Pulsed Electro-acoustic Method Research Articles

Thermally stimulated depolarization current and space charge measurements on low‐density polyethylene: Influence of the presence of antioxidant

AbstractThe purpose of this study is an investigation upstream of polymer insulator ageing and rupture. We studied the electrical and physicochemical properties of a low‐density polyethylene (LDPE) used in high‐power insulated cables. Space charge measurements using pulsed electroacoustic method and thermally stimulated depolarization current (TSDC) were carried out on LDPE samples, with and without antioxidant, at different temperatures. TSDC peaks were observed only in the presence of an antioxidant. Furthermore, a TSDC anomalous peak was revealed for the sample containing an antioxidant and polarized at 50°C. All the TSDC peaks are interpreted as trapped charges and can be explained by measuring the space charge distribution within the sample bulk. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A New Method for Space Charge Measurements Under Periodic Stress of Arbitrary Waveform by the Pulsed Electro-Acoustic Method

A new method for space charge measurement resorting to the pulsed electroacoustic (PEA) method under periodic stress of arbitrary waveform is presented. The originality of the work consists in using a long memory digital oscilloscope combined to the method used to sample one period of the HV stress into several profiles. There is no need for synchronization between pulse generation and HV stress and hence no hardware change of classic PEA system. The pulse generator provides a probing pulse of 5 ns duration, at a maximum frequency of 1 kHz. With these features, the phase of the HV stress can be resolved into 200 profiles by frequency adjustment of the pulse generator. Several periods of the HV stress are necessary for obtaining the set of profiles; however the typical measurement time is less than 20 s for f > 0.2 Hz. Preliminary results obtained on a crosslinked polyethylene film under 50 Hz ac stress are shown to demonstrate the feasibility.

Study on Space Charge Behavior Related to the Residual Charge Method for Diagnosing Water Tree Degradation of Polymer Insulated Power Cables

The residual charge method is expected to be a powerful tool to detect the water tree degradation of polymer insulated power cables. In this method, DC voltage is firstly applied to electrify the degraded region. Some of the charges would be deeply trapped and stayed stably, even after the DC voltage is removed and the system is short circuited. AC voltage is subsequently applied in order to release the trapped charges. The DC component current, or the integration of it, is considered to have a correlation with the degree of degradation. This paper discusses the detail of the mechanism by which the DC component signal appears. The specimen was carefully prepared so that it contained water trees with uniform length. Space charge measurement was performed by pulsed electroacoustic method. The decay process of charges under AC voltages was interpreted into the energy depth at which the charge had been trapped, assuming that the charges were detrapped by the process of Poole-Frenkel type. It was suggested that the charges trapped between 0.8-1.2 eV can be detected as the DC component current. The shallower would be released by thermal energy at ambient temperature while the system was short circuited. The deeper would not be released by realistic AC voltages. The result showed that the transition of DC component current in the residual charge method represents the behavior of space charges having been trapped at deferent energy levels. It is believed that the results give useful information to apply the method to power cables.

Research on Simulation of Deep Charging for Spacecraft Dielectrics

针对航天器介质深层充电问题,提出了一种基于蒙特卡罗模拟和充电动力学RIC模型的介质电荷分布及电场预估新方法,利用地面试验验证了其正确性.航天器介质平板充电过程被简化为屏蔽铝板与分层介质组成的Geant 4模型,通过统计方法计算出了实际入射束流下Teflon介质内的注入电流密度和剂量率分布曲线,利用RIC模型获得了背面接地时介质中的电荷密度和电场分布,利用脉冲电声法(PEA)对不同束流密度辐照下的Teflon内部空间电荷密度进行了测量.数值模拟和地面试验结果表明,Teflon在100 keV能量电子辐照下,电荷密度和电场随着束流密度的增加而不断增大,其电荷密度峰值位置约为0.042 mm,且背面接地时接地侧电场最大.由于Geant 4粒子输运模拟和RIC模型具有通用性,因此该方法适用于各种航天器介质材料.

Space charge analysis of electrothermally aged XLPE cable insulation

Cross-linked polyethylene (XLPE) is currently widely used as an insulating material for power cables due to its good physical properties, however when in use it undergoes an electrical ageing process. Its ability to trap electric charge can give rise to space charge accumulation in the bulk of the polymer and produce localised electric stresses that can lead to cable failure, since the electric field will be increased above the design stress in some regions favouring the initiation of degradation there. In this work the PEA (pulsed electroacoustic) method was used to compare the charge dynamics in three samples (XLPE cable peelings) aged in different ways (electrothermally in the laboratory, field aged in service and thermally aged in the laboratory). Very different transient behavior was found depending upon the ageing history. This is related to differences in the migration of chemical species in the insulation layer, which are known to act as charge traps. All materials showed heterocharge peaks when the space charge reached stability, the magnitude of which seems to be related to the severity of the ageing.

Spatio-temporal Charge Distribution in Electric Double Layer Capacitors observed by pulsed Electro Acoustic Method

Spatio-temporal Charge Distribution in Electric Double Layer Capacitors observed by pulsed Electro Acoustic Method

Space charge distribution and crystalline structure in quenched polytetrafluoroethylene

Three polytetrafluoroethylene (PTFE) specimens were prepared under different cooling rates after sintering. The space charge distribution in PTFE specimens under direct current electrical field was measured by the pulsed electro-acoustic method (PEA). It was found that the amount of space charges decreased and field distribution tended to be uniform in the quenched specimen. Differential scanning calorimeter (DSC) and wide-angle X-ray diffraction (WAXD) showed that crystallinity and crystalline size of PTFE decreased after quenching whereas the crystalline form of PTFE remained the same. The structure of crystallites became disorderly and imperfect. All the changes in crystalline structure after quenching might decrease the number of space charges trapped in specimens and enhance the transmission of the charge-carriers in amorphous regions, which probably resulted in a decrease of the accumulation of space charges.

Characteristic of charge accumulation in glass materials under electron beam irradiation

Space charge formation in various glass materials under electron beam irradiation was investigated. The charging of spacecrafts occurs in plasma and radiation environments. In particular, we focused on an accident caused by internal charging in a glass material that was used as the cover plate of a solar panel array, and tried to measure the charge distribution in glass materials under electron beam irradiation using a pulsed electroacoustic (PEA) method. In the case of quartz glass (pure SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), no charge accumulation was observed either during or after the electron beam irradiation. On the contrary, charge accumulation was observed in glass samples containing metal oxide impurities. It is found that the polarity of the observed charges depends on the contents of the impurities. To identify which impurity dominates the polarity of the accumulated charge, we measured charge distributions in several glass materials containing various metal oxide impurities. Furthermore, the dependence of the polarity of accumulated charges on the composition of glass materials is discussed using energy band models

Measurement of the surface potential decay of corona-charged polymer films using the pulsed electroacoustic method

In this paper, the pulsed electroacoustic (PEA) technique that allows the determination of space charge in a dielectric material has been used to monitor the electrical potential decay of corona-charged polyethylene films of different thicknesses. To prevent possible disturbance of the surface charge during the PEA measurements, two thin polyethylene films were placed on both sides of the corona-charged sample. Charge profiles measured at different times were used to calculate the potential across the sample. The obtained potential decay was compared with the potential measured using the conventional method. Good agreement has been obtained. More importantly, the charge profile obtained using the PEA technique indicates that bipolar charge injection has taken place.

Spatio-temporal charge behavior in electric double layer capacitors observed by pulsed electro acoustic method

The use of the pulsed electro acoustic (PEA) method allowed us to perform the direct observations of spatio-temporal charge distributions in EDLCs based on polarizable nanoporous carbonaceous electrode. The negative charge density became the maximum, about −173 C/m 3 at the region where was near to anode layer in EDLCs for case of dc voltage 2.5 V, while the positively charged density became the maximum, about 70.7 C/m 3 at the region where it was located around the cathode layer. The behavior of negative and positive charges measured by the PEA method reflected the hetero-charges distribution in EDLCs. The performance of the sample was found to be better in terms of the capacitance ( C s) with a maximum value of 55.4 F/g than general EDLCs which use organic electrolyte.

Space charge distributions in glass fibre/epoxy resin composites under dc 10 kV mm−1 electric field

In this paper, the authors discuss one- and three-dimensional space charge distributions in glass fibre/epoxy resin composites. By the conventional pulsed electroacoustic (PEA) method, only a one-dimensional distribution of the average charge over a whole area parallel to the two electrodes can be observed. Therefore, the authors have developed a new PEA system capable of measuring a three-dimensional space charge distribution. Using this system, they measured the charge distribution in glass fibre/epoxy resin composites made of lattice-woven glass fibre and epoxy resin. It has become clear that spatial variation in signal intensity observed depends on the internal structure of the composite. There appear repetitious positions where a high charge density is observed on the same lateral cross section along the vertical direction in the composite. Such positions are consistent with the intersections of the glass fibres. Accumulation of mobile charge carriers or appearance of polarization charge due to mismatch of the ratio of the conductivity and permittivity between the glass fibre and the epoxy resin is thought to be responsible for the PEA signals.

Assessment of Diffusion of an Antistatic Agent in One Side of EVA/LDPE Laminate Film Using Space Charge Measurement

An antistatic agent is often used for avoiding electrification of polymer films. In some cases, the film has a double-layer structure to improve its adhesive property. As an example, an ethylene-vinylacetate copolymer (EVA) film in which an antistatic agent is mixed, corresponding to “EVA(ASA)”, is laminated with a low-density polyethylene (LDPE) film. In such a case, there is a possibility that the antistatic property of the EVA may be lost because of the diffusion of the antistatic agent into the LDPE side.A space charge study on the EVA(ASA)/LDPE laminate was carried out using the pulsed electroacoustic method under DC voltage. The space charge once formed at EVA(ASA)/LDPE interface decreased with time, and propagated into LDPE. A space charge profile at EVA (ASA)/LDPE interface was also calculated with difference of conductivities between LDPE and EVA(ASA). The space charge profile at EVA(ASA)/LDPE interface was qualitatively corresponded to that from space charge measurement. As a result, it was suggested that diffusion of the antistatic agent led to this space charge behavior. It was considered that measurements of space charge profiles would enable the assessment of diffusion of antistatic agent in multi-layer.

Space-Charge Detection and Behavior Analysis in Electron Irradiated Polymers

Charges accumulate on the spacecraft surface through various processes such as conduction, irradiation, ionization, and polarization. These charges can affect the space system operations via an electric current flowing in the structure or a locally generated electric field. This paper is focused on the analysis of electron behavior in polymeric films such as polymethylmetaacrylate and Teflon subjected to an electron irradiation. The charge distribution is detected during and after the irradiation in situ by pulsed electroacoustic method. Surface-potential and surface-current measurements are also performed to get further information on the charge displacement with time.

A preliminary study of space charge distribution measurements at nanometer spatial resolution

The continuous reduction in size of devices, such as integrated circuits or micro-electro-mechanical systems (MEMS), results in the need to control with better and better resolution the materials involved, and in particular the electrical properties of the insulating and semiconducting parts. In this paper we propose an approach applicable to space charge measurement methods for improving the resolution to the nanometer range by using femtosecond laser pulses. It is shown that a resolution of about 60 nm in SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> can be achieved with thermal and pressure wave propagation methods. Concerning the pulsed electro-acoustic method, the interfacial displacement as small as 100 fm can be measured at THz rate

Pulse Acoustic Technology for Measurement of Charge Distribution in Dielectric Materials for Spacecraft

Recently, some accidents in spacecraft due to charging up by irradiation of charged particles have been reported. Some of them are caused by a surface discharge, which normally takes place in a plasma environment in space. Some others seem to be caused by a discharge due to an accumulation of charge in the bulk of materials in a relatively high-altitude environment. To investigate the charge accumulation in the bulk of materials, the authors have been developing an internal charge measurement system. The internal charge accumulation in dielectric materials under irradiation of artificial radioactive rays is observed using the developed system, which employs the so-called pulsed electroacoustic method and pressure wave propagation method based on pulse acoustic measurement techniques. The developed system is applicable to the measurement of the charge distribution in dielectrics in air atmosphere or vacuum environments under electron beam, proton beam, and gamma ray irradiations. Using the system, we measured bulk charge distributions in polymeric films and glass materials. In this paper, summaries of some typical measurement results are presented following a brief explanation of measurement principles

Space charge behaviors of electric double layer capacitors with nanocomposite electrode

Space charge distributions of electric double layer capacitors (EDLCs) based on polarizable nanoporous electrodes, containing acetylene black and ketjen black as electrode materials, were investigated by a pulsed electro acoustic (PEA) method. The charge distributions of positive/negative ions were spatially uneven and charge accumulation region concentrated on the central part of the electrode. The polarizable electrodes with ketjen black had higher space charge density. The use of the PEA method allowed us to perform the direct observations of spatio-temporal charge distributions in EDLCs. From the results of cyclic voltammetry, it is clear that EDLCs based on the ketjen black have better capacitive behavior. The specific capacitance of about 55.8 F/g of EDLCs using the polarizable electrodes with ketjen black was obtained. It can be found that ketjen black plays an essential role in the improvement of the charge density and the electrostatic capacity in EDLCs.

Space charge measurements on multi-dielectrics by means of the pulsed electroacoustic method

The pulsed electroacoustic (PEA) method is now widely accepted as one of the most simple and effective techniques for the measurement of the dynamic space charge distribution in solid dielectrics. Recently, the PEA method has been applied also to laminar test objects composed of two or more layers of different dielectrics (multi-dielectrics). However, when a multi-dielectric is tested by means of the PEA method, the different acoustic and electric properties of the materials affect the detected space charge signal. In this paper, the principle of the PEA technique is reviewed in case the test object is a multi-dielectric. The generation, transmission and reflection of electrically-induced acoustic waves are described. Based on the proposed approach, results of PEA measurements performed on various kinds of multi-dielectrics are presented and discussed.

Description of charge transport in polyethylene using a fluid model with a constant mobility: fitting model and experiments

A numerical model for describing bipolar charge transport and storage in polyethylene has been developed recently. The present paper proposes a comparison of the model outputs with experimental data in three different direct current (DC) voltage application protocols (step field increase and polarization/depolarization schemes). Three kinds of measurement have been realized for the three different protocols: space charge distribution using the pulsed electro-acoustic method, external current and electroluminescence. Simulation under AC stress has also been attempted on the basis of the model parameters that were derived from the DC case. Model limitations and possible improvements are discussed.

Space charge distributions of an electric double layer capacitor with carbon nanotubes electrode

Space charge distributions of an electric double layer capacitors (EDLCs) based on polarizable nanoporous electrodes, containing carbon nanotubes (CNTs) as electrode material, were investigated by a pulsed electro acoustic (PEA) method. The EDLCs samples were prepared using CNTs and carbon black (i.e. acetylene and ketjen black) as electrode materials with different types pore structures. The charge distributions of positive/negative ions were spatially uneven and charge accumulation region concentrated on central part of electrode. The polarizable electrodes with ketjen black and CNTs-5 wt.% had higher space charge density. From the results of discharge characteristics, it is clear that EDLCs based on the ketjen black/CNTs-3 wt.% have better capacitive behavior. The specific capacitance of about 14 F/g of EDLCs using the polarizable electrodes with ketjen black and CNTs-3 wt.% were obtained. It can be found that CNTs plays an essential role in the improvement of the charge density and the electrostatic capacity in EDLCs. The use of PEA method allowed us to perform the direct observations of spatio-temporal charge distributions in EDLCs based on CNTs.

Space Charge Characteristic of Nano-composite Film of MgO/LDPE under DC Electric Field

This paper deals with the effect of magnesium oxide (MgO) nano-filler to stabilize internal electric field under DC voltage application. A low-density polyethylene (LDPE) film containing the MgO nano-filler (nano-composite film) was subjected to space charge measurement by applying DC voltages. The pulsed electroacoustic method was employed for the measurement. In addition, conduction current under the corresponding conditions was measured and correlated with the space charge evolution.When the average DC field was as low as 80 kV/mm, very little space charge was observed with the “non-filled film, whereas a positive space charge was observed with “filled film. The density of the positive space charge in the vicinity of the anode was higher compared to that in the bulk. The more distant the position from the anode, the lower the charge density. The conduction current under the same condition was found to be lower with higher content of the MgO nano-filler. The conduction current determined by the space charge in the vicinity of the anode was calculated for the specimen with each content of MgO nano-filler, and good agreement between the estimated current and the measured one was found. It is concluded that the MgO nano-filler seems to trap the positive space charge in the vicinity of the anode and suppresses conduction current by reducing the local field at the anode.