Dynamic ageing research of cross‐linked polyethylene cable insulation based on temporal‐spatial dimension under combined electro‐thermal effect

Abstract

Dynamic ageing process of cross‐linked polyethylene (XLPE) cable insulation under combined electro‐thermal effect is investigated by the construction of theoretical analysis model and the practice of operation‐simulated ageing test. Firstly, theoretical analysis model is constructed from time and spatial dimensions. From the time dimension, in the light of the impeding trend of internal stress to external stress, the XLPE ageing process of Steady state ‐Transition state ‐Steady state (STS) is proposed to illustrate the dynamic ageing process of XLPE. From the spatial dimension, the insulation is divided into three scales to quantify the ageing. Secondly, to practice the theoretical analysis model, an operation‐simulated ageing test was conducted on two high voltage alternating current cables with service years of 15 and 30 for 540 days. Subsequently, relevant diagnostic measurements were applied to analyse the influence of physicochemical characteristics on the dielectric and heat transfer performances of the cables. The results show that the degradation of the actual operating cable is an extremely slow process. On the one hand, the response in physical changes of morphology counterbalances the external stress, maintaining the stability. On the other hand, once the chemical changes occur, negative feedback mechanism tends to impede the occurrence of further degradation by regulating fields distribution.

Influence of Combined Electrothermal Aging on Dielectric and Thermal Properties of HVAC XLPE Cable

“…To quantitatively analyze the migration of low polar molecules on the perfor of the cable insulation, the aromatic ring index (ARI), vinyl index (VI), and pheno (PI) are introduced. The definition of these three indexes is as follows [14]: In Figure 5a, it is observed that prominent absorption peaks at 1596, 1650, and 3370 cm −1 exist in the inner insulating layers of S7. For S7-1 and S7-2, minor changes in these peaks in the range of 1700 to 1800 cm −1 , compared to S7, indicate that thermaloxidative aging hardly happens during the aging test.…”

“…To quantitatively analyze the migration of low polar molecules on the performances of the cable insulation, the aromatic ring index (ARI), vinyl index (VI), and phenol index (PI) are introduced. The definition of these three indexes is as follows [14]:…”

“…The nonphysical discontinuities in the calculated electric field distribution displayed in Figure 11 at the three XPLE layer interphases result directly from such simplification. The electric field distribution in each layer can be obtained with the following equations [14]:…”