In order to investigate the influence of cross-linking byproducts on dielectric and mechanical properties of 110k V cross-linked polyethylene(XLPE)cable insulation,we selected the undegassed XLPE cable insulation whic...In order to investigate the influence of cross-linking byproducts on dielectric and mechanical properties of 110k V cross-linked polyethylene(XLPE)cable insulation,we selected the undegassed XLPE cable insulation which is heated at 70℃in laboratory for different duration in terms of heating time,to prepare XLPE samples with different mass loss ratio.We carried out Fourier transform infrared spectroscopy(FTIR)test,electric breakdown test at 50 Hz,pulsed electro-acoustic(PEA)measurement and tensile test for XLPE samples.In FTIR spectrogram,the characteristic absorption peaks were observed to appear at 1 680 cm-1 and 1 600 cm-1,which can be related to two kinds of cross-linking byproducts includingα-methylstyrene and acetophenone.The intensity of these absorption peaks decreases with the increase of mass loss ratio.It can be proposed that the mass loss of XLPE samples in the process of thermal treatment is caused by volatiliztion ofα-methylstyrene and acetophenone.Therefore,the change of mass loss ratio can reflect the change of content ofα-methylstyrene and acetophenone in the process of thermal treatment.The results of electric breakdown test showed that the reduction ofα-methylstyrene and acetophenone leads to the enhancement of electric breakdown strength at 50 Hz.PEA measurement results showed that heterocharge is produced and accumulated when cross-linking byproducts are present,whereas no heterocharge is found whenα-methylstyrene and acetophenone are absent.The formation of heterocharge is attributed to ionization of cross-linking byproducts under electric stress.Based on these results,it can be suggested that when AC electric field is applied on XLPE samples,the occurrence of ionization of cross-linking byproducts results in the increase of free carriers in XLPE insulation,leading to a lower electric breakdown strength.The results of tensile test showed that tensile strength is proportional to the mass loss ratio of XLPE samples,which suggests that cross-linking byproducts can reduce the tensile strength of XLPE insulation.展开更多
Cables that have been in service for over 20 years in Shanghai, a city with abundant surface water, failed more frequently and induced different cable accidents. This necessitates researches on the insulation aging st...Cables that have been in service for over 20 years in Shanghai, a city with abundant surface water, failed more frequently and induced different cable accidents. This necessitates researches on the insulation aging state of cables working in special circumstances. We performed multi-parameter tests with samples from about 300 cable lines in Shanghai. The tests included water tree investigation, tensile test, dielectric spectroscopy test, thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR), and electrical aging test. Then, we carried out regression analysis between every two test parameters. Moreover, through two-sample t-Test and analysis of va- riance (ANOVA) of each test parameter, we analyzed the influences of cable-laying method and sampling section on the degradation of cable insulation respectively. Furthermore, the test parameters which have strong correlation in the regression analysis or significant differ- ences in the t-Test or ANOVA analysis were determined to be the ones identifying the XLPE cable insulation aging state. The thresholds for distinguishing insulation aging states had been also obtained with the aid of statistical analysis and fuzzy clustering. Based on the fuzzy in- ference, we established a cable insulation aging diagnosis model using the intensity transfer method. The results of regression analysis indicate that the degradation of cable insulation accelerates as the degree of in-service aging increases. This validates the rule that the in- crease of microscopic imperfections in solid material enhances the dielectric breakdown strength. The results of the two-sample t-Test and the ANOVA indicate that the direct-buried cables are more sensitive to insulation degradation than duct cables. This confirms that the tensile strength and breakdown strength are reliable functional parameters in cable insulation evaluations. A case study further indicates that the proposed diagnosis model based on the fuzzy inference can reflect the comprehensive aging state of cable insulation well, and that the cable service time has no correlation with the insulation aging state.展开更多
基金Project supported by Key Technology and Engineering Demonstration Application of High Conveying Capacity High-Voltage Cable and Accessories(5442GY120040)
文摘In order to investigate the influence of cross-linking byproducts on dielectric and mechanical properties of 110k V cross-linked polyethylene(XLPE)cable insulation,we selected the undegassed XLPE cable insulation which is heated at 70℃in laboratory for different duration in terms of heating time,to prepare XLPE samples with different mass loss ratio.We carried out Fourier transform infrared spectroscopy(FTIR)test,electric breakdown test at 50 Hz,pulsed electro-acoustic(PEA)measurement and tensile test for XLPE samples.In FTIR spectrogram,the characteristic absorption peaks were observed to appear at 1 680 cm-1 and 1 600 cm-1,which can be related to two kinds of cross-linking byproducts includingα-methylstyrene and acetophenone.The intensity of these absorption peaks decreases with the increase of mass loss ratio.It can be proposed that the mass loss of XLPE samples in the process of thermal treatment is caused by volatiliztion ofα-methylstyrene and acetophenone.Therefore,the change of mass loss ratio can reflect the change of content ofα-methylstyrene and acetophenone in the process of thermal treatment.The results of electric breakdown test showed that the reduction ofα-methylstyrene and acetophenone leads to the enhancement of electric breakdown strength at 50 Hz.PEA measurement results showed that heterocharge is produced and accumulated when cross-linking byproducts are present,whereas no heterocharge is found whenα-methylstyrene and acetophenone are absent.The formation of heterocharge is attributed to ionization of cross-linking byproducts under electric stress.Based on these results,it can be suggested that when AC electric field is applied on XLPE samples,the occurrence of ionization of cross-linking byproducts results in the increase of free carriers in XLPE insulation,leading to a lower electric breakdown strength.The results of tensile test showed that tensile strength is proportional to the mass loss ratio of XLPE samples,which suggests that cross-linking byproducts can reduce the tensile strength of XLPE insulation.
基金Project supported by National Natural Science Foundation of China（51277117）, Shang- hai Science and Technology Comrmssion（11 DZ2283000）.
文摘Cables that have been in service for over 20 years in Shanghai, a city with abundant surface water, failed more frequently and induced different cable accidents. This necessitates researches on the insulation aging state of cables working in special circumstances. We performed multi-parameter tests with samples from about 300 cable lines in Shanghai. The tests included water tree investigation, tensile test, dielectric spectroscopy test, thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR), and electrical aging test. Then, we carried out regression analysis between every two test parameters. Moreover, through two-sample t-Test and analysis of va- riance (ANOVA) of each test parameter, we analyzed the influences of cable-laying method and sampling section on the degradation of cable insulation respectively. Furthermore, the test parameters which have strong correlation in the regression analysis or significant differ- ences in the t-Test or ANOVA analysis were determined to be the ones identifying the XLPE cable insulation aging state. The thresholds for distinguishing insulation aging states had been also obtained with the aid of statistical analysis and fuzzy clustering. Based on the fuzzy in- ference, we established a cable insulation aging diagnosis model using the intensity transfer method. The results of regression analysis indicate that the degradation of cable insulation accelerates as the degree of in-service aging increases. This validates the rule that the in- crease of microscopic imperfections in solid material enhances the dielectric breakdown strength. The results of the two-sample t-Test and the ANOVA indicate that the direct-buried cables are more sensitive to insulation degradation than duct cables. This confirms that the tensile strength and breakdown strength are reliable functional parameters in cable insulation evaluations. A case study further indicates that the proposed diagnosis model based on the fuzzy inference can reflect the comprehensive aging state of cable insulation well, and that the cable service time has no correlation with the insulation aging state.
