Low Dielectric Strength Research Articles

Study on protection measures of lightning electromagnetic pulse in automatic weather station

Due to automatic meteorological station, the distribution of the unique geographical location and environment, the equipment has a large number of sensors and electronic components, and a highly integrated, combined with the electronic components of low dielectric strength, compression ability and the ability to resist electromagnetic interference and weak ability to resist shock current and lightning electromagnetic pulse is easy to damage to electronic equipment. Therefore, this paper analyzes the existing problems and harms in lightning protection design of automatic weather station system in Shanxi Province, and puts forward improvement and protection measures.

Peano‐Hydraulically Amplified Self‐Healing Electrostatic Actuators Based on a Novel Bilayer Polymer Shell for Enhanced Strain, Load, and Rotary Motion

The hydraulically amplified self‐healing electrostatic actuator is an emerging driving component for soft robotics, which is composed of a flexible dielectric polymer shell that is partially covered by conductive electrodes and filled with a liquid dielectric. However, the low permittivity and dielectric strength of the polymer shell remain a challenge that limits the actuator performance. Herein, a Peano‐hydraulically amplified self‐healing electrostatic actuator is constructed by innovatively integrating a bilayer polymer shell for combined favorable properties of high dielectric strength, dielectric permittivity, and elastic modulus. Compared with a traditional single‐layer shell actuator, the new bilayer actuator architecture generates an increased strain (164%) at 5 kV and improves load‐bearing capability (620 mN) at 6 kV, thereby providing a significantly enhanced actuation performance. The new actuator is further applied in driving a ratchet system, which converts the reciprocating motion of the actuator into a rotating motion and a flexible output torque, in order to protect the rotating components from impact. The high strain and load characteristics of the bilayer configuration and the easy‐to‐deform characteristics of the new actuator design make it an attractive approach to fabricate complex geometries and achieve a variety of motion modes in soft systems.

Fabrication and Characterization of Semi-Crystalline and Amorphous Dielectric Polymer Films for Energy Storage

Dielectric polymer films are energy storage materials that are used in pulse power operations, power electronics and sustainable energy applications. This paper reviews energy storage devices with focus on dielectric film capacitors. Two prominent examples of polymer dielectrics Polyetherimide (PEI) and Poly (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride) (THV) have been discussed. Polyetherimide (PEI) is an amorphous polymer recognized for its high-temperature capability, low dielectric loss and high dielectric strength. THV is a semi-crystalline polymer with high dielectric constant, high-temperature capability and charge-discharge efficiency. The primary focus of this paper is to introduce the reader to the fabrication procedures and characterization techniques used in research labs for processing of dielectric polymers. The fabrication and characterization process of both polymers has been discussed in detail to shed the light on experimental process in this area of research.

Theoretical study of the decomposition mechanism of a novel eco-friendly insulation medium HFO-1336mzz(E) considering the effect of trace humidity

As a strong greenhouse gas, sulfur hexafluoride used in electrical equipment has been advocated to be replaced. HFO-1336mzz(E), an eco-friendly insulation alternative medium with excellent insulation performance and environmental effect, deserves studied deeply. In this paper, the decomposition mechanism of HFO-1336mzz(E) is studied by density functional theory calculations. The effect of trace water on the decomposition properties is also considered and studied. Besides, multiple linear regression models are used to assess the insulation properties of main decomposition products that came from HFO-1336mzz(E). The results show that more than 15 molecules are formed in the decomposition process of HFO-1336mzz(E), among which CF3CH=C=CF2, CF2=CF–CH=CF2, C2F6, and HF are the most abundant products. Besides, C2F4, CF2=CFH, and C2H2 could be taken as typical products for diagnosing the serve fault degree that occurred in the electrical equipment. In terms of insulation properties, CF3CH=C=CF2 and CF2=CF–CH=CF2, two of the main products, with big volumes have excellent insulation strength that is slightly less than that of HFO-1336mzz(E). Small molecules with low dielectric strength such as CF3H, CF3OH, COF2, and HF, etc can also be produced in the presence of micro humidity. Luckily, the yield of these small molecules is small so that they will not have a significant impact on the insulation properties of the overall system. Remarkably, the presence of micro humidity will make it easier to generate toxic gas products such as COF2 and HF. Given these conditions, the acceptable moisture content in the power equipment is expected to propose before any application in the electrical industry. Relative studies on the decomposition mechanism of HFO-1336mzz(E)/H2O in this paper may be helpful to understand the subsequent scientific experimental research.

Ultrahigh Energy Storage Density and Efficiency in Bi0.5Na0.5TiO3-Based Ceramics via the Domain and Bandgap Engineering.

Environmentally friendly lead-free dielectric ceramics have attracted wide attention because of their outstanding power density, rapid charge/dischargerate, and superior stability. Nevertheless, as a hot material in dielectric ceramic capacitors, the energy storage performance of Na0.5Bi0.5TiO3-based ceramics has been not satisfactory because of their higher remnant polarization value and low dielectric breakdown strength, which is a problem that must be urgently overcome. In this work, the (1 - x) (0.6Na0.5Bi0.5TiO3 - 0.4Sr0.7Bi0.2TiO3) - xBa(Mg1/3Ta2/3)O3 (BNST-xBMT) systems were designed based on a dual optimization strategy of domain and bandgap to solve the above problems. As a result, a record-breaking ultrahigh energy density and excellent efficiency (Wrec = 8.58 J/cm3, η = 93.5%) were obtained simultaneously under 565 kV/cm for the BNST-0.08BMT ceramic. The introduction of Sr0.7Bi0.2TiO3 induces the formation of nanodomains in BNT-based ceramics, leading to slim P-E curves, and the further modification of Mg/Ta reduces the grain sizes and increases the bandgap width, resulting in significant enhancement of the dielectric breakdown strength. Moreover, excellent stability and superior discharge performance (Wd = 4.7 J/cm3, E = 320 kV/cm) in the BNST-0.08BMT ceramic were also achieved. The results suggest that the BNST-0.08BMT ceramic shows potential applicability for dielectric energy storage ceramics. Simultaneously, the composition-design concept in the system provides a good reference for the further development of ceramic dielectric capacitors.

Chemical adsorption on 2D dielectric nanosheets for matrix free nanocomposites with ultrahigh electrical energy storage

Relaxor ferroelectric polymers display great potential in capacitor dielectric applications because of their excellent flexibility, light weight, and high dielectric constant. However, their electrical energy storage capacity is limited by their high conduction losses and low dielectric strength, which primarily originates from the impact-ionization-induced electronmultiplication, low mechanical modulus, and low thermal conductivity of the dielectric polymers. Here a matrix free strategy is developed to effectively suppress electron multiplication effects and to enhance mechanical modulus and thermal conductivity of a dielectric polymer, which involves the chemical adsorption of an electron barrier layer on boron nitride nanosheet surfaces by chemically adsorbing an amino-containing polymer. A dramatic decrease of leakage current (from 2.4 × 10−6 to 1.1 × 10−7 A cm−2 at 100 MV m−1) and a substantial increase of breakdown strength (from 340 to 742 MV m−1) were achieved in the nanocompostes, which result in a remarkable increase of discharge energy density (from 5.2 to 31.8 J cm−3). Moreover, the dielectric strength of the nanocomposites suffering an electrical breakdown could be restored to 88% of the original value. This study demonstrates a rational design for fabricating dielectric polymer nanocomposites with greatly enhanced electric energy storage capacity.

Energy storage performance of BaTiO3-based relaxor ferroelectric ceramics prepared through a two-step process

As the industrial pillar of electronic ceramics, BaTiO3 ceramic is difficult to achieve large energy storing performance due to its high Pr and low dielectric breakdown field strength, making it difficult to satisfy their development requirements of miniaturization and lightweight of power electronic equipment. Therefore, a two-step strategy including adjusting the ratio of chemical elements to modify the microstructures and optimizing the preparation process to enhance electric breakdown strength has been proposed to greatly enhance the energy storing performance of lead-free ferroelectric ceramics, whose effectiveness has been proved within this investigation. Especially, the (Ba0.65Sr0.245Bi0.07)0.99Nd0.01TiO3 (BT-SBT-NdVPP) ceramic prepared by this strategy obtains a superhigh energy storage density of 4.2 J/cm3 under 460 kV/cm, and its temperature (30 ~ 100 °C) and frequency (10 ~ 400 Hz) stabilities under 300 kV/cm are pretty good. In addition, this ceramic has excellent pulse performance under 350 kV/cm between 30 and 150 °C. Therefore, this two-step strategy put forward within this investigation not only significantly improves the energy storage performance of BT-based ceramics but also provides a reference for the preparation of dielectric ceramics with high quality, which could has great potential for the practical industrial application.

AgNbO3 antiferroelectric film with high energy storage performance

Antiferroelectric materials with double hysteresis loops are attractive for energy storage applications, which are becoming increasingly important for power electronics nowadays. Among them, AgNbO3 based lead-free ceramics have attracted intensive interest as one of promising environmental-friendly candidates. However, most of the AgNbO3 based ceramics suffers from low dielectric breakdown strength (Eb). The limitation of low Eb is broken to some extent in this work. Here, AgNbO3 epitaxial films were fabricated by pulsed laser deposition, which possess high Eb of 624 kV/cm. The (001)AgNbO3 epitaxial film reveals typical antiferroelectric hysteresis loops when the applied electric fields are over 300 kV/cm. A recoverable energy density of 5.8 J/cm3 and an energy efficiency of 55.8% are obtained at 600 kV/cm, which demonstrates the great promise of the AgNbO3 film for energy storage applications.

Estimating the true piezoelectric properties of BiFeO3 from measurements on BiFeO3-PVDF terpolymer composites

• BiFeO 3 particles were embedded in non-conducting non-piezoactive PVDF terpolymer. • Dielectric and piezoelectric properties of BiFeO 3 -PVDF composite with different volume fraction were studied. • The piezoelectric charge and voltage coefficients of granular BiFeO 3 were determined by using Yamada and Poon model. BiFeO 3 is an interesting multiferroic material with potential use in sensors and transducers. However, the high coercive field and low dielectric strength of this material make the poling process extremely difficult. Poling becomes a lot easier if the ceramic particles are incorporated in a non-conductive polymer with comparable dielectric properties. In this work, unstructured composites consisting of BiFeO 3 particles in a non-piezoactive PVDF terpolymer matrix are made with a ceramic volume fraction ranging from 20% to 60%. The highest piezoelectric charge and voltage constant values (d 33 = 31 pC/N and g 33 = 47 mV m/N) are obtained for a BiFeO 3 -PVDF terpolymer composite with a volume fraction of 60%. The Poon model is chosen to analyse the volume fraction dependence of the dielectric constant while the modified Yamada model is used to analyse the piezoelectric charge constant data. It is concluded that the maximum possible piezoelectric constant for bulk BiFeO 3 can be as high as 56 pC/N.

Dielectric Constant Enhancement with Low Dielectric Loss Growth in Graphene Oxide/Mica/Polypropylene Composites

Polypropylene has been widely used as dielectric material in organic thin-film capacitors due to their high breakdown strength, low dielectric loss and self-healing capability. However, polypropylene’s energy density is relatively low. Increasing the energy density of polypropylene by adding materials with a high dielectric constant is commonly used. Still, it often leads to an increase in dielectric loss, lower dielectric strength and other shortcomings. In this study, a thin 2D platelet of mica/graphene oxide composite material was made from exfoliated mica as a substrate and attached by graphene oxide. The mica/graphene oxide platelets were added to polypropylene to make a plastic dielectric composite. The non-conductive flat inorganic additive can increase the dielectric constant and dielectric strength of the composite without increasing dielectric loss. The tiny mica/graphene oxide platelets can significantly improve the dielectric properties of polypropylene. The results show that by adding a small amount (less than 1 wt%) mica/graphene oxide, the relative dielectric constant of polypropylene can increase to more than 3.7 without causing an increase in dielectric loss and the dielectric strength of polypropylene can also enhance.

Wideband antenna array pattern based on reinforcement epoxy materials & breast cancer diagnostic by composites

Abstract In this study, it is proposed to measure the numerical values of the depths of cancer tissues in the cancer organ. The creation of broadband antennas and the identification of cancer organs is a primary objective. A ΨU -shaped 2 × 2 grid antenna with a geographical coordinate has been modelled using mathematical modelling; simulated by Advanced Design Simulator (ADS); optimised using Moments of Methods (MoM); designed using Microwave Monolithic Integrated Circuits (MMIC) as the prototype and analytic microwave analysis by Agilent N99917A Analyzer represented Microwave Analyzer. It contains 18.64 × 17.92 × 1 mm3 compact dimensions. The model consists of the 2 × 2 array with four ΨU -shaped radiation slots, printed on a dielectric thickness of 1 mm of FR4 material and conductive ground level. The wideband spectrum from 4.5 GHz to 5.5 GHz was transmitted to 5.26 GHz operating frequency. In addition, the broadband antenna, a structure with a low profile and four number of radiating slots, is available. These broadband antennas have been developed for the application of breast cancer detection, which is the secondary provision of study. These broadband antennas with a dielectric model similar to the human breast are available on Debye test beds. These broadband antennas have impressed the materials for coupling that serve as the coupling medium. The findings were higher than the air medium. The higher and lower dielectric strength was demonstrated in these coupling materials. The average of distributed answers has been obtained. Distances between the cancerous organ and transceivers antennas, dielectric intensity and travelling times of spreading answers respectively have been determined by the degree of cancer present in the cancerous organ with the assistance of speed of propagation. This distributed response was therefore obtained in the Debye test bed from the cancer organ. Therefore the numerical depth value, which is validated under existing Debye test beds, and the coverage of the cancerous organ depth.

Theoretical study of the decomposition mechanism of C5F10O in the presence of Cu vapor

C5F10O is one of the promising SF6 replacements in power switchgears due to its low global warm potential and high dielectric strength. As Cu metal evaporated by discharges and overheat faults in power switchgears will change the decomposition mechanism and products of C5F10O, the interaction between C5F10O and Cu vapor is important to evaluate the arc-quenching behavior but seldom reported yet. Therefore, this paper is focused on the impacts of Cu vapor, mainly released from the contacts in circuit breakers, on the decomposition mechanism and products of C5F10O. The molecular geometries, harmonic vibrational frequencies, and energetic information of products, reactants, and transition states in C5F10O + Cu decomposition pathways including 19 reactions were calculated by density functional theory. The main decomposition reactions and products were selected based on the analysis of rate constants. This work is hopeful to evaluate the arc-quenching behavior of C5F10O-insulated power equipment considering the evaporation from Cu contacts.

Incorporation of elaborately Synthesized BNNSs by a mild mechanical stirring process for the concurrent enhancement of thermal conductivity and dielectric breakdown strength of PVDF

Due to the growing energy demands, it is highly desirable to concurrently improve the thermal conductivity and dielectric breakdown strength of dielectric film capacitors. Polyvinylidene fluoride (PVDF) is hitherto regarded as a most satisfactory alternative for dielectric capacitors but with relatively low thermal conductivity and dielectric breakdown strength. Herein, a major contribution is made to the concurrent enhancement of PVDF-based thermal conductivity and dielectric properties. It can be readily achieved through the incorporation of as-prepared high-quality few-layered boron nitride nanosheets (BNNSs) with a minimized loading (defined as PVDF-BNNSs). BNNSs dispersion with intact structure and a large aspect ratio is prepared by a unique mild mechanical stirring process assisted by dimethyformamide/1-butanol (DMF/1-butanol) solvent and a low power ultrasonic. Encouragingly, the characteristic breakdown strength with a maximum value of 334 MV/m reaches for PVDF-BNNSs composite only with 3 vol% BNNS loading, to be 1.6 times of pure PVDF. It also presents a high discharged energy density up to 9.9 J cm-3, along with an efficiency of 68.3%. Synchronously, the thermal conductivity accomplishes a high value of 1.12 W/m·K with only 8 vol% BNNS loading. A further theoretical analysis reveals that high-quality appropriate BNNSs loading could be preferentially arranged in parallel with PVDF surface. It indicates that BNNSs have good interface compatibility with PVDF, thus to improve its associated performances concurrently.

Formation mechanism, dielectric properties, and energy-storage density in LiNbO3-doped Na0.47Bi0.47Ba0.06TiO3 ceramics

The development of ferroelectric (FE) ceramics with high recoverable energy-storage density (Wrec) critically affects the miniaturization and integration of advanced pulse-power capacitors. However, most lead-free FE materials have the shortcomings of large remanent polarization and low dielectric breakdown strength. In this work, a strategy of composition control was implemented to improve the Wrec of lead-free ceramics. The effects of Li and Nb ion incorporation on the structure, dielectric, and ferroelectric properties of the highly insulating (Na0.5Bi0.5)TiO3–BaTiO3 (NBT–BT) ceramic was investigated. X-ray diffraction analysis of the samples revealed that the pure phase was isostructural to (Na0.5Bi0.5)TiO3. Dielectric measurements exhibited two pronounced anomalies which shift a certain angle within the depolarization-temperature range. The effects of LiNbO3 content on the breakdown characteristics and discharge energy storage of NBT–BT ceramics were investigated. An enhanced discharged energy density of 1.05 J/cm3, calculated from a hysteresis loop, was observed at x = 4 mol%. The improved structure also resulted in an increase of up to 61% in breakdown strength.

Study of Dielectric Characteristics and Energy Storage Properties of Sr<sub>0.7</sub>Bi<sub>0.2</sub>TiO<sub>3</sub> Doped with CaTiO<sub>3</sub>

Sr0.7Bi0.2TiO3 (SBT), a kind of lead-free relaxor ferroelectric, is attracting more and more attention for pulse energy storage applications due to the low remnant polarization and high energy storage efficiency (h). However, relatively low dielectric breakdown strength (DBS) limited the recoverable energy storage density (Wrec). Herein, CaTiO3 with high intrinsic DBS was introduced in SBT. The novel solid solutions (1-x)SBT-xCT with x = 0 - 0.15 shows pure pseudo-cubic perovskite structure. When x = 0.05, the maxium polarization are improved, and the CT doping decreases the average grain size, leading to an enhanced DBS. A high energy storage properties of 1.59 J/cm3 with the h of 87.4% at 220 kV/cm is achieved in 0.95SBT-0.05CT, which demonstrates that this 0.95SBT-0.05CT is prospective materials for energy storage application.

High performance and colossal permittivity of (Nb+La) co-doped rutile TiO2 ceramics induced by composition regulation

Donor-acceptor co-doped rutile TiO 2 ceramics with colossal permittivity have been paid more attention recent years. However, the application of the ceramics in high-energy-density storage devices was limited by the low breakdown strength of co-doped TiO 2 colossal permittivity ceramics, therefore the dielectric properties of Nb x La 0.004 Ti 0996-x O 2 (x:0.004=1:1, 1.02:1, 1.04:1, 1.06:1, 1.08:1) ceramics were investigated. Colossal permittivity with low dielectric loss and high dielectric strength was found in Nb x La 0.004 Ti 0.996-x O 2 (x:0.004=1.04:1) ceramics. The enhancement dielectric properties with larger Nb5+ doping concentration in co-doped ceramics provide the colossal permittivity mechanism in (Nb+La) co-doped TiO 2 ceramics could be attribute to the electron-pinned defect-dipole effect. Furthermore, finding the proper donor concentration is a feasible way to enhance the dielectric strength to satisfy the condition for application in high-energy-density storage devices.

Giant energy storage density in PVDF with internal stress engineered polar nanostructures

Abstract High power dielectric capacitors with high energy density are needed in order to develop modern electronic and electrical systems, including hybrid vehicles, telecommunication infrastructures and portable electronic devices. Relaxor ferroelectric polymers (RFP) are considered to be the most promising candidates for the next generation of capacitors owing to their relatively high energy storage density. However, the commercialization of RFP capacitors in power systems is hindered by their high cost and low dielectric breakdown strength. In this study, inexpensive, free-standing nano-crystalline (~3.3 nm) poly (vinylidene fluoride) (PVDF) films with high β phase content (~98%), “relaxor-like” ferroelectric behaviour and high breakdown strength (880 kV/mm) were fabricated using the facile Press & Folding (P&F) technique. An internal stress dominated polarization switching model is proposed to explain the origin of the relaxor-like ferroelectric behaviour. The internal stress generated during pressing alters the intermolecular chain distance of the (200) plane of β-PVDF from 4.24 A in internal stress free films to 4.54 A in P&F films, corresponding to a tensile strain and residual stress of 7.11% and 142 MPa, respectively. The internal stress acts to partially reverse the polarization on reversal of the applied electric field. This, combined with preferred in-plane orientation of the crystallites, results in a polar nanostructure with high polarization reversibility at high electric fields. A giant discharged energy storage density of 39.8 J/cm3 at 880 kV/mm was achieved for P&F films, which surpasses all previously reported polymer-based materials.

Novel Ca doped Sr0.7Bi0.2TiO3 lead-free relaxor ferroelectrics with high energy density and efficiency

Sr0.7Bi0.2TiO3 with high relaxor behavior and energy storage efficiency (η) is expected to be applied in power energy storage capacitors. However, its energy storage density is limited by the relatively low dielectric breakdown strength (DBS). Herein, Sr0.7Bi0.2CaxTiO3 (SBT-xC, x = 0 ∼ 0.15) was prepared to decrease the average grain size of Sr0.7Bi0.2TiO3. This can effectively eliminate the oxygen vacancy and decrease the electrical conductivity and leakage current, which result in the enhanced DBS. Meanwhile, Ca doping increases the relaxor behavior and dielectric constant. When x = 0.1, the composition exhibits high DBS of 480.2 kV/cm and excellent energy storage properties, such as high energy storage density of 2.1 J/cm3 with high η of 97.6 % at 290 kV/cm, considerable thermal stability and great frequency stability. Moreover, SBT-0.1C shows high power density of 50.1 MW/cm3. These results suggest that SBT-0.1C is a potential candidate for high performance dielectric energy storage applications.

Switching Behaviour of a Series Connection of a Vacuum Interrupter and a Gas Circuit Breaker

After being in the focus of sciences' and industry's research and development activities for many years, the investigation of possible SF6 gas-alternatives has been even more intensified after the revision of the European F-Gas regulation 517/2014. As natural gases yield a significantly lower dielectric strength in comparison to SF6, new challenges arise for the design of high voltage switchgear. Vacuum interrupters are environmentally friendly, reliable and able to withstand steep rising transient recovery voltages. In the last years, first installations of switchgear based on vacuum switching technology in sub-transmission level are in operation. One option for the realization of a SF6 free high voltage switchgear for transmission level is the combination of a gas circuit breaker filled with an atmospheric gas with a vacuum interrupter in a hybrid switchgear. In this contribution the voltage distribution and switching behavior of a hybrid circuit breaker is experimentally investigated.

Enhanced dielectric breakdown strength in TiO2-SiO2-Al2O3 based ceramics prepared through hot-press assisted liquid phase sintering

Linear dielectric ceramics have received much attention due to high power density, fast discharge speed and ultralow dielectric loss, which are expected as promising candidates for the pulsed power system applications. However, their relatively low dielectric breakdown strength usually cannot meet the requirements of practical application. In this work, we adopt hot-press sintering method to enhance the dielectric breakdown strength of the TiO2-SiO2-Al2O3 based ceramics, and the dielectric breakdown strength reaches 77.5 kV/mm, which is 1.8 times as large as samples prepared by conventional sintering method. The effect of different sintering methods on microstructure, dielectric properties and dielectric breakdown strength is investigated. The improvement of dielectric breakdown strength can be ascribed to improved bulk density, smaller grain size, and reduced reduction of Ti4+ to Ti3+, associated with the applied external pressure and lower sintering temperature. Eventually, large power density (18.20 MW/cm3) is obtained in pulse overdamped discharge circuit. Meanwhile, the stored energy is also released in a short time (about 11.3 ns to release 90% of saturated energy density value).