Charge dynamics and its energetic features in polymeric materials

Abstract

Modeling charge transport and linking charge dynamics with dissipative processes responsible for electrical ageing are a challenging objective for developing a mature approach in insulation design. Such an approach is exemplified here for polyethylenebased materials by introducing two models describing bipolar Space Charge Limited Current in transient and steady states. They rely on two classical descriptions of the distribution function of the energy levels of trap states -single trapping level or exponential distribution. Their predictions are discussed as regards the experimental behavior. They notably highlight the importance of recombination processes in explaining the sigmoidal shape of the steady-state current-voltage characteristic. Also, bipolar charge transport seems to be a necessary factor for the observed features of oscillatory charge packets. The energetic features of charge dynamics is reviewed with particular emphasis on recombination phenomena because the latter promote electronically excited states that are chemically reactive and could be involved in ageing reaction. The relationship between charge recombination and electroluminescence is highlighted through experiments and simulation. The spectral analysis of the emitted light advocates the existence of massive chemical/physical degradation in the electrical regime where recombination is a major factor of the Space Charge Limited Current (SCLC).

On the nature of high field charge transport in reinforced silicone dielectrics: Experiment and simulation

“…When a solid looses its crystallographic order, the variation of atomic potential creates localized electronic states at the band tails called Anderson localization 14 . Other factors like impurities and chemical defects also introduce low lying localized states extending into the gap [15][16][17] . The term "trap" often refers to these localized states.…”

Self-healing during electrical treeing: A feature of the two-phase liquid-solid nature of silicone gels

“…[13][14][15][16][17][18][19][20][21][22][23][24][25][26]), including silicone rubber [27]. The equivalent breakdown phenomena in liquids i.e.…”

Study of the factors that suppress space charge accumulation in LDPE nanocomposites

“…Each of these processes can be expected to be independent and controlled by different rate equations with different parameters [20]. In [10] it has been shown that at uniform temperature, delayed extraction leads to the formation of heterocharge, whereas recombination and superposition of charge carriers of opposite polarity lead to a suppression of heterocharge accumulation.…”

“…Delayed extraction is a natural consequence of the model but it depends upon the polarity of the electrodes in relation to the specific dielectric material. In unfilled LDPE the trap distribution can be assumed to be dominated by the large concentration of shallow traps (see [20] and references therein). Therefore if a Fermi level can be defined for these materials it will be nearly centrally placed in the band gap.…”