Abstract
Cellulose insulation polymer (paper/pressboard) has been widely used in high voltage direct current (HVDC) transformers. One of the most challenging issues in the insulation material used for HVDC equipment is the space charge accumulation. Effective ways to suppress the space charge injection/accumulation in insulation material is currently a popular research topic. In this study, an aluminium oxide functional film was deposited on a cellulose insulation pressboard surface using reactive radio frequency (RF) magnetron sputtering. The sputtered thin film was characterized by the scanning electron microscopy/energy dispersive spectrometer (SEM/EDS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). The influence of the deposited functional film on the dielectric properties and the space charge injection/accumulation behaviour was investigated. A preliminary exploration of the space charge suppression effect is discussed. SEM/EDS, XPS, and XRD results show that the nano-structured Al2O3 film with amorphous phase was successfully fabricated onto the fibre surface. The cellulose insulation pressboard surface sputtered by Al2O3 film has lower permittivity, conductivity, and dissipation factor values in the lower frequency (<103 Hz) region. The oil-impregnated sputtered pressboard presents an apparent space-charge suppression effect. Compared with the pressboard sputtered with Al2O3 film for 90 min, the pressboard sputtered with Al2O3 film for 60 min had a better space charge suppression effect. Ultra-small Al2O3 particles (<10 nm) grew on the surface of the larger nanoparticles. The nano-structured Al2O3 film sputtered on the fibre surface could act as a functional barrier layer for suppression of the charge injection and accumulation. This study offers a new perspective in favour of the application of insulation pressboard with a nano-structured function surface against space charge injection/accumulation in HVDC equipment.
Highlights
Pursuing high efficiency in electric power transmission and renewable energy has led to rapid developments in high voltage high voltage direct current (HVDC) transmission systems
Images untreatedpressboard pressboard and and the prepared by magnetron images forfor untreated thepressboard pressboardsurface surface prepared by magnetron sputtering of the
The nano-structured Al2 O3 film was successfully fabricated on a cellulose insulation pressboard surface by reactive radio frequency (RF) magnetron sputtering
Summary
Pursuing high efficiency in electric power transmission and renewable energy has led to rapid developments in high voltage HVDC transmission systems. One of the most challenging issues in HVDC insulation material development and insulation structure design is the space charge accumulation within the insulation material [1]. Polymers 2017, 9, 502 system can result in a distortion of the electric field distribution, i.e., an enhanced electric field in one region, and a reduced electric field in another. This leads to material degradation in the high electric field region, and affects system reliability [2,3,4,5]. Effective ways to suppress space charge accumulation have been considered the key foundation in designing and ensuring the safety of polymeric HVDC insulation material [1].
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