Space charge behavior at physical interfaces in cross-linked polyethylene under DC field (original) (raw)
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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
Space charge dynamic at the physical interface in cross-linked polyethylene under DC field
IEEE Transactions on Dielectrics and Electrical Insulation, 2000
In this paper the behavior of positive charge formed in the vicinity of the Semi-conducting sheet anode at room temperature and under applied dc has been investigated just after the reversal of the sample, and when the sample was combined with another sample without pre-stressing using the pulsed electro acoustic (PEA) method. The results suggest that the PEA system can only show the net charge density, and the space charge distribution is drastically changed when the sample is reversed just after the removal of the applied voltage (depolarization), or when this sample was combined with another without pre-
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.
IEEE Transactions on Dielectrics and Electrical Insulation, 2019
The discontinuous charge relaxation time related to the electrical conductivity and permittivity, i.e., traditional Maxwell-Wagner relaxation, is the prevailing explanation for the interfacial charge behavior in multi-layered dielectrics. However, the unipolar/bipolar charge dynamics and the corresponding mechanisms from a microscopic viewpoint remain unclear. This work focuses on the dynamics of the interfacial charges in cross-linked polyethylene (XLPE)/ethylene-propylene-diene (EPDM) dual layers to reveal the interfacial charge mechanisms using the energy band structure. The interfacial charge accumulation behavior of the XLPE/EPDM duallayered structures is clearly observed under electrical stress. Either unipolar or bipolar charges occur at the interface, accompanied by charge injection, and trapping then occurs. The positive charges prefer to accumulate and migrate on the XLPE side. The homo-charges at the interface always remain on the EPDM side. The number of negative charges is higher than the number of positive charges at the interface. The bipolar interfacial charges are ascribed to the charge transfer process that occurs at the interface because of the energy level alignment that is revealed by the electronic energy structures of XLPE and EPDM. The trapping sites, along with the charge injection and transport, contribute to the interfacial charge behavior. Index Terms-space charge, interface, energy band structure, trapping site, energy level charge behavior [11]. Research works related to the space charge in cross-linked polyethylene (XLPE)/ethylene propylene rubber (EPR) dual layers have presented various results. Positive charge accumulation was observed at the interface of the XLPE (cathode)/EPR (anode) system under a field of 10 kV/mm [12]. Consequently, the electric field inside the XLPE is enhanced.
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.
Effects of crosslinking byproducts on space charge formation in crosslinked polyethylene
IEEE Transactions on Dielectrics and Electrical Insulation, 2005
Space charge is formed in cables insulated with crosslinked polyethylene. It has not been clear whether the crosslinking byproducts or the crosslinked polymer morphology is responsible for the space charge formation. In order to clarify this point additive-free non-crosslinked low-density polyethylene, additive-free crosslinked polyethylene, and degassed crosslinked polyethylene were soaked in the crosslinking byproducts and the space charge distribution was measured after dc voltage application. Samples tested are divided into two categories. The first category is a soaked single-layered sheet and the second category is a two-layered specimen consisting of a soaked sheet and a non-soaked sheet. As a result, the following conclu-() sions were obtained. 1 Cumyl alcohol is responsible for homo-charge layers in () front of the electrodes in both low-density and crosslinked polyethylene sheets. 2 Acetophenone is responsible for hetero-charge formation in crosslinked polyethy-() lene, presumably as a synergistic effect with water. 3 ␣-methylstyrene has no effect on space charge formation in low-density polyethylene, while it assists charge () trapping in crosslinked polyethylene. 4 Charge trapping occurs easier in degassed crosslinked polyethylene than in low-density polyethylene, probably because of carbonyl groups induced by crosslinking.
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.
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.
Space Charge Behaviour at LDPE Interface under AC Electric Stress
This paper reports on measurements of space charge characteristics in single and two-layer of low-density polyethylene (LDPE) films subjected to an applied voltage with a range of frequencies from dc to 50 Hz. Space charge was measured using the pulsed electroacoustic (PEA) technique. To measure charge distributions under ac electric fields at different angles, the point-on-wave method has been used. To obtain a good signal to noise ratio under ac conditions, the measured signals were averaged between 1000 and 2000 times. Experimental results demonstrated that frequency is a significant factor that affects bulk charge formation/distribution. In addition, interfacial charge between polymer and polymer in the two-layer arrangement was influenced by the type of electrode material.
Journal of Applied Physics, 2008
The time resolved fast pulsed electroacoustic method is used to investigate the space charge characteristics in an additive-free poly͑propylene-ethylene͒ copolymer in film form. The 190 m thick films, sandwiched by aluminum ͑at the lower electrode͒ and semiconducting material ͑at the upper electrode͒, were submitted to dc and low frequency ac stress for various durations at various temperatures. The results show that under dc stress, homocharges accumulate near the lower electrodes and heterocharge near the upper electrode at 25°C whereas at 50°C, besides the similar space charge behavior as at 25°C in the vicinity of the electrodes, a region of symmetric separation of charges of opposite polarity is detected in the bulk. In addition, the time for the symmetric separation emergence under high voltage application depends on the field intensity, being shorter for higher field. Similar charging characteristics were also found at 50°C under low frequency ͑5 mHz͒ square 50 kV/mm rms stress, with surprisingly periodical feature, while only injected charge was observed at 0.1 Hz square rms 50 kV/mm stress. Combining dc data with ac data, it is shown that the space charge build up results from two contributing processes: the space charge formation adjacent to the electrode is due to electronic carriers injection and drift, whereas the symmetric space charge in the bulk shows ionic transport characteristics, which can be well fitted with an ionic transport model.