 1 , the method comprises the following steps:

[0042] Step S001, respectively collect the ultra-high frequency electromagnetic signal and transient grounding voltage signal of the ring main unit at each moment, and form a high frequency sequence and a voltage sequence in time sequence.

[0043] This embodiment uses an ultra-high frequency sensor to collect ultra-high frequency electromagnetic signals during the operation of a ring main unit with nitrogen as the insulating medium. The ultra-high frequency sensor is placed inside the cable compartment of the nitrogen ring main unit, and the collection frequency is 600MHz. At the same time, the transient grounding voltage signal is collected by a transient grounding sensor fixed on the nitrogen ring main unit, and the collection frequency is also 600MHz. The time length of each collection is 6ms, and the ultra-high frequency electromagnetic signal and the transient grounding voltage signal are collected synchronously and in real time. It should be understood that the ultra-high frequency signal of a partial discharge is at the nanosecond ns level and lasts for about 1us. The data collection diagram of the partial discharge test of the ring main unit is shown in the figure below. Figure 2 As shown, 1, 2, and 3 represent nitrogen ring network cabinet, ultra-high frequency sensor, and transient ground voltage sensor, respectively. The acquisition frequency of ultra-high frequency electromagnetic signal and transient ground voltage signal, as well as the acquisition time length, can be set by the implementer according to the actual situation, and this embodiment does not limit it.

[0044] A signal amplifier is used to amplify the collected UHF electromagnetic signal and transient grounding voltage signal, and a bandpass filter is used to filter the amplified UHF electromagnetic signal and transient grounding voltage signal. Finally, the filtered UHF electromagnetic signal and transient grounding voltage signal are converted into discrete digital signals through an analog-to-digital converter. In order to eliminate the impact of the dimensions between the data, the discrete digital signals are Z-score normalized, and the discrete UHF electromagnetic signals and transient grounding voltage signals after normalization are combined into high-frequency sequences and voltage sequences in time sequence. The schematic diagram of the UHF electromagnetic signal when no partial discharge occurs in the ring network cabinet is shown in Figure 1. Figure 3 As shown in the figure, the schematic diagram of ultra-high frequency electromagnetic signal when partial discharge occurs in the ring main unit is as follows Figure 4 shown.

[0045] It should be noted that Z-score normalization processing is an existing well-known technology, and the implementer can choose other existing normalization processing methods according to actual conditions, and this embodiment does not limit it here.

[0046] Step S002, obtaining all peaks in the high frequency sequence, analyzing the changing trend of each peak with time sequence, the difference between each peak and the adjacent peak, and the size sequence relationship between the peaks, and determining the sociability index of each peak.

[0047] When partial discharge occurs in the nitrogen ring main unit, it will radiate electromagnetic wave signals with a frequency of up to hundreds of MHz. At the same time, due to the short duration of partial discharge, if partial discharge occurs, obvious instantaneous fluctuations will appear in the signal collected by the ultra-high frequency sensor.

[0048] Through further analysis of the signals collected by the ultra-high frequency sensor, it was found that after filtering, if the nitrogen ring main unit did not have partial discharge, the overall fluctuation of the signal would be relatively gentle. However, if partial discharge occurred in the nitrogen ring main unit, several more significant transient peaks would appear in the signal. The transient peaks were large and the differences between them were large.

[0049] Based on the above analysis, the high-frequency sequence is used as the input of the peak and trough detection algorithm. The output of the peak and trough detection algorithm is all the peaks in the high-frequency sequence (i.e., the peak values). According to the order of each peak in the high-frequency sequence, all peaks are combined into a peak sequence.

[0050] In the peak sequence, the i-th peak is taken as an example for analysis. With the sequence number of each peak in the peak sequence as the horizontal axis and the peak as the vertical axis, the least square method is used to obtain the fitting straight line of all peaks in the peak sequence, and the vertical distance between the i-th peak point and the fitting straight line is recorded as the distance difference index of the i-th peak; since there are a large number of similar peaks in the high-frequency sequence, even if there are more significant transient peaks, they are individual cases and their number is relatively small, so the slope of the fitting straight line is small and close to 0, so if there is no abnormality in the i-th peak, the vertical distance between the i-th peak and the fitting straight line is small.

[0051] It should be noted that the peak and trough detection algorithm, the least squares method, and the vertical distance calculation between a point and a line are all existing well-known technologies and will not be elaborated here. The implementer can choose other existing peak detection algorithms and straight line fitting algorithms according to actual conditions, and this embodiment does not limit this.

[0052] In the peak sequence, the difference between the ith peak and the previous peak is calculated, recorded as the first difference, the difference between the ith peak and the next peak is calculated, recorded as the second difference, and the product of the mean of the first difference and the second difference and the ith peak is recorded as the peak mutation index of the ith peak. All peaks in the peak sequence are sorted from large to small. If the peaks are the same, they are arranged according to the order in the peak sequence; the sequence number of the ith peak after sorting is recorded as the relative ranking of the ith peak.

[0053] It should be understood that the difference represents the degree of difference between two variables, and can be specifically calculated by using the absolute value of the difference, the ratio, the square of the difference, etc. This embodiment uses the absolute value of the difference as the calculation method for the difference.

[0054] In this embodiment, the sociability index of each peak value may be calculated as follows: ; In the formula, is the sociability index of the ith peak; B is the distance difference index of the ith peak; C is the peak mutation index of the ith peak; D is the relative ranking of the ith peak; is a preset value greater than 0. In order to avoid the denominator being 0, in this embodiment The implementer can set it according to the actual situation, and this embodiment does not limit it here.

[0055] If the distance difference index B is smaller, it means that the i-th peak is closer to the fitting line, and the possibility of a significant mutation in the i-th peak is smaller; if the peak mutation index C is smaller, it means that the difference between the i-th peak and the two previous and next peaks is smaller, and the i-th peak is smaller; if the relative ranking D is larger, it means that the i-th peak is smaller relative to other peaks; therefore, if the sociability index The larger it is, the more likely it is that the i-th peak is a normal peak, and the smaller the possibility that an abnormal mutation has occurred at the i-th peak.

[0056] If the distance difference index B is larger, it means that the i-th peak is farther away from the fitting line; if the peak mutation index C is larger, it means that the difference between the i-th peak and the two previous and next peaks is larger, and the i-th peak is more likely to be larger; if the relative ranking D is smaller, it means that the i-th peak is more likely to be a significant mutation peak relative to other peaks; therefore, if the sociability index The smaller it is, the greater the possibility that the i-th peak has undergone an abnormal mutation.

[0057] Step S003, perform threshold segmentation based on the group index of all peaks to obtain each suspected significant peak and each regular peak; analyze the difference in change trend between all suspected significant peaks and all regular peaks, as well as the difference in average level, to determine the peak consistency index of the high-frequency sequence.

[0058] Since the more significant transient peak value generated by the partial discharge phenomenon is significantly different from the normal peak value, the calculated sociability index will also be significantly different. Therefore, the peak value can be further divided by the sociability index.

[0059] The group index of all peaks in the peak sequence is used as the input of the Otsu threshold method, and the output of the Otsu threshold method is recorded as the first division threshold. All peaks with group index less than or equal to the first division threshold are recorded as suspected significant peaks, and the remaining peaks are recorded as regular peaks. In the order of group index from large to small, the group indexes of all suspected significant peaks are combined into a suspected sequence, and the group indexes of all regular peaks are combined into a regular sequence.

[0060] The suspected sequence and the regular sequence were fitted with a least square method, recorded as the suspected fitting line and the regular fitting line, and the absolute value of the difference in slope between the suspected fitting line and the regular fitting line was recorded as the trend difference G between the suspected sequence and the regular sequence. At the same time, in order to further calculate whether the sociability index between the suspected sequence and the regular sequence conforms to the same data trend distribution, the suspected sequence and the regular sequence were used as the input of the KS (Kolmogorov-Smirnov) test, and the output of the KS test was the test value P. The larger the P value, the more consistent the data distribution of the suspected sequence and the regular sequence, and the smaller the P value, the greater the difference in data distribution between the suspected sequence and the regular sequence.

[0061] It should be noted that Otsu threshold method and KS test are both existing well-known technologies and will not be described in detail here. The implementer can select other existing threshold segmentation algorithms and hypothesis testing algorithms according to actual conditions, and this embodiment does not limit them here.

[0062] In this embodiment, the peak consistency index of the high frequency sequence may be calculated as follows: ; Wherein, F is the peak consistency index of the high-frequency sequence, P is the test value, G is the trend difference between the suspected sequence and the regular sequence, and H is the mean difference between the suspected sequence and the regular sequence, specifically: the absolute value of the difference between the mean of the suspected sequence and the mean of the regular sequence, is a preset value greater than 0. The implementer can set it according to the actual situation, and this embodiment does not limit it here.

[0063] If no partial discharge occurs in the ring main unit, the similarity of the group index of all peaks is high. After division, the difference between the elements in the suspected sequence and the conventional sequence is small. Therefore, after sorting, both the suspected sequence and the conventional sequence show a slowly decreasing data trend, and the data distribution is relatively consistent. Therefore, the larger the P value, the smaller the trend difference G; at the same time, since the difference in element values ​​between the suspected sequence and the conventional sequence is small, the mean difference H is also smaller; therefore, if the peak consistency index F is larger, it means that the group index corresponding to each peak in the high-frequency sequence is more consistent, and the possibility of no abnormal peaks is greater.

[0064] Since partial discharge will lead to a large difference in the group index between peaks, if partial discharge occurs, the data in the suspected sequence will have a significant decreasing trend after sorting, and since the normal peak distribution is relatively consistent, the data trend in the conventional sequence is relatively stable, so the difference in the slope of the fitting line between the suspected sequence and the conventional sequence will be greater and no longer have consistent data distribution characteristics, so the smaller the P value, the greater the trend difference G; at the same time, since partial discharge will lead to a large difference in the corresponding group index between abnormal peaks and normal peaks, the greater the mean difference H. Therefore, if the peak consistency index F is smaller, it means that there are significant differences between the peaks within the high-frequency sequence, the possibility of abnormal peaks is greater, and the possibility of partial discharge is greater.

[0065] Step S004, divide the voltage sequence into subsequences, perform threshold segmentation based on the discreteness of all subsequences, and obtain each fluctuating subsequence and each stable subsequence; analyze the average level of the group index of the peak value at the same time as the elements in all fluctuating subsequences, and the difference in the discreteness of all fluctuating subsequences and all stable subsequences, and determine the stability index of the ring network cabinet in combination with the peak consistency index.

[0066] If partial discharge occurs in the nitrogen ring main unit, the shielding layer of the nitrogen ring main unit will be discontinuous due to the gaps in the wall of the nitrogen ring main unit, causing the electromagnetic waves caused by partial discharge to pass out of the nitrogen ring main unit and generate induced current on the outside of the nitrogen ring main unit. Then, due to the wave impedance, a transient voltage to the ground is generated on the wall of the cabinet. Therefore, if partial discharge occurs in the nitrogen ring main unit, significant abnormal fluctuations will also appear in the voltage signal, which is manifested in that the fluctuation range of the peak and valley values ​​significantly exceeds the fluctuation range of the normal voltage signal, and the fluctuation is violent and short-lived.

[0067] Based on the above analysis, the voltage sequence is used as the input of the BG (Bernaola Galvan) sequence segmentation algorithm, and the output of the BG algorithm is the subsequences after the voltage sequence is segmented. The discreteness of each subsequence is calculated, and all the discreteness is used as the input of the Otsu threshold method. The output of the Otsu threshold method is recorded as the second partition threshold, and all subsequences with a discreteness greater than or equal to the second partition threshold are recorded as fluctuating subsequences, and all remaining subsequences are recorded as stable subsequences. The BG algorithm is an existing well-known technology and will not be described here. The implementer can choose other existing sequence segmentation algorithms according to actual conditions, and this embodiment does not limit it here.

[0068] It should be understood that the degree of dispersion can be specifically calculated by using variance, standard deviation, coefficient of variation, etc. This embodiment uses variance as the calculation method for the degree of dispersion.

[0069] The peak value appearing in the high-frequency sequence within the time series range corresponding to each fluctuation subsequence is obtained and recorded as the fluctuation high-frequency peak value. The average of the group indexes of all the fluctuation high-frequency peak values ​​corresponding to all fluctuation subsequences is recorded as the fluctuation mean. The fluctuation mean can reflect the situation in which the peak value of the data in the high-frequency sequence suddenly changes when the voltage sequence fluctuates.

[0070] The mean of the discreteness of all the fluctuating subsequences is calculated and recorded as the first mean, the mean of the discreteness of all the stable subsequences is calculated and recorded as the second mean, and the difference between the first mean and the second mean is recorded as the average fluctuation difference of the voltage sequence.

[0071] The stability index of the ring main unit can be calculated as follows: ; In the formula, K is the stability index of the ring main unit; F is the peak consistency index of the high-frequency sequence; L is the fluctuation mean; M is the average fluctuation difference. The flow chart of the construction of the stability index of the ring main unit is as follows: Figure 5 shown.

[0072] If the peak consistency index F is larger, it means that although the data in the high-frequency sequence fluctuates, the fluctuation is relatively consistent; if the corresponding fluctuation mean L is larger, it means that there is a greater possibility that no peak mutation occurs in the high-frequency sequence data corresponding to the fluctuation subsequence; if the average fluctuation difference M is smaller, it means that even if the voltage sequence is divided, the degree of fluctuation between each subsequence is still relatively similar. Therefore, the larger the stability index K, the greater the possibility that no partial discharge occurs in the nitrogen ring main unit, and the better the insulation performance of the nitrogen ring main unit.

[0073] If the peak consistency index F is smaller, it means that the difference between the peaks in the high-frequency sequence is greater, and the possibility of a significant mutation peak is greater; if the corresponding fluctuation mean L is smaller, it means that when the voltage signal fluctuates greatly, the possibility of abnormal fluctuations in the ultra-high frequency signal at the corresponding moment is greater; if the average fluctuation difference M is larger, it means that the difference between the abnormal fluctuation signal and the normal fluctuation signal in the voltage signal is greater, and it is more consistent with the characteristics of the partial discharge phenomenon. Therefore, the smaller the stability index K is, the greater the possibility of partial discharge in the nitrogen ring main unit, and the greater the possibility of the insulation performance of the nitrogen ring main unit being affected.

[0074] Step S005: determining the partial discharge condition of the ring main unit based on the stability index of the ring main unit.

[0075] In this embodiment, the Sigmoid function is used to normalize the stability index K of the nitrogen ring main unit. If the normalized stability index is greater than or equal to the preset threshold, it is determined that the insulation performance of the nitrogen ring main unit is good and no local discharge occurs. If the normalized stability index is less than the preset threshold, it is determined that there is a problem with the insulation performance of the nitrogen ring main unit and local discharge has occurred. At this time, the nitrogen ring main unit needs to be repaired in time to ensure the safety and stability of the power system.

[0076] In this embodiment, the preset threshold is artificially limited to 0.5, and the implementer can set it according to the actual situation. This embodiment does not limit it here; the implementer can also choose the normalization method of the stability index of the nitrogen ring network cabinet according to the actual situation.

[0077] It should be noted that the above sequence of the embodiments of the present application is for description only and does not represent the advantages and disadvantages of the embodiments. The above is a description of a specific embodiment of this specification. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0078] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0079] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Modifications to the technical solutions recorded in the aforementioned embodiments, or equivalent replacement of some of the technical features therein, do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A partial discharge test method for a ring main unit in a ring main distribution system, characterized in that: The method comprises the following steps: Collect the ultra-high frequency electromagnetic signals and transient grounding voltage signals of the ring main unit at each moment, and form high frequency sequences and voltage sequences according to the time sequence; Obtain all peaks in the high-frequency sequence, perform straight line fitting on all peaks, and use the distance between the peak and the corresponding straight line as the distance difference index; obtain the peak mutation index based on the mean of the difference between the peak and the adjacent peaks and the peak forward fusion, and determine the sociability index of each peak based on the forward fusion result of the distance difference index and the peak mutation index and the ranking of the peaks; Perform threshold segmentation based on the group index of all peaks to obtain each suspected significant peak and each regular peak; analyze the difference in change trend between all suspected significant peaks and all regular peaks, as well as the difference in average level, to determine the peak consistency index of the high-frequency sequence; The voltage sequence is divided into subsequences, and threshold segmentation is performed based on the discreteness of all subsequences to obtain each fluctuating subsequence and each stable subsequence; the average level of the group index of the peak value at the same time as the elements in all fluctuating subsequences is analyzed and recorded as the fluctuation mean, and the difference in the discreteness of all fluctuating subsequences and all stable subsequences is recorded as the average fluctuation difference; the stability index of the ring network cabinet is determined according to the fluctuation mean, the average fluctuation difference and the peak consistency index; The expression of the stability index is: ; Wherein, K is the stability index of the ring main unit, F is the peak consistency index of the high-frequency sequence, L is the fluctuation mean, and M is the average fluctuation difference; Determining the partial discharge condition of the ring main unit based on the stability index; The determination process of the sociability index is: Obtaining a fitting straight line for all peaks in the high-frequency sequence in time sequence, and determining a distance difference index for each peak based on a positional relationship between each peak and the fitting straight line; Calculate the mean of the difference between each peak and its adjacent peak in time sequence, and use the product of the mean and each peak as the peak mutation index of each peak; arrange all peaks in descending order, and record the sequence number of each peak after arrangement as the relative ranking of each peak; The multiplication result of the distance difference index of each peak value and the peak mutation index is calculated, and the sum of the multiplication result and a preset value greater than 0 is calculated, and the ratio of the relative ranking of each peak value to the sum is used as the sociability index.

2. A partial discharge testing method for a ring main unit in a ring main distribution system as claimed in claim 1, characterized in that: The distance difference index is the vertical distance between each peak and the fitting straight line.

3. A partial discharge testing method for a ring main unit in a ring main power distribution system as claimed in claim 1, characterized in that: The obtaining of each suspected significant peak value and each conventional peak value includes: The suspected significant peak is the peak whose sociability index is less than or equal to the segmentation threshold, and the regular peak is the peak whose sociability index is greater than the segmentation threshold.

4. A partial discharge testing method for a ring main unit in a ring main distribution system as claimed in claim 1, characterized in that: The process of determining the peak consistency index is as follows: Arrange the group indexes of all suspected significant peaks and all regular peaks in descending order to obtain suspected sequences and regular sequences; record the difference in the slope of the fitted straight line between the suspected sequence and the regular sequence as the trend difference; record the difference in the mean of the suspected sequence and the regular sequence as the mean difference; A hypothesis test is performed on the suspected sequence and the regular sequence to obtain a test value; and the peak consistency index is obtained by combining the trend difference, the mean difference and the test value.

5. A partial discharge testing method for a ring main unit in a ring main power distribution system as claimed in claim 4, characterized in that: The peak consistency index is calculated as follows: ; In the formula, F is the peak consistency index of the high-frequency sequence, P is the test value, G is the trend difference between the suspected sequence and the regular sequence, H is the mean difference between the suspected sequence and the regular sequence, The default value is greater than 0.

6. A partial discharge testing method for a ring main unit in a ring main power distribution system as claimed in claim 1, characterized in that: The obtaining of each fluctuating subsequence and each stable subsequence comprises: Calculate the discrete degree of all elements of each subsequence. The fluctuating subsequence is a subsequence whose discrete degree is greater than or equal to the segmentation threshold, and the stationary subsequence is a subsequence whose discrete degree is less than the segmentation threshold.

7. A partial discharge testing method for a ring main unit in a ring main power distribution system as claimed in claim 1, characterized in that: The determining of the partial discharge condition of the ring main unit based on the stability index includes: If the normalized value of the stability index is greater than or equal to a preset threshold, it is determined that no partial discharge occurs in the ring main unit; otherwise, it is determined that partial discharge occurs in the ring main unit.

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