This paper reveals a correlation between morphology and thermal parameters on cross-linked polyethylene (XLPE) cable with different insulating states. Several cables were selected to detect the physicochemical and thermal parameters of the XLPE. The results show that the cable ampacity is determined by the thermal parameters, which are deeply subjected to the morphology of the XLPE. The molecular chain and crystal structure of the XLPE have a close connection with the thermal resistivity. The physicochemical parameters of carbonyl index (CI) and unsaturated band index (UBI) from Fourier transform infrared spectrum (FTIR) and melting range (R m) from differential scanning calorimetry (DSC) can be the indicator to evaluate the diversity of the thermal resistivity. The change of thermal capacity is governed by the crystal distribution of the XLPE. The physicochemical parameters of crystallinity (χ) and lamellar thickness (L) from DSC can be the indicator to evaluate the change of the thermal capacity. In addition, FWHM of the crystallization peak W , crystalline rate index (T 0-T P) and cross-linking degree (G) can also be the indicator of the thermal parameters. Finally, this paper proposes a more accurate on-line monitoring method for electric power industry by detecting thermal parameters to diagnose the operating cables in the practical application.
This paper verifies the fluctuation on thermal parameters and ampacity of the high-voltage cross-linked polyethylene (XLPE) cables with different insulation conditions and describes the results of a thermal aging experiment on the XLPE insulation with different operating years in different laying modes guided by Comsol Multiphysics modeling software. The thermal parameters of the cables applied on the models are detected by thermal parameter detection control platform and differential scanning calorimetry (DSC) measurement to assure the effectivity of the simulation. Several diagnostic measurements including Fourier infrared spectroscopy (FTIR), DSC, X-ray diffraction (XRD), and breakdown field strength were conducted on the treated and untreated specimens in order to reveal the changes of properties and the relationship between the thermal effect and the cable ampacity. Moreover, a new estimation on cable ampacity from the perspective on XLPE insulation itself has been proposed in this paper, which is also a possible way to judge the insulation condition of the cable with specific aging degree in specific laying mode for a period of time.Energies 2019, 12, 2994 3 of 22 insulation endured the most severe electrical and thermal stresses. These obtained specimens were all cleaned by alcohol to remove the surface impurities.
This paper describes changes on micro-structure and aggregation structure of cross-linked polyethylene (XLPE) with different thermal histories after different times of overheating treatment to analogize the short-term fault or emergency overload in actual operating cables. 5, 10 and 20 times overheating treatment were conducted on a spare cable and a retired cable with service years of 32, whose insulation were analyzed by the diagnostic measurements of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermogravimetry (TG). The results show that the spare cable has presented a trend of improvement on the insulation properties after overheating treatment below 20 times, but slight deterioration occurs after 20 times overheating treatment; the retired cable with service years of 32 has presented a trend of degradation on the insulation properties at the first 5 times overheating treatment, and a severe deterioration occurs after 20 times overheating treatment.
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