High-voltage cable buffer layer ablation defect detection method

Abstract

The invention relates to a high-voltage cable buffer layer ablation defect detection method, which comprises the following steps of: firstly, clamping a high-frequency current sensor at a terminal grounding lead of a cable to be detected, and then, carrying out simulated discharge experiments on buffer layers with different structures under the conditions of different voltage amplitudes, different water contents, different pressures, different contact areas and the like; and finally, carrying out terahertz continuous wave scanning imaging on the cable so as to observe the morphology change of each layer in the cable, and after the operation is completed, through the difference of the types and the volume fractions of the gases generated in each ablation stage of the buffer layer and in combination with an artificial intelligence technology, calculating the morphology change of each layer in the cable. The defect state of the buffer layer of the high-voltage cable is detected; the device has the advantages of being accurate and reliable in detection and good in use effect.

Description

Technical Field

[0001] The invention belongs to the technical field of electric power detection, and in particular relates to a method for detecting ablation defects of a high-voltage cable buffer layer. Background Art

[0002] High-voltage power cable is an important power transmission equipment in the power grid. It plays an important role in the safe and stable operation of power loads. At the same time, it has the characteristics of small line path width, easy line path selection, concealed burial, not easily affected by the surrounding environment and pollution, and high power transmission reliability. However, during the long-term use of high-voltage cables, the buffer layer of the cable will produce white spots due to moisture, or the gap between the buffer layer and the aluminum sheath is too large, resulting in poor electrical contact between the buffer layer and the aluminum sheath, which in turn causes the electric field at that location to be distorted. When the field strength is greater than the breakdown voltage of the air, it will cause local discharge, resulting in the buffer layer being damaged. The layer will be ablated, and as the discharge continues, the insulating shielding layer will continue to be ablated, eventually leading to the breakdown of the cable body; in recent years, there have been reports of XPLE cable buffer layer ablation failures at voltage levels of 110kV and above; according to statistics, from 2010 to 2019, there were 11 cable failures at voltage levels of 110kV and above in Beijing, of which 6 were caused by cable buffer layer ablation, accounting for as high as 54.5%, seriously endangering the safe operation of the cable system; therefore, in order to solve the above problems, it is necessary to develop a high-voltage cable buffer layer ablation defect detection method that is accurate, reliable and effective. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a method for detecting ablation defects of a high-voltage cable buffer layer which is accurate, reliable and has good use effect.

[0004] The object of the present invention is achieved by: a method for detecting ablation defects of a high-voltage cable buffer layer, comprising the following steps: Step 1: Clamp the high-frequency current sensor to the terminal ground lead of the cable to be tested; Step 2: Conduct simulated discharge experiments on the buffer layer under different conditions, that is, when the field strength is greater than the air breakdown voltage, local discharge will occur at the white spot defect in the buffer layer, thereby forming a conductive circuit. At this time, charges in the normal area will flow into the earth through the terminal grounding lead, and then the charges of the earth will flow from the grounding lead into the defects of the buffer layer, thereby maintaining the voltage balance of the two parallel branches and generating a pulse current; finally, the generated pulse current is coupled to the high-frequency current sensor, and transmitted to the analytical instrument through the signal transmission line between the high-frequency current sensor and the analytical instrument, and finally the information characteristics such as the apparent discharge amount and discharge phase of the pulse current are observed on the analytical instrument; in this process, the characteristic gas generated by the discharge of the cable to be tested is collected by using a gas sampling bag through the cooperation of the air pump and the air valve; Step 3: Scan the cable to be tested, and use the terahertz continuous wave imaging method to utilize the different thicknesses and densities of the materials and white spots of the cable to be tested, as well as the different absorption capacities of the scanning rays, so as to scan and record the intensity information of the continuous terahertz wave of the detection cable after transmission or reflection point by point. Then, convert the information into a current signal and input it into the terminal computer, finally forming a digital image of the cable, so as to observe the morphological changes of each layer inside the cable; Step 4: Based on the difference study of the ablation defects of the cable buffer layer, an intelligent recognition model for cable buffer layer defects is established. That is, according to the description of steps 2 and 3, simulated discharge experiments are carried out on buffer layers of different structures under different voltage amplitudes, different water contents, different pressures, different contact areas, etc., and the collected gas is detected while recording the digital image of the cable. The change trend of the gas generation rate under different conditions is obtained by the change of the gas volume fraction; Step 5: By combining artificial intelligence technology with the difference in the types and volume fractions of the gases produced by the buffer layer at each ablation stage, the defect state of the high-voltage cable buffer layer can be detected.

[0005] The gas is detected in step 4, specifically including: detecting the moisture and hydrogen in the test gas respectively.

[0006] In step 3, continuous imaging can be performed through the cooperation of scanning points, and non-destructive detection of tiny defects inside the cable can be performed, which has the advantages of good stability, fast imaging speed, high system integration, and diverse imaging methods.

[0007] Beneficial effects of the present invention: the present invention first utilizes the local discharge occurring at the white spot defect in the buffer layer to form a conductive circuit, and then the charge in the normal area of ​​the cable will flow into the earth through the terminal grounding lead, and the charge of the earth will flow from the grounding lead into the defect in the buffer layer to maintain the voltage balance of the two parallel branches, thereby generating a pulse current, and then coupling the pulse current to the high-frequency current sensor, and transmitting it to the analytical instrument through the signal transmission line between the high-frequency current sensor and the analytical instrument, and finally observing the information characteristics such as the apparent discharge amount and the discharge phase of the pulse current on the analytical instrument, and collecting the gas generated in this process for detection; at the same time, the terahertz continuous wave is used to scan the cable point by point, and the intensity information of the continuous terahertz wave after transmission or reflection is recorded, and then the information is converted into a current signal and input into the terminal computer, and finally a digital image of the cable is formed. The present invention uses terahertz continuous wave scanning imaging to observe the changes in the morphology of each layer inside the cable. The present invention can not only perform non-destructive detection of tiny defects inside the cable, but also clearly image the buffer layer defects through time domain or frequency domain methods. It has the advantages of good stability, fast imaging speed, high system integration, and diverse imaging methods. In addition, the present invention obtains the ablation failure characteristics of the high-voltage cable buffer layer and the change law of the buffer layer performance in actual operation through the combination of simulated discharge experiments and terahertz continuous wave imaging, and reveals the cause and mechanism of the high-voltage cable failure caused by the buffer layer. Finally, through the differences in the types and volume fractions of the gases generated by the buffer layer in each ablation stage, combined with artificial intelligence technology, the defect state of the high-voltage cable buffer layer can be detected. In general, the present invention has the advantages of accurate and reliable detection and good use effect. DETAILED DESCRIPTION

[0008] The present invention is further described below.

[0009] Embodiment: A method for detecting ablation defects of a high-voltage cable buffer layer comprises the following steps: Step 1: Clamp the high-frequency current sensor to the terminal ground lead of the cable to be tested; Step 2: Conduct simulated discharge experiments on the buffer layer under different conditions, that is, when the field strength is greater than the air breakdown voltage, local discharge will occur at the white spot defect in the buffer layer, thereby forming a conductive circuit. At this time, charges in the normal area will flow into the earth through the terminal grounding lead, and then the charges of the earth will flow from the grounding lead into the defects of the buffer layer, thereby maintaining the voltage balance of the two parallel branches and generating a pulse current; finally, the generated pulse current is coupled to the high-frequency current sensor, and transmitted to the analytical instrument through the signal transmission line between the high-frequency current sensor and the analytical instrument, and finally the information characteristics such as the apparent discharge amount and discharge phase of the pulse current are observed on the analytical instrument; in this process, the characteristic gas generated by the discharge of the cable to be tested is collected by using a gas sampling bag through the cooperation of the air pump and the air valve; Step 3: Scan the cable to be tested, and use the terahertz continuous wave imaging method to utilize the different thicknesses and densities of the materials and white spots of the cable to be tested, as well as the different absorption capacities of the scanning rays, so as to scan and record the intensity information of the continuous terahertz waves of the detection cable after transmission or reflection point by point. After that, the information is converted into a current signal and input into the terminal computer, and finally a digital image of the cable is formed to observe the changes in the morphology of each layer inside the cable; through the mutual coordination of the scanning points, continuous imaging can be achieved, and non-destructive detection of tiny defects inside the cable can be performed, which has the advantages of good stability, fast imaging speed, high system integration, and diverse imaging methods; Step 4: Based on the difference study of the ablation defects of the cable buffer layer, an intelligent recognition model for cable buffer layer defects is established. That is, according to the description of steps 2 and 3, simulated discharge experiments are carried out on buffer layers of different structures under different voltage amplitudes, different water contents, different pressures, different contact areas, etc., and while recording the digital image of the cable, the collected gas is detected (specifically, the moisture and hydrogen in the test gas are detected separately), and the change trend of the gas generation rate under different conditions is obtained through the change of the gas volume fraction; Step 5: By combining artificial intelligence technology with the difference in the types and volume fractions of the gases produced by the buffer layer at each ablation stage, the defect state of the high-voltage cable buffer layer can be detected.

[0010] When the present invention is used, first, a conductive circuit is formed by utilizing the local discharge occurring at the white spot defect in the buffer layer. After that, electric charges will flow into the earth through the terminal grounding lead in the normal area of ​​the cable, and the electric charges of the earth will flow from the grounding lead into the defect of the buffer layer to maintain the voltage balance of the two parallel branches, thereby generating a pulse current. Then, the pulse current is coupled to the high-frequency current sensor, and transmitted to the analytical instrument through the signal transmission line between the high-frequency current sensor and the analytical instrument. Finally, the information characteristics such as the apparent discharge amount and the discharge phase of the pulse current are observed on the analytical instrument, and the characteristic gas generated by the discharge of the cable to be detected is collected by using a gas sampling bag through the cooperation of an air pump and an air valve, and the gas is detected after the gas is collected. At the same time, the cable is scanned point by point using a terahertz continuous wave, and the intensity information of the continuous terahertz wave after transmission or reflection is recorded. Then, the information is converted into a current signal and input into the terminal The end computer finally forms a digital image of the cable, thereby observing the changes in the morphology of each layer inside the cable. The present invention uses the method of terahertz continuous wave scanning imaging, which can not only perform non-destructive detection on tiny defects inside the cable, but also clearly image the defects of the buffer layer through time domain or frequency domain methods. It has the advantages of good stability, fast imaging speed, high system integration, and diverse imaging methods. In addition, the present invention obtains the ablation failure characteristics of the buffer layer of the high-voltage insulated corrugated metal sheathed power cable and the change law of the buffer layer performance in actual operation through the combination of simulated discharge experiments and terahertz continuous wave imaging, and reveals the cause and mechanism of the high-voltage cable failure caused by the buffer layer. Finally, through the difference in the type and volume fraction of the gas generated by the buffer layer in each ablation stage, combined with artificial intelligence technology, the defect state of the high-voltage cable buffer layer can be detected; in general, the present invention has the advantages of accurate and reliable detection and good use effect.

[0011] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for detecting ablation defects of a high-voltage cable buffer layer, characterized in that: The following steps are involved: Step 1: Clamp the high-frequency current sensor to the terminal ground lead of the cable to be tested; Step 2: Conduct simulated discharge experiments on the buffer layer under different conditions, that is, when the field strength is greater than the air breakdown voltage, local discharge will occur at the white spot defect in the buffer layer, thereby forming a conductive circuit. At this time, charges in the normal area will flow into the earth through the terminal grounding lead, and then the charges of the earth will flow from the grounding lead into the defects of the buffer layer, thereby maintaining the voltage balance of the two parallel branches and generating a pulse current; finally, the generated pulse current is coupled to the high-frequency current sensor, and transmitted to the analytical instrument through the signal transmission line between the high-frequency current sensor and the analytical instrument, and finally the information characteristics such as the apparent discharge amount and discharge phase of the pulse current are observed on the analytical instrument; in this process, the characteristic gas generated by the discharge of the cable to be tested is collected by using a gas sampling bag through the cooperation of the air pump and the air valve; Step 3: Scan the cable to be tested, and use the terahertz continuous wave imaging method to utilize the different thicknesses and densities of the materials and white spots of the cable to be tested, as well as the different absorption capacities of the scanning rays, so as to scan and record the intensity information of the continuous terahertz wave of the detection cable after transmission or reflection point by point. Then, convert the information into a current signal and input it into the terminal computer, finally forming a digital image of the cable, so as to observe the morphological changes of each layer inside the cable; Step 4: Based on the difference study of the ablation defects of the cable buffer layer, an intelligent recognition model for cable buffer layer defects is established. That is, according to the description of steps 2 and 3, simulated discharge experiments are carried out on buffer layers of different structures under different voltage amplitudes, different water contents, different pressures, different contact areas, etc., and the collected gas is detected while recording the digital image of the cable. The change trend of the gas generation rate under different conditions is obtained by the change of the gas volume fraction; Step 5: By combining artificial intelligence technology with the difference in the types and volume fractions of the gases produced by the buffer layer at each ablation stage, the defect state of the high-voltage cable buffer layer can be detected.

2. A method for detecting ablation defects of a high-voltage cable buffer layer according to claim 1, characterized in that: The gas is detected in step 4, specifically including: detecting the moisture and hydrogen in the test gas respectively.

3. A method for detecting ablation defects of a high-voltage cable buffer layer according to claim 1, characterized in that: In step 3, continuous imaging can be performed through the cooperation of scanning points, and non-destructive detection of tiny defects inside the cable can be performed, which has the advantages of good stability, fast imaging speed, high system integration, and diverse imaging methods.