Charge Recombination Induced Luminescence of Chemically Modified Cross-Linked Polyethylene Materials

Abstract

Very little is known on the chemical nature of the deep trapping centres that play a role in charge storage in insulating polymeric materials. The analysis of the luminescence emitted during a process of charge recombination can be helpful to unravel the nature of such centres. The spectral features of the luminescence induced by charge recombination are analyzed for three different cross-linked polyethylene (XLPE) materials, chemically-modified or not. In two XLPE formulations, a controlled amount of chemical groups containing an aromatic ring has been grafted to the polymer chains. The other formulation is the same XLPE without chemical modification. Photoluminescence is investigated to settle a background to identify the species involved in charge recombination. It is excited on films at room and liquid nitrogen temperature providing fluorescence and phosphorescence spectra. The luminescence excited by the recombination of trapped electrical charges is subsequently analyzed at low temperature and compared to the photoluminescence emission. The results obtained on chemically-modified XLPE provide a basis to identify the species involved in charge recombination in the non modified material. It turns out that aromatic compounds are involved in photo-and charge recombination-induced luminescence in all the tested XLPE, and that the luminescence has the same spectral features for the two stimulations, contrary to what is observed for low density polyethylene.

Interface tailoring for charge injection control in polyethylene

“…These attempts more often concern the bulk properties of materials. For example, and because atomistic modelling allows the estimation of the trap depths due to chemical species introduced into the structure of polyethylene [10,11], researches focus on chemically doping of the polymer for HVDC applications [12]. Later researches focus on nanocomposite materials, with as goal to reduce space charge build-up in existing matrices, and/or to provide materials with relevant thermo-mechanical properties avoiding the crosslinking step [13][14][15].…”

Advanced Characterization Techniques Based on Luminescence in XLPE and Modified XLPE

“…All of these works are based on integral light and do not use the spectral distribution of the light for bringing understanding. For a qualitative comparaison of information brought by FTIR and photoluminescence, one may consider Figure 6 with phosphorescence spectra of benzophenone (a) [50] compared to that of XLPE grafted with a benzophenone derivative (b) [10]. Carbonyl derivatives have intense phosphorescence from their 3 (n  *) states.…”

“…The last set of samples investigated was XLPE with grafted groups on it [10]. The project participated in the general objective to develop anti-treeing compounds, often called voltage arresters, for XLPE insulation.…”

“…Figure 6. Phosphorescence spectra of benzophenone (a) in ethanol[50] and of XLPE grafted with benzophenone protonoxy (b) [10]…”

High Temperature Insulation Materials for DC Cable Insulation — Part III: Degradation and Surface Breakdown

“…In order to evaluate the reliability of different high temperature insulation materials in harsh operating environments, important aging factors must be studied in complex conditions. These factors mainly include space charge and surface charge transport behaviors [6][7][8], insulation breakdown and surface flashover trigger mechanism [9][10][11][12], insulation aging mechanisms and charge suppression methods [13][14][15][16], etc. However, uncertain factors in complex environments, such as the temperature variation due to the changing of engine output power, the gas pressure changes when aircraft reaches different altitudes, local contamination due to leakage of oil or environmental pollution, directly influence the insulation performance, leading to greatly increased complexity and difficulty for related fundamental and applied researches.…”