Influence of BaTiO/sub 3/ additive and electrode material on space-charge formation in polyethylene. Evidence from thermal step space-charge measurements (original) (raw)
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Morphology Effects on Space Charge Characteristics of Low Density Polyethylene
… Journal of Applied …, 2011
Low density polyethylene (LDPE) film samples with different morphology were prepared by three kinds of annealing methods which were different in cooling rates in this study. A pulsed electro-acoustic (PEA) space charge measurement system was improved to solve the surface discharge problems for small samples applied with a high voltage. Negative direct current (DC) fields from 50 to above 220 kV/mm were applied to the samples. The influences of morphologies on space charge and space charge packet characteristics were measured by the improved high voltage withstand (HVW) PEA system. Mobility and trap depth of released charges were calculated by space charge decay. It was found that there is a different probability of space charge packet initiation under applied field from À60 to À100 kV/mm. Average velocity and mobility of the space charge packets were calculated by space charge packet dynamics. It was found that the lower cooling rate samples have higher crystallinity, more homo-charge accumulation, lower mobility and deeper trap depth. The mechanism of morphological effects on space charge phenomena have been presumed to give a plausible explanation for their inherent relationships. The morphology in the metal-dielectric interface and in the bulk is convincingly suggested to be responsible for the injection and propagation processes of space charge. A model of positive space charge initiation in LDPE samples was also suggested and analyzed. The mechanism of morphological effects and the charge injection model are well fit with the injection and propagation processes of space charge. The different effects of morphology in the metal-dielectric interface and in the bulk of polymers are stressed.
Effect of electrodes on space charge in cross-linked polyethylene under DC field
Journal of Electrical Engineering
Space charge behaviour at physical interfaces in cross-linked polyethylene (XLPE) films submitted to DC field has been investigated as a function of the nature of the interfaces using the pulsed electro-acoustic technique. Aluminium, gold and carbon black-loaded polyethylene were used as electrodes to investigate space charge built-up in a single dielectric layer. Charge injection rather than ionic species migration is seen to control space charge distribution in agreement with the storage conditions of the XLPE films. It is shown that the sign and distribution of space charge depend drastically on the nature and polarity of the electrodes
The Effects of Nano Fillers on Space Charge Distribution in Cross-Linked Polyethylene
International Journal of Electrical and Computer Engineering (IJECE), 2017
The performance of polymeric insulation will be distorted by the accumulation of space charge. This will lead to local electric field enhancement within the insulation material that can cause degradation and electrical breakdown. The introduction of nanofillers in the insulation material is expected to reduce the space charge effect. However, there is a need to analyze potential nanofillers to determine the best option. Therefore, the objective of this research work is to examine two types of nanofillers for Cross-Linked Polyethylene (XLPE); Zinc Oxide (ZnO) and Acrylic (PA40). The effects of these nanofillers were measured using the Pulsed-Electro Acoustic (PEA) method. The development of space charge is observed at three different DC voltage levels in room temperature. The results show that hetero charge distribution is dominant in pure XLPE materials. The use of both nanofiller types have significant effect in decreasing the space charge accumulation. With nanofillers, the charge profile changed to homo-charge distribution, suppressing the space charge formation. Comparison between both the nanofillers show that PA40 has better suppression performance than ZnO.
Charging and Discharge Currents in Low-Density Polyethylene and its Nanocomposite
Energies, 2020
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 th...
2008 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2008
In this report the pulsed elcetroacoustic (PEA) technique was employed to examine the space charge pattern in acetophenone and alpha-methylstyrene soaked low-density polyethylene (LDPE) samples. The samples were stressed at three different voltages; 5kV, 8kV and 10kV, and the charge patterns in the sample bulk were compared with that obtained from the clean LDPE. These chemicals are observed to assist the transportation of the charges in the sample bulk. Each of these chemicals is in favour of different charge polarity. It seems that acetophenone assists the transportation of negative charges meanwhile the transportation of positive charges is assisted by the alphamethylstyrene. It is proposed that the chemicals provide shallow traps that aid the movement of the charges.
The temperature dependence of space charge accumulation in cross-linked polyethylene
Journal of Thermal Analysis and Calorimetry, 1997
This paper presents the results of laser-induced-pressure-pulse (LIPP) measurements of space charge accumulation in 0.5 mm thick planar XLPE samples with aluminium electrodes, over the temperature range 30–90°C. The applied field strength was 10 kV mm−1. The increase in transit time of the pressure pulse across the sample with increasing temperature indicated that Young's modulus decreased by 50% from 30
Space charge dynamics in low density polyethylene under DC electric fields
Journal of Physics: Conference Series, 2008
In this paper space charge dynamics in low-density polyethylene (LDPE) under different dc electric fields, ranging from 25 kV/mm to 125 kV/mm, have been investigated using the pulsed electroacoustic (PEA) technique. Bipolar space charges have been found to present in the sample and the amount of charge increases with both the applied electric field and the duration of electric field applied. Double injection is believed to be responsible for the charge measured. Negative charge dominates due to electrode configuration used in the research. The formation of charge leads to an increase in the maximum electric field. Results show that the maximum electric field depends on both the magnitude and the duration of the applied field. The charge decay after the removal of the applied field shows a fast decaying rate for the charge formed at high applied electric field.
Analysis of space charge formation in LDPE in the presence of crosslinking byproducts
IEEE Transactions on Dielectrics and Electrical Insulation, 2000
Cross-linking byproducts are suspected to be the main contributing factor in space charge formation observed in XLPE. To investigate the mechanism behind this phenomenon, low density polyethylene was soaked into three main crosslinking byproducts, acetophenone,methylstyrene and cumyl alcohol, and space charge measurements were performed using the Pulse Electroacoustic technique (PEA). It has been found that soaking LDPE in cumyl alcohol introduces more charges into the system, with homocharges and heterocharges accumulating within the sample compared to the additive free sample. In contrast,methylstyrene and acetophenone reduce the amount of accumulated charges. In terms of charge decay, all three byproducts enhance the decay process in the insulator. Further investigations were conducted in conditions where two byproducts are present in a sample. The results shows that acetophenone is a dominant byproduct in determining the charge density patter built up during the charging process, whilst the rate of charge decay is observed to be high in the presence of-methylstyrene in the sample.
2013 Annual Report Conference on Electrical Insulation and Dielectric Phenomena, 2013
ABSTRACT Abstract- Space charge behavior at dielectric interfaces in multi-layer Fluorinated Ethylene Propylene (FEP) and Low Density Polyethylene (LDPE) subjected to a dc field has been investigated as a function of the temperature using the pulsed electro acoustic (PEA) technique. A sandwich structure constituted by two dielectric films not identical FEP/LDPE was used to study the charging propensity of electrode/dielectric and dielectric/ dielectric interface. The time dependence of the space charge distribution was subsequently recorded at different temperature under field (polarization) and short circuit condition (depolarization). Experimental results demonstrated that charge injected process take place in all cases. However it is shown that the amount of interfacial charge depends drastically on the temperature. It has greater influence on the distribution, injection and mobility of space charge in the bulk and at dielectric/ dielectric interfaces.
We are interested in the behavior under tension of metal dielectric interfaces and dielectric / dielectric towards the formation of space charges. The material in question is a widely used polyethylene as an insulator in high voltage cables. The space charges are measured by the pulsed electroacoustic technique during the polarization and depolarization. We considered a period for interfaces formed by the contact metal / semiconductor and polyethylene / polyethylene, and the association of two films of polyethylene, (thus obtaining a physical interface between two similar materials ). The results show that the formation and dissipation of space charges depend on the nature of interfaces and a 'physical' interface is not a barrier to the transport of charges.