Abstract
Charging and discharge currents measured in low-density polyethylene (LDPE) and LDPE/Al2O3 nanocomposite are analyzed. The experiments were conducted at temperatures of 40–80 °C utilizing a consecutive charging–discharging procedure, with the charging step at electric fields varying between 20 and 60 kV/mm. A quasi-steady state of the charging currents was earlier observed for the nanofilled specimens and it was attributed to the enhanced trapping process at polymer–nanofiller interfaces. An anomalous behavior of the discharge currents was found at elevated temperatures for both the studied materials and its occurrence at lower temperatures in the nanofilled LDPE was due to the presence of deeply trapped charges at polymer–nanofiller interfaces. The field dependence of the quasi-steady charging currents is examined by testing for different conduction mechanisms. It is shown that the space-charge-limited process is dominant and the average trap site separation is estimated at less than 2 nm for the pristine LDPE and it is at about 5–7 nm for the LDPE/Al2O3 nanocomposite. Also, location of the trapping sites in the band gap structure of the nanofilled material is altered, which substantially weakens electrical transport as compared to the unfilled counterpart.
Highlights
IntroductionExtruded high voltage direct current (HVDC) cables have become increasingly popular for interconnecting electric power grids and integrating renewable energy resources (e.g., offshore wind farms and concentrating solar power plants) into electric power systems
Extruded high voltage direct current (HVDC) cables have become increasingly popular for interconnecting electric power grids and integrating renewable energy resources into electric power systems
Note that the model parameters for electrons and holes, the charge transport process and electric field distribution introduction of the deep trap level (1.5 eV) in the model for the nanocomposite leads to a reduction of are simulated symmetrical about thecurrent middleby point of the the discharge current can bein calculated the conduction a factor ofsample
Summary
Extruded high voltage direct current (HVDC) cables have become increasingly popular for interconnecting electric power grids and integrating renewable energy resources (e.g., offshore wind farms and concentrating solar power plants) into electric power systems. As compared to mass impregnated HVDC cables, the extruded ones offer various technological advantages, including higher transmission capability, compactness at the same power rating, lower weight, and lower environmental impact [1]. Today, extruded HVDC cables can operate at voltage levels up to 640 kV with the transmission capacity up to 3 GW [2]. The ultra-low dc conductivity of XLPE can be achieved, for example, by further purifying the material or by doping nanometric filler particles into the polymer matrix. The implementation of the former approach may no longer be cost-effective and, the latter one evokes much interest
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