CN117310402B

CN117310402B - Method and system for testing flashover characteristics of low-temperature insulating material

Info

Publication number: CN117310402B
Application number: CN202311204359.6A
Authority: CN
Inventors: 白金; 周秀; 杨鑫; 田天; 陈磊; 罗艳; 李泽成; 马云龙; 刘威峰
Original assignee: Changsha University of Science and Technology; State Grid Ningxia Electric Power Co Ltd; Electric Power Research Institute of State Grid Ningxia Electric Power Co Ltd
Current assignee: Changsha University of Science and Technology; State Grid Ningxia Electric Power Co Ltd; Electric Power Research Institute of State Grid Ningxia Electric Power Co Ltd
Priority date: 2023-09-18
Filing date: 2023-09-18
Publication date: 2024-06-04
Anticipated expiration: 2043-09-18
Also published as: CN117310402A

Abstract

The invention provides a method and a system for testing the flashover characteristic of a low-temperature insulating material, wherein the method comprises the following steps: step-up test is carried out on the low-temperature insulating material to obtain a first voltage value of first flashover; testing the low-temperature insulating material with a first voltage value, and performing step-down testing on the low-temperature insulating material when flashover occurs to obtain a second voltage value; determining initial repeatability performance of the low-temperature insulating material according to the first voltage value and the second voltage value; according to the initial repeatability performance, performing overvoltage test on the low-temperature insulating material to obtain a preset number of flashover voltage values; weighting the flashover voltage values to obtain target flashover voltage values with preset numbers; determining a target flashover voltage value as a sample point to be detected and a comparison sample point set to be clustered, and obtaining a clustering result; and determining the repeatability performance of the low-temperature insulating material according to the clustering result. The impact surface flashover characteristics of the low-temperature insulating material in liquid nitrogen are determined by testing.

Description

Method and system for testing flashover characteristics of low-temperature insulating material

Technical Field

The invention relates to the technical field of electric power, in particular to a method and a system for testing flashover characteristics of a low-temperature insulating material.

Background

In the past, the development of the transmission voltage class of superconducting power devices represented by high-temperature superconducting cables, along with the improvement of the voltage level, the research of insulating materials suitable for liquid nitrogen environment and the electric performance thereof are increasingly important. The method is suitable for relatively less insulating materials and supporting dielectric materials in liquid nitrogen, and the research on the insulating materials and the supporting dielectric materials is mainly used for measuring the electrical performance parameters of the materials in liquid nitrogen. However, taking the insulation design of the cold insulation high temperature superconducting cable terminal as an example, not only the internal breakdown prevention, partial discharge reduction, but also the surface flashover of the interface between the low temperature insulating material and the liquid nitrogen are prevented. However, there is less research on the material surface flashover characteristics in liquid nitrogen, and there is a need to enhance the research in this area.

The glass fiber reinforced epoxy resin composite material has good low-temperature characteristics (including electrical property, tensile stress, shrinkage rate and the like), and is a block-shaped low-temperature insulating material and a supporting dielectric material which are most commonly applied. The use of these materials should take into account their flashover properties along the surface in liquid nitrogen in addition to their breakdown properties, partial discharge, dielectric losses, etc. At present, no research on the mechanism and the characteristics of the surface flashover of the material in liquid nitrogen is seen. While research to enhance this technique requires first giving a test method for its impact surface flashover characteristics in liquid nitrogen.

Disclosure of Invention

In view of the above, the present invention provides a method and a system for testing the flashover characteristics of a low temperature insulating material. The impact surface flashover characteristics of the low-temperature insulating material in liquid nitrogen are determined by testing.

In a first aspect of the embodiment of the present invention, there is provided a method for testing a flashover characteristic of a low temperature insulating material, the method comprising:

Step-up test is carried out on the low-temperature insulating material in a flashover test device at preset time intervals until flashover occurs, so that a first voltage value of primary flashover is obtained;

after a preset time interval, testing the low-temperature insulating material by using the first voltage value to obtain a first test result;

Under the condition that the first test result represents that flashover occurs, step-down testing is conducted on the low-temperature insulating material at preset time intervals until flashover does not occur any more, and a corresponding second voltage value is obtained;

determining initial repeatability performance of the low-temperature insulating material according to the first voltage value and the second voltage value;

According to the initial repeatability performance, performing overvoltage test of a preset time interval on a target position of the low-temperature insulating material to obtain a preset number of flashover voltage values;

Determining a preset number of flashover voltage values as sample points to be detected and a comparison sample point set to perform weighted clustering to obtain a clustering result, wherein the comparison sample points in the comparison sample point set are sample points with known repeatability;

and determining the repeatability performance of the low-temperature insulating material according to the clustering result.

Optionally, before determining the preset number of flashover voltage values as the sample points to be detected and the comparison sample point set to perform weighted clustering, and obtaining a clustering result, the method further includes:

based on the obtained known sample points and the repeatability performance of the known sample points, a corresponding flashover voltage characteristic sequence and a corresponding repeatability performance sequence are constructed, wherein the flashover voltage characteristic sequence and the repeatability performance sequence are expressed as follows:

A＝[a₁,a₂,...,a_t]

B_i＝[b_1i,b_2i,...,b_ti]

Wherein a represents a repetitive performance sequence, a _t represents the repetitive performance of the t-th known sample point, B _i represents an i-th flashover voltage signature sequence, and B _ti represents an i-th flashover voltage signature in the t-th known sample point;

Performing information entropy and joint entropy calculation on the flashover voltage characteristic sequence and the repeatability performance sequence to obtain a first information entropy of the flashover voltage characteristic sequence, a second information entropy of the repeatability performance sequence and joint entropy of the flashover voltage characteristic sequence and the repeatability performance sequence;

carrying out gray correlation analysis on the repetitive performance sequence and the flashover voltage characteristic sequence to obtain gray correlation degree between the repetitive performance sequence and the flashover voltage characteristic sequence;

determining the weight of the flashover voltage characteristic sequence according to the first information entropy, the second information entropy, the joint entropy and the gray correlation degree;

Determining the preset number of flashover voltage values as weighted clustering of the sample points to be detected and the comparison sample point set to obtain a clustering result, wherein the method comprises the following steps:

and carrying out weighted clustering on the sample points to be detected and the comparison sample point set based on the weight of the flashover voltage characteristic sequence to obtain a clustering result.

Optionally, the determining the preset number of flashover voltage values as weighted clustering is performed on the sample points to be detected and the comparison sample point set, so as to obtain a clustering result, and the method includes:

Calculating the compactness of each sample point in a sample point set formed by the sample point to be tested and the comparison sample point set, and obtaining a compactness result;

Determining a compactness average value of all sample points according to the compactness result, deleting each sample point with compactness lower than the compactness average value, and obtaining a target sample point;

And screening a first number of initial clustering centers from the target sample points based on a set rule, and performing iterative optimization on the initial clustering centers for preset times through a weighted clustering algorithm to obtain a final clustering result.

Optionally, the determining the repeatability performance of the low-temperature insulating material according to the clustering result includes:

Determining the target category to which the sample point to be detected belongs according to the clustering result;

And determining the repeatability performance of the comparison sample points in the target category as the repeatability performance of the low-temperature insulating material corresponding to the sample points to be detected.

Optionally, the method further comprises:

In the case where the first test result indicates that flashover does not occur, it is determined that the low temperature insulating material is excellent in reproducibility.

Optionally, the determining initial repeatability performance of the low-temperature insulating material according to the first voltage value and the second voltage value includes:

Determining a voltage difference between the second voltage value and the first voltage value;

In the case where the voltage difference satisfies a set condition, it is determined that the initial repeatability performance of the low temperature insulating material is poor.

Optionally, the performing an overvoltage test for a preset time interval on the target position of the low-temperature insulating material according to the initial repeatability performance to obtain a preset number of flashover voltage values includes:

Performing a first overvoltage test on a target location of the low temperature insulating material at a second target voltage value under conditions where the initial repeatability performance appears to be poor;

determining whether flashover occurs in the last overvoltage test of any one overvoltage test;

under the condition that flashover occurs in the previous overvoltage test, the test voltage value after the test voltage value of the previous overvoltage test is reduced by a set voltage value is used for conducting any one overvoltage test;

Under the condition that no flashover occurs in the previous overvoltage test, determining whether no flashover occurs in any overvoltage test performed before any one overvoltage test;

Under the condition that no flashover occurs in the overvoltage test performed before any one overvoltage test, performing any one overvoltage test with a voltage value of a third preset percentage of the previous overvoltage test;

Under the condition that the overvoltage test performed before any one overvoltage test has an overvoltage test with flashover, performing any one overvoltage test with an intermediate value between the test voltage value of the last overvoltage test and the test voltage value of the overvoltage test with flashover nearest to the last overvoltage test;

And determining the test voltage value of the overvoltage test with the flashover as a flashover voltage value, and ending the overvoltage test until the flashover voltage value of the preset number is obtained.

In a second aspect of the embodiments of the present invention, there is provided a test system for flashover characteristics of a low temperature insulation material, the system comprising:

the first voltage value determining module is used for performing step-up test on the low-temperature insulating material in the flashover test device at preset time intervals until flashover occurs, so as to obtain a first voltage value of first flashover;

The first testing module is used for testing the low-temperature insulating material by the first voltage value after a preset time interval to obtain a first testing result;

The second voltage value determining module is used for performing step-down testing on the low-temperature insulating material at preset time intervals until no flashover occurs under the condition that the first test result represents that flashover occurs, so as to obtain a corresponding second voltage value;

the initial repeatability performance determining module is used for determining the initial repeatability performance of the low-temperature insulating material according to the first voltage value and the second voltage value;

The flashover voltage value determining module is used for carrying out overvoltage test on the target position of the low-temperature insulating material at preset time intervals according to the initial repeatability performance to obtain flashover voltage values with preset numbers;

the weighting processing module is used for respectively weighting the preset number of flashover voltage values to obtain the preset number of target flashover voltage values;

The clustering module is used for determining the flashover voltage values with preset numbers as sample points to be detected and carrying out weighted clustering on a comparison sample point set to obtain a clustering result, wherein the comparison sample points in the comparison sample point set are sample points with known repeatability performance;

And the repeatability performance determining module is used for determining the repeatability performance of the low-temperature insulating material according to the clustering result.

Aiming at the prior art, the invention has the following advantages:

The embodiment of the invention provides a test method for flashover characteristics of a low-temperature insulating material. Step-up test is carried out on a low-temperature insulating material in a flashover test device at preset time intervals until flashover occurs, so that a first voltage value of primary flashover is obtained; after a preset time interval, testing the low-temperature insulating material by using a first voltage value to obtain a first test result; under the condition that the first test result represents that flashover occurs, step-down testing is conducted on the low-temperature insulating material at preset time intervals until flashover does not occur any more, and a corresponding second voltage value is obtained; determining initial repeatability performance of the low-temperature insulating material according to the first voltage value and the second voltage value; according to the initial repeatability performance, performing overvoltage test of a preset time interval on a target position of the low-temperature insulating material to obtain a preset number of flashover voltage values; determining a preset number of flashover voltage values as sample points to be detected and a comparison sample point set to perform weighted clustering to obtain a clustering result, wherein the comparison sample points in the comparison sample point set are sample points with known repeatability; and determining the repeatability performance of the low-temperature insulating material according to the clustering result. The impact surface flashover characteristics of the low-temperature insulating material in liquid nitrogen are determined by testing.

The foregoing description is only an overview of the present invention, and is intended to be implemented in accordance with the teachings of the present invention in order that the same may be more clearly understood and to make the same and other objects, features and advantages of the present invention more readily apparent.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

Fig. 1 is a flowchart of a method for testing flashover characteristics of a low-temperature insulating material according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a flashover test apparatus used in a method for testing a flashover characteristic of a low-temperature insulating material according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a flashover waveform of a flashover test when no load exists and the electrode spacing is 5mm in a method for testing a flashover characteristic of a low temperature insulation material according to an embodiment of the present invention;

FIG. 4 is a chart of flashover voltage of a G/R low temperature insulation material in a flashover test method of the flashover characteristics of the low temperature insulation material according to an embodiment of the present invention;

FIG. 5 is a discharge delay bar chart of a flashover test performed on a G/R low temperature insulation material in a method for testing a flashover characteristic of a low temperature insulation material according to an embodiment of the present invention;

fig. 6 is a chart of flashover voltage of flashover tests performed on two different materials in a method for testing flashover characteristics of a low-temperature insulating material according to an embodiment of the present invention;

Fig. 7 is a graph showing the relationship between flashover voltage and creepage distance of two different materials for flashover test in the test method of flashover characteristics of a low temperature insulation material according to the embodiment of the present invention;

FIG. 8 is a schematic diagram of a crack after flashover of a G/R low temperature insulation material in a method for testing flashover characteristics of a low temperature insulation material according to an embodiment of the present invention;

fig. 9 is a schematic diagram of a test system for flashover characteristics of a low-temperature insulating material according to an embodiment of the present invention.

Detailed Description

Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

Fig. 1 is a flowchart of a method for testing flashover characteristics of a low-temperature insulating material according to an embodiment of the present invention, as shown in fig. 1, where the method includes:

Step S101: and step-up testing is carried out on the low-temperature insulating material in the flashover testing device for a preset time interval until flashover occurs, so as to obtain a first voltage value of the first flashover.

In this embodiment, before the test of the flashover characteristic of the low-temperature insulating material is performed by the test method of the flashover characteristic of the low-temperature insulating material provided by the invention, a flashover test device is first set. As shown in fig. 2, the specific structure of the flashover test device includes: impulse voltage generator, voltage divider, container for holding liquid nitrogen, oscillograph and electrode. The surge voltage generator is preferably capable of providing standard lightning waves with peak values ranging from 30kV to 400kV (wave front time T1 and half-wave peak time T2 are respectively 1.2 mu s and 50 mu s, and errors are respectively within 30% and 20%). The voltage divider is preferably a resistive-capacitive voltage divider with a transformation ratio of 420. The oscilloscope is preferably Tektronix and is connected in parallel to the low-voltage side of the voltage divider, and uses matched waveform analysis software to output parameters such as apparent peak value, wave front time, half-wave peak time and the like. The container is preferably a foam container, and the dimensions are preferably 400mm, 300mm and 300mm in length, width and height, respectively, and 100mm in thickness. The electrodes are preferably a pair of stainless steel ring electrodes. The method for testing the flashover characteristics of the low-temperature insulating material is suitable for testing the flashover characteristics of the impact surface of the low-temperature insulating material in liquid nitrogen. It should be understood that the above-described surge voltage generator, voltage divider, oscilloscope, container, and electrode are only one preferred embodiment, and that other parameters of the surge voltage generator, voltage divider, oscilloscope, container, and electrode may be selected as well, without specific limitation.

In this embodiment, after the flashover test device is arranged, the low-temperature insulating material is repeatedly wiped with alcohol to ensure that the surface of the low-temperature insulating material is clean, then the two electrodes are sleeved on the low-temperature insulating material, the distance between the two electrodes is set to be a preset distance, the two electrodes and the low-temperature insulating material are immersed in liquid nitrogen of the flashover test device, and after the liquid nitrogen is not boiled, the flashover test is started. Wherein, the low-temperature insulating material for testing is preferably made into a round bar with the outer diameter of 40mm and the length of 50 CM; the preset interval may be set to be greater than 0 interval according to the test requirement, which is not particularly limited herein. It should be understood that the external dimensions of the low-temperature insulating material for testing are just one preferred embodiment, and other external dimensions may be set as well, which are not particularly limited herein.

In this embodiment, the test procedure is as follows: by means of the impulse voltage generator, an initial voltage value is applied to the low-temperature insulating material via the electrodes, and it is determined whether the initial voltage value causes flashover of the low-temperature insulating material. When the initial voltage value is applied to the low-temperature insulating material and no flashover occurs, in order to avoid the influence of the change of environmental factors caused by the previous flashover test on the test result of the next flashover test, after each flashover test, a new flashover test is performed after a preset time interval.

And in the second flashover test, the positions of the two electrodes on the low-temperature insulating material are kept unchanged, and a preset voltage value is added on the basis of the test voltage value applied by the first flashover test to serve as the test voltage value applied by the second flashover test, and then the second flashover test is carried out. When the second flashover test is carried out or no flashover occurs on the low-temperature insulating material, the third flashover test is carried out after a preset time interval in order to avoid the influence of the change of environmental factors caused after the flashover test on the subsequent flashover test. And in the third flashover test, the positions of the two electrodes on the low-temperature insulating material are kept unchanged, a preset voltage value is added on the basis of the test voltage value applied by the second flashover test to serve as the test voltage value applied by the third flashover test, and then the third flashover test is carried out. And circulating in this way until the low-temperature insulating material is first subjected to flashover, recording a test voltage value of a flashover test in which flashover is first subjected to flashover, and determining the test voltage value as a first voltage value. That is, each time a flashover test is performed, a preset voltage value is increased based on the test voltage value of the previous flashover test, and a new flashover test is performed after a preset time interval, and simultaneously, the positions of the two electrodes on the low-temperature insulating material are kept unchanged until a flashover occurs for the first time in the flashover test. The initial voltage value may be set to a smaller value according to the basic characteristics of the low-temperature insulating material, and is not particularly limited herein. The preset time interval is preferably 5 minutes, it should be understood that this is only a preferred embodiment, and the preset time interval may also be set to other values according to the difference of the actually tested low-temperature insulating materials and/or the difference of the requirements of the actually tested scenes, which is not particularly limited herein. The preset voltage value is preferably 2kv, it should be understood that this is only a preferred embodiment, and the preset voltage value may also be set to other values according to the different low-temperature insulating materials actually tested and/or the different requirements of the actual test scenario, which is not specifically limited herein.

Step S102: and after a preset time interval, testing the low-temperature insulating material by using the first voltage value to obtain a first test result.

In this embodiment, after the first voltage value of the low-temperature insulating material is obtained, after a preset time interval, the positions of the two electrodes on the low-temperature insulating material are kept unchanged, and a flashover test is continuously performed at the first voltage value, so as to obtain a corresponding first test result.

Step S103: and under the condition that the first test result represents that flashover occurs, performing step-down test on the low-temperature insulating material for a preset time interval until flashover does not occur any more, and obtaining a corresponding second voltage value.

In this embodiment, under the condition that the obtained first test result indicates that flashover occurs, a new step-down flashover test is started with a first target voltage value lower than the first voltage value until the flashover test does not occur any more, and at this time, a corresponding second voltage value without flashover is obtained. Specifically, when the obtained first test result represents that flashover occurs, after a preset time interval, the positions of the two electrodes on the low-temperature insulating material are kept unchanged, and the flashover test is performed by a first target voltage value, so that a first test result is obtained. And when the first test result represents that flashover still occurs, keeping the positions of the two electrodes on the low-temperature insulating material unchanged, reducing a preset voltage value on the basis of a first target voltage value, and continuing to perform flashover test after a preset time interval to obtain a first test result. And when the first test result represents that flashover still occurs, keeping the positions of the two electrodes on the low-temperature insulating material unchanged, reducing a preset voltage value on the basis of the test voltage of the last flashover test, and continuing the flashover test after a preset time interval to obtain a first test result. And circulating in this way until no flashover occurs in the process of one flashover test, and determining that the test voltage value corresponding to the one flashover test is the second voltage value. That is, from the first target voltage value, when the flashover test is performed each time, the preset voltage value is reduced based on the test voltage value of the previous flashover test, and after the preset time interval, the new flashover test is performed, and meanwhile, the positions of the two electrodes on the low-temperature insulating material are kept unchanged, so that the step-down flashover test is performed circularly until the flashover test does not occur, and the test voltage value of the flashover test is recorded as the second voltage value. The first target voltage value is preferably a voltage value obtained by reducing a preset voltage value based on the first voltage value, and it should be understood that this is only a preferred embodiment, and the first target voltage value may also be set to other values greater than the first voltage value according to different actually tested low-temperature insulating materials and/or different actual test scene requirements, which is not specifically limited herein.

Step S104: and determining initial repeatability performance of the low-temperature insulating material according to the first voltage value and the second voltage value.

Step S105: and according to the initial repeatability performance, performing overvoltage test of a preset time interval on the target position of the low-temperature insulating material to obtain a preset number of flashover voltage values.

In this embodiment, after the first voltage value and the second voltage value of the low-temperature insulating material are obtained, the first voltage value and the second voltage value are compared, and a comparison result is obtained. And determining whether the repeatability performance of the low-temperature insulating material is good or not according to the comparison result. When the initial repeatability performance of the low-temperature insulating material is poor based on the first voltage value and the second voltage value of the low-temperature insulating material, in order to obtain a more accurate evaluation result, the overvoltage test is continuously carried out on the low-temperature insulating material, and when the overvoltage test is carried out, the two electrodes sleeved on the low-temperature insulating material are adjusted to the target position of the low-temperature insulating material which is not subjected to any flashover test, namely the target position of the low-temperature insulating material is the position of the low-temperature insulating material which is not subjected to any flashover test.

Meanwhile, in order to avoid the influence of the distance between the two electrodes sleeved on the low-temperature insulating material on the test result, the distance between the two electrodes sleeved on the low-temperature insulating material in the overvoltage test process is also set to be the preset distance.

In order to obtain a more accurate overvoltage test result, compared with the current test voltage value of randomly setting an overvoltage test (the overvoltage test voltage value is directly caused to deteriorate the repeatability of a low-temperature insulating material, and the overvoltage test voltage value can be obtained after a plurality of tests are performed after the overvoltage test voltage value is too low, and the repeatability evaluation of the insulating material is also influenced), the method determines that the second preset percentage of the first voltage value of the low-temperature insulating material is a second target voltage value, and the second target voltage value is used as the test voltage value for performing the overvoltage test for the first time. The second preset percentage is preferably 110%, for example, when the first voltage value obtained by performing the flashover test on the low-temperature insulating material is 100kv, the second target voltage value of the low-temperature insulating material is set to 110kv, which is understood to be a preferred embodiment, and the second preset percentage may also be set to other values according to different actually tested low-temperature insulating materials and/or different actually tested scene requirements, which is not limited herein specifically.

In this embodiment, starting from the second target voltage value, an overvoltage test is performed for a preset time interval on the target position of the low-temperature insulating material until a preset number of flashover voltage values are obtained. The test voltage value set by the overvoltage test is the flashover voltage value under the condition that flashover occurs in the overvoltage test process.

Step S106: and determining the preset number of flashover voltage values as sample points to be detected and a comparison sample point set to perform weighted clustering to obtain a clustering result, wherein the comparison sample points in the comparison sample point set are sample points with known repeatability.

In this embodiment, after a preset number of flashover voltage values of the low-temperature insulating material are obtained, the preset number of flashover voltage values are determined to be a corresponding sample point to be tested, and then weighted clustering is performed on the sample point to be tested and a set of comparison sample points, so as to obtain a corresponding clustering result. Each comparison sample point of the comparison sample points is also a point represented by a preset number of flashover voltage values, wherein the preset number of flashover voltage values of the comparison sample points are known quantities which can well represent the repeatability performance of the corresponding low-temperature insulating material and are obtained by acquiring historical test data of other low-temperature insulating materials, and the repeatability performance of the comparison sample points is known. The comparison sample point set comprises sample points with good repeatability and sample points with poor repeatability. The method comprises the steps that a plurality of categories are obtained by clustering only a comparison sample point set, wherein the comparison sample points included in each category are sample points with the same repeatability performance, for example, 4 categories are obtained by performing weighted clustering on the comparison sample point set, namely category 1, category 2, category 3 and category 4, the obtained category 1 is a comparison sample point with good repeatability performance, the category 2 is a comparison sample point with poor repeatability performance, the category 3 is a comparison sample point with poor repeatability performance, and the category 4 is a comparison sample point with good repeatability performance. The number of the sample points in the comparison sample point set is determined according to the application scenario, for example, 500 sample points, or 1000 sample points, etc., which is not specifically limited herein.

Step S107: and determining the repeatability performance of the low-temperature insulating material according to the clustering result.

In this embodiment, according to the clustering result, it is determined which category the sample point to be measured belongs to, and then it is determined whether the repeatability performance of the comparison sample point in the category to which the sample point to be measured belongs is good or bad. Under the condition that the repeatability performance of the comparison sample point in the category of the sample point to be detected is good, determining that the repeatability performance of the low-temperature insulating material corresponding to the sample point to be detected is good; and under the condition that the repeatability performance of the comparison sample point in the category of the sample point to be detected is poor, determining that the repeatability performance of the low-temperature insulating material corresponding to the sample point to be detected is poor.

In combination with the above embodiment, in an implementation manner, the embodiment of the invention further provides a method for testing the flashover characteristic of the low-temperature insulating material. In the method for testing the flashover characteristic of the low-temperature insulating material, before step S106, the method further includes steps S061 to S064:

Step S061: based on the obtained known sample points and the repeatability performance of the known sample points, a corresponding flashover voltage characteristic sequence and a corresponding repeatability performance sequence are constructed, wherein the flashover voltage characteristic sequence and the repeatability performance sequence are expressed as follows:

A＝[a₁,a₂,...,a_t]

B_i＝[b_1i,b_2i,...,b_ti]

Where A represents the repetitive performance sequence, a _t represents the repetitive performance of the t-th known sample point, B _i represents the i-th flashover voltage signature sequence, and B _ti represents the i-th flashover voltage signature in the t-th known sample point.

In this embodiment, a large number of known sample points are obtained first, any one of the known sample points is a sample point represented by a preset number of flashover voltage values, and at the same time, the repeatability performance of each known sample point is known, and the flashover voltage values of the preset number of the known sample points are known amounts which are obtained by obtaining historical test data of other low-temperature insulating materials and can well represent the repeatability performance of the low-temperature insulating materials corresponding to the known sample points. Based on the obtained large number of known sample points and the repeatability performance of the known sample points, a corresponding flashover voltage characteristic sequence and a corresponding repeatability performance sequence are constructed, wherein the flashover voltage characteristic sequence and the repeatability performance sequence are expressed as follows:

A＝[a₁,a₂,...,a_t]

B_i＝[b_1i,b_2i,...,b_ti]

wherein a represents a repetitive performance sequence; a _t represents the repeatability performance of the t known sample point; b _i represents the ith flashover voltage signature sequence consisting of the ith flashover voltage values of all known sample points; the maximum value n of i represents the number of flashover voltage characteristics in known sample points, and the number is the same as the preset number of the low-temperature insulating materials to be tested; b _ti denotes the ith flashover voltage characteristic in the t-th known sample point.

Step S062: and carrying out information entropy and joint entropy calculation on the flashover voltage characteristic sequence and the repeatability performance sequence to obtain a first information entropy of the flashover voltage characteristic sequence, a second information entropy of the repeatability performance sequence and joint entropy of the flashover voltage characteristic sequence and the repeatability performance sequence.

In this embodiment, after the flashover voltage characteristic sequence and the repeatability performance sequence are constructed, information entropy and joint entropy calculation are performed on the flashover voltage characteristic sequence and the repeatability performance sequence to obtain a first information entropy of the flashover voltage characteristic sequence, a second information entropy of the repeatability performance sequence, and a joint entropy of the flashover voltage characteristic sequence and the repeatability performance sequence, where a calculation formula is as follows:

Wherein H (a) is a second information entropy of the repetitive performance sequence; h (B _i) is the first information entropy of the ith flashover voltage signature sequence; h (a, B _i) is the joint entropy between the repetitive performance sequence and the ith flashover voltage signature sequence; p (a _p) is the edge probability distribution corresponding to the repeatability performance corresponding to the p-th known sample point; p (b _qi) is the edge probability distribution of the q-th flashover voltage feature in the i-th flashover voltage feature sequence; p (a _p,b_qi) is the joint probability distribution of the repeatability performance corresponding to the p-th known sample point and the q-th flashover voltage characteristic of the i-th flashover voltage characteristic sequence.

Step S063: and carrying out gray correlation analysis on the repeatability performance sequence and the flashover voltage characteristic sequence to obtain gray correlation degree between the repeatability performance sequence and the flashover voltage characteristic sequence.

In this embodiment, gray correlation analysis is performed on the obtained repetitive performance sequence and the flashover voltage characteristic sequence at the same time, so as to obtain gray correlation between the repetitive performance sequence and the flashover voltage characteristic sequence, and the calculation formula is as follows:

Wherein e represents a known sample point, and gamma _i is the gray correlation degree between the ith flashover voltage characteristic sequence B _i and the repeatability performance sequence A; ζ _i (e) is the correlation coefficient between the ith flashover voltage characteristic sequence B _i as a comparison sequence and the repetitive performance sequence a as a reference sequence; ρ is the resolution factor; Δ _i is the absolute difference between the ith flashover voltage signature sequence B _i as a comparison sequence and the repetitive performance sequence a as a reference sequence.

Step S064: and determining the weight of the flashover voltage characteristic sequence according to the first information entropy, the second information entropy, the joint entropy and the gray correlation degree.

In this embodiment, according to the first information entropy, the second information entropy, the joint entropy and the gray correlation degree obtained by the above calculation, the weight of each flashover voltage characteristic sequence is calculated according to the following calculation formula:

wherein J _i is the i-th weighted association, w _j is the weight of the J-th flashover voltage characteristic sequence, J _S is the sum of the weighted associations of all flashover voltage characteristics, n is the number of flashover voltage characteristics in the known sample point, and the number is the same as the number of flashover voltage values of the preset number of low-temperature insulating materials to be tested.

Step S106 includes step S1061: and carrying out weighted clustering on the sample points to be detected and the comparison sample point set based on the weight of the flashover voltage characteristic sequence to obtain a clustering result.

In this embodiment, a predetermined number of flashover voltage values of the low-temperature insulating material are determined as a corresponding sample point to be measured. And then, based on the weight of each flashover voltage characteristic sequence obtained through calculation, carrying out weighted clustering on the sample points to be detected and the comparison sample point set to obtain a clustering result.

In combination with the above embodiment, in an implementation manner, the embodiment of the invention further provides a method for testing the flashover characteristic of the low-temperature insulating material. In the method for testing the flashover characteristics of the low-temperature insulating material, the step S106 includes steps S1061 to S1063

Step S1061: and calculating the compactness of each sample point in the sample point set formed by the sample point to be tested and the comparison sample point set, and obtaining a compactness result.

In this embodiment, for each sample point in a sample point set composed of a sample point to be measured and a comparison sample point set, the compactness of each sample point is calculated as follows:

Wherein Tigh (x _i) is the compactness of the ith sample point in the sample point set, G _z(x_i) is the z sample points closest to the ith sample point in the sample point set, x _j is the j sample point in the G _z(x_i set, and D (x _i,x_j) is the distance between the two points x _i and x _j.

Step S1062: and determining the compactness average value of all the sample points according to the compactness result, and deleting each sample point with the compactness lower than the compactness average value to obtain a target sample point.

In this embodiment, after the compactness value of each sample point in the sample point set is obtained by calculation, summing all the compactness values, taking an average value, then comparing the compactness value of each sample point with the average value, deleting the sample points corresponding to the compactness value with the value smaller than the average value, wherein the deleted sample points are not involved in the selection of the subsequent initial clustering center, but are still involved in the subsequent clustering. And then determining a first quantity according to the number of categories which need to be obtained through clustering, for example, determining that the first quantity is 2 when 2 categories need to be obtained through clustering and determining that the first quantity is 3 when 3 categories need to be obtained through clustering. The first number may be set according to actual sample point data, which is not specifically limited herein. After determining the first number, selecting one target sample point with highest compactness from the target sample points remained after deletion as a first initial clustering center, and then selecting one target sample point farthest from the first initial clustering center from the target sample points remained after deletion as a second initial clustering center, wherein the selection of the rest initial clustering centers is based on a set rule, and the expression of the set rule is as follows:

c_i∈X^':max(D_min(c_i,c₁),D_min(c_i,c₂),...,D_min(c_i,c_i-1)),i＝3,4,5,...,m.

wherein c _i is the i-th initial cluster center; x ^' is a set formed by deleting the residual target sample points after the sample points corresponding to the compactness value with the value smaller than the compactness average value are deleted; the value of m is the same as the first number. The specific meaning of the expression is that each target sample point which is closest to each selected initial cluster center in X ^' is calculated, then the distance value is compared, and one target sample point with the largest distance value is selected as a new initial cluster center. For example, a first initial cluster center c1, a second initial cluster center c2 and a third initial cluster center c3 have been selected, at this time, selection of a fourth initial cluster center is performed, and first, each target sample point in X ^', which is closest to c1, c2 and c3 respectively, is calculated, so as to obtain a target sample point d1 closest to c1, where the distance value is 5; obtaining that the distance d2 of the target sample point is nearest to the distance c2, wherein the distance value is 8; obtaining that the distance d3 of the target sample point is nearest to the distance c3, wherein the distance value is 2; at this time, since the distance value 8 is maximum, the target sample point d2 is selected as the 4th initial cluster center.

Step S1063: and screening a first number of initial clustering centers from the target sample points based on a set rule, and performing iterative optimization on the initial clustering centers for preset times through a weighted clustering algorithm to obtain a final clustering result.

In this embodiment, after the first number of initial cluster centers is selected, the distance between each sample point in the sample point set formed by the sample point to be detected and the comparison sample point set and each cluster center (may be an initial cluster center or a new cluster center in the iterative process) is calculated, where the distance calculation formula is as follows:

Wherein w _j is the weight corresponding to the jth flashover voltage feature sequence; s _lj and s _kj are the j-th flashover voltage values of the first and the k-th sample points in the sample point set formed by the sample point to be tested and the comparison sample point set, and a clustering center exists in the first and the k-th sample points.

In this embodiment, each sample point in the set of sample points is classified to the nearest one of the initial cluster centers based on the distance minimization principle. And after classifying each sample point in the sample point set to the initial clustering center, obtaining a corresponding clustering result. Based on the obtained clustering result, taking an average value of sample points belonging to the same category as a new clustering center, thus obtaining a first number of new clustering centers before new rounds of clustering, then clustering again with the obtained first number of new clustering centers until the clustering centers are not changed any more, or ending the clustering after the clustering with set iteration times, and obtaining a final clustering result. It should be understood that the distance calculation formula used in each round of clustering is the distance calculation formula described above.

In this embodiment, the purpose of weighting is to obtain a preset number of flashover voltage values of the low-temperature insulating material, where the influence degrees of the flashover voltage values of the preset number on the repeatability of the low-temperature insulating material are different, so that each flashover voltage value is weighted according to the difference of the influence degrees of the flashover voltage values on the repeatability of the low-temperature insulating material, so that the difference of the influence degrees of the flashover voltage values on the repeatability of the low-temperature insulating material is considered in determining the repeatability of the low-temperature insulating material, and the repeatability of the low-temperature insulating material can be evaluated more accurately.

In combination with the above embodiment, in an implementation manner, the embodiment of the invention further provides a method for testing the flashover characteristic of the low-temperature insulating material. In the method for testing the flashover characteristics of a low temperature insulating material, step S107 includes steps S1071 to S1072:

step S1071: and determining the target category to which the sample point to be detected belongs according to the clustering result.

In this embodiment, after the clustering result is obtained, the sample points to be detected and the set of comparison sample points are clustered into a plurality of categories. And determining the category to which the sample point to be detected belongs, and determining the category to which the sample point to be detected belongs as a target category.

Step S1072: and determining the repeatability performance of the comparison sample points in the target category as the repeatability performance of the low-temperature insulating material corresponding to the sample points to be detected.

In this embodiment, the repeatability performance of the comparison sample point in the target class is determined to be good, if the repeatability performance of the comparison sample point in the target class is good, the repeatability performance of the low-temperature insulating material corresponding to the sample point to be measured is determined to be good, and if the repeatability performance of the comparison sample point in the target class is poor, the repeatability performance of the low-temperature insulating material corresponding to the sample point to be measured is determined to be poor.

In combination with the above embodiment, in an implementation manner, the embodiment of the invention further provides a method for testing the flashover characteristic of the low-temperature insulating material. In the method for testing flashover characteristics of a low temperature insulation material, the method further includes step S1030:

Step S1030: in the case where the first test result indicates that flashover does not occur, it is determined that the low temperature insulating material is excellent in reproducibility.

In this embodiment, when the first test result obtained by performing the flashover test on the low-temperature insulating material indicates that flashover does not occur, it is indicated that flashover test on the low-temperature insulating material needs to be performed with a test voltage value higher than the first voltage value to possibly cause flashover of the low-temperature insulating material, and in this case, it can be determined that the test voltage value at which flashover occurs for the second time is higher than the first voltage value, which indicates that the repeatability performance of the low-temperature insulating material is excellent.

In combination with the above embodiment, in an implementation manner, the embodiment of the invention further provides a method for testing the flashover characteristic of the low-temperature insulating material. In the method for testing the flashover characteristics of the low temperature insulating material, step S104 includes steps S1041 to S1042:

step S1041: a voltage difference between the second voltage value and the first voltage value is determined.

Step S1042: in the case where the voltage difference satisfies a set condition, it is determined that the initial repeatability performance of the low temperature insulating material is poor.

In the present embodiment, after the first voltage value and the second voltage value of the low-temperature insulating material are obtained, the two are subjected to a difference. When the reduction amplitude of the second voltage value is larger than or equal to a first preset percentage compared with the first voltage value, the voltage difference between the second voltage value and the first voltage value is determined to meet the set condition, the initial repeatability performance of the low-temperature insulating material is determined to be poorer, the repeatability performance of the low-temperature insulating material is further evaluated, and when the reduction amplitude of the second voltage value is smaller than the first preset percentage compared with the first voltage value, the voltage difference between the second voltage value and the first voltage value is determined to not meet the set condition, the initial repeatability performance of the low-temperature insulating material is determined to be better, and the repeatability performance of the low-temperature insulating material is not further evaluated. The first preset percentage is preferably 20%, for example, the first voltage value is 100kv, the second voltage value is 70kv, and the second voltage value is reduced by 30% compared to the first voltage value and 30% is greater than 20% at this time, so that the initial repeatability of the low-temperature insulating material is determined to be lower, and the repeatability of the low-temperature insulating material is further evaluated, which is understood to be a preferred embodiment, and the first preset percentage can also be set to other values according to the difference of the actually tested low-temperature insulating material and/or the difference of the requirement of the actually tested scene, which is not particularly limited herein.

In combination with the above embodiment, in an implementation manner, the embodiment of the invention further provides a method for testing the flashover characteristic of the low-temperature insulating material. In the method for testing the flashover characteristics of a low temperature insulating material, step S105 includes steps S1051 to S1052:

s1051: in the case where the initial repeatability performance appears to be poor, a first overvoltage test is performed on the target location of the low temperature insulating material at a second target voltage value.

S1052: it is determined whether a flashover occurred in the last overvoltage test of any one overvoltage test.

S1055: and under the condition that the previous overvoltage test is flashover, performing any one overvoltage test according to the test voltage value of the previous overvoltage test, wherein the test voltage value is reduced by a set voltage value.

S1054: and under the condition that no flashover occurs in the previous overvoltage test, determining whether no flashover occurs in the overvoltage test performed before any one overvoltage test.

S1055: and under the condition that no flashover occurs in the overvoltage test performed before any one overvoltage test, performing any one overvoltage test with the voltage value of the third preset percentage of the previous overvoltage test.

S1056: and under the condition that the overvoltage test performed before any one overvoltage test has the overvoltage test with flashover, performing any one overvoltage test with an intermediate value between the test voltage value of the last overvoltage test and the test voltage value of the overvoltage test with flashover nearest to the last overvoltage test.

S1057: and determining the test voltage value of the overvoltage test with the flashover as a flashover voltage value, and ending the overvoltage test until the flashover voltage value of the preset number is obtained.

In this embodiment, when it is determined that the initial repeatability performance of the low-temperature insulating material is poor, a second preset percentage of the first voltage value of the low-temperature insulating material is determined to be a second target voltage value, which is to be used as a test voltage value for performing the overvoltage test for the first time.

In this embodiment, the specific test procedure of the overpressure test is: and performing overvoltage test at the same target position of the low-temperature insulating material, performing overvoltage test once at preset time intervals, and performing first overvoltage test at a second target voltage value. When any one overvoltage test is performed, it is determined whether a flashover occurs in the last overvoltage test of the any one overvoltage test. Under the condition that the previous overvoltage test of the random overvoltage test is in flashover, the voltage value obtained after the test voltage value of the previous overvoltage test is reduced by a set voltage value is used as the test voltage value of the random overvoltage test, and then the random overvoltage test is carried out according to the test voltage value. And further determining whether the over-voltage test performed before the any one over-voltage test does not have flashover under the condition that the last over-voltage test of the any one over-voltage test does not have flashover. And under the condition that no flashover occurs in the overvoltage test performed before the any one overvoltage test, taking the voltage value of the third preset percentage of the last overvoltage test of the any one overvoltage test as the test voltage value of the any one overvoltage test, and performing the any one overvoltage test by using the test voltage value. Under the condition that the overvoltage test which is performed before the any one overvoltage test has the overvoltage test with the flashover, taking an intermediate value between the test voltage value of the last overvoltage test of the any one overvoltage test and the test voltage value of the overvoltage test with the flashover which is nearest to the last overvoltage test as the test voltage value of the any one overvoltage test, and performing the any one overvoltage test with the test voltage value. Meanwhile, for the overvoltage test with flashover, recording the test voltage value corresponding to the overvoltage test as the flashover voltage value, and ending the overvoltage test until the flashover voltage value with the preset number is obtained, namely, not carrying out new overvoltage test. The set voltage value is determined to be a larger voltage value based on a second target voltage value of the corresponding low-temperature insulating material, if the second target voltage value is 200KV, the set voltage value is determined to be 20KV, and if the second target voltage value is 400KV, the set voltage value is determined to be 40KV; the purpose of this is to avoid the damage to the low temperature insulating material caused by the flashover, so that after the repeatability performance of the low temperature insulating material is reduced, the condition that the flashover occurs can be achieved by only reducing a smaller voltage value for a new overvoltage test each time, and the finally measured flashover voltage values of the preset number are a group of arithmetic series with smaller value differences, and the obtained flashover voltage values of the preset number are inaccurate and cannot well represent the repeatability characteristics of the low temperature insulating material. Wherein the third preset percentage is preferably 110%, it should be understood that this is only a preferred embodiment, and the third preset percentage may also be set to other values according to the difference of the actually tested low-temperature insulating materials and/or the difference of the requirement of the actually tested scene, which is not particularly limited herein. The preset number is preferably 10, and it should be understood that this is only a preferred embodiment, and the preset number may also be set to other values according to the difference of the actually tested low-temperature insulating materials and/or the difference of the requirement of the actually tested scene, which is not limited herein specifically.

In this embodiment, the above-mentioned method for testing overvoltage can properly increase the test voltage value of the overvoltage test when no flashover occurs in the overvoltage test on the low-temperature insulating material with one test voltage value, and properly decrease the test voltage value of the overvoltage test when flashover occurs in the overvoltage test on the low-temperature insulating material with one test voltage value, so as to obtain a preset number of flashover voltage values that more accurately represent the repeatability characteristics of the low-temperature insulating material.

For example, assuming that the second target voltage value for the overvoltage test is 200kv, the set voltage value is 20kv, the third preset percentage is 110%, and the preset number is 5. At this time, the low-temperature insulating material is subjected to the first overvoltage test at 200kv, and if no flashover occurs, this test voltage value indicates that the low-temperature insulating material cannot be subjected to the flashover, at this time, the overvoltage test is continued at 110% (the third preset percentage) at 200kv, that is, at 220kv, and at this time, if flashover occurs, the first flashover voltage value of 220kv among the preset number of flashover voltage values is recorded. Then reducing 20kv (set voltage value) on the basis of 220kv, that is, continuing to perform the overvoltage test at 200kv, wherein if no flashover occurs, the reduced amplitude of the test voltage value is excessively large, so that the low-temperature insulating material does not generate flashover, and continuing to perform the next overvoltage test, wherein the overvoltage test generating flashover exists before the next overvoltage test, and meanwhile, the last overvoltage test generating no flashover in the next overvoltage test, thus taking the intermediate value 210kv between the test voltage value of 200kv of the last overvoltage test and the test voltage value of 220kv of the last overvoltage test generating flashover nearest to the last overvoltage test, at this time, if flashover occurs, 210kv is recorded as a second flashover voltage value of the preset number of flashover voltage values. Then, the overvoltage test is continued by reducing 20kv (the set voltage value) on the basis of 210kv, that is, 190kv, and at this time, if flashover occurs, the third flashover voltage value of the preset number of flashover voltage values is recorded as 190 kv. Then reducing 20kv (set voltage value) on the basis of 190kv, namely continuing to perform the overvoltage test at 170kv, wherein if no flashover occurs, the reduced amplitude of the test voltage value is excessively large, so that the low-temperature insulating material is not subjected to flashover, the next overvoltage test is continued, the overvoltage test with flashover exists before the next overvoltage test, meanwhile, the last overvoltage test with flashover does not occur in the next overvoltage test, thus taking an intermediate value of 180kv between the test voltage value 170kv of the last overvoltage test and the test voltage value 190kv of the last overvoltage test with flashover from the last overvoltage test, if no flashover occurs, the next overvoltage test is continued, and the overvoltage test with flashover occurs before the next overvoltage test, and meanwhile, no flashover occurs in the last overvoltage test of the next overvoltage test, so that the next overvoltage test is performed by taking the intermediate value 185kv between the test voltage value 180kv of the last overvoltage test and the test voltage value 190kv of the last overvoltage test with flashover, and if flashover occurs, the fourth flashover voltage value among the preset number of flashover voltage values is recorded 185 kv. Then, the overvoltage test is continued by reducing 20kv (the set voltage value) on the basis of 185kv, that is, 165kv, and at this time, if flashover occurs, the fifth flashover voltage value of the preset number of flashover voltage values of 165kv is recorded. The 5 flashover voltage values thus obtained were 220kv,210kv,190kv,185kv,165kv, respectively, in succession.

In one embodiment of the invention, the above embodiments are all flashover tests and corresponding overvoltage tests and clustering treatments performed on the low-temperature insulating material at the same electrode distance, and in order to ensure the accuracy of the test results, the invention can also perform flashover tests and corresponding overvoltage tests and clustering treatments on the low-temperature insulating material at a plurality of electrode distances. For example, the flashover test and the corresponding overvoltage test and clustering process of the above embodiments were performed with the distance between the electrodes set to 5mm to obtain the reproducibility of the low-temperature insulating material at the distance between the electrodes of 5 mm; then setting the distance between the electrodes to be 10mm, and performing flashover test and corresponding overvoltage test and clustering treatment of the embodiment to obtain the repeatability performance of the low-temperature insulating material when the distance between the electrodes is 10 mm; then setting the distance between the electrodes to be 15mm, and performing flashover test and corresponding overvoltage test and clustering treatment of the embodiment to obtain the repeatability performance of the low-temperature insulating material when the distance between the electrodes is 15 mm; finally, setting the distance between the electrodes to be 20mm, and carrying out the flashover test and the corresponding overvoltage test and clustering treatment of the embodiment to obtain the repeatability performance of the low-temperature insulating material when the distance between the electrodes is 20 mm. Therefore, the final repeatability performance evaluation is more accurate by testing the repeatability performance of the low-temperature insulating material at different electrode distances.

Meanwhile, in the above embodiment of the present invention, the initial repeatability performance of the low temperature insulating material is determined based on only one first voltage value and one second voltage value at the same position for the low temperature insulating material, and in order to ensure the accuracy of the determined initial repeatability performance, the present invention may also perform flashover test on a plurality of positions of the low temperature insulating material, respectively, to obtain a plurality of sets of results composed of the first voltage value and the second voltage value, and determine that the initial repeatability performance of the low temperature insulating material is poor as long as the voltage difference between 1 set of the first voltage value and the second voltage value in the plurality of sets of results satisfies the set condition. For example, the same flashover test as in the above embodiment is performed at position 1, obtaining a first voltage value and a second voltage value at position 1; then performing the same flashover test as in the previous embodiment at position 2 to obtain a first voltage value and a second voltage value at position 2; finally, the same flashover test as in the previous embodiment is performed at position 3, obtaining a first voltage value and a second voltage value at position 3. Based on the obtained 3 sets of results consisting of the first voltage value and the corresponding second voltage value, it is determined that the initial repeatability performance of the low-temperature insulating material is poor as long as the voltage difference between the first voltage value and the second voltage value in one set of results satisfies the set condition.

In one embodiment of the present invention, based on the first voltage values obtained in the above embodiment, the discharge time delay in the flashover process is recorded for the flashover test corresponding to each first voltage value, and the discharge time delay and the first voltage value have a one-to-one correspondence.

In a specific embodiment, the invention adopts a typical glass fiber reinforced epoxy resin composite material as a test sample of a low-temperature insulating material, firstly, a waveform which is captured by an oscilloscope and is generated by an impact flashover test when the space between electrodes is 5mm and is obtained after being analyzed by LIANAPAC impact waveform analysis software is selected, and the waveform is shown in figure 3. The test results of the first voltage value and the second voltage value during the flashover test are shown in fig. 4, and the results of the discharge time delay of the first voltage value and the discharge time delay of the second voltage value during the flashover test are shown in fig. 5. The abscissa in fig. 4 and 5 indicates the pitch of the ring electrodes, each of which is tested 5 times at each electrode pitch, each test having 2 columns representing the first voltage value and the second voltage value at the same position (fig. 4), and the discharge time delay of the first voltage value and the discharge time delay of the second voltage value (fig. 5), respectively. As can be seen from the test results, the second flashover voltage value at the same position is greatly reduced at each interval, and the voltage reduction rate is increased along with the increase of the electrode interval. The discharge time delay of the second flashover voltage value is also greatly reduced relative to the first voltage value.

And (3) continuing the flashover test on the glass fiber reinforced epoxy resin composite material according to the flashover test implementation mode, wherein when the electrode spacing is 5mm,10mm,15mm and 20mm respectively, the first flashover voltage is 62.47kV,93.28kV,117.96kV and 165.78kV respectively. Then, the voltage is continuously reduced from high to low at intervals of 10kV, and each test sample is subjected to flashover until the voltage is reduced to 30kV. This is the case for each pitch, thus indicating that the sample in-plane strike flashover voltage decreases progressively with increasing number of flashovers, i.e. if in-plane flashover occurs, the flashover voltage decreases to an extremely low level after continuous pressurization. The discharge time delay measured in each time is shown in table 1, and at four electrode intervals, the discharge time delay in continuous flashover at the same position is larger for the first time, and is greatly reduced for the second time, and then is kept within 1 mus. From the two test results, the impact surface flashover of the G/R material in liquid nitrogen has the following characteristics: under the same interval, the higher the voltage value of the first flashover is, the larger the flashover voltage drop rate is when the flashover occurs again; the more flashovers, the lower the flashover voltage value. At the same interval, flashovers continue to occur, and the discharge time delay is significantly reduced until it reaches a very low level.

In general, when the voltage of the flashover along the impact surface of the same gap is reduced, the discharge time delay is correspondingly increased, so that the voltage-second characteristic curve is met. The impact surface flashover characteristic of the G/R material in liquid nitrogen is obviously different from the rule, so that the impact surface flashover arc is inferred to change the glass fiber reinforced epoxy resin composite material and the surface shape and the like, thereby leading to the rule opposite to the volt-second characteristic.

In order to obtain the relation between the flash-over voltage of the first impact surface in liquid nitrogen and the creepage distance, the first voltage values of the two materials when the flash-over occurs for the first time are tested by adopting the flash-over test implementation mode provided by the invention, namely a glass fiber reinforced epoxy resin composite material (G/R) and an extruded polytetrafluoroethylene material (PTFE for short), the test is carried out according to the flash-over test implementation mode provided by the invention, the first voltage values of the test sample at different positions are measured (after the first voltage value is tested at one position, the electrode position is replaced immediately, and the position is ensured not to have the flash-over during the re-measurement). As shown in fig. 6, the abscissa n represents the test result of the nth test, and the coordinate point corresponds to the first voltage value of 20 times at each electrode interval. The data of fig. 6 were processed according to weber probability distribution to obtain a first voltage value U _epoxy of 0.1% flashover probability for glass fiber reinforced epoxy composites at electrode spacings d of 5mm, 10mm, 15mm and 20mm, respectively, and a first voltage value U _PTFE of 0.1% flashover probability for polytetrafluoroethylene materials, as shown in table 2.

Fitting the relation between the first voltage value of 0.1% flashover probability and the gap distance of two materials in liquid nitrogen by using a power function curve to obtain the following formula:

U_epoxy＝11.4021d^0.8218

U_PTFE＝14.7047d^0.7703

Wherein U _epoxy、U_PTFE unit is kV, d represents creepage distance, and unit is mm. Fig. 7 shows a fitted curve of flashover voltage versus gap distance, providing a basis for the outer insulation design of a superconducting device. As can be seen from FIG. 7, the ballistic interfacial flashover voltage of the G/R material is slightly lower than that of the PTFE material in liquid nitrogen. The dielectric constants of the comparative materials were found to be: the dielectric constant of polytetrafluoroethylene at normal temperature is 2.55, and the dielectric constant of polytetrafluoroethylene at low temperature is 2.2; the dielectric constant of the glass fiber reinforced epoxy resin is 5.7 at normal temperature, and is 4.6 at 77K, 4.1-4.9 are adopted according to different types of epoxy resin, and the dielectric constant of the PTFE material is more similar to liquid nitrogen. The greater the deviation of the dielectric constants of the solid dielectric and the liquid dielectric, the more severe the distortion of the electric field distribution at the interface, the more distorted the electric field lines will be, and the lower the flashover voltage at the interface will be, resulting in a slightly lower in-plane flashover voltage for the G/R material than for the PTFE material. Thus, the dielectric constant of a solid dielectric is an important factor affecting the impact of the surface flashover voltage in liquid nitrogen.

In order to observe the flashover trace of the test article after flashover, the flashover trace of the glass fiber reinforced epoxy resin composite material test article at each interval is observed, and no matter how many flashovers occur, only one flashover trace is found, namely, after the flashover occurs for the first time, the subsequent flashover is also carried out along the flashover trace for the first time. Arc trace was observed with MZDH1065T high magnification continuous variable magnification single tube video microscope at a magnification of 38. Figure 8 shows the burn trace of the flashover arc on the surface of the test article after the first flashover at a pitch of 20 mm. As can be seen in fig. 8, the surface flashover arc caused a deeper burn mark to the surface of the glass fiber reinforced epoxy composite rod. The severe damage to the G/R material sample surface by flashover arcing is related to two factors: first, the arc and the quenching at the high temperature and the liquid nitrogen damage the surface shape of the sample. The impact flashover arc can cause larger temperature rise on the surface of the sample in a very short time even under the liquid nitrogen temperature area, after the arc is ended, the surface of the sample is quickly returned to the liquid nitrogen temperature, and the surface condition of the sample can be damaged under abrupt temperature rise and fall changes. Secondly, the high temperature of the electric arc and the impact of charged ions cause the glass fiber reinforced epoxy resin composite material sample to be thermally decomposed. The black arc trace in fig. 8 illustrates that the instantaneous high temperature of the flashover arc causes thermal decomposition of the surface layer of the sample material. After the test is finished, the tested glass fiber reinforced epoxy resin rod and polytetrafluoroethylene rod are respectively put into a vacuum drying oven for drying, and the surface resistance of the two samples between the ring and the ring electrode is measured by using a DL16-BD2671 type digital megameter. The ring-ring electrode spacing is set to be 5mm, a direct-current voltage of 1000V is applied, and the glass fiber reinforced epoxy resin composite material sample is free from any damage, and the surface resistance is 2873MΩ; the glass fiber reinforced epoxy resin composite material sample with flashover trace has a surface resistance of 1952MΩ. It can be seen that the flashover arc has an obvious effect on the surface resistance of the surface layer material of the glass fiber reinforced epoxy resin composite material, and the resistivity after flashover is obviously reduced, which indicates that new substances with lower resistivity are generated in the flashover channel. According to the analysis of the change characteristics of the flashover voltage and the flashover trace, when the glass fiber reinforced epoxy resin composite material in the liquid nitrogen is subjected to surface flashover for the first time, the electric arc decomposes the test sample, and the electric conduction of the first flashover channel is increased by coke which is a decomposition product. When the flashover occurs again, the shape of the flashover channel is more irregular from the position close to the cathode, and the electric field is more uneven due to the action of the alike products, so that field emission electrons are more likely to occur. The increase in conductance of the flashover channel also facilitates the completion of flashover. The gas generated by decomposition is adsorbed in the looser flashover channel, and is desorbed under the impact of charged particles when flashover is performed again, thereby being beneficial to the formation of a gasification layer. Thus, when flashover occurs again, the flashover channel is unchanged and the flashover voltage drops. The more the flashover times, the more the products decomposed by the surface test sample are, the more the flashover is facilitated, and the more the flashover voltage is reduced. It can be seen that the severe arc burning trace on the surface changes the surface condition and also decomposes the sample material, which is a main cause of poor repeatability of the surface flashover voltage of the glass fiber reinforced epoxy resin composite material in liquid nitrogen. From this, the following conclusions can be drawn:

(1) In the liquid nitrogen environment, the repeatability of the surface impact flashover voltage of the glass fiber reinforced epoxy resin composite material is poor, and the higher the flashover voltage is at the same position, the larger the reduction rate of the flashover voltage is when the flashover occurs again; the more flashovers, the greater the flashover voltage drop.

(2) The surface flashover in liquid nitrogen requires a higher flashover arc energy. The flashover arc changes the surface condition of the material, and simultaneously the epoxy resin matrix is decomposed to form obvious arc marks, so that the surface resistivity and the surface shape are changed, and the flashover arc is a main reason for poor repeatability of the surface impact flashover voltage of the glass fiber reinforced epoxy resin composite material in liquid nitrogen.

(3) The impact surface flashover characteristic of G/R in liquid nitrogen and the fitting curve of the impact flashover voltage and the gap distance of 0.1% flashover probability distributed from Weber can provide reference for the selection and design of the outer insulating material of superconducting power equipment.

A second aspect of the present invention provides a system for testing a flashover characteristic of a low temperature insulation material, as shown in fig. 9, the system 900 comprising:

The first voltage value determining module 901 is configured to perform a step-up test for a low-temperature insulating material in a flashover test device at a preset time interval until flashover occurs, so as to obtain a first voltage value of a first flashover;

the first testing module 902 is configured to test the low-temperature insulating material with the first voltage value after a preset time interval, so as to obtain a first testing result;

The second voltage value determining module 903 is configured to perform a step-down test on the low-temperature insulating material for a preset time interval until no more flashover occurs, under the condition that the first test result indicates that flashover occurs, to obtain a corresponding second voltage value;

An initial repeatability performance determination module 904 configured to determine an initial repeatability performance of the low temperature insulating material according to the first voltage value and the second voltage value;

The flashover voltage value determining module 905 is configured to perform an overvoltage test for a preset time interval on a target position of the low-temperature insulating material according to the initial repeatability performance, so as to obtain a preset number of flashover voltage values;

A clustering module 906, configured to determine a preset number of flashover voltage values as sample points to be detected and a comparison sample point set to perform weighted clustering, so as to obtain a clustering result, where the comparison sample points in the comparison sample point set are sample points with known repeatability;

and the repeatability performance determining module 907 is configured to determine the repeatability performance of the low-temperature insulating material according to the clustering result.

Optionally, the system 900 further includes:

the sequence construction module is used for constructing a corresponding flashover voltage characteristic sequence and a corresponding repeatability performance sequence based on the obtained known sample points and the repeatability performance of the known sample points, and the flashover voltage characteristic sequence and the repeatability performance sequence are expressed as follows:

A＝[a₁,a₂,...,a_t]

B_i＝[b_1i,b_2i,...,b_ti]

The entropy calculation module is used for carrying out information entropy and joint entropy calculation on the flashover voltage characteristic sequence and the repeatability performance sequence to obtain a first information entropy of the flashover voltage characteristic sequence, a second information entropy of the repeatability performance sequence and joint entropy of the flashover voltage characteristic sequence and the repeatability performance sequence;

The gray correlation degree determining module is used for carrying out gray correlation analysis on the repeatability performance sequence and the flashover voltage characteristic sequence to obtain gray correlation degree between the repeatability performance sequence and the flashover voltage characteristic sequence;

the weight determining module is used for determining the weight of the flashover voltage characteristic sequence according to the first information entropy, the second information entropy, the joint entropy and the gray correlation degree;

the clustering module 906 includes:

and the clustering sub-module is used for carrying out weighted clustering on the sample points to be detected and the comparison sample point set based on the weight of the flashover voltage characteristic sequence to obtain a clustering result.

Optionally, the clustering module 906 includes:

The compactness calculation module is used for calculating the compactness of each sample point in the sample point set formed by the sample point to be detected and the comparison sample point set to obtain a compactness result;

The target sample point determining module is used for determining a compactness average value of all sample points according to the compactness result, deleting each sample point with the compactness lower than the compactness average value and obtaining a target sample point;

and the clustering sub-module is used for screening a first number of initial clustering centers in the target sample points based on a set rule, and carrying out iterative optimization on the initial clustering centers for preset times through a weighted clustering algorithm to obtain a final clustering result.

Optionally, the repeatability performance determining module includes:

The target category determining module is used for determining the target category to which the sample point to be detected belongs according to the clustering result;

and the repeatability performance determination submodule is used for determining the repeatability performance of the comparison sample points in the target category as the repeatability performance of the low-temperature insulating material corresponding to the sample points to be detected.

Optionally, the system 900 further includes:

and the first repeatability performance determining module is used for determining that the repeatability performance of the low-temperature insulating material is excellent under the condition that the first test result indicates that no flashover occurs.

Optionally, the initial repeatability performance determining module includes:

A voltage difference determining module for determining a voltage difference between the second voltage value and the first voltage value;

an initial repeatability performance determination sub-module for determining that the initial repeatability performance of the low temperature insulating material is poor if the voltage difference satisfies a set condition.

Optionally, the flashover voltage value determining module includes:

The first overvoltage test module is used for carrying out first overvoltage test on the target position of the low-temperature insulating material at a second target voltage value under the condition that the initial repeatability performance is poor;

The first flashover determining module is used for determining whether flashover occurs in the last overvoltage test of any overvoltage test;

The second overvoltage test module is used for carrying out any one overvoltage test according to the test voltage value obtained by reducing the test voltage value of the previous overvoltage test by a set voltage value under the condition that the previous overvoltage test is flashover;

the second flashover determining module is used for determining whether flashover does not occur in any overvoltage test performed before any one overvoltage test under the condition that flashover does not occur in the previous overvoltage test;

The third overvoltage test module is used for carrying out any one overvoltage test by a third preset percentage of voltage values of the last overvoltage test under the condition that no flashover occurs in the overvoltage test carried out before any one overvoltage test;

The fourth overvoltage test module is used for carrying out the random overvoltage test by using the intermediate value between the test voltage value of the previous overvoltage test and the test voltage value of the overvoltage test which has the latest flashover and is positioned away from the previous overvoltage test under the condition that the overvoltage test which is carried out before the random overvoltage test has the overvoltage test with the flashover;

The flashover voltage value determining module is used for determining a test voltage value of an overvoltage test with flashover as a flashover voltage value until the overvoltage test is ended when the flashover voltage value with the preset number is obtained.

In this specification, each embodiment is described in a related manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments.

The foregoing description is only of the preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for testing the flashover characteristics of a low temperature insulation material, the method comprising:

Determining the repeatability performance of the low-temperature insulating material according to the clustering result;

and performing overvoltage test on the target position of the low-temperature insulating material at preset time intervals according to the initial repeatability performance to obtain a preset number of flashover voltage values, wherein the method comprises the following steps of:

Under the condition that the initial repeatability performance is poor, performing a first overvoltage test on a target position of the low-temperature insulating material with a second target voltage value, wherein the second target voltage value is a preset percentage of the first voltage value;

2. The method for testing the flashover characteristics of a low-temperature insulating material according to claim 1, wherein before determining a preset number of flashover voltage values as a set of sample points to be tested and a set of comparison sample points for weighted clustering, the method further comprises:

Wherein, Representing repetitive performance sequences,/>Represents the/>Repeatability performance of individual known sample points,/>Represents the/>Sequences of flashover voltage signatures,/>Represents the/>First/>, among known sample pointsA plurality of flashover voltage characteristics;

3. The method for testing the flashover characteristics of a low-temperature insulating material according to claim 1, wherein determining the flashover voltage values of the preset number as the set of sample points to be tested and the set of comparison sample points for weighted clustering, to obtain a clustering result, comprises:

4. The method for testing the flashover characteristics of a low temperature insulation material according to claim 1, wherein determining the repeatability of the low temperature insulation material according to the clustering result comprises:

5. The method for testing the flashover characteristics of a low temperature insulation material according to claim 1, further comprising:

6. The method for testing the flashover characteristics of a cryogenic insulation material according to claim 1, wherein said determining the initial repeatability of the cryogenic insulation material based on the first voltage value and the second voltage value comprises:

7. A system for testing the flashover characteristics of a cryogenic insulation material, the system comprising:

The repeatability performance determining module is used for determining the repeatability performance of the low-temperature insulating material according to the clustering result;

wherein, the flashover voltage value determining module comprises:

The first overvoltage test module is used for carrying out first overvoltage test on the target position of the low-temperature insulating material with a second target voltage value under the condition that the initial repeatability performance is poor, wherein the second target voltage value is a preset percentage of the first voltage value;