Charge trapping and detrapping in polymeric materials: Trapping parameters

Abstract

Space charge formation in polymeric materials can cause some serious concern for design engineers as the electric field may severely be distorted, leading to part of the material being overstressed. This may result in material degradation and possibly premature failure at the worst. It is therefore important to understand charge generation, trapping, and detrapping processes in the material. Trap depths and density of trapping states in materials are important as they are potentially related to microstructure of the material. Changes in these parameters may reflect the aging taken place in the material. In the present paper, characteristics of charge trapping and detrapping in low density polyethylene (LDPE) under dc electric field have been investigated using the pulsed electroacoustic (PEA) technique. A simple trapping and detrapping model based on two trapping levels has been used to qualitatively explain the observation. Numerical simulation based on the above model has been carried out to extract parameters related to trapping characteristics in the material. It has been found that the space charge decaying during the first few hundred seconds corresponding to the fast changing part of the slope was trapped with the shallow trap depth 0.88 eV, with trap density 1.47 × 1020 m−3 in the sample volume measured. At the same time, the space charge that decays at longer time corresponding to the slower part of the slope was trapped with the deep trap depth 1.01 eV, with its trap density 3.54 × 1018 m−3. The results also indicate that trap depths and density of both shallow and deep traps may be used as aging markers as changes in the material will certainly affect trapping characteristics in terms of trap depth and density.

An improved model to estimate trapping parameters in polymeric materials and its application on normal and aged low-density polyethylenes

“…Factually, these traps might exist with a range of levels in wide band-gap of insulation material. Typically, it was suggested that shallow and deep traps can be correlated with physical and chemical defects in the polymeric material respectively 7,14,19,24 . Physical defects can be created by changes in crystallinity, morphological structure and molecular weight while chemical defects can be produced by oxidation and hydrolysis process 9,24 .…”

“…(iv) Both studies tried to separate traps with a range of energy levels into two equivalent levels 13 or ranges 15 . And it is noteworthy in works based on Chen's model 13,14,19 , the two energy levels, i.e. shallow and deep traps, have been reported relating with physical and chemical defects in polymeric materials respectively.…”

“…In recent years, many approaches have been developed on determination or estimation of these trapping parameters for various insulation materials, especially polyethylene [13][14][15][16][17][18] . Chen proposed a trapping-detrapping model based on two energy levels.…”

“…Chen proposed a trapping-detrapping model based on two energy levels. And thereafter in 14,19 , by employing the charge detrapping part in the model established by Chen, trapping parameters of low density polyethylene(LDPE) and also gamma-irradiated LDPE were estimated. It has been revealed that physical and chemical modifications brought by irradiation process is reflected on the changes in trapping parameters.…”

Charge transport model in nanodielectric composites based on quantum tunneling mechanism and dual-level traps

“…12 There are two kinds of charge transport mechanisms, which can represent the charge conduction processes for the shallow trap and the deep trap, respectively. For the shallow traps, the trapped charges can overcome the potential barrier and hop to the neighbour trip site by the effect of thermal vibration, which depends on the temperature and electric field.…”