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Dielectric energy-storage capacitors are among the main enabling technologies in high-density power converters, in which lead-free relaxor ferroelectric ceramics have been paid particular attention to. However, low energy-storage performance at elevated temperature and high electric field, and the lack of application-oriented evaluation are among the primary blocks stumbling their progress. As a demonstration, 0.87BaTiO3-0.13Bi[Zn2/3(Nb0.85Ta0.15)1/3]O3 (BTBZNT) lead-free relaxor ferroelectric ceramics were modified by linear dielectric CaZrO3 (CZ) with various contents of 0, 0.1, 0.2, and 0.3 (CZ0, CZ1, CZ2, and CZ3). XRD and Raman results reveal major perovskite phases, and densely sintered ceramics were witnessed from the SEM images. Unchanged weakly coupled relaxor behavior was confirmed by the big critical coefficient of 1.6–1.8 from the modified Curie–Weiss law and the large activation energy of 0.29–0.32 eV from the Volgel–Fulcher fittings, and CZ was found to suppress high-temperature loss. From the normal polarization–electric field (P–E) loops, CZ0 is optimal for energy-storage owing to the highest discharged energy density and modest efficiency. Nevertheless, from the application-oriented DC-biased P–E loops, CZ1 is oppositely superior to CZ0 because of the higher permittivity and lower loss leading to higher discharged energy density and efficiency at DC-biased electric field. Moreover, CZ1 outperforms CZ0 in the higher capacitance density and lower temperature rise at higher temperature and electric field. Enhanced DC-biased energy-storage performance in BTBZNT ceramics modified by CZ was achieved, which should enlighten the advance of energy-storage ceramics targeting the application in high-density power converters. [ABSTRACT FROM AUTHOR]

With the development of the power industry and the increase in the capacity of power systems, vacuum switches have been developed rapidly. The distribution characteristics of the vacuum arc can reflect the working conditions of the vacuum switch. So, it is vital to understand the distribution characteristics in the vacuum arc burning process for understanding the interruption performance of vacuum switches. Based on the 3D magnetohydrodynamic model, we investigated the high-current vacuum arc burning process by modeling and numerical simulation. The research findings show a certain correspondence between the change in plasma parameters values and the change in arc current. The distribution of plasma parameters is uniform when the current is small. The distribution of plasma parameters in the first 1/4 cycle is more uniform than in the second 1/4 cycle. The evolution characteristics of the arc plasma parameters for interruption before the arc current maximum differ significantly from those for interruption after the arc current maximum and current maximum. The results of this study can provide a reference for the design and improvement of vacuum switches. [ABSTRACT FROM AUTHOR]

With the advantages of environmental protection, small size, and light weight, the vacuum circuit breaker has been widely used in power systems. At present, it is developing toward the direction of high voltage and high current. In this paper, the magnetic field simulation model of a cup-shaped axial magnetic contact system is established, and the actual magnetic field data in the arc area are obtained as the boundary conditions, and then a three-dimensional steady-state magnetohydrodynamic model of the vacuum arc is established. The plasma parameter distribution characteristics in the vacuum arc area are studied by changing the number of slots in the contact plate, the angle of the contact cup chute, the length of the slot in the contact plate, and the central process hole. On this basis, a new type of embedded axial magnetic contact system including an embedded magnetic ring and a reverse contact cup is proposed, and the influence of changing the angle and number of inclined slots of the embedded contact cup on the arc distribution characteristics at the peak current and current zero is further studied. The simulation results show that the new structure contact is helpful to the breaking capacity of the vacuum switch and has a guiding significance for the design of the vacuum circuit breaker. By comparison, our simulation results have the same trend with the experimental results of other researchers. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers (VCBs) are widely used in power distribution systems. When the VCB in a switchgear interrupts the short circuit current, the U type loop, which consists of a vacuum interrupter, an external busbar and a conductive rod, generates an external transverse magnetic field (ETMF). This field deflects the vacuum arc and affects the interruption performance of the VCB. In this paper, the real magnetic field data of the arc region are obtained by establishing a simulation model of an electrode system, taking into account the real ETMF and real axial magnetic field (AMF). Furthermore, the three dimensional steady magnetohydrodynamic model of the vacuum arc is established by using real magnetic field data as the boundary condition. The vacuum arc characteristics under the combined effect of AMF and the asymmetric transverse magnetic field (TMF) are studied. The simulation results show that the ETMF considerably changes the Bx of the arc column, which demonstrates asymmetry in the positive and negative directions, whereas By demonstrates a weaker asymmetry. Moreover, the asymmetric TMF deflects the distributions of the vacuum arc plasma and increases the partial heat flux density and axial current density. With the increase in the severity of the short circuit, the TMF asymmetry of the arc region is enhanced and the deflection of the vacuum arc plasma is also enhanced. [ABSTRACT FROM AUTHOR]

Presents a study which examined the effects of carbon content, tensile force and temperature on the electrical resistance of carbon-filled liquid silicone rubber composites. Review of related literature; Methodology; Results and discussion.

Quantum cascade laser (QCL) with porous structure is reported in this work. The porous structure is fabricated onto the wafer top surface towards the sides of the QCL waveguide by electro-chemical etching. The pore size of the porous structure is in hundreds of nanometers. Experimental results show that QCL with porous structure exhibits better beam quality. The far field of the typical 60 μm-ridge-width QCL is modulated from double-lobed shape to single-lobed shape due to the utilizing of porous structure. The full width at half maximum is 5.26°, which agrees very well with that of fundamental transverse mode. An interesting spectra behavior is also observed. The QCL with porous structure represents a temperature tuning rate of 0.49 nm/K, which is comparable to distributed feedback QCL. [ABSTRACT FROM AUTHOR]

The boom in high-power-density electronics and advanced pulsed power systems has led to a requirement for high-energy-density dielectric capacitors, for which the key enabler is the availability of dielectric materials with high energy densities and high efficiencies. Although antiferroelectric ceramics are promising dielectric materials with high energy densities, they have low efficiencies. In this study, we address this problem through the core–shell structure design. A phase-field model is developed by considering the core as antiferroelectric and the shell as linear dielectric, and the polarization hysteresis loops are determined. The results show that the polarization–electric field loop of the core–shell sample is slanted, with a delayed saturation polarization, decreased maximum polarization, and declined hysteresis loss compared with the pure sample. This phenomenon becomes more distinct with increasing shell fraction and decreasing shell permittivity, and vanished hysteresis is achieved in samples with a high shell fraction and a low shell permittivity. Through deconvolution, it is determined that the underlying mechanism of energy storage is the difference in the antiferroelectric polarization contribution of various shell parameters. It is found that a giant energy density of 15.5 J/cm3 and an ultrahigh efficiency of 99.7% at the saturation polarization can be achieved concurrently for a certain core–shell sample; these values considerably exceed the corresponding values (5.0 J/cm3 and 52.8%) for the pure sample. The findings of this study can serve as guidance for engineering core–shell structures, thus paving the way for enhancing the energy-storage performance of antiferroelectric ceramics. [ABSTRACT FROM AUTHOR]