Abstract
During the long-term operation of high-voltage cross-linked polyethylene (XLPE) cables, the cable will gradually deteriorate under the effect of various aging factors. Thermal aging is one of the key factors directly related to the long-term operation reliability of the XLPE cables. In this paper, the thermal aging samples are prepared for PDC measurement. Based on the polymer trap theory and the extended Debye model, the shape of PDC curve, depolarization charge, parameters of the extended Debye model, aging factor (A), elongation at break retention rate (EB%) and their relationships under different thermal aging degrees are analyzed. The results show that the depolarization current curve and the depolarization charge can preliminarily judge the aging condition of the XLPE, but it is not accurate enough. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{3}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\tau _{3}$ </tex-math></inline-formula> of the branch, with the largest time constant must be the most sensitive to cable aging. With the increase of aging degree, the A shows an upward trend, and has a nonlinear relationship with EB%. Under the aging temperature of 140 °C, after 15–25 days of aging, the A suggests the samples are in the moderate to severe aging stage, and the PDC test should be performed on carried out for the cables with that have been used for 21 years of operation to evaluate the insulation aging condition. The study reveals that the PDC-based parameters can be serviced as an effective tool for the aging condition prediction of XLPE cable insulation.
Highlights
Nowadays, XLPE power cable has been used more and more widely [1], [2]
The thermal aging caused by cable overheating will bring irreversible damage to the XLPE insulation, and the high temperature will promote the formation of water trees and electricity tree to a certain extent, which leads to the decline of cable insulation performance eventually [6]–[8]
It is necessary to assess the insulation performance of XLPE cables going through thermal aging
Summary
XLPE power cable has been used more and more widely [1], [2]. As the most important equipment for energy transmission in the power grid, the XLPE cable will cause unpredictable losses to the national economy once it fails. The polarization/ depolarization current (PDC) method based on the dielectric response principle has been gradually recognized by scholars and used in the condition diagnosis of high voltage electrical equipment, with its advantages of using light equipment, short test time, and reflecting sufficient information [14]. To diagnose the insulation condition of the XLPE cables with different thermal aging degrees, the artificial accelerated thermal aging experiment at 140 °C of XLPE is carried out, and a high voltage time domain dielectric response test platform is built for the first time. Based on this platform, the polarization/depolarization current variation of 10kV XLPE cables is tested and analyzed. The elongation at break that is greatly affected by thermal aging is discussed
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