CN111398748A - Impulse arc image edge detection method and device - Google Patents
Impulse arc image edge detection method and device Download PDFInfo
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Abstract
The invention discloses a method and a device for detecting an edge of an impact arc image, belonging to the technical field of edge detection of the impact arc image; the technical problem to be solved is as follows: the improvement of the structure of the method and the device for detecting the edge of the impulse arc image is provided; the technical scheme for solving the technical problem is as follows: the method comprises the following steps: establishing a semi-closed self-energy type quenching chamber quenching impact arc test field; comparing and analyzing the test result and the simulation result, and shooting the movement and extinguishing images of the impact arc in the semi-closed arc extinguishing chamber by using a high-speed camera at different moments; analyzing and processing the acquired impact arc image; sending the obtained accurate image of the discharge edge area to a data processing device for further processing, analyzing the dissipation characteristic of the electric arc in the semi-closed self-energy type arc extinguishing chamber through software arranged in the data processing device, and finally obtaining a multi-stage semi-closed type arc extinguishing chamber series connection structure applied to a distribution line; the method is applied to the detection of the edge of the impulse arc image.
Description
Technical Field
The invention discloses a method and a device for detecting an edge of an impulse arc image, and belongs to the technical field of edge detection of impulse arc images.
Background
The frequent occurrence of lightning accidents can cause great threat to the safe operation of a power grid, and along with the rapid increase of the scale of the power grid and the continuous improvement of the reliability requirement, the lightning protection level of a reinforced circuit is imperative. In the process of discharging electricity to the ground by thunderclouds, the rapid change of the electromagnetic field of the space around the discharge channel can generate induced overvoltage on a nearby overhead line, the thunderclouds can even directly hit a power distribution overhead line to generate extremely high lightning overvoltage, when the lightning overvoltage exceeds a certain value, the flashover and even disconnection of the power distribution line can be caused, the damage of a power supply network is caused, and the reliability of power supply of a power distribution system is directly influenced.
In view of the above hidden troubles, a lightning overvoltage protection measure is required to be taken for the medium-voltage distribution network system. At present, the lightning overvoltage of a medium-voltage distribution network system adopts protection measures mainly including two types: the blocking type protection measures can be divided into improving the lightning withstand insulation characteristic of a distribution line, adopting an overhead ground wire to intercept direct lightning, reducing induced overvoltage on a lead and installing a line lightning arrester to clamp overvoltage at two ends of a protected insulator; the basic principle of the dredging type protection measure is to dredge electric arcs and prevent the electric arcs from burning wires. Including extending the flashover path, partially stripping the insulated conductor, employing parallel protection gaps, etc.
The multistage semi-closed arc extinguishing chamber series connection structure has excellent arc extinguishing performance, the structure is applied to a distribution line, the problem of lightning protection of the distribution network at present can be effectively solved, the existing analysis is not perfect enough for the dissipation characteristic of electric arcs in a semi-closed self-energy type arc extinguishing chamber at present, and the structure of an arc extinguishing device can be improved only by perfecting the research on the dissipation characteristic of electric arcs in the semi-closed self-energy type arc extinguishing chamber and judging the advantages and disadvantages of the arc extinguishing performance according to the dissipation characteristic.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to solve the technical problems that: the improvement of the structure of the method and the device for detecting the edge of the impulse arc image is provided.
In order to solve the technical problems, the invention adopts the technical scheme that: an impulse arc image edge detection method comprises the following steps:
the method comprises the following steps: establishing a semi-closed self-energy type quenching chamber quenching impact arc test field:
step 1.1: printing a test sample by using a 3D printer according to the designed semi-closed arc extinguishing chamber structure;
step 1.2: connecting each test device and the test article according to the test circuit diagram;
step 1.3: after the connection and installation are finished, the working state of the impulse discharge loop is checked, and the normal work of the charge loop and the complete connection of the discharge loop are ensured;
step 1.4: debugging the impact current generator, and enabling the impact current generator to output a specified impact current waveform under the condition of no-load short circuit by changing the values of the wave modulation inductor and the wave modulation resistor;
step 1.5: adjusting the focal length of the camera according to the position relation between the high-speed camera and the sample until a clear image can be displayed in the control software, and then fixing the positions of the high-speed camera and the sample;
step 1.6: opening a high-speed camera, and setting parameters such as a frame rate, a trigger mode and the like;
step 1.7: setting a charging voltage value of the impact current generator, setting corresponding charging time according to the impact voltage value for charging, triggering the impact current generator after charging is finished, and checking whether the oscilloscope successfully triggers the high-speed camera;
step 1.8: adjusting parameters such as the frame rate of control software in real time according to the image condition obtained by shooting, and obtaining and recording an ideal detection state through repeated tests;
step two: and comparing and analyzing the test result and the simulation result, and shooting the movement and extinguishing images of the impact arc in the semi-closed arc extinguishing chamber by using a high-speed camera at different moments:
before shooting, setting the semi-closed self-energy arc extinguishing chamber to be broken down at the moment of 0 mu s, and restraining an arc column in the semi-closed arc extinguishing chamber at the moment of breaking down; the method comprises the steps that an impact current generator is controlled to gradually increase an impact current value to enable the radius of an arc column to be gradually increased, impact waves generated by impact arcs act on the arc column after being reflected, the arc column moves towards an opening of an arc extinguishing chamber under the action of impact air flow, and the brightness of the arcs gradually becomes stronger and then gradually weakens along with the gradual reduction of arc currents;
shooting images in the whole arc brightness change period by using a high-speed camera;
step three: analyzing and processing the acquired impact arc image, wherein the processing steps comprise:
step 3.1: image graying treatment: obtaining an electric arc RGB image by a high-speed camera, and carrying out gray processing on an original image;
step 3.2: and (3) image filtering processing: filtering the gray level image of the arc to obtain a high-quality impact arc image, specifically filtering salt and pepper noise and Gaussian noise in the image by adopting a median filter and a Gaussian filter;
step 3.3: image segmentation processing: the image is segmented by adopting an Otsu algorithm to remove an aperture image surrounding the impact arc;
step 3.4: extracting the image edge of the impact discharge area by adopting a Candy edge extraction algorithm to finally obtain an accurate image of the discharge edge area;
step four: and sending the obtained accurate image of the discharge edge area to a data processing device for further processing, analyzing the dissipation characteristic of the electric arc in the semi-closed self-energy type arc extinguishing chamber through software built in the data processing device, and finally obtaining a multi-stage semi-closed type arc extinguishing chamber series connection structure applied to the distribution line.
The median filtering method adopted in the step 3.2 specifically comprises the following steps: replacing the value of one point in the digital image with the median of each point value in the neighborhood of the point to make the pixel value around the point close to the real value so as to eliminate the isolated noise point, wherein the calculation process is as follows: for a set of numbers x1，x2，...，xnIn other words, n numbers are arranged in order of magnitude of xi1≤xi2≤…≤xinThen, the following conditions are satisfied:
in the formula: medDefining y as a function of the median of the sequence, x1，x2，...，xnThe median value of (d);
when the median filtering is carried out, a sliding window containing odd pixels is defined, the pixel value in the middle of the window is replaced by the median value of all the pixel values in the window, the input sequence is set as { xi, I ∈ I }, wherein I is a natural number set or subset, the window length is n, and the output signal value of the filter is yi＝Med{xi-u,…,xi,…,xi+u}。
The gaussian filtering method adopted in the step 3.2 specifically comprises the following steps: the value of each pixel point is obtained by weighted averaging of the pixel point and other pixel values in the neighborhood through weighted averaging of the whole image;
defining S as a pixel (x)0，y0) (x, y) represents the element in S, f (x, y) represents the gray-scale value of the (x, y) point, a (x, y) represents the weight of each point, then for pixel (x, y)0，y0) Is used for Gauss filtrationThe calculation formula of the wave smoothing process is as follows:
the concrete steps of the Otsu algorithm adopted in the step 3.3 are as follows: firstly, automatically selecting a threshold, dividing an image into a background part and a target part according to the gray characteristic of the image, and keeping the maximum variance between the background part and the target part in order to minimize the misclassification probability of the background image and the target image, namely, meeting the following requirements:
in the above formula: n is the number of image pixels, C0The number u of pixel points of which the gray value of the pixel in the image is less than the threshold value T0Is C0Average gray scale of pixel points, C1The number u of pixel points with the pixel gray value larger than the threshold value T1Is C1Average gray level of the pixel points; binarizing the image according to a threshold value T which maximizes the inter-class variance D:
in the process of identification: g is the gray value of a pixel point on the image, and (i, j) is the position coordinate of a certain pixel point on the image, and the image segmentation processing is realized through image binarization.
The specific steps of extracting the image edge of the impact discharge area in the step 3.4 are as follows:
defining the edge of an image as a part with discontinuous or sharp change of local gray scale of the image, describing the process of gray scale change in the image according to a physical process causing the gray scale change of the image, and detecting pixel points with local significant change in the image;
defining the image gradient as the rate of image gray scale change, wherein the calculation formula of the image gradient is as follows:
in the above formula, Gx and Gy represent the gray scale change rate of a certain pixel in the image in the x direction and the y direction respectively,
t represents transposition;
the gradient magnitude is calculated as:
the calculation formula of the gradient direction is:
the edge image extraction method is realized by calculating a local maximum value of gradient, returns a pixel value according to the obtained gradient value of a certain pixel, sets the pixel with a large gradient value as white and the pixel with a small gradient value as black, and extracts the edge.
An impact arc image edge detection device comprises an impact current generator, an arc extinguishing chamber provided with a test sample, a Rogowski coil, a capacitive voltage divider, an oscilloscope, a high-speed camera and a data processing device, wherein the Rogowski coil is arranged in the arc extinguishing chamber;
the current output end of the impulse current generator is connected with an ignition ball gap, and the ignition ball gap is respectively connected with the input end of the arc extinguishing chamber and the input end of the capacitive voltage divider through a pulse ignition device;
the output end of the arc extinguishing chamber is connected with the Rogowski coil in series and then is connected with the current measuring end of the oscilloscope;
the output end of the arc extinguishing chamber is connected with the output end of the capacitive voltage divider in parallel and then is connected with the voltage measuring end of the oscilloscope;
and the signal trigger end of the oscilloscope is connected with the high-speed camera, and the signal output end of the high-speed camera is connected with the data processing device.
The impulse current generator is a commercially available module, the impulse current of the test is 2kA, and the waveform is 8/20 us.
The Rogowski coil is a non-contact Rogowski coil, and the Rogowski coil is used as a current sensor to form a current measuring system with an oscilloscope;
the specifications of the Rogowski coil are as follows: the inner diameter b is 54mm, the outer diameter a is 102mm, and the thickness c is 25 mm.
The capacitive voltage divider and the oscilloscope form a voltage measuring system, and the voltage division ratio of the capacitive voltage divider is 2000: 1.
The arc extinguishing chamber is specifically printed by a 3D printer;
in the printing process, polylactic acid P L A is used as a printing material, and a fused deposition modeling FDM method is used for printing a sample;
the 3D printer specifically is the Allctc 3D printer.
Compared with the prior art, the invention has the beneficial effects that: aiming at the defects of the prior art, the invention provides an impact test device of a semi-closed arc extinguishing chamber and an impact arc image detection method, wherein the impact current discharge test platform of the semi-closed self-energy arc extinguishing chamber is built, a high-speed camera is used for observing the process from the movement to the extinguishing of an impact arc sprayed out of the semi-closed self-energy arc extinguishing chamber, the edge detection method of the impact arc image is improved, and the time when the arc is completely sprayed out of the chamber is determined by extracting the area image characteristics of the arc; the whole process simplifies the test steps, the shooting imaging efficiency is high, the effect is good, the whole moving and extinguishing process of the impact arc in the chamber can be obtained, the parameters such as airflow speed in the chamber are obtained, the change rule of the parameters is researched, and the experiment effect of the arc dissipation characteristic in the semi-closed self-energy arc extinguishing chamber is effectively improved.
Drawings
The invention is further described below with reference to the accompanying drawings:
FIG. 1 is a schematic structural diagram of a quenching impact arc detection device of a semi-closed arc extinguishing chamber according to the present invention;
FIG. 2 is a schematic diagram of the movement and extinguishing process of the impulse arc at different times in the semi-enclosed arc extinguishing chamber according to the present invention;
FIG. 3 is a schematic diagram of filtering and edge extraction of an impulse discharge image of a semi-enclosed arc extinguishing chamber according to the present invention;
FIG. 4 is an enlarged view of the 59.4 μ s impulse arc image of FIG. 2;
FIG. 5 is a graph of the extracted gray scale data of FIG. 4;
FIG. 6 is a graph showing the area change of the image of the impact arc at different times according to the present invention.
Detailed Description
The invention provides an impact test and impact arc image characteristic research method of a semi-closed arc extinguishing chamber, which can accurately obtain images of the motion and extinguishing process of an impact arc in the chamber, the change value of airflow speed in the chamber and the time of the maximum value of the airflow speed.
The existing detection method is to detect the electric arc which is continuously burnt, wherein the electric arc has long duration time which is millisecond grade; the method improves the detection method of the impact arc image to realize instantaneous observation, utilizes the high-speed camera to realize high photographing speed, can display the frame number of 1000000fps per second, can truly and smoothly reflect the motion process and the form of the arc, has the arc duration as short as microsecond level, has the maximum arc area from the beginning of burning to 112.2 mus, starts extinguishing the arc at 118.8 mus, has high air flow speed in the arc extinguishing chamber, synchronously triggers the high-speed camera based on the oscilloscope, has high reliability, and can truly obtain the evolution of the arc image based on the image processing technology.
According to the invention, a test platform for quenching an impact arc by a semi-closed self-energy arc extinguishing chamber is established, and a 380V alternating current power supply charges a charging capacitor through boosting and rectifying in a test. And after the charging voltage reaches a preset value, the ignition ball gap applies ignition pulse through the pulse ignition device to realize breakdown discharge, so that impact large current injected into the test sample is formed. The large current flowing through the test sample passes through a non-contact Rogowski (Rogowski) coil and forms a current measuring system with a digital storage oscilloscope to measure the impact current value; the capacitive voltage divider and the digital storage oscilloscope form a current measuring system for measuring voltage data. The oscilloscope is used as a trigger source signal of the high-speed camera and is connected with the high-speed camera, once the semi-closed self-energy arc extinguishing chamber is broken down, the oscilloscope sends a trigger signal to the high-speed camera, the high-speed camera shoots the process that the semi-closed self-energy arc extinguishing chamber quenches the impact arc, and the process is transmitted to the processor with the uniform IP address through the network cable.
And calculating the average moving speed of the electric arc in the chamber according to the shot movement and extinguishing images of the impact electric arc in the semi-closed self-energy type arc extinguishing chamber at different moments. Then, the impact discharge image is subjected to gray processing, median and Gaussian filtering, image segmentation and edge extraction to perform arc image processing, so that the change of the arc area represented by the pixel value after the impact arc is ejected from the chamber can be obtained, and the arc extinguishing duration time and the time when the airflow speed in the chamber is maximum are judged according to the change image.
The method mainly aims at researching the dissipation characteristic of the electric arc in the semi-closed self-energy type arc extinguishing chamber to build a test platform, obtains the air flow speed of the chamber through calculation, and finally obtains the detection data of the change of the area of the impact electric arc through a corresponding image processing and analyzing method.
As shown in fig. 1, specifically, the structure diagram of the detection device for quenching the impact arc by building the semi-closed self-energy arc extinguishing chamber is provided, and the detection device mainly comprises an impact current generator, a voltage divider, a rogowski coil, an oscilloscope, a high-speed camera, a test sample, a data processor and the like.
In the test, a 380V alternating current power supply in the impulse current generator charges a charging capacitor through boosting and rectification, the maximum value of the direct current charging rated voltage of a capacitor bank can reach 100kV, the maximum value of the short-circuit output current can reach 200kA, and when the charging voltage reaches a preset value, an ignition ball gap applies ignition pulses through a pulse ignition device to realize breakdown discharge, so that the impulse heavy current injected into a test sample is formed; the impulse current waveforms with different wave front time and half peak time can be obtained by changing the inductance and the wave adjusting resistance in each link of the impulse current generator, and the impulse currents with different peak values can be obtained by changing the charging voltage of the control capacitor bank.
In the detection process, impact current and voltage data are important parameters to be measured, in order to carry out fine measurement on impact current and impact voltage values of a semi-closed arc extinguishing chamber, a non-contact Rogowski (Rogowski) coil is selected to be used as a current sensor, and the current sensor and an oscilloscope form a current measurement system, the D-type core-through current sensor of the U.S. Pearson company is adopted, and the structural size of the D-type core-through current sensor is as follows: the inner diameter b is 54mm, the outer diameter a is 102mm, the thickness c is 25mm, and the performance indexes are as follows: lower limit of low frequency f1160Hz, upper limit of high frequency f2The output-input ratio V/A is 0.025, and the maximum allowable peak current is 20 KA; the invention selects a capacitive voltage divider and an oscilloscope to form a voltage measuring system, and the voltage dividing ratio of the voltage divider is 2000: 1; the oscilloscope is used as a trigger source signal of the high-speed camera, once the semi-closed self-energy arc extinguishing chamber is broken down, the oscilloscope sends a trigger signal to the high-speed camera, and the high-speed camera shoots the process that the semi-closed self-energy arc extinguishing chamber quenches the impact arc.
The high-speed camera is in a photon FASTCAM SA5 model, is provided with a 12-bit monochromatic chip (36-bit RGB color), 20-micron pixel points, has adjustable frame rate up to 1000000fps according to pixels, and is controlled to shoot by Photon's Fastcamera Viewer (PFV) software.
The test of the quenching impact arc test of the semi-closed self-energy arc extinguishing chamber comprises the following specific implementation steps: firstly, printing a test sample according to a designed cavity structure, and connecting each test device and the test sample according to a test circuit diagram; after wiring is finished, checking the working state of an impulse discharge loop to ensure that the charging loop works normally and the discharging loop is connected completely, debugging an impulse current generator according to a test scheme, and changing the values of a wave modulation inductor and a wave modulation resistor to enable the impulse current generator to output a specified impulse current waveform under the condition of no-load short circuit; then according to the position relation between the high-speed camera and the test article, adjusting the focal length of the camera until the control software displays a clear image, fixing the positions of the high-speed camera and the test article, opening the control software of the high-speed camera, setting a frame rate, a trigger mode and the like; and setting a charging voltage value of the impact current generator, setting charging time according to the impact voltage value to start charging, triggering the impact current generator after charging is finished, checking whether the oscilloscope successfully triggers the high-speed camera, adjusting the frame rate of control software according to the condition of a shot image, and the like, and repeating the test for many times.
After the test is finished, the test result and the simulation result are compared and analyzed, fig. 2 shows the movement and the extinguishing image of the impact arc in the semi-closed self-energy type arc extinguishing chamber shot by the high-speed camera at different moments, the semi-closed self-energy type arc extinguishing chamber is set to be broken down at 0 mu s, the arc column is restrained in the semi-closed arc extinguishing chamber at the moment of breaking down, the radius of the arc column is gradually increased along with the increase of the impact current value, when the radius of the arc column is larger than the size of the chamber, the arc column is expanded out of the chamber, the impact arc is still in a multistage series arc extinguishing structure in the process, and the arc brightness is strong, as shown in (1) - (2) of fig. 2;
meanwhile, the shock wave generated by the shock arc is reflected and then acts on the arc column, the arc column moves towards the opening of the chamber under the action of the shock airflow, the brightness of the arc is gradually enhanced and then gradually reduced along with the gradual reduction of the arc current, as shown in (3) - (6) of fig. 2, because of the rapidly changing shock current, the change of the arc temperature lags behind the change of the arc current;
until 39.6 mus, the arc plasma moves out of the chamber gradually, and the arc brightness and the arc diameter are reduced gradually, as shown in fig. 2(7) - (11);
after 59.4 mus, the impact arc plasma almost moves out of the chamber, under the action of the drift and diffusion of charged particles, the charged particles in the arc plasma gradually decrease, the arc temperature gradually decreases, the brightness gradually decreases until 422.4 mus arc is completely extinguished, as shown in figure 2(12) - (24);
the opening depth of the chamber is 11mm, the time for the arc to be completely ejected from the chamber is about 59.4 μ s when the arc is shot as a moving image, and the average speed of the arc moving in the chamber is about 11mm/59.4 μ s-185.2 m/s.
Extracting an arc form by digital image processing, weakening image interference information by removing useless information in an image, recovering and enhancing real information of the image, and then simplifying useful information of the image to the maximum extent so as to further detect and extract the characteristics of the image; the digital image processing object is an image matrix capable of representing an image, and the general image matrix has the advantages of large information amount, high calculation speed, wide occupied frequency band, high precision, rich content, wide application range and the like.
The specific arc image processing steps are as follows:
1. graying of an image: the arc image obtained by the high-speed camera is an RGB image, but actually the RGB image does not reflect morphological features of the image, and only color adjustment is performed in an optical principle, and brightness of the image actually reflects features of the image, so that it is necessary to perform gradation processing on the original image.
2. Image filtering: the invention adopts a median filter and a Gaussian filter respectively to filter salt and pepper noise and Gaussian noise in the image.
The basic principle of median filtering is to replace the value of one point in the digital image with the median of each point value in the neighborhood of the point, and to make the pixel value around the point close to the true value, so as to eliminate the isolated noise point. The median value is defined as: for a set of numbers x1，x2，...，xnIn other words, if n numbers are arranged in order of magnitude as xi1≤xi2≤…≤xinThen, the following conditions are satisfied:
in the formula: medFirst, a sliding window containing odd number of pixels is defined, the value of the pixel in the middle of the window can be replaced by the median of the pixel values in the window, the input sequence is { xi, I ∈ I }, I is a natural number set or subset, the window length is n, then the filter output is:
yi＝Med{xi-u,…,xi,…,xi+u}；
gaussian filtering is a linear smoothing filter. By carrying out weighted average on the whole image, the value of each pixel point is obtained by carrying out weighted average on the value of each pixel point and other pixel values in the neighborhood. Assuming S is a neighborhood set of pixels (x0, y0), (x, y) represents an element in S, f (x, y) represents a gray scale value of a point (x, y), and a (x, y) represents a weight of each point, then (x0, y0) is smoothed, which can be expressed as:
3. image segmentation: in order to remove the surrounding aperture around the impact arc, an Otsu algorithm is adopted for image segmentation, thereby laying a foundation for edge detection. The principle of the algorithm is that the image is divided into 2 parts of a background and a target according to the gray level characteristics of the image, the larger the inter-class variance between the background and the target is, the larger the difference of the 2 parts forming the image is, and when part of the target is mistaken for the background or part of the background is mistaken for the target, the difference of the 2 parts is reduced. Thus, a segmentation that maximizes the inter-class variance means that the probability of false scores is minimized, i.e.:
in the formula: the number of image pixels is N; the number of pixel points in the image with the gray value of the pixel less than the threshold T is marked as C0Average gray of u0(ii) a The number of pixels with gray value greater than threshold T is marked as C1Average gray of u1. Binarizing the image according to a threshold value T which maximizes the inter-class variance D:
4. candy edge extraction: the edge of an image generally refers to a part with discontinuous or sharp change of local gray scale of the image, and the edge detection is a process for describing gray scale change in the image according to a physical process causing the gray scale change of the image, namely detecting pixel points with local significant change in the image. The image gradient refers to the rate of change of the image gray level, and the change of the image gray level can be generally reflected by the gradient, which can be defined as a vector:
in the formula, Gx and Gy respectively represent the gray scale change rate of a certain pixel in the image in the x direction and the y direction, and the amplitude and the direction of the gradient are respectively:
according to the definition of the image edge and the image gradient, the gradient amplitude on the image edge is large, so that the edge detection method can be realized by calculating the local maximum value of the gradient, and then the value of the pixel is returned according to the obtained gradient value, for example, the pixel with the large gradient value is set to be white, and the pixel with the small gradient value is set to be black, so that the edge can be extracted.
According to the different selected templates, a plurality of different edge detection operators appear in the edge detection, and the edge detection operator based on the optimization algorithm proposed by Canny has good signal-to-noise ratio and detection precision, so that the method adopts a Canny edge detection method to extract the edge of the impact discharge region.
The results of graying, median and gaussian filtering, image segmentation and edge extraction on the impact discharge image are shown in fig. 3, and the processing results show that the impact discharge image subjected to image preprocessing is more favorable for analysis and accurate extraction of the edges of the discharge area is realized.
Typical impulse arc images were taken for analysis, and FIG. 4 is an image of the impulse arc taken by a high speed camera at time 59.4 μ s. As can be seen from fig. 4, since the striking arc emits strong light immediately after being ejected from the chamber, the brightness of the air around the arc is greatly increased, the aperture is surrounded by the arc, the false contour phenomenon is easily generated, and the actual shape of the arc is difficult to observe. Therefore, it is necessary to perform edge detection on the image of the striking arc to obtain a contour image of the arc.
Fig. 5 shows the gray distribution of the impact arc gray image. The division between white and black is in several levels, typically ranging from 0 to 255, called "grey levels", black corresponding to a grey value of 0 and white to a grey value of 255. According to the gray scale distribution display of fig. 5(b), the gray scale value intervals have a distribution which is somewhat different, except that the black background portion having the gray scale of 0 has about 90 pixel values, and the arc column brightest portion having the gray scale of 253 has about 720 pixel values. The gray distribution histogram shows the characteristic of uneven brightness distribution of the impact arc column. Fig. 5(c) clearly shows that the gray value of the central region of the arc column is the maximum and reaches the saturation value, and the gray value is continuously reduced along the radial direction, which indicates that the plasma density and temperature of the central region of the arc column are high, and the plasma of the arc column is continuously diffused outwards due to the pressure gradient inside the plasma, and the plasma at the edge of the arc column is relatively thin, so that the gray value is also low.
By using the arc image processing method, the change rule (represented by pixel values) of the arc area after the impact arc is sprayed out of the chamber is researched based on the impact arc image feature extraction process. Fig. 6 is an area variation curve of an image of an impact arc at different times. It can be seen that the area of the arc rapidly increases within 0-59.4 mus, because the arc plasma is ejected from the chamber by the high-speed gas flow, and the arc plasma continuously diffuses in the air to reach a maximum value around 59.4 mus, at which point the arc is considered to have been ejected completely from the chamber. 59.4-422.4 μ s, the area of the arc is reduced, because the arc plasma is exposed in the air, the charged particles inside the arc are continuously compounded and diffused, the deionization is enhanced, the temperature of the arc is gradually reduced, and the brightness of the arc is darkened until the arc is finally extinguished.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. An impulse arc image edge detection method is characterized in that: the method comprises the following steps:
the method comprises the following steps: establishing a semi-closed self-energy type quenching chamber quenching impact arc test field:
step 1.1: printing a test sample by using a 3D printer according to the designed semi-closed arc extinguishing chamber structure;
step 1.2: connecting each test device and the test article according to the test circuit diagram;
step 1.3: after the connection and installation are finished, the working state of the impulse discharge loop is checked, and the normal work of the charge loop and the complete connection of the discharge loop are ensured;
step 1.4: debugging the impact current generator, and enabling the impact current generator to output a specified impact current waveform under the condition of no-load short circuit by changing the values of the wave modulation inductor and the wave modulation resistor;
step 1.5: adjusting the focal length of the camera according to the position relation between the high-speed camera and the sample until a clear image can be displayed in the control software, and then fixing the positions of the high-speed camera and the sample;
step 1.6: opening a high-speed camera, and setting parameters such as a frame rate, a trigger mode and the like;
step 1.7: setting a charging voltage value of the impact current generator, setting corresponding charging time according to the impact voltage value for charging, triggering the impact current generator after charging is finished, and checking whether the oscilloscope successfully triggers the high-speed camera;
step 1.8: adjusting parameters such as the frame rate of control software in real time according to the image condition obtained by shooting, and obtaining and recording an ideal detection state through repeated tests;
step two: and comparing and analyzing the test result and the simulation result, and shooting the movement and extinguishing images of the impact arc in the semi-closed arc extinguishing chamber by using a high-speed camera at different moments:
before shooting, setting the semi-closed self-energy arc extinguishing chamber to be broken down at the moment of 0 mu s, and restraining an arc column in the semi-closed arc extinguishing chamber at the moment of breaking down; the method comprises the steps that an impact current generator is controlled to gradually increase an impact current value to enable the radius of an arc column to be gradually increased, impact waves generated by impact arcs act on the arc column after being reflected, the arc column moves towards an opening of an arc extinguishing chamber under the action of impact air flow, and the brightness of the arcs gradually becomes stronger and then gradually weakens along with the gradual reduction of arc currents;
shooting images in the whole arc brightness change period by using a high-speed camera;
step three: analyzing and processing the acquired impact arc image, wherein the processing steps comprise:
step 3.1: image graying treatment: obtaining an electric arc RGB image by a high-speed camera, and carrying out gray processing on an original image;
step 3.2: and (3) image filtering processing: filtering the gray level image of the arc to obtain a high-quality impact arc image, specifically filtering salt and pepper noise and Gaussian noise in the image by adopting a median filter and a Gaussian filter;
step 3.3: image segmentation processing: the image is segmented by adopting an Otsu algorithm to remove an aperture image surrounding the impact arc;
step 3.4: extracting the image edge of the impact discharge area by adopting a Candy edge extraction algorithm to finally obtain an accurate image of the discharge edge area;
step four: and sending the obtained accurate image of the discharge edge area to a data processing device for further processing, analyzing the dissipation characteristic of the electric arc in the semi-closed self-energy type arc extinguishing chamber through software built in the data processing device, and finally obtaining a multi-stage semi-closed type arc extinguishing chamber series connection structure applied to the distribution line.
2. The impulse arc image edge detection method according to claim 1, wherein: the median filtering method adopted in the step 3.2 specifically comprises the following steps: replacing the value of one point in the digital image with the median of each point value in the neighborhood of the point to make the pixel value around the point close to the real value so as to eliminate the isolated noise point, wherein the calculation process is as follows:
for a set of numbers x1，x2，...，xnIn other words, n numbers are arranged in order of magnitude of xi1≤xi2≤…≤xinThen, the following conditions are satisfied:
in the formula: medDefining y as a function of the median of the sequence, x1，x2，…，xnThe median value of (d);
when the median filtering is carried out, a sliding window containing odd pixels is defined, the pixel value in the middle of the window is replaced by the median value of all the pixel values in the window, the input sequence is set as { xi, I ∈ I }, wherein I is a natural number set or subset, the window length is n, and the output signal value of the filter is yi＝Med{xi-u,…,xi,…，xi+u}。
3. The impulse arc image edge detection method according to claim 2, wherein: the gaussian filtering method adopted in the step 3.2 specifically comprises the following steps: the value of each pixel point is obtained by weighted averaging of the pixel point and other pixel values in the neighborhood through weighted averaging of the whole image;
defining S as a pixel (x)0，y0) (x, y) represents the element in S, and f (x, y) represents the neighborhood set of (x, y) pointsThe gray scale value a (x, y) represents the weight of each point, and then the pixel (x) is subjected to0，y0) The calculation formula for performing the gaussian filtering smoothing process is as follows:
4. the impulse arc image edge detection method of claim 3, wherein: the concrete steps of the Otsu algorithm adopted in the step 3.3 are as follows: firstly, automatically selecting a threshold, dividing an image into a background part and a target part according to the gray characteristic of the image, and keeping the maximum variance between the background part and the target part in order to minimize the misclassification probability of the background image and the target image, namely, meeting the following requirements:
in the above formula: n is the number of image pixels, C0The number u of pixel points of which the gray value of the pixel in the image is less than the threshold value T0Is C0Average gray scale of pixel points, C1The number u of pixel points with the pixel gray value larger than the threshold value T1Is C1Average gray level of the pixel points;
binarizing the image according to a threshold value T which maximizes the inter-class variance D:
in the process of identification: g is the gray value of a pixel point on the image, and (i, j) is the position coordinate of a certain pixel point on the image, and the image segmentation processing is realized through image binarization.
5. The impulse arc image edge detection method of claim 4, wherein: the specific steps of extracting the image edge of the impact discharge area in the step 3.4 are as follows:
defining the edge of an image as a part with discontinuous or sharp change of local gray scale of the image, describing the process of gray scale change in the image according to a physical process causing the gray scale change of the image, and detecting pixel points with local significant change in the image;
defining the image gradient as the rate of image gray scale change, wherein the calculation formula of the image gradient is as follows:
in the above formula, Gx and Gy represent the gray scale change rate of a certain pixel in the image in the x direction and the y direction respectively,
t represents transposition;
the gradient magnitude is calculated as:
the calculation formula of the gradient direction is:
the edge image extraction method is realized by calculating a local maximum value of gradient, returns a pixel value according to the obtained gradient value of a certain pixel, sets the pixel with a large gradient value as white and the pixel with a small gradient value as black, and extracts the edge.
6. An impulse arc image edge detection device, characterized by: the device comprises a surge current generator, an arc extinguishing chamber provided with a test sample, a Rogowski coil, a capacitive voltage divider, an oscilloscope, a high-speed camera and a data processing device;
the current output end of the impulse current generator is connected with an ignition ball gap, and the ignition ball gap is respectively connected with the input end of the arc extinguishing chamber and the input end of the capacitive voltage divider through a pulse ignition device;
the output end of the arc extinguishing chamber is connected with the Rogowski coil in series and then is connected with the current measuring end of the oscilloscope;
the output end of the arc extinguishing chamber is connected with the output end of the capacitive voltage divider in parallel and then is connected with the voltage measuring end of the oscilloscope;
and the signal trigger end of the oscilloscope is connected with the high-speed camera, and the signal output end of the high-speed camera is connected with the data processing device.
7. The apparatus according to claim 6, wherein: the impulse current generator is a commercially available module, the impulse current of the test is 2kA, and the waveform is 8/20 us.
8. The apparatus according to claim 6, wherein: the Rogowski coil is a non-contact Rogowski coil, and the Rogowski coil is used as a current sensor to form a current measuring system with an oscilloscope;
the specifications of the Rogowski coil are as follows: the inner diameter b is 54mm, the outer diameter a is 102mm, and the thickness c is 25 mm.
9. The apparatus according to claim 6, wherein: the capacitive voltage divider and the oscilloscope form a voltage measuring system, and the voltage division ratio of the capacitive voltage divider is 2000: 1.
10. The apparatus according to claim 6, wherein: the arc extinguishing chamber is specifically printed by a 3D printer;
in the printing process, polylactic acid P L A is used as a printing material, and a fused deposition modeling FDM method is used for printing a sample;
the 3D printer specifically is the Allctc 3D printer.
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