Abstract
Low-density polyethylene (LDPE), as an excellent dielectric insulating material, is widely used in electrical equipment insulation, whereas its low thermal conductivity limits its further development and application. Hexagonal boron nitride (h-BN) filler was introduced into LDPE to tailor the properties of LDPE to make it more suitable for high-voltage direct current (HVDC) cable insulation application. We employed melt blending to prepare h-BN/LDPE thermally conductive composite insulation materials with different contents. We focused on investigating the micromorphology and structure, thermal properties, and electrical properties of h-BN/LDPE composites, and explained the space charge characteristics. The scanning electron microscope (SEM) results indicate that the h-BN filler has good dispersibility in the LDPE at a low loading (less than 3 phr (3 g of micron h-BN particles filled in 100g of LDPE)), as well as no heterogeneous phase formation. The results of thermal conductivity analysis show that the introduction of h-BN filler can significantly improve the thermal conductivity of composites. The thermal conductivity of the composite samples with 10 phr h-BN particles is as high as 0.51 W/(m·K), which is 57% higher than that of pure LDPE. The electrical performance illustrates that h-BN filler doping can significantly inhibit space charge injection and reduce space charge accumulation in LDPE. The interface effect between h-BN and the substrate reduces the carrier mobility, thereby suppressing the injection of charges of the same polarity and increasing the direct-current (DC) breakdown strength. h-BN/LDPE composite doped with 3 phr h-BN particles has excellent space charge suppression effect and high DC breakdown strength, which is 14.3% higher than that of pure LDPE.
Highlights
At present, high-voltage direct current (HVDC) transmission has shown a large-capacity, low-loss development trend, and people have put forward higher requirements for transmission reliability.with the increased transportation capacity of HVDC transmission systems, Materials 2020, 13, 4738; doi:10.3390/ma13214738 www.mdpi.com/journal/materialsMaterials 2020, 13, 4738 the internal space charge accumulation of the cable insulation layer and the heat accumulation phenomenon during transportation will limit the further development and application of the cable [1,2].Previous studies have pointed out that the accumulation of space charge in the cable insulation distorts the local electric field, which leads to partial discharge and even electrical breakdown of the insulation materials
The Low-density polyethylene (LDPE) and micron-sized Hexagonal boron nitride (h-BN) particles were weighed and mixed uniformly, and the mixture was put into a torque rheometer (Harbin Hapro electric technology Co., Ltd., Harbin, China.) for blending, at a blending temperature of 120 ◦ C
By comparing the characteristic peaks of the composite material before and after attaching the h-BN filler, it is found that the crystal planes of the diffraction peaks corresponding to the h-BN filler and LDPE in the composite are consistent with the crystal planes of the standard diffraction peaks
Summary
High-voltage direct current (HVDC) transmission has shown a large-capacity, low-loss development trend, and people have put forward higher requirements for transmission reliability.with the increased transportation capacity of HVDC transmission systems, Materials 2020, 13, 4738; doi:10.3390/ma13214738 www.mdpi.com/journal/materialsMaterials 2020, 13, 4738 the internal space charge accumulation of the cable insulation layer and the heat accumulation phenomenon during transportation will limit the further development and application of the cable [1,2].Previous studies have pointed out that the accumulation of space charge in the cable insulation distorts the local electric field, which leads to partial discharge and even electrical breakdown of the insulation materials. Materials 2020, 13, 4738 the internal space charge accumulation of the cable insulation layer and the heat accumulation phenomenon during transportation will limit the further development and application of the cable [1,2]. The standard polymer insulation composites have low thermal conductivity, which makes it difficult to dissipate heat promptly, and eventually causes the internal temperature of the insulation material to rise [3,4,5]. If the long-term operating temperature of the cable equipment is over high, it may lead to accelerated insulation aging of the cable, shortened service life, and even thermal breakdown to damage the cable [6,7]. Polyethylene is widely used for electrical equipment insulation due to its excellent mechanical properties, dielectric properties, corrosion resistance, and low price, pure polyethylene has poor heat dissipation properties, limiting its application in cable equipment preparation
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