Abstract
Compared with traditional insulation materials, such as cross-linked polyethylene (XLPE), polypropylene (PP) is famous for its better recyclable and thermal properties, as well as its good electrical performance. However, the problem of poor impact strength has restricted the application of pure PP in high-voltage, direct current (HVDC) cables. In this paper, styrene-ethylene-butylene-styrene block copolymer (SEBS) was used as a toughening filler, and nano-SiO2 was expected to improve the electric properties of the nano-composite. By controlling the masterbatch system, the dispersion characteristics of nano-SiO2 in the ternary composite system were changed. When PP/SiO2 was used as the masterbatch and then blended with SEBS, nano-SiO2 tended to disperse in the PP phase, and the number of nano-particles in the SEBS phase was lower. When PP/SEBS was used as the masterbatch, nano-SiO2 was distributed in both the PP phase and the SEBS phase. When SEBS/SiO2 was used as the masterbatch, nano-SiO2 tended to be dispersed in the SEBS phase. The different dispersion characteristics of nano-SiO2 changed the crystallization and mechanical properties of the ternary composite system and produced different electrical performance improvement effects. The results of our experiment revealed that the space charge suppression capability was positively correlated with the direct current (DC) breakdown strength improvement effect. Compared with the DC performance of 500 kV commercial XLPE materials, the self-made PP-based ternary composite system has better space charge suppression effects and higher DC breakdown strength. When nano-SiO2 was more dispersed in the PP phase, the space charge improvement effect was best. When the nano-SiO2 particles were more dispersed in the SEBS phase, the expected electrical property improvement was not obtained. Scanning electron microscopy showed that the nano-SiO2 particles in the SEBS phase were more dispersed at the interface than in the SEBS matrix, indicating that the nano-particles were poorly dispersed, which may be a reason why the electrical properties of the composite system were not significantly improved.
Highlights
In recent years, with the introduction of concepts such as the super grid and the global energy interconnection, the demand for high-voltage power cables has increased
The dispersion characteristics of nano-particles in ternary composites composed by nano-particles, styrene-ethylene-butylene-styrene block copolymer (SEBS), and PP can be effectively controlled by changing the masterbatch system
For PP/SiO2 /SEBS, more nano-SiO2 was dispersed in the PP phase, and the optimal space charge suppression effect and the highest direct current (DC) breakdown strength were obtained
Summary
With the introduction of concepts such as the super grid and the global energy interconnection, the demand for high-voltage power cables has increased. Intercontinental power interconnection over long distances across the sea needs to be achieved with high-voltage DC (direct current) cables [1]. Based on chemically pure technology, some manufacturers have effectively suppressed the space charge by reducing the content of chemical impurities in XLPE and have successfully developed ±500 kV high-voltage, direct current (HVDC) cable XLPE insulation material [3]. Japanese researchers filled XLPE with nano-particles, which obtained significant space charge suppression effects, and successfully developed a ±500 kV high-voltage DC cable [4]. XLPE insulation has been successfully applied to HVDC cables, it is a thermoset material that cannot be recycled. In order to find high-performance, recyclable, environmentally friendly polymer insulation materials, thermoplastic polymer materials have received increasing attention in recent years [5]
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