Fast and slow charge packets in polymeric materials under DC stress (original) (raw)
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Modeling of transient space charge distribution in polymer
Journal of Electrostatics, 1997
Low density polyethylene (LDPE) is one of the principal polymers used for the insulation of dc power cables. The application of a dc electrical field in this material leads to the movement of injected charges and internal charges for the establishment of a field distorsion in the material. This process constitutes one of the principal causes of the dielectric breakdown from which is depended the life time. Consequently, the knowledge of the origin of space charge or internal field is important and necessary for the behaviour study of insulator under electrical stress. For this, numerical modeling of transient space charge distribution in low density polyethylene (LDPE) of 1 mm thick is presented in this paper in order to explain the experimental results on the time variation of space charge distribution under dc voltage stresses up to 100 kV at room temperature using the pressure wave propagation method (PWP) which has been recently set up in our Laboratory. These experiments have made in evidence the formation of homo-space charges close to the electrodes. The amount of these homocharges increases with time duration of the voltage application. The simulation is made on the basis of electrons and holes injection from the cathode and anode respectively with the hopping transport in the material bulk taking into account the bipolar carrier trapping phenomenon. The theoretical results of modeling have shown the accumulation of homo-space charges near the electrodes as it has been also found by experiments. Following our assumptions, it seems that, this accumulation of charges could be due to the injection process and their capture closest the electrodes.
A study on the ageing of polymeric materials in the presence of space charge
2016
The use of polymeric power cables for high voltage direct current HVDC has become increasingly popular for renewable power sources such as offshore wind farms. The long term reliability of polymeric cables operating under DC conditions is still unknown and therefore of concern to the industry. However, there is no an explicit consideration of how the injected charges can cause effects to the prediction of the life-time. Thus, it is important to develop an ageing model can assist of understanding the effect of these charges on the insulating material. Regarding to the polymeric material that are used as an electrical insulation, the presence of space charges could be the consequence of material degradations that are thermally activated and accelerated by the presence of electric field. The dynamics of space charge, therefore, can be potentially used to characterise the material. In this direction, an ageing model in which parameters have clear physical meanings has been developed and...
Fast charge packet dynamics in XLPE insulated cable models
2007 Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, 2007
This paper deals with the investigation of space charge accumulation dynamics in XLPE electrical insulation. In particular, very fast charge packets, i.e., having large mobility, are observed to be injected from both electrodes and to cross the insulation bulk, thereby contributing to heterocharge build-up at the opposing electrodes after just a few seconds from the beginning of polarization. The mobility of these charges, depending significantly on temperature, is estimated through observation of charge packets as a function of time.
Charge trapping and detrapping in polymeric materials: Trapping parameters
Journal of Applied Physics, 2011
Space charge formation in polymeric materials can cause some serious concern for design engineers as the electric field may severely be distorted, leading to part of the material being overstressed. This may result in material degradation and possibly premature failure at the worst. It is therefore important to understand charge generation, trapping, and detrapping processes in the material. Trap depths and density of trapping states in materials are important as they are potentially related to microstructure of the material. Changes in these parameters may reflect the aging taken place in the material. In the present paper, characteristics of charge trapping and detrapping in low density polyethylene (LDPE) under dc electric field have been investigated using the pulsed electroacoustic (PEA) technique. A simple trapping and detrapping model based on two trapping levels has been used to qualitatively explain the observation. Numerical simulation based on the above model has been carried out to extract parameters related to trapping characteristics in the material. It has been found that the space charge decaying during the first few hundred seconds corresponding to the fast changing part of the slope was trapped with the shallow trap depth 0.88 eV, with trap density 1.47 Â 10 20 m À3 in the sample volume measured. At the same time, the space charge that decays at longer time corresponding to the slower part of the slope was trapped with the deep trap depth 1.01 eV, with its trap density 3.54 Â 10 18 m À3. The results also indicate that trap depths and density of both shallow and deep traps may be used as aging markers as changes in the material will certainly affect trapping characteristics in terms of trap depth and density. V C 2011 American Institute of Physics.
Journal of Applied Physics
This paper focuses on the study of internal charging of four space used polymers: polyetheretherketone, fluorinated ethylene propylene, polyimide films, and epoxy based material (Epoxy FR4). Experiments were carried out for each material using the GEODUR facility (Toulouse, ONERA) that mimics the geostationary space environment behind shielding. Two different irradiation currents have been applied: 1 pA/cm 2 and 10 pA/cm 2. 1 pA/cm 2 is used to analyze the charging behavior and the intrinsic electrical properties of each polymer. 10 pA/cm 2 is used to study the influence of high electric field levels on their charging behavior. In this paper, two different numerical tools used for the study of internal charging are presented: Monte-Carlo Internal Charging Tool (MCICT) and Transport of Holes and Electrons Model under Irradiation in Space (THEMIS). MCICT has been used in the space community for several years. THEMIS has been recently developed at ONERA and is compared to MCICT. Both numerical tools showed consistent results for the 1 pA/cm 2 integrated current but with deviations for the 10 pA/cm 2 integrated current, supposedly due to nonlinear electric field effects on charge transport. THEMIS has a more refined physical model for the conductivity than MCICT. It studies more accurately the electron-polymer interactions and the charge transport kinetics of polymers under space radiations. Subsequently, the analysis of the underlying physical phenomena responsible for the polymers' charging behaviors will be carried out with THEMIS. In addition, studying these phenomena will permit to assess the risks of electrical discharges that may occur on a spacecraft in orbit (e.g., Geostationary (GEO) spacecraft) or during an elliptic trajectory (e.g., sub-GEO) in an Electric Orbit Raising case [
The electro-mechanical effect from charge dynamics on polymeric insulation lifetime
AIP Advances, 2015
For polymeric material used as electrical insulation, the presence of space charges could be the consequence of material degradations that are thermally activated but increased by the application of an electric field. The dynamics of space charge, therefore, can be potentially used to characterize the material. In this direction, a new aging model in which parameters have clear physical meanings has been developed and applied to the material to extrapolate the lifetime. The kinetic equation has been established based on charge trapping and detrapping of the injected charge from the electrodes. The local electromechanical energy stored in the region surrounding the trap is able to reduce the trap-depth with a value related to the electric field. At a level where the internal electric field exceeds the detrapping field in the material, an electron can be efficiently detrapped and the released energy from detrapping process can cause a weak bond or chain scission i.e. material degradat...
Numerical Modeling of Charge Transport in Polymer Materials Under DC Continuous Electrical Stress
Transactions on Electrical and Electronic Materials, 2015
Our work is based on the development of a numerical model to develop a methodology for predicting the aging and breakdown in insulation due to the dynamics of space charge packets. The model of bipolar charge transports is proposed to simulate space charge dynamic for high DC voltage in law-density polyethylene (LDPE), taking into account the trapping and detrapping of recombination phenomena, this model has been developed and experimentally validation. Theoretical formulation of the physical problem is based on the Poisson, the continuity and the transport equations as well as on the appropriate models for injection. Numerical results provide temporal and local distributions of the electric field, the space charge density for the different kinds of charges, conduction and displacement current densities, and the external current.
Analysis of charging and discharging currents in polyethyleneterephthalate
Physica Status Solidi (a), 1994
Charging and discharging currents in polyethyleneterephthalate samples for different polarization times, temperatures, and fields and for different measuring intervals are measured. Special attention is paid to external measuring circuit. The current obeys a Curie-von Schweidler law only for short times. The charging current changes its shape if the polarization time is long or the polarization field is high, depending on the product time x field. The discharging current is strongly dependent on the external resistance used in measuring circuit. Three characteristic parts are observed. The first part fits well with a Debye relaxation function. The second part seems to be a straight line and the slope is dependent on measuring resistance and the charge existing in the sample. As the resistance is higher, the slope is higher. The third part, reported for the first time in this paper, represents the current that is released from the sample for a long time and sometimes is considered as a parasitic current. If the external resistance is big enough, this current can lead to increases of the voltage on the sample. The slope of the discharge current is dependent on the charge contained in the sample. On a mesure les courants de chargement ct de dechargement pour differents temps, champs et temperatures de polarization et pour difftrents intervales de mesure. Les courants satisfont la lois de Curie-von Schweidler seulement pour de petites intervales du temps de mesure. Le courant de chargement change sa forme si le temps de polarisation est long ou si I'intensitt du champ Clectrique de polarisation est assez grande. I1 depend du produit champ x temps. On a obtenu trois zones characteristiques pour le courant de dechargement comme une fonction de temps. La premiere zone est bien approximte par une fonction de relaxation du type Debye. La deuxitme est lineaire dont sa pente depend de la resistance externe de mesure. Si la resistance croit, la pente croit aussi. La troisitme zone qu'on met en evidence pour la premiere fois dans ce travail, represente un courant qui est longuement tlibere par 1' echantillon. Si la resistance externe est grande ce courant peut provoquer la croissance de la tension sur I ' khantillon. La forme du courant de dechargement depend de la charge accumulee dans I'tchantillon. I) Str. Copou N 27, 6600 Iasi, Roumania.
The missing link - The role of space charge in polymeric insulation lifetime
Proceedings of 2014 International Symposium on Electrical Insulating Materials, 2014
Polymeric insulation in power equipment experiences degradation and ageing under service conditions. The determination of remaining life plays a key part in the asset management. This requires an ageing indicator which can be used to monitor the status of the insulation. In this paper a simple model based on trap creation has been proposed and a concept of critical trap density can be used to describe the lifetime of the insulation. Assuming the power law relationship between the trap creation and the electric field, the empirical inverse power law can be derived. This allows one to relate the physical mechanisms and ageing processes (trap generation). Since the number of traps and energy depth of traps have direct influence on charge dynamics, using the two energy levels of trap depth model developed previously it is possible to estimate the trap density through changes in space charge dynamics. Further work is necessary to establish the direct relationship between trap density and the remaining life of the polymeric insulation.