Abstract:SUMMARYPolymer nanocomposites are attracting attention as emerging insulating materials. We measured the thermally stimulated depolarization current (TSDC) in low-density polyethylene (LDPE)/MgO nanocomposites while varying measuring such parameters as the temperature increase rate and the intensity of the applied electric field. A TSDC peak that spreads over a wide temperature range from 0 °C to 60°C was observed in all samples. As the amount of MgO nanofiller increases, the TSDC peak height decreases. Furthe… Show more
“…[10]. Results of TSC measurements suggested that such localized states can be around 1.6-2.0 eV away from extended states [7,30,31]. The numerical model proposed in this work considering the second trapping center at the energy depth of 1.5 eV gives a satisfactory explanation for the observation of ADC at a lower temperature (60 • C) for the nanocomposite as compared to the pure LDPE.…”
Section: Impact Of Nanofillers On Electrical Conductionmentioning
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.
“…[10]. Results of TSC measurements suggested that such localized states can be around 1.6-2.0 eV away from extended states [7,30,31]. The numerical model proposed in this work considering the second trapping center at the energy depth of 1.5 eV gives a satisfactory explanation for the observation of ADC at a lower temperature (60 • C) for the nanocomposite as compared to the pure LDPE.…”
Section: Impact Of Nanofillers On Electrical Conductionmentioning
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.
“…Thus for LDPE/MgO nanocomposite, the trap depth may be 1–5 eV with the highest level corresponding to the applied field strength of ~200 kV/mm. Further, the trap depth of ~2 eV has been detected in LDPE/MgO nanocomposite by analyzing results of thermally stimulated currents and the origin of these deep traps have been explained by the effect of nanofillers [25]. Based on these findings, the trap depth should be set higher than that for unfilled LDPE.…”
Section: Results Of the Simulations And Discussionmentioning
Abstract:A bipolar charge transport model is employed to investigate the remarkable reduction in dc conductivity of low-density polyethylene (LDPE) based material filled with uncoated nanofillers (reported in the first part of this work). The effect of temperature on charge transport is considered and the model outcomes are compared with measured conduction currents. The simulations reveal that the contribution of charge carrier recombination to the total transport process becomes more significant at elevated temperatures. Among the effects caused by the presence of nanoparticles, a reduced charge injection at electrodes has been found as the most essential one. Possible mechanisms for charge injection at different temperatures are therefore discussed.
“…There have been a number of studies of the mechanisms underlying the low space charge accumulation and high volume resistivity. For example, Ishimoto and colleagues measured thermally stimulated currents in polyethylene‐based nanocomposites and pointed out the possibility that the nanoparticles formed new trap levels, thus strongly constraining the space charge . Maezawa and colleagues proposed a new mechanism in which nanoparticles act as deep trap sites by forming potential wells .…”
Section: Long‐term DC Characteristics Of Dc‐xlpe Insulationmentioning
confidence: 99%
“…. A life exponent was chosen on the basis of the V − t characteristic of DC‐XLPE cable . The impulse withstand voltage (as typified by the lightning impulse voltage) was calculated by Eq.…”
Section: Cable Structure and Insulation Designmentioning
SUMMARY
The long‐term dc properties of DC‐XLPE insulation materials, which have been developed for dc use, were investigated. It was found that the lifetime of DC‐XLPE under dc voltage application is extended by the addition of nano‐sized filler. The time dependence of the space charge distribution at 50 kV/mm was observed for 7 days. Almost no accumulation of space charge in DC‐XLPE was found. The 250‐kV DC‐XLPE cables and accessories were manufactured and subjected to a type test and PQ test for use in the Hokkaido–Honshu dc link facility owned by the Electric Power Development Co., Ltd. These tests were performed under conditions that included a polarity reversal test for line commutated converter (LCC) systems as recommended in CIGRE TB 219. The test temperature was 90 °C. The type test and PQ test were successfully completed. The DC‐XLPE cable and accessories were installed in summer 2012 for the Hokkaido–Honshu dc link. After the installation of the dc extruded cable system, a dc high‐voltage test at 362.5 kV (=1.45 PU) for 15 min was successfully completed in accordance with CIGRE TB 219. This dc extruded cable system was put into operation in December 2012 as the world's highest‐voltage extruded dc cable in service and the world's first dc extruded cable for a LCC system including polarity reversal operation.
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