Breakdown Strength Measurements Research Articles

Mechanical and electrical performance of glass fiber reinforced plastic insulation for cryogenic application in fusion magnet irradiated in fast breeder reactor

In a superconducting (SC) magnet fusion reactor, the insulation material used has to withstand significant fluxes of neutrons and neutron-induced gamma radiation. Epoxy-based glass fiber-reinforced plastic (GFRP) composites are the insulation system for fusion magnets and are highly demanding. This insulation system requires excellent mechanical and electrical performance under mixed neutron and gamma radiation at cryogenic temperatures. The insulation material developed consists of boron-free S-glass fiber impregnated with a two-component modified Diglycidyl ether of Bisphenol-A (DGEBA) epoxy resin. An anhydride-cured DGEBA resin system is not suitable for cryogenic temperatures. Therefore, to overcome this thermal stress issue in cryogenic components of SC magnets, a high-toughness, flexible, aromatic amine-cured epoxy resin system was developed for the insulation system. In order to assess the radiation resistance for mechanical and electrical properties, the composite samples were irradiated in the fast breeder test reactor (FBTR) at IGCAR, Kalpakkam, India. The irradiation experiment was carried out for a neutron fluence of 1.0E+21 n/m2 and a gamma dose of 0.4 MGy at a full reactor power of 32 MWt. The tensile strength, interlaminar shear strength, and breakdown strength measurements were investigated before and after irradiation at room temperature and 77 K. The test results indicate that no significant degradation was observed in the properties of the irradiated samples up to the above-mentioned radiation doses.

Dielectric breakdown strength measurement of silicon nitride ceramics by McKewon electrode

Dielectric breakdown strength measurement of silicon nitride ceramics by McKewon electrode

Characterization of Photocurable IP-PDMS for Soft Micro Systems Fabricated by Two-Photon Polymerization 3D Printing.

Recent developments in micro-scale additive manufacturing (AM) have opened new possibilities in state-of-the-art areas, including microelectromechanical systems (MEMS) with intrinsically soft and compliant components. While fabrication with soft materials further complicates micro-scale AM, a soft photocurable polydimethylsiloxane (PDMS) resin, IP-PDMS, has recently entered the market of two-photon polymerization (2PP) AM. To facilitate the development of microdevices with soft components through the application of 2PP technique and IP-PDMS material, this research paper presents a comprehensive material characterization of IP-PDMS. The significance of this study lies in the scarcity of existing research on this material and the thorough investigation of its properties, many of which are reported here for the first time. Particularly, for uncured IP-PDMS resin, this work evaluates a surface tension of 26.7 ± 4.2 mN/m, a contact angle with glass of 11.5 ± 0.6°, spin-coating behavior, a transmittance of more than 90% above 440 nm wavelength, and FTIR with all the properties reported for the first time. For cured IP-PDMS, novel characterizations include a small mechanical creep, a velocity-dependent friction coefficient with glass, a typical dielectric permittivity value of 2.63 ± 0.02, a high dielectric/breakdown strength for 3D-printed elastomers of up to 73.3 ± 13.3 V/µm and typical values for a spin coated elastomer of 85.7 ± 12.4 V/µm, while the measured contact angle with water of 103.7 ± 0.5°, Young's modulus of 5.96 ± 0.2 MPa, and viscoelastic DMA mechanical characterization are compared with the previously reported values. Friction, permittivity, contact angle with water, and some of the breakdown strength measurements were performed with spin-coated cured IP-PDMS samples. Based on the performed characterization, IP-PDMS shows itself to be a promising material for micro-scale soft MEMS, including microfluidics, storage devices, and micro-scale smart material technologies.

Influence of the stoichiometric ratio on the material properties and the aging behavior of anhydride-cured epoxy systems

Abstract When partial discharge and dielectric heating effects can be excluded, comparatively little is known about the aging behavior of polymeric insulation materials under combined environmental and electric field stress. Since it was found in an earlier study that hygroelectrical stress leads to a strong reduction in the residual breakdown strength of anhydride-cured epoxy samples, the goal of this contribution is to determine if a material modification could enhance the insulation performance under hygroelectrical stress. For this purpose, epoxy samples of different stoichiometric ratios (SRs) were manufactured and hygroelectrically stressed. The material properties were evaluated by AC breakdown strength measurements as well as by Fourier-transform infrared (FTIR) spectroscopy before and after each aging sequence. Gravimetric analysis quantified the water diffusion behavior and the (steady-state) water absorption during exposure to different relative humidity levels at room temperature. The breakdown strength decreases for both increasing and decreasing SR compared to S R = 95 % . Moreover, FTIR measurements revealed that an increase of the SR leads to a higher amount of unreacted anhydride which correlates with an increasing amount of absorbed water. Thus, the mutual presence of water in the atmosphere and of unreacted anhydride in the epoxy material is identified as the main risk factor for epoxy degradation under the influence of electrical stress, since unreacted anhydride favors stronger water absorption and the presence of water inside the material is attributed to a lowering of the potential barrier for molecular bond breaking. Remarkably, the breakdown strength of non-aged samples is lower at S R = 80 % compared to S R = 95 % , but the long-term performance with respect to insulation aging is enhanced, which correlates with the non-/less-existing unreacted anhydride in the material.

Effect of Moisture Content on the Performance of PPLP as a Dielectric for HTS Power Cable

For the operation of High Temperature Superconducting (HTS) power cables at high voltage levels, the electric field distribution depends on the relative permittivity of dielectric materials. In HTS cables, PolyPropylene Laminated Paper (PPLP) is used as a cold dielectric material and is wrapped helically along the length of the conductor thereby electrically insulating it. During the installation and maintenance process of HTS cables, termination units and joint boxes, the PPLP is often exposed to moisture. The presence of moisture affects the dielectric breakdown strength and dielectric losses. The effect of moisture content in PPLP at ambient and liquid nitrogen temperature has been studied to determine the breakdown strength, relative permittivity (εr) and dissipation factor (tan δ). Effect of moisture content on the performance of PPLP via the measurement of dielectric breakdown strength and relative permittivity for various temperatures and moisture content are discussed in this paper.

Enhancing breakdown strength and lifetime of multilayer dielectric films by using high temperature polycarbonate skin layers

Polymer multilayer films (MLFs) hold a potential to achieve high energy density, high temperature rating, and high breakdown strength simultaneously for next-generation film capacitors. Under extreme conditions such as high AC electric fields and high temperatures, an important dielectric loss mechanism is the homocharge injection from metal electrodes and subsequent charge recombination (i.e., AC electronic conduction) at the electrode/dielectric interfaces. In this work, the mechanism of the AC electronic conduction loss is studied for high-temperature polycarbonate (HTPC)/poly(vinylidene fluoride) (PVDF) MLFs with either HTPC (MLF@HTPC) or PVDF skin layers (MLF@PVDF). Based on the DC/AC breakdown strength and lifetime measurements, it is observed that homocharge injection was more significant for MLF@PVDF than MLF@HTPC. Using the electric displacement-electric field loop analysis, dielectric losses from both AC electronic conduction and ferroelectric switching (PVDF) are quantified. A dipolar electric double layer model at the electrode/PVDF interfaces is proposed to explain the more significant ferroelectric switching and charge injection in MLF@PVDF. From these experimental results, it is concluded that enhanced breakdown strength and lifetime can be achieved for MLF@HTPC because of the reduced homocharge injection and AC electronic conduction at high electric fields and high temperatures.

Volume and Surface Resistivity Measurement of Insulating Materials Using Guard-Ring Terminal Electrodes

Recently, eco-friendly energy conversion policies have been being promoted through de-nuclearization and de-coal. For this purpose, a super grid should be built to optimize sustainable renewable energy resources such as solar and wind power. Accordingly, considering the various problems such as technology and cost, a system for efficient energy transmission is required. Hence, research is being actively conducted to apply it, owing to the development of the high voltage direct current (HVDC) system. Among HVDC systems, the cable system is extremely important, in addition to the measurement of the dielectric breakdown strength, space charge, and volume resistivity of insulating materials. The existing resistivity measurement method measures both the volume and surface resistivity using a three-terminal electrode that is used in the international standards of American Society for Testing and Materials (ASTM) D 257 and International Electrotechnical Commission (IEC) 60093. However, the circuit configuration differs depending on the measurement of the volume and surface resistivity; moreover, when a DC voltage is applied to the insulator, a charging current flows and there are multiple samples to be measured, which takes a considerable amount of time. Therefore, in this study, we proposed a new type of resistivity measurement system that is based on the existing three-terminal electrode system. Furthermore, we produced a system capable of simultaneously measuring the volume and surface resistivity. Finally, using this system, we compared and analyzed the volume and surface resistivity of five insulating materials.

Influence of xylene on the dielectric response of an organoclay‐containing nanocomposite

The dielectric effect, investigated using dielectric spectroscopy and DC dielectric breakdown strength measurements, of introducing xylene into a composite system containing polyethylene, a co-polymer of ethylene and vinyl acetate and an organoclay can be understood in light of X-ray diffraction data. In dielectric spectroscopy, although organoclay alone changes the dielectric response of the polymer blend and xylene has no effect on the unfilled polymer blend, when both xylene and organoclay are present, a synergistic response is revealed at the 1 Vrms amplitude voltage used to acquire the dielectric data. In contrast to this, in DC, dielectric breakdown strength measurements revealed that, under high field conditions, both the xylene and organoclay, independently, caused a decreased breakdown strength. This work was undertaken in order to examine the generality of the possible effects of labile, low molar mass impurities on electrical properties of comparable systems, which may be processed through solvent-based routes.

Investigation on Cable Rejuvenation by Simulating Cable Operation

Further research on retired cable rejuvenation via heat treatment was investigated in this paper. Three retired cables with service year of 7, 15 and 30 years were used and annealed at different temperatures following two different heat treatment methods. In the first test, two short cables with a length of 5 m were prepared and cut into five equal segments. Four segments of each cable were annealed at 90, 95, 100, and 105 °C to simulate the cable operation. Then, the cross-linked polyethylene (XLPE) from the cable insulation was peeled, and the peels from the inner, middle and outer positions were selected and subjected to the differential scanning calorimetry (DSC), DC conduction current, and dielectric breakdown strength measurements. The thermal and electrical performance of these samples were analyzed, and the optimum annealing temperature was determined. In the second test, three identical long cables were connected to a transformer, joints, and terminals to build two experimental circuits. The cables were annealed at the optimum temperature determined in the first test. The same measurements were performed on XLPE samples taken from the same positions as those in the first test. The results showed that the short cables exhibited the best thermal and electrical performance when annealed at 95 °C. The three long cables annealed at 95 °C verified that the thermal and electrical properties of the cable insulation were significantly improved. The results of the two different annealing methods, which closely represent the actual cable operations, verified the feasibility that old cables without overheating history could be rejuvenated via heat treatment.

Interplay between nanoparticles and water on dielectric properties of nanofluids

This paper deals with the interaction of nanoparticles (NPs) in transformer oil and water in the oil and its effect on the electrical properties of the nanoffuid (NF). The breakdown strength and dielectric spectrum measurements under AC for various concentrations of natural SiO 2 and water in mineral oil were studied. Mineral oil-based SiO 2 NFs exhibit significantly higher breakdown voltage than that of base oil under high water content. However, there is an optimal range of NP concentration and water content for maximum breakdown voltage. The results of dielectric spectrum indicate that the dielectric constants of NFs and base oil are greatly affected by water content. The real relative permittivity of oil samples increases exponentially with water content at decreasing frequency (f≤10 Hz). The imaginary relative permittivity of NFs is less than that of the base oil in all cases. Based the experimental results reported, a model on the interplay between NPs and water in transformer oil is presented. The model can broadly explain the influence of the coexistence of NPs and water on the dielectric properties of transformer oil.

Dielectric breakdown strength measurements with silicone-based single-layer dielectric elastomer transducers

Dielectric elastomer transducers (DETs) consist of an elastic dielectric film sandwiched between compliant electrodes. Applying an electric voltage leads to an electrostatic pressure between the electrodes which causes a deformation of the DET due to the elastic dielectric. The dielectric breakdown field strength of the elastomer restricts the applied voltage. For highly efficient DETs, their dielectric breakdown strength during operation has to be known. In this work, eight different breakdown test scenarios with self-fabricated single-layer DET samples made of the silicone film Elastosil® Film 2030 (Wacker Chemie AG) are conducted. They differ in type of the applied electrical voltage (DC/AC), mechanical load of the silicone film and setup of the DET samples. The DETs show a nominal dielectric breakdown strength between 96 and 200 V μm−1 during operation depending on the applied voltage, prestretch and the setup of the DET. Applying protective silicone film layers on top and bottom of the electrodes leads to a reduced damage of the DET after the breakdown of the weakest point and prevents the complete failure of the transducer.

Effect of voltage stabilizers on the space charge behavior of XLPE for HVDC cable application

Space charge accumulation inside the cross-linked polyethylene (XLPE) insulation is one of the most serious problems in HVDC cable operation. In this paper, the voltage stabilizers that have excellent compatibility with XLPE are used to suppress the space charge in XLPE insulation. Three different voltage stabilizers, 4,4'-Difluorobenzophenone, 4,4'-Dihydroxybenzophenone, and 4,4'-Bis (dimethyl amino) benzyl, denoted as A, B, and C, respectively, were added into XLPE material with additive content of 0.5 wt%, and neat XLPE was used as a control. The differential scanning calorimeter (DSC) test, tensile test, DC conductivity and breakdown strength measurements were employed to characterize the thermal, mechanical and electrical properties of the samples respectively. Moreover, the space charge behaviors were investigated using the PEA method, and the trap-controlled carrier mobility was evaluated by the depolarization processes of the space charge. The mechanical and thermal analyses indicate that the presence of voltage stabilizers does not significantly change the microstructure of XLPE, as required for the preparation of HVDC cable insulation. Though the influence of voltage stabilizers on DC conductivity is not obvious, a higher breakdown strength was found in the voltage-stabilizer modified XLPE samples. In addition, XLPE modified by the voltage stabilizers B and C with higher trap-controlled carrier mobility show a good ability to suppress space charge in XLPE insulation, that is, less space charge accumulation and faster space charge dissipation than the neat XLPE. The experimental results reveal that the voltage stabilizers B and C show great promise for use in HVDC cable application.

Impact ionization and transport properties of hexagonal boron nitride in a constant-voltage measurement

The electrical evaluation of the crystallinity of hexagonal boron nitride (h-BN) is still limited to the measurement of dielectric breakdown strength, in spite of its importance as the substrate for 2-dimensional van der Waals heterostructure devices. In this study, physical phenomena for degradation and failure in exfoliated single-crystal h-BN films were investigated using the constant-voltage stress test. At low electrical fields, the current gradually reduced and saturated with time, while the current increased at electrical fields higher than ~8 MV/cm and finally resulted in the catastrophic dielectric breakdown. These transient behaviors may be due to carrier trapping to the defect sites in h-BN because trapped carriers lower or enhance the electrical fields in h-BN depending on their polarities. The key finding is the current enhancement with time at the high electrical field, suggesting the accumulation of electrons generated by the impact ionization process. Therefore, a theoretical model including the electron generation rate by impact ionization process was developed. The experimental data support the expected degradation mechanism of h-BN. Moreover, the impact ionization coefficient was successfully extracted, which is comparable to that of SiO2, even though the fundamental band gap for h-BN is smaller than that for SiO2. Therefore, the dominant impact ionization in h-BN could be band-to-band excitation, not defect-assisted impact ionization.

Effect of resin/hardener stoichiometry on electrical behavior of epoxy networks

By changing the ratio of resin to hardener, a series of epoxy resin samples has been produced with differing network structures and different retained chemical functionalities. The resulting materials were characterized by thermal analysis, dielectric spectroscopy, DC conductivity, and DC and AC breakdown strength measurements, to explore the effect of network structure and chemical composition on molecular dynamics and electrical properties. Differential scanning calorimetry showed that the glass transition temperature is primarily determined by the crosslinking density and indicates that, under the range of conditions employed here, side reactions, such as etherification or homopolarization, are negligible. Conversely, changes in DC conductivity with resin stoichiometry appear to occur as a result of changes in the chemical content of the system, rather than variations in network structure or dynamics. Specifically, we suggest that the DC conductivity is markedly affected by the residual amine group concentration in the system. While DC conductivity and DC breakdown appear broadly to be correlated, AC breakdown results indicated that this parameter does not vary with changing stoichiometry, which suggests that the AC and DC breakdown strengths are controlled by different mechanisms.

Dielectric properties of diblock copolymers containing a polyarylene ether nitrile block and a polyarylene ether ketone block

The block copolymers poly(arylene ether nitrile ketone) (PENK) composed of a poly(arylene ether nitrile)s block and a poly(arylene ether ketone) block were prepared from biphenol, 2,6-dichlorobenzonitrile and 4,4′-difluorobenzophenone (DFBP) by the nucleophilic aromatic substitution reaction. The molecular structure of PENK was characterized by the Fourier transform infrared spectrum (FT-IR) testing. The properties of the PENK polymers were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) characterization, mechanical testing, dielectric and breakdown strength measurement. According to the DSC characterization, only one glass transition temperature (~ 216 °C) of all the polymers is observed and remained even treated at a temperature of 360 °C, indicating that the block polymer PENK has a homogeneous morphology. In addition, PENK polymers exhibit excellent thermal stability and mechanical strength, the thermal decomposition temperature of the polymers ranges from 530 to 535 °C, and the tensile strength of them ranges from 100 to 117 MPa. The energy storage density of PENK films is closely related to the molecular structure of them. The results show that with the increase of DFBP, the energy storage density increases from 0.62 to 1.11 J/cm3.

Effect of Zn2P2O7 additive on the electrical breakdown strength and energy storage properties of (Ba0.6Sr0.4)0.85Bi0.1TiO3 ceramics

(Ba0.6Sr0.4)0.85Bi0.1TiO3 (abbreviated as BSBT) ceramics doped with x wt% Zn2P2O7 (x = 0, 1, 5, 10, 15) were synthesized. The influence of Zn2P2O7 on microstructures and electrical properties of BSBT ceramics were studied. Microstructural observation indicated that Zn2P2O7 doping could inhibit the growth of grain and improve the microstructure homogeneity of BSBT ceramics. Dielectric measurements exhibited a relaxor-like characteristic for all samples. Breakdown strength measurements indicated that undoped BSBT ceramics owned a breakdown strength of 122 kV/cm. However, with increasing Zn2P2O7 content, the breakdown strength enhanced monotonously, and the maximum breakdown strength reached 326 kV/cm at x = 15. Meanwhile, the energy storage efficiency was improved greatly by Zn2P2O7 addition. The results suggest that BSBT ceramics doped with Zn2P2O7 could be taken for a candidate for energy storage applications. In addition, the correlation between energy storage efficiency and interface polarization was qualitatively discussed by complex impedance spectra.

Design of High Voltage Electrical Breakdown Strength measuring system at 1.8K with a G-M cryocooler

Impregnating resins as electrical insulation materials for use in ITER magnets and feeder system are required to be radiation stable, good mechanical performance and high voltage electrical breakdown strength. In present ITER project, the breakdown strength need over 30 kV/mm, for future DEMO reactor, it will be greater than this value. In order to develop good property insulation materials to satisfy the requirements of future fusion reactor, high voltage breakdown strength measurement system at low temperature is necessary. In this paper, we will introduce our work on the design of this system. This measuring system has two parts: one is an electrical supply system which provides the high voltage from a high voltage power between two electrodes; the other is a cooling system which consists of a G-M cryocooler, a superfluid chamber and a heat switch. The two stage G-M cryocooler pre-cool down the system to 4K, the superfluid helium pot is used for a container to depress the helium to superfluid helium which cool down the sample to 1.8K and a mechanical heat switch connect or disconnect the cryocooler and the pot. In order to provide the sufficient time for the test, the cooling system is designed to keep the sample at 1.8K for 300 seconds.

DC electrical breakdown dependence on the radial position of specimens within HVDc XLPE cable insulation

Because of temperature gradients and inhomogeneous cooling rates after extrusion, the performances of HVDC XLPE cable insulation at radial position are not uniformly distributed. DC breakdown strength measurements of HVDC XLPE cable insulation specimens in inner insulation (near conductor shield), middle insulation and outer insulation (near insulation shield) have been carried out and show that DC breakdown strength of specimens in middle insulation is relatively lower than that of in inner and outer insulation at 30, 50 and 70 °C. At 90 °C, there is no significant difference of DC breakdown strength of specimens at radial position. Thus the micro performances of XLPE specimens at different radial position have been studied by FTIR, DSC, SEM and XRD. FTIR measurements show that cross-linked by-products (benzyl alcohol and acetophenone) content in middle insulation is higher; DSC measurements shows that crystallinity of specimens in middle insulation is slightly higher; SEM measurements show that the grains of specimens in middle insulation are unevenly distributed and their sizes have obvious difference; the results of XRD measurements show a higher content of by-products, a higher crystallinity and a larger crystalline interplanar spacing (a larger grain size) of specimens in middle insulation, which are consistent with FTIR, DSC and SEM analysis. Therefore, cross-linked by-products, crystallinity and crystal morphology together make DC breakdown strength of specimens in middle insulation lower.

Characterization of the dielectric endurance of reinforced recycled PET using electro-thermal aging test

This paper presents the advantages of dielectric characterization by electro-thermal aging testing in the durability analysis of reinforced recycled polyethylene terephthalate (PET), as compared to short-term dielectric breakdown strength measurements. Dielectric breakdown strength measurements were carried out at room temperature according to ASTM D149-a, while electro-thermal aging tests were conducted in air at different constant temperatures ranging from 140 to 170 °C, using an experiment setup comprising a cell test arranged in a point-to-plane configuration, with a very small air gap of 50±1 μm. The tests were conducted at an AC voltage of amplitude 7 kV rms on eight different reinforced recycled PET samples. The degradation of recycled PET-based composites during exposure to corona discharges at elevated temperatures was characterized by optical microscopy and scanning electron microscopy (SEM). The main goal of this study is to characterize and to determine the relationship between the addition of different inorganic reinforcements, such as mica and glass fibers, to a recycled PET matrix, as well as the resistance to dielectric failure during electro-thermal aging. The effect of plasticizers on the dielectric endurance of recycled PET-based composites was also investigated. Results obtained showed that glass fibers contribute to the enhancement of the resistance to dielectric failure. Our experiments also revealed that the dielectric behaviour of these composites can be affected by the presence of plasticizers. In addition, the size of additives such as mica can greatly improve the resistance to the dielectric breakdown caused by electrothermal aging.

Boron nitride filled epoxy with improved thermal conductivity and dielectric breakdown strength

Abstract The present work aims at studying epoxy-matrix composites using boron nitride (BN) as filler for thermal management in electrical applications. Several factors were investigated: the combination of micro- and nano-sized particles, the use of a silane coupling agent (SCA) as well as different dispersion techniques. Composites containing from 10 w% up to 20 w% of filler were manufactured by conventional casting. Several concentrations of nano-sized particles and SCA were considered. The ball-milling (BM) method was used to create an effective dispersion of the filler in the matrix. Thermal conductivity measurements were performed on the samples as the core of the study along with a morphological analysis, dielectric spectroscopy and breakdown strength measurements. The thermal conductivity of the neat resin shows up to a fourfold increase for the composite containing 20 w% of BN, which is among the highest improvements ever reported in literature at this BN content. High concentration of SCA has a significant positive effect on the thermal conductivity of the material while ball milling proves to be an efficient method in breaking the large aggregates present in the nano-powder. Moreover, the addition of BN results in an increase of the breakdown strength of the host matrix (about 10%) accompanied by improved robustness (less scattering of the measured values), both very important factors for any electrical application.