Abstract
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.
Highlights
The converter transformer is essential equipment for high voltage direct current transmission systems that transform alternating current (AC) electric energy into direct current (DC) electric energy and its dependability directly influences the stable operation of an energy system
The temperature electric field stress of pressboards varying with time on the pulsed (PEA) and system
These carriers scatter with trap across the trap energy level and they change to a bound state with a certain probability causing the trapping of carriers
Summary
The converter transformer is essential equipment for high voltage direct current transmission systems that transform alternating current (AC) electric energy into direct current (DC) electric energy and its dependability directly influences the stable operation of an energy system. As a key material for insulation, oil-paper insulation is widely used in converter transformers Once this insulation loses efficacy, the transformer may malfunction irreversibly. Space charge distribution results in the distortion of the electric field causing the insulating system to lose efficacy. The microstructure and nanofiller-MMT of the moisture content than dispersitydispersity of the pressboard pressboard nanocomposites was characterized using scanning electron microscopy (SEM). (HITACHI, nanocomposites was characterized using scanning electron microscopy (SEM) Japan), Japan), and the and representative images forimages neat pressboard and nano-MMT/pressboard composites composites are shown in. 2. Representative scanning electron microscopy (SEM) images of (a) neat pressboard and montmorillonite (MMT)/pressboard nanocomposites filled with (b) 1 wt %, (c) 2.5 wt %, and (d) 5.0
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