Space Charge Accumulation Characteristics Research Articles

Study on space charge accumulation characteristics of silicone elastomer under DC voltage

AbstractThe electric field distortion caused by the accumulation of space charge in the insulating dielectric is easy to lead to accelerated ageing and even breakdown. In this paper, the space charge characteristics and the interfacial electric field change with time of silicone elastomer under different polarity DC voltages are studied. The results show that the homopolar charge injection is dominant in the silicone elastomer, and the electric field threshold is less than 4 kV/mm. The accumulation of homopolar charge weakens the interfacial electric field, resulting in the reduction of charge injection, and the interfacial electric field and spatial charge distribution gradually stabilise over time. In addition, the electric field at the interface does not decrease to the charge injection field threshold when it reaches stability. A time‐varying electric field model of the metal‐dielectric interface under a direct current field is derived and a calculation method for the time of charge accumulation to stabilise is proposed, based on the Schottky injection model and the relation between current density and volume charge density. The accuracy of the model is verified by comparing it with the experimental results of the stability time of silicone elastomer. This model is used to estimate the time when space charge accumulation reaches stability by means of the electric field threshold and the interface barrier, which can provide reference for the experimental measurement of space charge.

Characteristics of Space Charge Accumulation Under Unipolar Square Wave Voltage

Characteristics of Space Charge Accumulation Under Unipolar Square Wave Voltage

Study on space charge accumulation characteristics of 320 kV cross-linked polyethylene cable joints

High-Voltage Direct Current (HVDC) cable accessories are the key equipment to connect HVDC cables, and also the weak link in the cable system. In order to investigate the transport characteristics of space charge in cable joints, a two-dimensional axisymmetric cable joint model was established using the bipolar charge transport model, and its space charge and electric field distribution were analyzed through numerical simulation. Furthermore, the effects of the trap depth based on molecular chain displacement and temperature field on interface charge distribution of cable joint were compared with the basic model, respectively. The results show that the stress cone root and the top of the high-voltage shield are easy to accumulate space charges, which will lead to electric field distortion. The trap depth based on molecular chain displacement is larger than that of basic model at the insulation interface, which hinders the charge transport. The model without considering the effect of temperature field accumulates less charge, and the electric field and space charge at the stress cone root and the top of the high-voltage shield change gently with time. The above research results can provide a reference for the design and optimization of cable joints.

Analysis of Influence Factors on Space Charge Accumulation Characteristics of 320 kV XLPE Cable

Analysis of Influence Factors on Space Charge Accumulation Characteristics of 320 kV XLPE Cable

Investigation of the Space Charge Accumulation Characteristics of the Fluorinated Polymer under Electron Beam Irradiation using the Non-contact Type Electrode

Investigation of the Space Charge Accumulation Characteristics of the Fluorinated Polymer under Electron Beam Irradiation using the Non-contact Type Electrode

Influence of Gamma Irradiation and Water Aging on the Space Charge Characteristics of Epoxy Micro-Nano Composites.

Epoxy micro-nano composites are well-known to exhibit enhanced electrical, mechanical as well as thermal properties compared to base epoxy resin. Yet, a clear understanding need to be achieved on the long-term aging performance of the epoxy micro-nano composites. The present review article is a comprehensive study on the impact of gamma irradiation and water aging on the space charge characteristics of epoxy micro-nano composites that are applicable as insulant in high-voltage power apparatus. Ion-trapping nanoparticles, which possess good oxidation resistance and high ion trapping ability, are being chosen as nanofillers along with silica micro fillers in epoxy micro-nano composite material for improving the reliability of electrical insulation structures. The epoxy micro-nano composite specimens were subjected to gamma irradiation (4 kGy and 8 kGy) and water aging (under room temperature and at 90 °C), to analyze the effect of aging on space charge accumulation and charge decay characteristics. The mean magnitude of accumulated space charge density of epoxy micro-nano composites tends to increase with an increase in gamma irradiation dose as well as an increment in water diffusion coefficient. The mean lifetime of the space charge decay during depoling has significantly reduced after gamma irradiation and is converse with water aged specimen. Voltage polarity reversal studies have indicated that a part of homo-charge injected from electrodes remained as hetero-charge just after polarity reversal and could result in the distortion of electric field thereby increasing the electric field enhancement factor.

Space Charge Accumulation Characteristics in HVDC Cable under Temperature Gradient

One of the main issues that affect the development of high-voltage direct-current (HVDC) cable insulation is the accumulation of space charge. The load operation of an HVDC cable leads to the formation of a radially distributed temperature gradient (TG) across the insulation. In this study, the space charge accumulation in a cross-linked polyethylene (XLPE) cable is measured under a DC electric field and TG using the pulsed electro-acoustic (PEA) method, and the effect of the TG on the space charge behavior is investigated. In addition, the bipolar charge transport (BCT) model and the conductivity model based on an improved cylindrical geometry are used to simulate the charge behavior in the HVDC XLPE cable under TG, and the experimental and simulated results are compared. The results show that the higher temperature of the cable conductor promotes the accumulation of homocharge near the side of high temperature. Additionally, with the increase of the TG, not only does more heterocharge accumulates adjacent to the side of low temperature, but more space charge also extends into the bulk of the cable insulation. More attention should be paid to the conductor shield layer and the insulation shield layer in HVDC cables. Moreover, the BCT model can more accurately describe the experimental results than the conductivity model.

Space charge behavior of polyimide at cryogenic temperatures

In this paper, the space charge behavior of polyimide at cryogenic temperatures is studied. The pulsed electro-acoustic (PEA) and thermally stimulated current (TSC) methods are exploited to evaluate the space charge distribution, quantification of space charge accumulation and trap characteristics of polyimide. The results show that the change of space charge accumulation at 273 to 123 K is divided into three temperature regimes. At 273-223 K, the space charge accumulation decreases significantly with decreasing temperature, which is mainly due to the suppression of charge generation and migration. At 223-173 K, the negative space charge gradually increases with decreasing temperature and dominates the space charge distribution. Analysis shows that this is due to the significant decrease of trap level in the sample, which improves the carrier mobility and promotes the electron injection and migration. According to quantum chemical calculation and dielectric spectroscopy measurement, the rotational displacement motion of water molecules related to γ relaxation in polyimide produces more shallow electron traps, which may be the main reason for the decrease of trap level. When the temperature is below 173 K, the space charge accumulation decreases with decreasing temperature. This study provides guidance for low temperature insulation design.

Effect of TiO2 nanoparticles on DC breakdown performance of transformer oil-impregnated pressboard

Transformer oil-based nanofluid-impregnated pressboard (NIP) with TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles has been previously shown to exhibit substantially higher AC breakdown strength than that of pure oil-impregnated pressboard (OIP). In this study, OIP and NIP with TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles were prepared and experiments on DC breakdown strength of were performed. It was found that NIP possesses higher resistance to DC breakdown strength than that of OIP. To reveal the working mechanism, a pulsed electro acoustic (PEA) device was used to measure the space charge accumulation and dissipation characteristics in OIP and NIP. The results show that the density of deep level traps in NIP is visibly reduced owing to the addition of TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles and homopolar space charge accumulation on both sides of NIP is suppressed. Moreover, the charges injected from electrodes into NIP under DC voltage is also restrained owing to the increase of the Schottky potential barrier. Thus, the DC breakdown performance of NIP is considerably improved.

Effect of BN nanosheet concentration on space charge characteristics in XLPE/BNNS nanocomposites

Space charge accumulation in insulation material is one of the key factors that threaten the safe operation of high voltage direct current (HVDC) cable. Nanocomposites have been considered as the potential material to solve the problem of charge accumulation in HVDC cable. In the work, the effect of boron nitride nanosheets (BNNSs) concentration on space charge accumulation characteristics in XLPE/BNNS nanocomposite have been explored. The experimental results indicate that space charge in nanocomposite can be effectively suppressed when a small amount of BN nanosheet (<0.5 wt%) is doped into the matrix. It is mainly due to the introduction of deep traps at the interface between electrode and nanocomposite, and the ‘charge barrier effect’ has been formed to inhibit charge injection. The trap level of nanocomposite is 0.95 eV and the trap number is 2.43 × 1020 m−3 for the concentration of 0.1 wt%. While, the charge inhibition effect in the nanocomposite becomes weaken with the increase of the BNNS concentration. PEA experimental results show that the accumulated charges increase when the concentration is 1 wt%, the charge amount in the composite reaches 1.08 × 10−5 C, and the local electric field distortion rate is 9.5%. For high concentration (>2 wt%∼3 wt%), the calculated results indicate that more relatively shallow traps are introduced in the composite, resulting in few accumulated charges. The trap level is 0.62 eV and the trapped charge density is 5.76 × 1020 m−3 at 5 wt%, which will enhance the charge hopping probability between the adjacent trap centers.

Investigation on dielectric and mechanical properties of epoxy reinforced with glass fiber and nano-silica composites

The composite materials of different filler concentration were fabricated by reinforcing the glass fiber and silica nanoparticles into epoxy to understand the variation in surface wettability, water droplet initiated discharge, dielectric parameters, surface charge, space charge and mechanical properties. Nanofiller inclusion has shown the enhanced surface properties viz. water droplet initiated corona inception voltage (CIV) and hydrophobicity. CIV is high under negative DC voltage followed with positive DC and AC voltage. It is realized that the dielectric constant is increased with the addition of nano-silica. The surface potential has decayed exponentially irrespective of the applied voltage polarity and the type of the sample, whereas, the 3 wt% sample showed the highest decay rate for an applied voltage. Silica filled composites have shown better space charge accumulation and decay characteristics initially and then deteriorated rapidly when the filler concentration is increased. The optimised filler concentration is found considering the minimal space chare accumulation, decay rate and the optimised electric field for the space charge analysis. Further, the optimised field conditions were devised for the optimum filler concentration for the prolonged life span and reliability of the insulation material. The mechanical storage modulus has increased with the addition of nanofiller. The plasma temperature calculated from the LIBS spectra has shown a direct correlation with the surface hardness of the material.

Effect of Doping Microcapsules on Typical Electrical Performances of Self-Healing Polyethylene Insulating Composite

Polyethylene cables, as important transmission equipment of modern power grid, would inevitably be slightly damaged, which seriously threatens the safety of the power supply. This paper has pioneered the preparation and typical performances of a self-healing polyethylene insulating composite. The self-healing performance to structural damage was verified by tests of electrical and mechanical damage. The effect mechanism of doping microcapsules on the electrical performance of polyethylene was emphatically analyzed. The results show that in appropriate conditions (such as 60 °C/30 min), the composite can not only repair the electrical tree and scratches, but also restore the insulation strength of damaged area. The effect of doping microcapsules on the electrical performances of polyethylene, such as breakdown strength, volumetric resistivity, dielectric properties, and space charge characteristics, are mainly related to impurity and the interface of microcapsule. Polarization and ionization of impurities can reduce the electrical performance of polyethylene. The interface not only improves the microstructure of polyethylene (such as how the heterogeneous nucleation effect increases the number of crystal regions, and the anchoring effect enhances the stability of amorphous regions), but also increases the charge traps. Moreover, the microstructure and charge trap can affect the characteristics of carrier transport, material polarization, and space charge accumulation, thus improving the electrical performance of polyethylene. In addition, the important electrical performance of the composite can meet the basic application requirements of polyethylene insulating material, which has good application prospects.

Acetylated SEBS Enhanced DC Insulation Performances of Polyethylene.

Acetophenone can significantly improve the dielectric properties of polyethylene (PE) insulation materials. However, it easily migrates from the PE due to its poor compatibility with the material, which limits its application. In this paper, the functional units of acetophenone were modified in polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) by an acetylation reaction, and SEBS was used as the carrier to inhibit the migration of acetophenone. The number of functional units in the acetylated SEBS (Ac-SEBS) was measured by 1H NMR and the effect of the acetylation degree of SEBS on its compatibility with PE was studied. Meanwhile, the effects of Ac-SEBS on PE’s direct current (DC) breakdown strength and space charge accumulation characteristics were investigated. It is demonstrated that Ac-SEBS can significantly improve the field strength of the DC breakdown and inhibit the accumulation of space charge in the PE matrix. This work provides a new approach for the application of aromatic compounds as voltage stabilizers in DC insulation cable materials.

Space charge accumulation characteristics in fluorinated insulating material under dc high stress

AbstractElectron beam irradiated fluorinated materials, which are used for an optical solar reflector of spacecraft, have been investigated using a space charge measurement system under dc high stress. It was found that a large amount of space charge accumulated in the electron beam irradiated ethylene‐tetrafluoroethylene and fluorinated ethylene‐propylene copolymer under dc high stress, while it was not observed in nonirradiated them. In this report, a dependence of relaxation time after the irradiation on the space charge accumulation characteristics was also studied.

Direct Imaging of Space-Charge Accumulation and Work Function Characteristics of Functional Organic Interfaces.

The tailoring of organic systems is crucial to further extend the efficiency of charge transfer mechanisms and represents a cornerstone for molecular device technologies. However, this demands control of electrical properties and understanding of the physics behind organic interfaces. Here, a quantitative spatial overview of work function characteristics for phthalocyanine architectures on Au substrates is provided via kelvin probe microscopy. While macroscopic investigations are very informative, the current approach offers a nanoscale spatial rendering of electrical characteristics which is not possible to attain via conventional techniques. Interface dipole is observed due to the formation of charge accumulation layers in thin F16 CuPc, F16 CoPc, and MnPc films, displaying work functions of 5.7, 6.1, and 5.0 eV, respectively. The imaging and quantification of interface locations with significant surface potential and work function response (<0.33 eV for material thickness <1 nm) show also a dependency on the crystalline state of the organic systems. The work function mapping suggests space-charge carrier regions of about 4 nm at the organic interface. This reveals rich spatial electric parameters and ambipolar characteristics that may drive electrical performance at device scales, opening a realm of possibilities toward the development of functional organic architectures and its applications.

Space Charge Accumulation Characteristics in Fluorinated Insulating Material under DC High Stress

Electron beam irradiated fluorinated materials, which are used for an OSR (Optical Solar Reflector) of spacecraft have been investigated using a space charge measurement system under DC high stress. It was found that a large amount of space charge accumulated in the electron beam irradiated ethylene-tetrafluoroethylene (ETFE) and fluorinated ethylene-propylene copolymer (FEP) under DC high stress, while it was not observed in non-irradiated them. In this report, a dependence of relaxation time after the irradiation on the space charge accumulation characteristics was also studied.

Effect of thermal stress on the space charge distribution of 160 kV HVDC cable insulation material

The injection and accumulation of space charge in the bulk of XLPE insulation will be intensified due to the ageing of HVDC cable insulation which will affect the normal operation of the HVDC cable. In this paper, the effects of thermal stress of different endurance time and temperature on the space charge distribution of HVDC cable were studied. The samples used in the tests were all slices of 160 kV DC cable insulation and the thermal stress temperatures were 90 and 135 °C, which represented the low temperature thermal stress and high temperature stress, respectively. The Pulsed Electro-Acoustic (PEA) method was used to measure the space charge accumulation and decay characteristics of the samples. And then, the electron trap properties of the test samples were analyzed based on the PEA space charge decay model. Meanwhile, in order to further understand the influence of thermal stress on the physicochemical property of the samples, Fourier Transform Infrared Spectrum (FTIR) and Differential Scanning Calorimetry (DSC) tests were conducted in this paper. The results showed that the 90 °C thermal treating could help to improve the crystalline morphologies of the XLPE at the early stage which led to the decrease of electro traps and space charge density. However, for a much longer thermal stress, the total amount of space charge would trend to increase with the gradually degradation of the XLPE caused by long term thermal stress. Besides, the high temperature thermal stress of 135 °C caused the rapid degradation of the XLPE molecular structure, reducing the crystallinity, creating more deep traps in the insulation and resulting in the accumulation of space charge. With more deep electron traps, the de-trapping process became much more difficult and slower.

Effect of Conductive Inorganic Fillers on Space Charge Accumulation Characteristics in Cross-linked Polyethylene

We have observed space charge profiles in cross-linked polyethylene (XLPE) under dc high electric field using the PEA (pulsed electro-acoustic) system to study the relationship between space charge behavior and dielectric breakdown. In our previous research work, we have found that a large amount of, so called, packet-like charge generates in low density polyethylene (LDPE) under high dc electric field of more than 100 kV/mm. The packet-like charge enhances the electric field locally in bulk of the sample, and then finally it leads a breakdown. On the other hand, a new type of XLPE which was made through adding conductive inorganic fillers, shows a good dc dielectric breakdown characteristic and high volume resistivity under dc stress. In this report, we tried to observe the space charge behavior under high dc electric field in this material. From the results, it is found that the charge injection is effectively suppressed by adding only a small amount of conductive inorganic fillers to XLPE.

低密度ポリエチレンの電気特性評価に対する検討

We investigated the electrical conduction and space charge accumulation of three kinds of LDPE. Although their density and MFR are almost the same, they show different conduction and space charge accumulation characteristics. In order to understand the electrical characteristics of LDPE deeply, we should use LDPE made by the same process and condition.

Interfacial properties of XLPE/EPDM laminates

Interfacial properties such as space charge accumulation and breakdown characteristics in crosslinked polyethylene (XLPE)/ethylene propylene diene terpolymer (EPDM) laminates were investigated. Homocharge is observed in EPDM containing 1,4-hexadiene while heterocharge is observed in EPDM containing 5-ethylene-2-norbornene. Interfacial charge develops when the EPDM is laminated with XLPE. The polarity of this interfacial charge reverses at less than a few tens of hours heat treatment at 80/spl deg/C dc breakdown voltage shows a sequential change of an increase, a decrease and a slight increase as a function of heat treatment time, which holds true for both interfacial and volume breakdown voltages. A maximum breakdown voltage is observed at 20 to 24 h heat treatment. After long heat treatment, silicone grease used in the interface shows lower interfacial breakdown voltage than silicone oil for the dc case, which was attributed to the additives in the grease and the molecular weight of silicone molecules in oil and grease. Details of the results are given and their origins discussed.