In this dissertation, each specimen blended at weight proportions of 80% HDPE to 20% EVA, 70% HDPE to 30% EVA, 60% HDPE to 40% EVA, and 50% HDPE to 50% EVA was manufactured respectively. FE-SEM, DSC, FT-IR and XRD analysis were carried out as the means of structural and chemical analysis. The insula...
In this dissertation, each specimen blended at weight proportions of 80% HDPE to 20% EVA, 70% HDPE to 30% EVA, 60% HDPE to 40% EVA, and 50% HDPE to 50% EVA was manufactured respectively. FE-SEM, DSC, FT-IR and XRD analysis were carried out as the means of structural and chemical analysis. The insulation performances of the proposed insulator were compared with conventional XLPE, main insulating material of CV cable on the basis of the investigation results of AC and DC insulation performances. Also, validity as an eco-friendly alternative insulating material was proved by extracting superior and inferior factor respectively. From the results of DSC and XRD analysis, the lower EVA contents in blended specimens were, the higher melting temperature and crystallinity of main crystal were. It seems that this phenomena was attributed to thermoplastic inter-penetrating network effect (TPIPN) in which EVA having low melting point penetrated into HDPE. Also, from the decreasing tendency of melting point as a function of blend ratios, it was confirmed that above resins have compatibility. From the results of FE-SEM analysis, morphology of HE82 and HE55 specimen has more continuous network structure than other specimens. As a result of FT-IR analysis, blending method with weight proportions was revealed as an useful means for quantitative introduction of polar group. AC dielectric breakdown strength of HE64 and HE55 specimen at 90[℃] was higher than other specimens. Polar groups introduced in molecular chains of blended specimens plays an important role in enhancement of thermal conductivity. It was estimated that thermal stability was improved. In case of HE82 specimen, tanδ values with raising electric stress were lower than those of 22[kV] class XLPE but similar to 154[kV] class XLPE. Therefore, reduction in dielectric loss of HE82 specimen could be expected. In case of HE82 and HE64 specimens, optimal amount of conductive polar groups introduced to molecular chains distributes over tree channel of inside wall and finally tree propagation seemed to be suppressed due to relaxation of electric field in tree channels. It is also because HE82 specimen has higher melting point than XLPE and has uniform micro-IPN structure. Optimal amount of polar group such as carbonyl(C=O) acts as trapping site, the temperature range(90[℃]) is not sufficient to supply energy to excite trapped carrier. Therefore volume resistivities became high due to decreased carrier density and mobility. From the space charge density, electric field and potential profiles with raising dc applied voltage and time in HE82, distortion of electric field distribution was improved. As EVA mixed into the bulks acts as nucleation sites in crystallization process of HDPE, the size of spherulites became decreased and finally formed continuous network structure. Ultimately it resulted from extinction of space charge in the interfacial region of spherulites. Also, DC dielectric breakdown strength of HE82 and HE64 specimens was higher than that of other specimens at the high temperature region. Because increased thermal energy caused detrapping of localized space charge, detrapped carriers rapidly moved and disappeared. It is considered that distortion of electric field is improved with raising temperature. Consequently, HE82 specimen has excellent thermal stability, high dielectric breakdown strength, treeing resistance. And distortion of electric field due to space charge accumulation was much smaller than conventional XLPE. Therefore, it is expected to be used as alternative insulating materials for AC distribution power cable of 22.9[kV], 154[kV] class and HVDC cable of 180[kV] class. As it was made by blending method between thermoplastic resins, above mentioned, cross-linking process is not necessary. Therefore waste insulator can be recycled as raw materials for uses such as jacket of low voltage insulation wire, insulation layer of medium voltage cable and various products.
In this dissertation, each specimen blended at weight proportions of 80% HDPE to 20% EVA, 70% HDPE to 30% EVA, 60% HDPE to 40% EVA, and 50% HDPE to 50% EVA was manufactured respectively. FE-SEM, DSC, FT-IR and XRD analysis were carried out as the means of structural and chemical analysis. The insulation performances of the proposed insulator were compared with conventional XLPE, main insulating material of CV cable on the basis of the investigation results of AC and DC insulation performances. Also, validity as an eco-friendly alternative insulating material was proved by extracting superior and inferior factor respectively. From the results of DSC and XRD analysis, the lower EVA contents in blended specimens were, the higher melting temperature and crystallinity of main crystal were. It seems that this phenomena was attributed to thermoplastic inter-penetrating network effect (TPIPN) in which EVA having low melting point penetrated into HDPE. Also, from the decreasing tendency of melting point as a function of blend ratios, it was confirmed that above resins have compatibility. From the results of FE-SEM analysis, morphology of HE82 and HE55 specimen has more continuous network structure than other specimens. As a result of FT-IR analysis, blending method with weight proportions was revealed as an useful means for quantitative introduction of polar group. AC dielectric breakdown strength of HE64 and HE55 specimen at 90[℃] was higher than other specimens. Polar groups introduced in molecular chains of blended specimens plays an important role in enhancement of thermal conductivity. It was estimated that thermal stability was improved. In case of HE82 specimen, tanδ values with raising electric stress were lower than those of 22[kV] class XLPE but similar to 154[kV] class XLPE. Therefore, reduction in dielectric loss of HE82 specimen could be expected. In case of HE82 and HE64 specimens, optimal amount of conductive polar groups introduced to molecular chains distributes over tree channel of inside wall and finally tree propagation seemed to be suppressed due to relaxation of electric field in tree channels. It is also because HE82 specimen has higher melting point than XLPE and has uniform micro-IPN structure. Optimal amount of polar group such as carbonyl(C=O) acts as trapping site, the temperature range(90[℃]) is not sufficient to supply energy to excite trapped carrier. Therefore volume resistivities became high due to decreased carrier density and mobility. From the space charge density, electric field and potential profiles with raising dc applied voltage and time in HE82, distortion of electric field distribution was improved. As EVA mixed into the bulks acts as nucleation sites in crystallization process of HDPE, the size of spherulites became decreased and finally formed continuous network structure. Ultimately it resulted from extinction of space charge in the interfacial region of spherulites. Also, DC dielectric breakdown strength of HE82 and HE64 specimens was higher than that of other specimens at the high temperature region. Because increased thermal energy caused detrapping of localized space charge, detrapped carriers rapidly moved and disappeared. It is considered that distortion of electric field is improved with raising temperature. Consequently, HE82 specimen has excellent thermal stability, high dielectric breakdown strength, treeing resistance. And distortion of electric field due to space charge accumulation was much smaller than conventional XLPE. Therefore, it is expected to be used as alternative insulating materials for AC distribution power cable of 22.9[kV], 154[kV] class and HVDC cable of 180[kV] class. As it was made by blending method between thermoplastic resins, above mentioned, cross-linking process is not necessary. Therefore waste insulator can be recycled as raw materials for uses such as jacket of low voltage insulation wire, insulation layer of medium voltage cable and various products.
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