The vacuum circuit breaker (VCB) is an important vacuum switch widely used in generator protection systems and medium-voltage distribution power systems. For observing the vacuum arc behavior variation and analyzing the dielectric recovery characteristics and interrupting capability of VCBs, an experimental platform for a 40.5kV/31.5kA/2500A VCB was established. Under the condition of typical short-circuit current breaking, the short-circuit current breaking test was carried out and the vacuum arc image was collected to obtain the curve of voltage versus current during the breaking process and the arc resistance distribution. By analyzing the variation trend of dynamic arc resistance, a physical and mathematical description of dynamic arc resistance was obtained by the curve fitting method. By comparing and analyzing the experimental data of arc resistance, it is shown that the physical and mathematical description can appropriately describe the spatiotemporal variation of arc resistance in the arcing interval.

Short-circuit faults are inevitable in split-winding transformers with stabilizing windings, and the resulting transient electromagnetic force may cause detrimental damages to the equipment. This paper focuses on a comprehensive analysis of the characteristics of the split-winding transformer with stabilizing windings under different short-circuit faults. In this regard, a FEM based on field-circuit coupled approach is proposed. And a SFFZ10-88000 kVA split-winding transformer with stabilizing windings is used as a prototype to investigate its transient performances with both full-crossing and half-crossing conditions under different short-circuit faults. The symmetrical component method is presented to compute short-circuit currents to compared with the simulation ones, and a prototype test model is established to verify the correctness of the proposed method. The results reveal that the axial forces exerted on the winding in half-crossing short-circuit faults are generally larger than those in full-crossing short-circuit faults. Moreover, there is a considerable short-circuit force in the stabilizing winding in cases of a single-phase earthed fault and a two-phase earthed fault and there is no current in the stabilizing winding under other short-circuit fault cases. The numerical modeling approach dealt with in this paper is expected to be useful in the design of the split-winding transformer with stabilizing windings.

A 30-kV direct current vacuum circuit breaker with double-break (DB-DC VCB) in series was taken into consideration; the interrupting current and the transient recovery voltage (TRV) under both synchronous and asynchronous interrupting conditions were measured, and the arcing process during the interrupting was captured by a high-speed camera. The continuous transition model (CTM) was used to simulate the postarc dielectric recovery characteristic during the asynchronous interrupting. The experimental and simulation results show that when one of the breaks in the DB-DC VCB is delayed under 5-kA current interrupting due to the dispersion performance of the mechanism, the two breaks will exhibit a significant difference in the arc characteristic and the TRV. The delayed break has higher arc energy, higher concentration of vaporized metal particles (VMPs), and lower postarc dielectric recovery capacity. The different break gap widths during the arcing process led to the arc characteristic difference. When the delay exceeds a critical value (0.5 ms), the VMPs between the break for the delayed break are difficult to dissipate and easy to reignite at the breakdown weak point.

We report successful fabrication of GaAs/Al_0.26Ga_0.74As double‐heterostructure laser diodes grown on patterned Si substrates by molecular beam epitaxy. The patterned substrates consist of exposed Si stripes with widths ranging from 9 to 70 μm and surrounded by 900 Å of SiN films on both sides. Oxide‐defined contact stripe lasers with stripe widths ranging from 3 to 50 μm (corresponding to each of the SiN‐defined stripe windows) were fabricated. Reduction of laser threshold current densities compared to similar lasers grown on nonpatterned Si substrates is observed, and is attributed to current confinement effect by the high‐resistivity polycrystalline GaAs/AlGaAs films surrounding the active devices. From the measurements on the longitudinal mode spectrum and far‐field patterns, lateral index guiding is also observed for the 10‐μm‐wide selective‐area grown laser.

Based on particle swarm optimization algorithm, a three-dimensional model of the contact system of vacuum interrupter is established. Combined with the particle swarm optimization algorithm and finite element magnetic field numerical simulation method, the contact structure parameters of a 400V/20kA vacuum interrupter is taken as the optimization variables, and the maximum magnetic field intensity at the arc root is determined as the optimization objective. The distribution of the maximum transverse magnetic field intensity at the contact gap under the optimum parameters has been illustrated and analyzed.

The flux-modulated machine based on air-gap magnetic flux modulation theory has become a focus in low speed and high torque density applications. In this paper, the optimal design of a large scale flux modulation (FM) permanent magnet (PM) generator with high temperature superconducting (HTS) bucks for wind energy conversion systems is presented. Firstly, the working performances of the generator with and without HTS bucks sandwiched between iron segments are analyzed and compared through finite element analyses (FEA). The FM effect enhancement by employing the HTS bucks is proved through the comparisons. Secondly, the sensitivities of the generator structural parameters on the back electromotive force (EMF) and the cogging torque amplitude are analyzed by Taguchi method to decide the optimization variables and their variation ranges. Thirdly, the structural parameters determined by the sensitivity analyses are optimized through the coupling of genetic algorithm (GA) and FEA to maximum the generator output power capacity. The calculation burden during optimization is reduced with a reduction on the optimization variable number through the Taguchi method based sensitivity analyses. Finally, the electromagnetic characteristics of the FMPM generator with optimized structural sizes are numerically investigated.