# Research on Lifespan Prediction of Cross-Linked Polyethylene Material for XLPE Cables
## 1 Introduction  
Cross-linked polyethylene (XLPE) cables, with excellent electrical and mechanical properties, have been widely used in alternating current (AC) and direct current (DC) transmission systems [1, 2]. As the operating time of XLPE cables goes by, the performance of the XLPE cables deteriorates, owing to their subject to electrical and thermal operating constraints permanently, which, in turn, result in an increase in the probability of electrical breakdown accidents [3, 4].  
Over the past few years, plenty of studies have been carried out to evaluate the aging performance of XLPE cables in the aging process. In [5, 6], the loss angle tangent test and tensile strength test were performed to evaluate the electrical properties and mechanical properties of XLPE cables. In [7, 8], researchers evaluated the electrical properties of XLPE cables in the aging process by employing the dielectric property test and the AC breakdown strength test.  
On this basis, some scholars proposed the use of one or several parameters summarized from the test results to characterize the aging degree of XLPE cables qualitatively or quantitatively in the aging process. In [9], the researchers evaluated the aging performance of XLPE cables by means of adielectric breakdown test, where the dielectric breakdown strength was proposed as a parameter to characterize the aging degree of cables. In [10; 11], gas chromatography-mass spectrometry, differential scanning calorimetry, oxidation induction time and measurements of dielectric loss tangent were utilized to monitor the aging performance of XLPE cables, and the dielectric loss tangent proved to be a reliable parameter for evaluating the aging performance of XLPE cables. Moreover, the researchers in [12] proposed the use of the carbonyl content to characterize the aging degree of XLPE cables. Unfortunately, due to the great influence of operating environments on the aging performance of XLPE cables, some deviations among the results calculated by the prediction methods and actual results remain unsolved.  
In this paper, XLPE cables of the same batch from Factory A, which ran from 1 to 8 years in Jiangsu Province, are sampled. The changing law of the aging characterization parameters is investigated by means of widely accepted methods, including the gel content test, differential scanning calorimetry (DSC) test, tensile test, hardness test, dielectric frequency spectrum test and dielectric AC breakdown voltage test and the test results are presented in Section 2. In Section 3, some aging characterization parameters are explored and these parameters significantly correlate with ageing times obtained by adopting correlation calculations. On this basis, a prediction method based on a Backpropagation (denoted as BP) neural network is proposed for determining the aging time of XLPE cables.  
Corresponding Parameters of Composite Insulator under Different Aging Years for Lifespan Prediction  
In this research, XLPE cables (recorded as A\({}_{1}\)-A\({}_{9}\)), which ran from 1 to 8 years in adjacent lines in Jiangsu Province (the average temperature is about 15 \({}^{\circ}\)C and the average humidity is about 80%) were sampled. In order to investigate the changing law of lifespan prediction parameters in different years, several widely accepted methods, including the gel content test, differential scanning calorimetry (DSC) test, tensile test, hardness test, dielectric property and breakdown voltage test are employed for XLPE cables aged for different numbers of years in this section.