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Epoxy resin (EP) insulations are widely considered as potential candidates for various applications. However, it is not suitable for high frequency (HF) and high temperature (HT) applications due to its low thermal conductivity. This research presents the tuning of thermal and electrical properties of EP via resin stoichiometry and incorporation of surface-modified hexagonal boron nitride (h-BN) nanofillers. In this research, the curing agent concentration for pure EP is optimized first based on high thermal stability and sufficiently reliable electrical properties. Second, the optimized pure EP is used as a base material to prepare epoxy/h-BN nanocomposites. Various physicochemical, thermal, and electrical characterizations are performed to analyze the properties of prepared materials. Results show that the higher curing agent concentrations offer a good balance between the thermal and electrical performance of the EP. However, the HF and HT stress exhibits detrimental effects on the breakdown strength and dielectric properties of the materials. Also, the addition of nanofillers further enhances the thermal properties while exhibiting sufficient electrical properties. By the control of resin stoichiometry and nanofiller addition, suitable composites for the HF and HT environment can be realized.

This paper presents the influence of thermal ageing on the physico-chemical and electrical properties of 500 kV extra high voltage direct current (EHVDC) XLPE cable insulation. EHVDC XLPE cable sections are placed in a thermal oven and thermally aged at 106 °C (melting peak temperature) for 250, 500 and 1000 h. After ageing, the inner, middle and outer layers of the cable insulation are characterized by Fourier transform infrared (FTIR) spectroscopy, oxidation induction time, X-ray diffraction (XRD), space charge, DC conductivity and DC breakdown measurements. The physicochemical analysis results show that the cross-linking by-products in the cable insulation are difficult to be completely removed during the ageing process, whereas the thermal ageing cannot completely consume the antioxidants in the materials. The space charge measurement results show that the hetero charges are accumulated inside the unaged middle layer samples. However, the space charge accumulation and electrical conductivity of the samples are significantly reduced after 1000 h ageing. Moreover, the DC breakdown strength of the inner and middle layer samples is continually increased with the increase of the ageing time. It is elucidated that the thermal ageing leads to the re-crystallization and re-degassing of samples, improving the space charge behavior and the charge carrier trapping phenomenon. It is proposed that the temperature of 106 °C could be used as a suitable degassing temperature for the EHVDC XLPE cable production.

This paper reports the effect of DC and pulse wave voltages on space charge characteristics of polyimide material for high-frequency insulation. The pulsed electroacoustic method is used to measure the charge distribution inside the material under the pulse wave voltages with different amplitudes, polarities, frequencies and duty ratios. Comparative results show that positive charge is more likely to accumulate inside the polyimide. The amount of accumulated charge under pulse wave voltages is larger than that under DC voltages. With frequency, more space charge is accumulated under negative pulse wave voltages with a frequency above 50 Hz, while it is not larger than 100 Hz under positive voltages. The maximum distortion of electric field appears under the negative pulse wave voltage with the frequency of 500 Hz, which is 1.19 times the applied field strength. When the duty ratio of the pulse wave voltage exceeds 50%, the distribution of accumulated charge tends to be stable. The research results can provide a reference for the practical application and modification design of polyimide materials in power electronic equipment.

In this paper, space charge behavior over a large range of electric field and temperature, of two kinds of epoxy resins are investigated using an improved pulsed electro-acoustic method. Significant influence of high electric field and high temperature on the space charge accumulation in epoxy are found. Hetero charge accumulation starts to build up at 80 °C under 120 kV/mm for amine-type hardener cured epoxy (EP-AM), while at 140 °C under 60 kV/mm for anhydride-type hardener cured epoxy (EP-AH). The accumulated charge increases with the increasing of electric field and temperature. The maximum enhancement of local electric field of is 135 and 123 % at 140 °C for EP-AM and EP-AH, respectively. Quantum chemical calculation is performed to clarify the mechanism of space charge characteristics in the two types of epoxy. It is indicated that ionization of remnant unreacted hardener and electrode injection may be the main sources of space charge. The interaction between molecular chains of EP-AH is stronger than that of EP-AM, which makes it have better space charge characteristics even under high temperature.

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 dual-layered 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.

This paper reports on the effects of four voltage stabilizers, m-aminophenylboric acid, 2-methoxy-5-pyridineboric acid, m-aminobenzoic acid and 4-dimethylaminobenzoic acid, on the insulation properties of polyethylene blends. 1 wt% voltage stabilizers were added into low density polyethylene (LDPE) blend containing 10 wt% high density polyethylene (HDPE) by a solution method. Physicochemical and electrical properties of the blends were analyzed by infrared spectroscopy, thermo-gravimetric analysis, differential scanning calorimetry, electric tree initiation tests, space charge and surface potential decay measurements. The results showed that the addition of the voltage stabilizers had a little effect on the thermal stability and melting properties of the LDPE/HDPE blend. When the voltage stabilizers were included into the blends, the tree initiation voltage (TIV) increased, in particular the blend with m-aminobenzoic acid showed the highest increase of 41% compared to the reference LDPE/HDPE. It was found that space charge accumulations of the blends were apparently suppressed by adding voltage stabilizers. Moreover, the blend with the m-aminobenzoic acid had the least space charge accumulation. The surface potential decay rate of the blends was significantly increased after adding voltage stabilizers. Quantum chemical calculations illustrated that the HOMO-LUMO energy gap was closely related to the TIV of the blends, whereas the m-aminobenzoic acid has the lowest energy gap level and the best effect of restraining the electrical tree initiation. The trap level calculation showed that the trap depth in the blends decreased with the addition of the voltage stabilizers, which was beneficial to suppress the accumulation of space charge in the materials.

This paper reports the effect of thermal ageing on the space charge characteristics, DC conductivities and trap energy distributions of 320 kV HVDC XLPE. Specimens were prepared by a heating press method in the laboratory. The specimens were placed in a thermal oven and thermally aged at 130 °C up to 30 days. Space charges were measured by a pulsed electro-acoustic setup. The results showed that the reference samples had limited hetero charge accumulations near both electrodes in the samples. The homo-charge accumulation was appeared with an increase of the aged time. The space charge accumulation in the samples was transferred from hetero-charge accumulation to homo-charge accumulation with an increase of the ageing time. The electric field distribution in the sample gradually increased with the appearance of the homo-charge accumulation, whereas the homo charges evidently distorted the electric field in the samples with the increasing ageing time. The DC conductivities of the aged samples consistently increased with the increase of the measured electric field. The obtained results of apparent mobility of the charge carriers, the activation energy and the trap energy density illustrated that thermal ageing could facilitate the homo-charge accumulation in the sample. The dominant effect of thermal ageing on the sample was elucidated by using various analytical techniques. It was found that the thermal ageing would affect the material properties and facilitate the increase of the trap energy density and the space charge accumulations in the samples.

This paper presents investigations on a usage of graphene as a voltage stabilizer for polyethylene blends in the potential recyclable high voltage direct current (HVDC) cable insulation. Thermal and electrical properties of the blends with/without graphene were evaluated by thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), electrical treeing tests, DC conductivity and space charge measurements. Trap energy distributions in the blends were estimated using the measured space charge decay data. The obtained results show that additive-like amounts of graphene can improve the thermal stability of the polyethylene blends. The influence of the graphene on the tree inception voltage (TIV) of the polyethylene blends is not significant, whereas the low density polyethylene/high density polyethylene (LDPE/HDPE) with/without graphene demonstrates the highest TIV comparing to the LDPE, LDPE/polypropylene, and their corresponding graphene added materials. It is found that the DC conductivity of the polyethylene blends with/without graphene increases consistently with the increase of the temperature. The conductivity of the LDPE/HDPE decreases apparently with the inclusion of graphene. It has been shown that space charge accumulations can be suppressed by the addition of graphene in the polyethylene blends. It is postulated that the high trap level and trap energy density of the polyethylene blends with graphene are closely connected to the suppression of the space charge accumulation in the blends.

The diagnosis of insulation performance in the high-voltage alternating current (HVAC) and high-voltage direct current (HVDC) systems has always attracted many researchers in the field of electrical engineering. New diagnostic technology and condition monitoring apparatus are of prime importance for HVAC and HVDC developments. In this study, we introduce a valuable technique called direct current integrated charge (DCIC-Q(t)) for determining the degradation of insulating materials by means of charge accumulation. This work demonstrates the typical results of full-size cross-linked polyethylene (XLPE) cables by using this effective method. Firstly, we describe the basic measurement principle of DCIC-Q(t) technique and the evaluation details of the degradation. Then, the validity of this technique is confirmed by comparing with the pulsed electroacoustic (PEA) results. The similar charge behaviors of polystyrene and low-density polyethylene are presented via the DCIC-Q(t) and PEA methods, which indicates the good availability of this technique. Three underground, full-size, 6.6-kV XLPE cables were diagnosed using the DCIC-Q(t) method. Two cables were degraded by water and electric stress for a different time under controlled conditions. The degradation extent can be evaluated easily by the charge accumulation from the DCIC-Q(t) results. Furthermore, based on the results of charge dynamics related to the applied voltage, the properties of the degraded cable by water tree are discussed.

The present work studies the space charge accumulation and decay in the degassed cross-linked polyethylene (XLPE) by detrapping mechanism and quantum chemical method. Experimentally, significant positive charge packets were observed at room temperature (300 K). Negative charges accumulated strikingly under high temperatures but with a fast decay during depolarization. The estimated bipolar carrier mobility and electron/hole trap depth that derived from the charge decay characteristics indicated that a shallow trap distribution (0.84–0.9 eV) dominates the space charge behavior. Additionally, a high temperature (>60 °C) benefits to evaluate the deep traps (0.9–1 eV). Quantum chemical analysis using density functional theory (DFT) demonstrated that both the localized states for shallow electron and hole traps exist in the electronic structure of the XLPE structures. The former is derived from the physical disorder and crosslinks. The latter is ascribed to the hopping interaction between the chain terminal and the other orientated chains. The calculation results about the charge trapping characteristics agree with the experiments. Furthermore, the role of charge injection at the electrode/dielectric interface is also discussed.

Investigation of space charge accumulation processes in a chemically cross-linked polyethylene for ac usage (XLPE) and a modified XLPE for dc usage (DC-XLPE) at voltage polarity reversal was carried out using pulsed electro-acoustic (PEA) measurement system. We found that a huge amount of so called packet-like charge, some of which partially increased the electric field in the material to more than twice of the average applied stress, generated in XLPE at the polarity reversal of DC stress. It enhanced the electric stress locally in the sample by almost twice of the applied average stress. On the other hand, we also found that the packet-like charge was not observed in DC-XLPE under the same experimental condition.

This work studies the space charge mechanisms of PE and PTFE by involving the combination of electronic structures and charge transfer processes at the interfaces of electrode/dielectrics. Experimentally, significant positive charge packets were observed in LDPE when subjected to a high electric stress. However, slight charge accumulations (mainly homo-charges) were observed inside polytetrafluoroethylene (PTFE) under the same condition. The electronic structures of PE and PTFE were calculated by density functional theory (DFT). After that, we obtained the electronic parameters, such as energy level, Fermi level, band gap and electron affinity. A negative electron affinity is determined in PE, indicating an interchain electron charge transport at the bottom of the conduction band. Nevertheless, a positive electron affinity in PTFE exhibits an intrachain electron charge transport. Moreover, injection and charge transfer at electrode/dielectrics interfaces were studied based on the calculated parameters. A low hole injection barrier dominates the positive charge injection and accumulation in LDPE, while a high electron barrier hinders the electron charge injection. In contrast, the hole injection barrier of PTFE is higher than that of LDPE. We discussed these different processes in this paper.

We developed a compact system for evaluating the deterioration of insulating materials used in high-voltage dc power apparatuses. The developed system can be used for simultaneous determination of three basic parameters important for evaluating the deterioration of high-voltage insulation materials, i.e., conductivity, dielectric constant, and charge accumulation. Charge accumulation, which is detrimental to high-voltage dc electrical apparatuses, such as power devices, transformers, and power cables, can be evaluated using this system. With this system, the charges accumulated are measured by integrating the current through a capacitor inserted between the highvoltage power source and the high-voltage apparatus to be tested. The obtained information is transmitted to the unit placed at ground potential. The evaluation is carried out by comparing the amount of initial charges in the insulating material with that of charges accumulated at a certain time after application of a high voltage. When the ratio of the charges accumulated at time (t) to that of the initial charge is 1, it is assumed that there was no charge accumulation; thus, no deterioration of the insulating material is assumed. However, when the ratio is greater than 1, the insulating material is considered to have deteriorated. Using the evaluation system, we developed, we examined the deterioration of insulating materials used in coaxial cables by exposure to 1) γ-rays and 2) high-temperature conditions. From these two experiments using the developed system, the deterioration of insulating materials was found to have advanced substantially when the charge accumulation ratio exceeded approximately over 2.0.

We studied the trapping of positive and negative charges in the chemical structures of polymers under a high electric field using a space charge measurement system. Positive charges accumulated in low-density polyethylene (LDPE), whereas positive and negative charges accumulated in polyimide (Kapton) and also in ethylene tetrafluoroethylene (ETFE) subjected to electron beam irradiation. To determine the charge-trapping sites in the chemical structures, a quantum chemical calculation was carried out using Density Function Theory (DFT) with Gaussian 09. The relationship between the energy band and the isosurface of orbital electrons at various energy levels was obtained. A threedimensional (3D) electrostatic potential distribution map was obtained for positively and negatively charged polymers to determine the relationship between a trapping site and the charge accumulation center in the 3D potential distribution map. Positive and negative charges in Kapton and ETFE films are trapped in trapping sites in chemical structures and the positive charges in an LDPE film are trapped in physical defects.

Oil-paper compound insulation has been widely used in power transformers for quite a long time because of its good performance. The paper insulation degrades under the combined stresses of thermal, electrical and chemical stresses during routine operations, resulting in the reduction of its degree of polymerization (DP) and hence its mechanical and electrical strength. Space charges in a dielectric material have a close relation to its electrical performance. Therefore, in this work, the effect of paper-aged states (with different DP values) on the space charge behavior in oil-impregnated paper insulation is investigated, and the pulsed electro-acoustic (PEA) method is used for the space charge distribution measurement. In order to achieve this purpose, new oil-impregnated paper samples are thermally-accelerated aged for different time interval to obtain different DP values, and then the residual oil in each sample is removed, and the Kraft paper samples are dried in a vacuum dry oven. After that, all paper samples are impregnated with new oil, and PEA measurements are performed at room temperature. The experimental results show that, when the external dc voltage is applied on the oil-paper sample, homo-charge injection occurs for all samples. The samples with different aging states exhibit quite different space charge characteristics for both voltage-on and voltage-off conditions. When the aged states are worse, for voltage-on condition, more charges are induced at cathode and anode, as well as more space charges are accumulated in the bulk. For voltage-off condition, the space charge decay rate shows no obvious change for different aged samples.

Surface discharge on dielectric materials seriously restricts the performance of many electrical and electronic systems. Based on Pockels electro-optic effect, the surface discharge on polymeric insulating materials has been investigated under HVAC in Atmospheric Air. Different polymer materials such as polyimide (PI), polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF) films are employed. One single cycle of sinusoidal HVAC with peak value of 5 kV and duration time of 50ms is applied on a needle-plate electrode configuration and the applied voltage starts from the positive or negative half-cycle, respectively. During the development process of surface discharge on different materials, the dynamic observation of surface charge distribution is recorded in a cycle by a high speed camera. The experimental results show that there is significant voltage polarity effect observed, and the radius of negative charge distribution is smaller than that of positive charges. The positive charge density on PET and PI is lower than that on PVDF, which are closely related to the enhancement of electric field by permittivity and thickness of polymer films. Moreover, PI, PET and PVDF samples behave different surface charge distribution. Positive streamer channels on PI and PET are gradually growing into a snake-like pattern with voltage applying, and positive streamers on PVDF develop instantaneously and exhibit as a regular spoke-like pattern. The influence factors on different discharge patterns are discussed in the paper.

In our previous paper, we found an interesting packet-like charge behavior in low- density polyethylene (LDPE) under high dc electric field of more than 1 MV/cm. When such a high dc electric field was applied to LDPE film, a huge amount of positive packet-like charge of more than 100 C/m3 was injected into the bulk of the film and it moved towards the cathode side increasing its amount of charge. The movement of the packet-like charge gradually became slowly, and then it stopped in the bulk as it seems to be a stable state. Consequently, the electric field near the cathode was sometimes enhanced by up to more than twice the applied electric field. To analyze the feature of the positive packet-like charge behavior in LDPE, we carry out a simple numerical simulation based on the experimental results in the previous paper. The model is considered the principle of conservation of charge and the hypothesis that there are two different conductivity in front and rear of the packet-like charge in the sample. The hypothesis is based on the idea that the zone where is passed through by the packet-like charge has a higher conductivity than that in front of the packet-like charge because the charge traps are filled by passing of the packet-like charge. By considering such a simple model, we have a good agreement between the numerical simulation and the experimental results.

Space charge accumulation in low-density polyethylene film containing a small amount of MgO nanoparticles (LDPE/MgO nanocomposite film) subjected to an electric field greater than 100 kV/mm has been studied using an improved pulsed electroacoustic (PEA) system. No marked space charge accumulation was observed in LDPE/MgO nanocomposite films. To determine the mechanism of no space charge accumulation in the LDPE/MgO nanocomposite film, we compared electric potential wells produced by a permanent dipole moment such as that of carbonyl groups (C=0) and an induced dipole consisting of MgO nanoparticles (spherical dielectrics) under a high electric field to create a trapping site for electric charge carriers. The trapping depth created by the permanent dipole moment such as that of the carbonyl groups (C=0) of chemical defects is approximately 0.45 eV. However, the potential well induced by high-permittivity dielectric nanoparticles (MgO) is about 1.5 to 5.0 eV, which is much deeper than that induced by chemical defects. The suppression of space charge formation is explained using the potential well model consisting of a dipole induced by a high-permittivity dielectric nanoparticle. We explained the suppression mechanism of charge accumulation in the LDPE/MgO film that contains deep traps.

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 SiO2), 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

It has been known that the electrical breakdown of insulating materials is strongly affected by the formation of space charge in the bulk of the materials. Many researchers have attempted to study the relationship between the space charge and the breakdown; however, it has not been clarified yet. Although the pulsed electroacoustic (PEA) method has been widely used to observe space charge profiles, previous works have not shown clear evidence of the influence of the space charge on the breakdown. Therefore, we have developed a new PEA system with an interval of 0.5 ms to observe the space charge distribution continuously under the ultra-high electric field. Using this system, we observed the space charge dynamics in the low-density polyethylene (LDPE) at and around the breakdown. We also investigated the dependence of the applied electric field on space charge behavior. From the results, it is found that the injected charge packet moved faster and deeper under a relatively lower electric field rather than that under a higher electric field. Furthermore, we found that the maximum electric field in each specimen was almost the same when the breakdown happened in a specimen.

In this paper electrical properties of a novel linear low-density polyethylene synthesized with a catalyst, developed by our unique technique, were measured. It was found that this polyethylene had a higher volume resistivity, a higher breakdown strength and less spacer charge accumulation than conventional high-pressure low-density polyethylene and linear low-density polyethylene. We also measured electrical properties of blends of the new polyethylene and the conventional low-density polyethylene and found that the blends which contained up to 90 wt% of the low-density polyethylene had nearly the same value as the new polyethylene. The morphologies of the polyethylene were observed by using transmission electron microscope (TEM) and found that the blends kept the characteristics shown in the new polyethylene up to 90 wt% of the low-density polyethylene content. The relationship between morphology and electrical properties is discussed and comparison is made between the new polyethylene with those of the conventional low-density polyethylenes.

This paper reports the results of an investigation into the space charge formation and decay at different material interfaces. In particular, the influence of the interface between electrode and polymer or polymer and polymer on the space charge dynamics has been studied. Planar samples were subjected to high dc electric stresses for extended periods of time and space charge measurements taken using the pulsed electroacoustic (PEA) technique. It has been found that the types of interface between electrode and polymer play a significant role in determining the charge distribution in the insulation and that the interface between polymer and polymer acts as a potential barrier to electrons whilst allowing positive charge carriers through easily.

The correlation between charge distribution in an aged crosslinked polyethylene (XLPE) cable and the location of water trees has been studied. The space charge radial distributions at different angle in the insulating wall of a service-aged XLPE coaxial cable, induced by application of a DC stress, were measured using the pulsed electroacoustic method. Furthermore, a cross section of sliced insulating wall was observed with an optical microscope to compare with the radial space charge distribution. The cable under investigation was electrically aged in service at 6.6 kV AC for 25 years in wet conditions. Water trees were found at the position in which space charge was observed. On the other hand, no water tree was found at the position in which the space charge was not observed. Judging from these results, the space charge measurement seems to be useful for the diagnosis of water trees in aged cables.

A new analysis of conduction current distributed in dielectrics based on simultaneous measurements of thermally stimulated current (TSC) and time dependent space charge distribution is proposed. A new system pulsed electro-acoustic (PEA) method has been developed to enable simultaneous measurement of the TSC and the dynamic space charge and electric field distributions as a function of temperature within insulators. With the new system, the relationship between the TSC and the time dependent electric field distribution in electron beam (e-beam) irradiated PMMA has been investigated. From the time dependent electric field, the displacement current in dielectrics is obtained. The TSC is a typical external current which is represented as an addition of the displacement current and a conduction current in dielectrics. This paper makes it clear that the conduction current as a function of position is determined by the simultaneous measurement of the external current and the dynamic space charge distribution.

The principles of both pulsed electro acoustic (PEA) and pressure wave propagation (PWP) methods for measuring the space charge distributions in solid dielectrics are summarized. The relationship between the charge distribution in a specimen and voltage signal of the PEA method or the current signal of the PWP method are expressed in the time and frequency domains. Furthermore, the calibration method of the amount of accumulated charge density using deconvolution techniques is described for both methods. To compare these two methods, PMMA samples with and without space charge are measured using both methods. In addition, the electric field and electric potential distributions are calculated and discussed. The experimental results obtained using both methods are almost the same.

The pulsed electroacoustic method (PEA) has been applied to observe space charge formation under ac application (7 kV/sub pk/, 50, 0.1 and 0.001 Hz) in water-treed polyethylene samples in order to understand the degradation mechanism of water trees. A system with phase-resolving capability has been developed to measure the space charge distribution at any phase angle of the applied ac voltage. By comparing the observed charge distributions with theoretically predicted ones, it has been shown that the interfacial polarization due to the difference in conductivity between the treed and the regions without trees dominate the space charge behavior. It has become clear that the PEA method can be a powerful nondestructive method for evaluating water tree length.

It is well known that the existence and accumulation of space charge in insulation can be harmful to polymer power cable. Although there is much research done on space charge distribution in various samples, there are still some important problems left unsolved, such as the mechanism of formation and elimination of space charge in dielectrics. Because of its superiority, the pulsed electro-acoustic (PEA) measurement method is used widely in the measurement of space charge in various geometries of samples such as the multiple layer plate and cylindrical cables. The space charge in crosslinked polyethylene (XLPE) power cable under dc voltage and heat treatment is investigated by the PEA method in this paper. After heat treatment, the space charge, which previously formed in cable insulation under the applied voltage, disappears. If electrical stress is applied to the insulation again, space charge will appear once more. However, after the cable is heated and degassed in vacuum for a long time, no matter how long the dc voltage is applied to the cable, no more space charge will be formed in the cable. The mechanism of formation and elimination of space charge under the effect of electrical and thermal stress is discussed. >