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| Modification of Cross-Linked Polyethylene Electrical Life Model Based on Statistical Characteristics of Failure Time |
| Wang Guodong1, Zhou Kai1, Li Yuan1, Li Shiyu2, Fu Yao1 |
1. College of Electrical Engineering Sichuan University Chengdu 610065 China;
2. State Grid Leshan Power Supply Company Leshan 614000 China |
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Abstract With the development of power system, the transmission voltage level of cable is continuously improved, and electrical stress plays a more and more important role in the failure process of cross-linked polyethylene (XLPE) insulation. It is necessary to deeply study the electrical aging life of XLPE. However, the influence of electrical stress on the performance of insulating materials is distributed in a probabilistic manner. Even under the same experimental condition, the insulation failure time of the samples also has a large dispersion. To improve the accuracy of electrical life assessment of cable insulation material, this paper modifies the traditional XLPE electrical life model based on the inverse power law according to the statistical characteristics of XLPE failure time.
First, the voltage endurance test was carried out on the XLPE sheet samples, and the failure time of XLPE under the action of different field strengths is counted. The XLPE sheet samples for the study was provided by a cable manufacturer with a size of 200 mm×200 mm×1 mm。According to the samples power frequency field strong breakdown test results and the standard GB/T 29311, the voltage endurance test field intensities were determined to be 36 kV/mm, 33 kV/mm, 32 kV/mm, 30 kV/mm and 28 kV/mm respectively.
Secondly, according to the voltage endurance test results, the statistical characteristics of the failure time of XLPE sheet samples were analyzed. In order to reduce the impact of subjective factors on the results, density based spatial clustering of applications with noise (DBSCAN) algorithm was used to divide the samples failure time according to the distribution concentration of data points. The results show that under the same field intensity, the failure time of XLPE was roughly distributed in three time intervals. The relationship between samples failure time and electric field intensity was analyzed. Combined with the observation results of material micro morphology, it can be seen that different failure time intervals of XLPE correspond to different insulation failure processes. When the electric field intensity was different, the dominant failure process was also different.
Finally, the traditional XLPE electrical life model based on the inverse power law was modified according to the statistical characteristics of the failure time of the XLPE sheet samples. The failure time of the dominant failure process samples was used to represent the electrical life of the XLPE sheet samples under the field intensity, and the modified XLPE electrical life model was obtained.
Compared with the traditional electric life model, the modified model determines the position of the inflection point in the E-t characteristic curve from the perspective of the statistical characteristics of the failure time. According to the modified model, when the electric field intensity E≥32 kV/mm, the XLPE life index n1=20.73; When the electric field intensity E<32 kV/mm, the XLPE life index n2=28.45.
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Received: 12 November 2021
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2023, Vol. 38 
