AC Dielectric Breakdown Strength Research Articles

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.

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.

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.

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.

Effect of the nature of clay on the thermo‐mechanodynamical and electrical properties of epoxy/clay nanocomposites

AbstractThe effect of nature of clay on the thermo–mechanodynamical and electrical properties of epoxy/clay nanocomposites prepared from bisphenolic epoxy resins and different nanoclays are presented. The thermal–mechanodynamical properties of the nanocomposites were studied by DMTA, showing significant increase in both elastic modulus and glass transition temperature. Short time AC dielectric breakdown strength measurements carried out on the nanocomposites showed an increase in dielectric breakdown strength for the nanocomposites prepared with organically modified clays. The space charges accumulated in the materials as studied by pulsed electroacoustics method showed a significant decrease in the space charge accumulation in the nanocomposites with organoclays as the nanofiller. Similarly the space charge decays almost completely in the nanocomposites prepared with organoclays as nanofiller. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

The DC- and AC-dielectric breakdown strength of magnetic fluids based on transformer oil

The DC- and AC-dielectric breakdown strength of magnetic fluids based on transformer oil

Influence of post-manufacturing residual mechanical stress and crosslinking by-products on dielectric strength of HV extruded cables

Residual mechanical stresses from manufacturing always exist in freshly extruded HV cables. These stresses are not uniformly distributed in the cable insulation bulk material. Five different HV cables were analyzed with respect to residual mechanical stresses and dielectric breakdown strength. Photoelastic measurements have been carried out and show that maximum residual stresses range from 4.5 to 6 MPa and are located near the conductor shield. Breakdown strength measurements with respect to mechanical stresses have also been performed up to, and above the maximum stresses observed. A significant decrease in ac breakdown strength was observed for stresses higher than 6 MPa. Typical crosslinking by-products from dicumyl peroxide (DCP) have been measured by FTIR spectroscopy at five radial positions in the insulation bulk. Measured by-products consisted in acetophenone and cumyl alcohol. FTIR measurements show that crosslinking by-products content is higher in the bulk of the insulation than near the conductor and insulation shields thus showing a diffusion process. Moreover, residual amount of cumyl alcohol is generally between 1 and 3 times that of acetophenone. No important effect of both by-products on the ac dielectric breakdown strength was observed.

Characteristics of Composite Insulation: Liquid-Impregnated Insulation

A description is given of composite insulation, i. e. swelling of polymers by oil, oil streaming electrification of solid dielectrics , and V-t characteristics of LN2-impregnated insulation due to partial discharge. Swelling can be accelerated by ultrasonic wave irradiation. This reduces the saturation time. Polypropy-lene-laminated paper would swell less inside its cable structure. Ac dielectric breakdown strength increases with swelling in the early stage and then decreases. Streaming electrification was found to be influenced by the oil flow rate, temperature, ac applied voltage, and the type of solid and liquid dielectrics. Surface roughness of solid dielectrics does affect the electrification greatly. Addition of benzotriazol at only ppm is effective in suppressing the electrification. V-t characteristics are divided into two regions for liquid nitrogen (LN2) impregnated insulation. The value of n in Vnt= const ranges from 50 to 100 in the first region, while it is around 5 to 10 in the second region.