A model and simulation of fast space charge pulses in polymers

Abstract

The transport of space charge packets across polyethylene and epoxy resin in high electric fields has been characterized as fast or slow depending on packet mobility. Several explanations for the formation and transport of slow space charge packets have been proposed, but the origins of fast space charge pulses, with mobilities above 10−11 m2 V−1 s−1, are unclear. In one suggested model, it is assumed that the formation of fast charge pulses is due to discontinuous electromechanical compression and charge injection at the electrode-insulation interface, and their transport is related to corresponding relaxation processes. In that model, charges travel as a pulse because of group polarization. This paper provides an alternative model based on the reduction of charge carrier activation energy due to charge density triggered polymer chain movement and subsequent chain relaxation times. The generation and transport of fast charge pulses are readily simulated by a bipolar charge transport model with three additional parameters: reduced activation energy, charge density threshold, and chain relaxation time. Such a model is shown to reproduce key features of fast space charge pulses including speed, duration, repetition rate and pulse size. This model provides the basis for a deep understanding of the physical origins of fast space charge pulses in polymers.

Improved space charge transport model in bi‐layer dielectrics—considering carrier dynamic equilibrium

“…In solid dielectrics, carriers are governed by a set of self-consistent equations as following [9][10][11][12][13][14]17]. The current continuity equation:…”

“…5a. Since the electric field strength inside a sample declines from 10 kV/mm to almost zero during the measurement, the carrier mobility should be lower than that under 10 kV/mm but higher than that under 0 kV/mm where µ mea is the measured carrier mobility, µ(0) and µ (10) are the carrier mobility under electric field strength of 0 and 10 kV/mm, respectively. By combining (24) and (30), the carrier mobility scopes of LDPE and EPDM can be determined as shown in Figs.…”

“…where σ(E) is the electric-field-dependent volume conductivity; σ(0) and σ (10) are the volume conductivities under electric field strength of 0 and 10 kV/mm; µ(E) is the electric-field-dependent carrier mobility. By setting the mobility of negative and positive carriers to their upper or lower limits, we obtain the scopes of the intrinsic carrier concentrations in LDPE and EPDM materials, as shown in Fig.…”

“…The bipolar charge transport model considers the Schottky injection, charge trappingdetrapping, charge drift-diffusion and charge recombination processes, the following microscopic transport parameters, e.g. carrier mobility, diffusion coefficient, recombination coefficient etc., can be defined flexibly as required [9][10][11][12][13][14].…”

Review of space charge measurement by pulsed electro-acoustic technique

“…The resulting acronyms are reported in the same table which is Table 1: Measurements, Methods Used and Implementations. Based on the Table 1, all previous researchers used PEA method (experimental) to determine space charge and only researchers [4,8] were used PEA method and numerical simulation to determine space charge profile. In addition, there are also some researchers that studied the electric field as a measurement.…”