Space charge characteristics in epoxy/nano-MgO composites: Experiment and two-dimensional model simulation

Abstract

Space charge accumulation in polymer dielectrics may lead to serious electric field distortion and even insulation failure during long-term operations of power equipment and electronic devices, especially under conditions of high temperature and direct current electric stress. The addition of nanoparticles into polymer matrices has been found effective in suppressing space charge accumulation and alleviating electric field distortion issues. Yet, the underlying mechanisms of nanoparticle doping remain a challenge to explore, especially from multi-dimensional composite insights. Here, a two-dimensional bipolar charge transport model with consideration of interface zones between organic/inorganic phases is proposed for the investigation into space charge behaviors of nanodielectrics. To validate the effectiveness and feasibility of the model, pulsed electroacoustic experiments are performed on epoxy/nano-MgO composites with different doping ratios of nanoparticles. Experimental observations match well with simulation anticipations, i.e., higher doping ratios of nanoparticles below the percolation threshold exhibit better capabilities to inhibit space charge accumulation. The deep traps (∼1.50 eV) generated in the interface zones are demonstrated to capture free charges, forming a reverse electric field in the region adjacent to electrodes and impeding the space charge migration toward the interior of the composite. This model is anticipated to provide theoretical insight for understanding space charge characteristics in polymer nanodielectrics and computing charge dynamics in extreme conditions where experiments are challenging to perform.

Space charge dynamics of epoxy/micro-Al2O3 composites under multi-physical fields

“…The applied mechanical force is inferred to produce microscopic defects or phase misalignments, which in turn introduce new energy levels and lowers the intrinsic energy gap of ideal insulating materials, as illustrated in figure 9(c). Unlike some previous works [59][60][61] that intentionally bring in deep traps through doping nanoparticles into polymer matrices, the increase in shallow trap density cannot restrict injected charges within local regions near electrodes and form reverse electric field to impede charge injection. Instead, charges can easily detrap from shallow traps and 'hop' among trap sites.…”

Detection of defect-induced luminescence in epoxy-based insulation materials via phase-resolved photon counting method

“…EL inception: At 2 kV, carriers are easily injected into the polymer surface and transfer between the surface states through a hopping process. During this migration, the Coulombic force facilitates their mutual attraction, resulting in an electrically neutral exciton [15].…”