Space charge suppression in environment-friendly PP nanocomposites by employing freeze-dried MgO with foam nanostructure for high-voltage power cable insulation

Abstract

Space charge accumulation along insulation thickness is still regarded as a critical issue during the operation of high-voltage direct current transmission cables, which will result in the distortion of the partial electric field, seriously causing the degradation or aging of the main insulation. Polypropylene (PP) environment-friendly thermoplastic cables without cross-linking have shown great potential, which tend to gradually substitute the traditional unrecyclable extruded cross-linked polyethylene cables. Here, the styrene-ethylene-butylene-styrene block copolymer is selected to optimize the mechanical properties of PP. An extremely small amount of MgO with a foam nanostructure synthesized through a designed freeze-drying process is introduced to suppress the accumulation of space charge and further improve the electrical properties of PP insulation. With a very low concentration of foamed MgO (0.2 phr), it is found that the injection and accumulation of space charge could be largely suppressed under 60 kV/mm and the DC conductivity of PP composites remains as low as ∼1.6 × 10−15 S/m. Besides, the DC breakdown strength of the composites is up to 315 kV/mm. Therefore, the PP-matrix composites can be considered as potential high-performance insulating materials in the non-cross-linking environment-friendly thermoplastic high-voltage power cable.

Improved High-Temperature Electrical Properties of Polymeric Material by Grafting Modification

“…Polymers have been extensively used as dielectric materials and electrical insulations in power electronics, soft robotics, electric energy storage, , and high voltage electrical insulations − due to their extraordinary properties, e.g., lightweight, high electrical resistivity, excellent voltage endurance, and low manufacturing cost. , The fundamental concern is that the combined effect of high temperature and high electric field charge injection and transport results in sharp increment of leakage current . Therefore, low breakdown strength and electrical deterioration limit the high-temperature performance of polymeric materials.…”

“…Although there are a variety of synthesis and modification methods that can be used to enhance the electrical properties of polymeric materials, usually these methods are effective only for room temperature application and are usually accompanied by the complexity of processing or electrical deterioration characteristics. Recent research has shown that inorganic nanostructures can be utilized to restrict charge carrier movement in polymeric materials, improving their performance. ,, The deep traps generated at microscopic interface composed of polymer matrix and nanofiller are responsible for the enhanced electrical characteristics, including electrical resistivity and breakdown strength. , These deep traps are localized states capturing charge carriers, limiting the increase of leakage current and charge injection. , Although polymer nanocomposites have shown considerable promise, this strategy’s effectiveness is primarily reliant on nanoparticle–polymer compatibility. Severe agglomeration may cause inhomogeneity of polymers performance, resulting in challenges for the mass manufacture of nanocomposite.…”

“…Recent research has shown that inorganic nanostructures can be utilized to restrict charge carrier movement in polymeric materials, improving their performance. 7,11,12 The deep traps generated at microscopic interface composed of polymer matrix and nanofiller are responsible for the enhanced electrical characteristics, including electrical resistivity and breakdown strength. 13,14 These deep traps are localized states capturing charge carriers, limiting the increase of leakage current and charge injection.…”

Electrical Property of Polypropylene Toughened by β Nucleating Agent

“…By doping MgO nanoparticles with different contents and surface modification processes in PP, the optimal parameters of space charge suppression were obtained [13,14]. By doping MgO nanofiller prepared by freeze-drying into iPP/SEBS blends, it was found that when the doping content is only 0.2 wt.%, the injection and accumulation of space charges are well inhabited, and the DC breakdown field strength is increased by more than 10% [15].…”

Effects of nanomagnesia and polypropylene-graft-maleic anhydride on the dielectric breakdown properties of polypropylene/ethylene propylene diene monomer blend

“…Elsewhere, modified MgO was found to mitigate the space charge and improve the DC breakdown strength of PP/polyolefin elastomer blend [32]. The use of MgO synthesized through a freeze-drying process [33] and surface decarbonization [34] were also found to increase the DC breakdown strength of PP/styrene-ethylene-butylene-styrene blend. These show that enhanced electrical characteristics of PP blends are attributed to the effect of the nanofiller surface modifications.…”