AC Dielectric Breakdown Research Articles

Experimental investigation of zinc ferrite/insulation oil nanofluid natural convection heat transfer, AC dielectric breakdown voltage, and thermophysical properties

Improving the thermal and dielectric properties of insulation oil (INO) with nanoadditives is an important challenge, and achieving dispersion stability in these nanofluids is quite challenging, necessitating further investigation. The main goal of this study is the synthesis and use of the hydrophobicity of zinc ferrite (ZnFe2O4) nanoparticles, which can improve both the thermal and dielectric properties of the INO. This oil is made from distillate (petroleum), including severely hydrotreated light naphthenic oil (75–85%) and severely hydrotreated light paraffinic oil (15–25%). A comprehensive investigation was carried out, involving the creation of nanofluids with ZnFe2O4 nanoparticles at various concentrations, and employing various characterization methods such as X-ray diffraction (XRD), Fourier-transform infrared (FTIR), scanning electron microscopy, energy dispersive X-ray (EDX), zeta potential analysis, and dynamic light scattering (DLS). The KD2 Pro thermal analyzer was used to investigate the thermal characteristics, including the thermal conductivity coefficient (TCC) and volumetric heat capacity (VHC). Under free convection conditions, the free convection heat transfer coefficient (FCHTC) and Nusselt numbers (Nu) were evaluated, revealing enhancements ranging from 14.15 to 11.7%. Furthermore, the most significant improvement observed in the AC Breakdown voltage (BDV) for nanofluids containing 0.1 wt% of ZnFe2O4 amounted to 17.3%. The most significant finding of this study is the improvement in the heat transfer performance, AC BDV, and stability of the nanofluids.

Investigating the Impact of Hardness on Dielectric Breakdown Characteristics of Polyurethane.

Polymeric materials play a vital role in high-voltage insulation, but their insulating properties can deteriorate over time, leading to insulation failures. The presence of voids resulting from manufacturing defects or external stresses can create a highly divergent field, further contributing to this issue. However, certain polymers, such as polyurethane (PU), possess self-healing properties that enable them to repair these voids and restore a uniform electric field distribution, thereby ensuring the reliability of the insulation. Surprisingly, the potential of PU as an insulating material in high-voltage applications remains unexplored. However, the self-healing capability of PU decreases with an increase in the hardness of the material. Therefore, in this study, the dielectric breakdown properties of PU with different levels of hardness, rated on the Shore scale as 40° (soft), 70° (medium), and 90° (hard), were investigated. The AC and DC dielectric breakdown characteristics of these PU variants and dielectric spectra were examined. Additionally, the study explores the relationship between the dielectric properties and the hardness of the material. Our findings revealed that the dielectric breakdown strength of PU increases as the material's hardness is increased under both AC and DC electric stress. However, this may come at the cost of reduced self-healing capabilities of PU. Therefore, there is a need to balance the hardness of the material with its ability to recover from breakdown events. The findings from this study can be useful for researchers and engineers, as they offer valuable insights into the dielectric properties of PU at various hardness levels.

Intrinsic AC Dielectric Breakdown Strength of Polyimide Films at the Extreme: New Breakthrough Insights on Thickness Dependence

AbstractTo date, the AC dielectric breakdown strength of polyimide (PI) films, as for most polymers, is understood to follow a thickness dependency with a measured power law exponent, n ≈ 0.5. However, this work experimentally demonstrates that the AC dielectric strength of PI films is quasi‐thickness independent. Evidence is presented showing that the thickness dependency described in the literature can be explained by an extrinsic failure mode, driven by partial discharges occurring at the dielectric‐oil‐electrode triple point. Triple points can be avoided by electrode encapsulation, which subsequently recovers a purely intrinsic failure mode for PI films over a large thickness range. Consequently, the AC dielectric strength of thick PI films is intrinsic and quasi‐thickness independent, at least for film thickness up to 60 µm. For the first time, a “theoretical” AC breakdown field for PI films is reported as ≈520 Vrms µm−1. Finally, the highest experimental breakdown field values are obtained here with 505 Vrms µm−1 and 705 Vµm−1 under AC and DC fields, respectively.

Experimental determination of electrical and thermo-physical characteristics of dielectric nanofluids based on volume fraction change

Dielectric insulating fluids perform critical tasks such as electrical insulation and cooling functions in power system equipment. Improving the thermal properties of insulating fluids extends the service life of power equipment, while improving their dielectric properties ensures a reliable and safe electricity supply. Therefore, studies on enhancing the thermal and dielectric qualities of dielectric fluids using nanoparticles have become more popular in recent years. In this study, the dielectric and thermo-physical properties of mineral oil-based SiO2 nanoparticle suspensions, namely nanofluids, have been investigated. An approximately 25.6% enhancement in AC breakdown voltage level has been obtained at a 0.05% critical volume fraction. It has been noted that the level of the AC breakdown voltage decreases when the critical volume fraction is exceeded. The thermal conductivity of the prepared nanofluid has changed logarithmically in the positive direction according to the rising number of nanoparticles per unit volume. Thermal conductivity has increased by around 8.55% for the critical volume fraction value, whereas thermal diffusivity has increased by approximately 22%. Similarly, when the number of particles in the nanofluid rises, the viscosity increases nonlinearly. The viscosity increase, which is undesirable for heat transfer, has been determined to be around 10.64% for the crucial volume fraction. These findings indicate that dielectric nanofluids hold significant potential for the future. The SEM analysis, on the other hand, explains the difficulties of assuring the long-term stability of nanofluids in the volume fraction with the highest AC dielectric breakdown voltage.

Convective heat transfer behavior and AC dielectric breakdown voltage of electric power transformer oil with magnetic colloidal nano-fluid: An experimental study

This research reports on an experimental investigation into the alternating insulation breakdown voltage (AC) and convective heat transfer behavior of nano-oil for application in electrical transformers. The base fluid of the examined nano-oil is nitro libra type transformer oil, one of the common mineral oils used in transformers. It contains iron oxide magnetic colloidal nanoparticles. Upon fabrication of the experimental apparatus in the lab, an experimental study on convection heat transfer is performed under laminar flow conditions and with a continuous heat flux applied to the wall. BA100 breakdown voltage measurement instrument based on the IEC 60156 standard is also used for alternating breakdown voltage testing. The current findings from the experimental investigation of convective heat transfer are compared with and verified by the experimental results available in the literature. The experimental results demonstrate that the convective heat transfer coefficient of the iron oxide magnetic nanoparticle-prepared nano-oil is on average 4.51% higher than that of base oil. These particles have an average size of 23 nm and a volume concentration of 0.1%. Additionally, compared to base oil, nano-oil with a volume concentration of 0.1% has a 23.8% higher dielectric breakdown voltage.

친환경 초고압 GIS Spacer 용, 에폭시/마이크로실리카/마이크로알루미나 혼합 복합체의 교류 절연파괴특성에 관한연구

In this paper, research was conducted to develop a new insulating material used for ultra-voltage GIS spacer under carbon-neutral and eco-friendly insulating gas. In order to take advantage of the advantages and disadvantages of micro silica in epoxy resin and the advantages and disadvantages of micro alumina, micro silica: micro alumina = 1:9, 3:7, 5:5, 7:3, 9:1 mixing ratio samples were prepared. micro silica has a lot of O-H groups in its particles, and there is no problem under eco-friendly insulating gas. Micro alumina has no O-H on the surface. However, it was used because of its excellent thermal conductivity properties. AC dielectric breakdown strength were evaluated by preparing samples with an increased packing content of micro silica and micro alumina. Furthermore, research was conducted to develop a new insulating material to be used for GIS Spacer under eco-friendly insulating gas.

Volume effect on AC dielectric breakdown strength of ester oil compared with that of mineral oil

Volume effect on AC dielectric breakdown strength of ester oil compared with that of mineral oil

Arc Ablation Resistance and Dielectric Strength Properties of PTFE/BN Composites

The substantial improvements in transmission voltage, which have been adopted to meet fast-growing energy demands, require more reliable power equipment and higher-quality insulating materials. The polytetrafluoroethylene (PTFE) nozzle, as the key part of a high-voltage circuit breaker, is often subjected to arc ablation and breakdown phenomena. Thus, it is very urgent to develop nozzles with better performance. In this study, PTFE/boron nitride (BN) composites were prepared. The relationships among the BN filler loading, thermal transition properties, spectral reflectance properties, arc ablation resistance, and AC dielectric breakdown performances, as well as their corresponding mechanisms, were studied. Experimental results show that the thermal conductivity and thermal diffusivity of PTFE/BN composites increased monotonously with BN loading, and that both parameters were improved by 41% and 44%, respectively, for 11 wt % composites compared with pure PTFE. Moreover, PTFE/BN composites had higher light reflectance in the wavelength range from 320 to 2500 nm. The PTFE/BN composites presented better arc ablation resistance performance with increased BN loading, which was improved by 88.5%. It is thought that the increased thermal conductivity, thermal diffusivity, the strong light reflectance, and surface sediment after arc ablation contribute to the improvement in arc ablation resistance performance. The AC breakdown strength of PTFE/BN composites was enhanced by 30.93%, attributed to the good heat dissipation properties introduced by the BN fillers. Thus, filling BN into the PTFE matrix would be helpful to solve the equipment issue that comes from the improvement in transmission voltage.

Effect of Temperature on AC Dielectric‐Breakdown Characteristics of Vegetable‐Based Electrical Insulating Oil Derived from Rice Oil

This paper reports the AC dielectric‐breakdown characteristics of a rice‐oil‐based electrical insulating oil as a function of oil temperature as well as the influence of thermal degradation on its performance (kinematic viscosity, AC dielectric breakdown, moisture amount, total acid number, and pour point). We manufactured rice ester oil using the ester‐exchange reaction. The results demonstrated the following. (i) The kinematic viscosity of the rice ester oil was lower than that of the rice and mineral oils. (ii) The AC breakdown strength of the rice ester oil was higher than that of the mineral oil. The AC breakdown strength of both insulating oils increased with the increase in the oil temperature. (iii) The moisture content of the rice ester oil was larger than that of the mineral oil. (iv) The total acid numbers of the rice ester and mineral oils were almost the same. (v) The pour point of the rice ester oil was higher than that of the mineral oil. In addition, the rice ester oil exhibited high resistance to heat stress compared with the mineral oil, but the former was unsuitable for use in cold climates. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Ameliorated Dielectric Performances of UV-Initiated Auxiliary Crosslinking Polyethylene

In photon-initiated crosslinking reactions of polyethylene molecules, the auxiliary crosslinkers in form of either monomer or homopolymer will cause bridging connections between polymeric molecules by transforming the irradiated photon energy to chemical energy under the assistance of photon-initiators, which can improve photon-initiation quantum efficiency and crosslinking uniformity. In the present study, the auxiliary crosslinkers of TAIC, TAC and TMPTA combining the macromolecular photon-initiator of BPL are employed into the ultraviolet (UV)-initiation technology to develop high-level crosslinked polyethylene (XLPE) insulation materials, whilst elucidating the structural and electrical mechanisms of the dielectric amelioration deriving from auxiliary crosslinking schemes. The specified photosensitive auxiliary crosslinkers can chemically bridge polyethylene molecules in the UV-initiated polyethylene crosslinking process, which can effectively promote polyethylene crosslinking degree but will slightly abate polyethylene crystallinity. Whereas, the orientation polarization and relaxation of molecular electric-dipoles on auxiliary crosslinkers cause additional dielectric permittivity and loss respectively, which will probably reduce insulation performances of XLPE. By contrast to XLPE benchmark, especially for grafting auxiliary crosslinker TAIC with the multiple-coupling carbonyl groups in a ring-conjugation, the preferable deep charge-traps can be introduced into polyethylene matrix to effectively improve electrical conductance and AC dielectric breakdown strength. This study provides experimental basis for developing the photon-initiated XLPE insulation materials with advanced dielectric performances required for manufacturing high-voltage grade cables.

Effect of Different Types of Fullerene Addition on AC Dielectric Breakdown Strength of Epoxy Resin

This research intends to investigate the applicability of fullerene as an electrically insulating filler. So far, the authors reported that the addition of a very small amount of fullerene C60 to epoxy resin (EP) improves the dielectric breakdown strength (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> ) by about 30%. This report presents the study on the effect of four different types of fullerenes as fillers added to EP on the improvement of E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> . Fullerenes used are mixtures of C60 and higher order one C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> with a different mixture rate, and the addition effect of sublimation-purified fullerene on E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> is also investigated. Experimental results reveal that samples added with sublimated fullerenes exhibit larger E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> than that of samples without sublimation. The sublimation-purified sample is also found to give almost no difference in E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> by the type or proportion of the added fullerenes C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> . An attempt is also made to discuss the mechanism of the improvement effect on E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> of fullerene by evaluating the electronic state of epoxies with different fullerene fillers and curing agent using quantum chemical calculation. As a result, it is shown that the introduction of C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">70</sub> into the EP considering the curing agent introduces electron traps of 0.64 and 0.72 eV, respectively. It is interpreted that the introduced electron traps suppress the electron avalanche, and consequently improves the breakdown strength.

Enhancement in electrical and thermal performance of high‐temperature vulcanized silicone rubber composites for outdoor insulating applications

AbstractHigh‐temperature vulcanized silicone rubber composites are highly desirable as outdoor insulating materials due to their immense thermal and electrical performance. The aim of this work is to study the role of co‐combined fillers (modified fumed silica [MFS], titanium dioxide [TiO2], with graphene [G]) on electrical and thermal properties of silicone rubber (S) composites. The dielectric response of S/MFS_10 phr and S/TiO2_20 composites tailored with 2 phr G was characterized by broadband dielectric spectroscopy. The hybrid filler/composites were found to show higher thermal stability when 2 phr G was added. In addition, a low quantity of G filler was found to slightly increase the AC dielectric breakdown strength of the S/MFS_10 and S/TiO2_20, where an improvement of 3 and 5% was found, respectively. Several steps were observed in the thermal decomposition of the S rubber composites by thermogravimetric analysis‐Fourier‐transform infrared spectroscopy. Our findings revealed great potentials for fabricating hybrid‐filler/silicone rubber composites with enhanced electrical and thermal properties for outdoor insulating applications.

Statistical analysis of AC dielectric breakdown in transformer oil-based magnetic nanofluids

Insulating nanofluids often exhibit better insulating properties than their base liquids. In particular, dielectric breakdown performance of insulating liquids may be remarkably enhanced by the presence of nanoparticles. The purpose of this paper is to demonstrate experimental evidence of the missing enhancing effect of the magnetic nanoparticles dispersed in transformer oil and to find potential reasons for the unimproved AC dielectric breakdown. The research is conducted on a long-term stable magnetic nanofluid with three different volume fractions of iron oxide nanoparticles coated with oleic acid. The AC dielectric breakdown voltage is investigated at various temperatures and statistically treated. Temperature-dependent viscosity, dissipation factor, and AC electric current are presented as supporting experimental results. In searching for the reason of the unimproved dielectric breakdown, we focus on the nanoparticle interface and consider the limited ability of the modified nanoparticles to act as charge trapping centers under the AC dynamic conditions.

노후 IV 전선의 절연파괴시험에 따른 통계적 수명 추정

In this study, the dielectric breakdown test was performed on the aged PVC insulated wires and the statistical life was estimated using the log-normal distribution probability. The sample is a 450 / 750V single-core PVC insulated wire collected from the inspection field. The AC dielectric breakdown test is conducted for three life groups of 0, 19, and 34 years to verify the change in the electrical insulation performance. The failure criterion assumes 50 % of the minimum design dielectric strength of IEC 60216-1, and the lifetime distribution is based on the lognormal distribution. The lifetime-dielectric breakdown voltage relation equation was derived from the linear fitting function of the percentile B50 of each life group. As a result, the breakdown voltage distribution by life group showed that the insulation strength of the IV wire decreased as the service life increased. As a result, three aging groups have shown that the insulation resistance performance of PVC insulators on IV wires decreases with longer service periods. And the life expectancy of PVC insulators of the IV wires according to the failure judgment criteria (50 ∼ 90 %) and failure rate (1 % and 50 %) is calculated from the relationship equation. As a result, the failure criteria and high failure rates confirm that the failure life is short.

Performance improvement of EPDM and EPDM/Silicone rubber composites using modified fumed silica, titanium dioxide and graphene additives

In this work, a polymeric composite was prepared from ethylene propylene diene monomer (EPDM) and silicone rubber (S) with additives of modified fumed silica (MFS), titanium dioxide (TiO2) and graphene. The dielectric and thermal performances of the EPDM-based composites were studied. An increase in the dielectric constant and AC dielectric breakdown strength was observed for the EPDM rubber composites containing MFS, TiO2, and graphene additives. In addition, the incorporation of the additives resulted7in a significant increase in the thermal stability (~30–50 °C) and thermal conductivity (~7–35%) of the composites. The combination of these various improvements gives suitable performance advantage to the polymeric composite for use in insulating applications.

Streamer evolution arrest governed amplified AC breakdown strength of graphene and CNT colloids

The present paper explores the concept of improving the AC dielectric breakdown strength of insulating mineral oils by the addition of graphene or carbon nanotubes (CNTs) to form stable dispersions. Experimental observations of graphene and CNT nano-oils show that not only improved average breakdown voltage, but also significantly improved reliability and survival probabilities of the oils under AC high voltage stressing is achieved. Improvement of the tune of ∼70–80% in the AC breakdown voltage of the oils has been obtained. The study examines the reliability of such nano-colloids using a two-parameter Weibull distribution and the oils show greatly augmented electric field bearing capacity. The fundamental mechanism responsible for such observed outcomes is reasoned to be delayed streamer development and reduced streamer growth rates due to effective electron scavenging. A mathematical model based on the principles of electron scavenging is proposed to quantify the amount of electrons scavenged by the nanostructures.

Development of industrial scale PVC nanocomposites with comprehensive enhancement in dielectric properties

This study aims to develop large-scale polyvinyl chloride (PVC) nanocomposites for industrial application with power cables. To achieve this goal, PVC/silicon dioxide and PVC/titanium dioxide nanocomposites were fabricated with two different loadings of nanoparticles: 0.3 and 0.6 wt.%, in the presence of a suitable coupling agent that was used to reduce the agglomeration of nanoparticles and enhance the compatibility with polymer matrix. The coupling agent used in this study was the amino silane, and the process followed in the nanocomposites preparation was the melt blending method. The dielectric properties of these synthesised nanocomposites were studied by measuring the AC dielectric breakdown strength under the uniform field, then compared with the simulation results. The relative permittivity (ɛr), loss tangent (tan δ), and DC electrical conductivity (σ) were also measured under frequencies ranging from 20 Hz to 1 MHz. In addition, the internal discharge measurements are performed using the traditional needle-plane configuration with the help of phase-resolved partial discharge (PD) analyser. This technique is used to analyse the PDs activity with respect to the phase angle of the applied voltage. It was found that the dielectric breakdown strength and PD resistance of the prepared samples are increased higher than that of the neat PVC; however, the ɛr, tan δ, and σ at 50 Hz are decreased.

Investigation of dielectric breakdown in silica-epoxy nanocomposites using designed interfaces

Adding nano-sized fillers to epoxy has proven to be an effective method for improving dielectric breakdown strength (DBS). Evidence suggests that dispersion state, as well as chemistry at the filler-matrix interface can play a crucial role in property enhancement. Herein we investigate the contribution of both filler dispersion and surface chemistry on the AC dielectric breakdown strength of silica-epoxy nanocomposites. Ligand engineering was used to synthesize bimodal ligands onto 15nm silica nanoparticles consisting of long epoxy compatible, poly(glycidyl methacrylate) (PGMA) chains, and short, π-conjugated, electroactive surface ligands. Surface initiated RAFT polymerization was used to synthesize multiple graft densities of PGMA chains, ultimately controlling the dispersion of the filler. Thiophene, anthracene, and terthiophene were employed as π-conjugated surface ligands that act as electron traps to mitigate avalanche breakdown. Investigation of the synthesized multifunctional nanoparticles was effective in defining the maximum particle spacing or free space length (Lf) that still leads to property enhancement, as well as giving insight into the effects of varying the electronic nature of the molecules at the interface on breakdown strength. Optimization of the investigated variables was shown to increase the AC dielectric breakdown strength of epoxy composites as much as 34% with only 2wt% silica loading.

Dielectric breakdown strength of magnetic nanofluid based on insulation oil after impulse test

In this study, the dielectric breakdown strength of magnetic nanofluids based on transformer mineral oil for use in power systems is reviewed. Nano oil samples are obtained from dispersion of the magnetic nanofluid within uninhibited transformer mineral oil NYTRO LIBRA as the base fluid. AC dielectric breakdown voltage measurement was carried out according to IEC 60156 standard and the lightning impulse breakdown voltage was obtained by using the sphere–sphere electrodes in an experimental setup for nano oil in volume concentration of 0.1–0.6%. Results indicate improved AC and lightning impulse breakdown voltage of nano oil compared to the base oil. AC test was performed again after applying impulse current and result showed that nano oil unlike the base oil retains its dielectric properties. Increase the dielectric strength of the nano oil is mainly due to dielectric and magnetic properties of Fe3O4nanoparticles that act as free electrons snapper, and reduce the rate of free electrons in the ionization process.

Comparison Between the DC and AC Breakdown Characteristics of Dielectric Sheets in Liquid Nitrogen

With the emergence of superconductor technology, high-temperature superconducting (HTS) power devices are quickly being developed. HTS power devices are receiving considerable attention due to their high capacity and low loss. Compared with ac HTS power devices, dc superconducting power devices have the advantage of zero resistance. To aid in the development of superconducting power devices, the ac and dc dielectric breakdown characteristics of dielectric sheets in liquid nitrogen ( LN2) should be better understood. In this paper, results are reported for ac and dc breakdown tests conducted in air (room temperature) on six types of sheets, including polypropylene laminated paper (PPLP), Nomex (polyamide) T410 fiber paper, Kapton (polyimide) 100HN, Kapton 100CR, Kapton 150FN019, and Kapton 150FCR019, and in LN2 on seven types of sheets, including PPLP, Kapton 100HN, Kapton 100CR, Kapton 150FN019, Kapton 150FCR019, Nomex T410, and Nomex T418 fiber paper. The insulation dielectric properties in air (room temperature) were compared with the insulation dielectric properties at a low temperature. At room temperature, the dc breakdown strength at 63.2% probability is 1.12-1.72 times the ac breakdown strength at 63.2% probability, and at a low temperature, the 63.2% probability of the dc breakdown strength is 1.52-2.14 times the 63.2% probability of the ac breakdown strength. Compared with the dielectric sheets of Kapton 150FCR019, Kapton 100CR, Kapton 150FN019, Kapton 100HN, and PPLP, Nomex T410 sheets have shown a remarkable increase in their dielectric strength in liquid nitrogen compared with air.