Identifying Faulty Feeder for Single-Phase High Impedance Fault in Resonant Grounding Distribution System

The identification of faulty feeder for single-phase high impedance faults (HIFs), especially in resonant grounding distribution system (RGDS), has always been a challenge, and existing faulty feeder identification techniques for HIFs suffer from some drawbacks. For this problem, the fault transient characteristic of single-phase HIF is analyzed and a faulty feeder identification method for HIF is proposed. The analysis shows that the transient zero-sequence current of each feeder is seen as a linear relationship between bus transient zero-sequence voltage and bus transient zero-sequence voltage derivative, and the coefficients are the reciprocal of transition resistance and feeder own capacitance, respectively, in both the over-damping state and the under-damping state. In order to estimate transition resistance and capacitance of each feeder, a least squares algorithm is utilized. The estimated transition resistance of a healthy feeder is infinite theoretically, and is a huge value practically. However, the estimated transition resistance of faulty feeder is approximately equal to actual fault resistance value, and it is far less than the set threshold. According to the above significant difference, the faulty feeder can be identified. The efficiency of the proposed method for the single-phase HIF in RGDS is verified by simulation results and experimental results that are based on RTDS

Data-Mining-Based Real-Time Optimization of the Job Shop Scheduling Problem

In the job-shop scheduling field, timely and proper updating of the original scheduling strategy is an effective way to avoid the negative impact of disturbances on manufacturing. In this paper, a pure reactive scheduling method for updating the scheduling strategy is proposed to deal with the disturbance of the uncertainty of the arrival of new jobs in the job shop. The implementation process is as follows: combine data mining, discrete event simulation, and dispatching rules (DRs), take makespan and machine utilization as scheduling criteria, divide the manufacturing system production period into multiple scheduling subperiods, and build a dynamic scheduling model that assigns DRs to subscheduling periods in real-time; the scheduling strategies are generated at the beginning of each scheduling subperiod. The experiments showed that the method proposed enables a reduction in the makespan of 2–17% and an improvement in the machine utilization of 2–21%. The constructed scheduling model can assign the optimal DR to each scheduling subperiod in real-time, which realizes the purpose of locally updating the scheduling strategy and enhancing the overall scheduling effect of the manufacturing system

Measuring high pressure equation of state of polystyrene using laser driven shock wave

High precision polystyrene equation of state data were measured using laser-driven shock waves with pressures from 180 GPa to 700 GPa. α quartz was used as standard material, the shock wave trajectory in quartz and polystyrene was measured using the Velocity Interferometer for Any Reflector (VISAR). Instantaneous shock velocity in quartz and polystyrene was obtained when the shock wave pass the interface. This provided ~1% precision in shock velocity measurements

High-power laser shock-induced dynamic fracture of aluminum and microscopic observation of samples

High-power laser induced shocks generated by “ShenGuang II” laser facility has been used to study spall fracture of polycrystalline aluminum at strain rates more than 106/s. The free surface velocity histories of shock-loaded samples, 150 μm thick and with initial temperature from 293 K to 873 K, have been recorded using velocity interferometer system for any reflector (VISAR). From the free surface velocity profile, spall strength and yield stress are calculated, it demonstrates that spall strength will decline and yield strength increase with initial temperature. The loaded samples are recovered to obtain samples' section and free surface metallographic pictures through Laser Scanning Confocal Microscopy. It is found that there are more micro-voids and more opportunity to appear bigger voids near the spall plane and the grain size increases with temperature slowly but smoothly except the sharply change at 893 K (near melting point). Besides, the fracture mechanisms change from mainly intergranular fracture to transgranular fracture with the increase of initial temperature