Experimental Study on Trap Characteristics of Nano-Montmorillonite Composite Pressboards

To improve space charge properties and the breakdown strength of insulation pressboard, nano-modifications with nano-montmorillonite fillers are developed using nanocomposite techniques in this study. Employing trap theory, charge carrier trapping characteristics are analyzed to interpret the space charge distribution modification from nano-montmorillonite (MMT) filling and explore the correlated mechanism of direct current (DC) breakdown strength enhancement. The trap energy level distribution is measured by a thermally stimulated current test and space charge distribution is tested with pulsed electro-acoustics. A DC power system is used to perform DC the breakdown experiment. The nano-MMT filler composite pressboard demonstrates increased trap density as filling concentration increases, which dominates the total trap charge quantity. Shielding layers formed from the trapped charges localized at the interface of the nano-MMT fillers with pressboard matrix reduce the injection of charge carriers from the electrodes and thus inhibit the internal space charge accumulation prophase and then charge carriers move to the interior of the pressboard. Space charge quantity increases with increasing trap density. However, the trapping of charges into the trap levels releases significant energy to destroy the primitive molecular chain of pressboard cellulose, resulting in reduced DC breakdown strength. The trap mechanism accounts for the modified space charge distribution and the enhanced DC breakdown strength deriving from nano-MMT fillers.