Evaluation of lightning-induced overvoltage on a 10 kV distribution line based on electromagnetic return-stroke model using finite-difference time-domain

Accurate simulation of lightning-induced overvoltage for overhead distribution lines is helpful to prevent lightning trip accidents.An electromagnetic return-stroke model was used to represent lightning and then a 3D finite-difference time-domain(FDTD)method was adopted to simulate the lightning-induced overvoltage on a distribution line without a field-line coupling model.How lightning-induced overvoltage behave for different ground conductivity and varying distance between the distribution line and the lightning channel was analysed.The results showed that the overvoltage waveforms at the centre point of the line corresponding to lightning strikes on the lossy ground and an ideal ground(σ=∞)were similar;however,the peak amplitudes of the waveform were affected by soil conductivity at a close distance.The relationship between magnitude of the overvoltage and distance can be described by a second-order exponential decay equation.Finally,the overvoltage calculated using the proposed model was compared with those obtained based on Agrawal's model and measurements made using the newly developed intelligent insulator on site.From these comparisons,it could be concluded that the FDTD method with the electromagnetic return-stroke model produces reasonably accurate results of the attenuated oscillation waveform,which can better reproduce the overvoltage on operational distribution lines.

Understanding the charging of supercapacitors by electrochemical quartz crystal microbalance

Supercapacitors are highly valued energy storage devices with high power density,fast charging ability,and exceptional cycling stability.A profound understanding of their charging mechanisms is crucial for continuous performance enhancement.Electrochemical quartz crystal microbalance(EQCM),a detection means that provides in situ mass change information during charging–discharging processes at the nanogram level,has received greatly significant attention during the past decade due to its high sensitivity,non-destructiveness and low cost.Since being used to track ionic fluxes in porous carbons in 2009,EQCM has played a pivotal role in understanding the charging mechanisms of supercapacitors.Herein,we review the critical progress of EQCM hitherto,including theory fundamentals and applications in supercapacitors.Finally,we discuss the fundamental effects of ion desolvation and transport on the performance of supercapacitors.The advantages and defects of applying EQCM in supercapacitors are thoroughly examined,and future directions are proposed.

Facile preparation of covalent organic frameworks@alginate composite beads for enhanced uranium(Ⅵ) adsorption

Covalent organic frameworks(COFs) have broad application prospects in adsorption and separation.Yet,as COFs are generally in powder form,their superior performance at the laboratory scale is difficult to transfer into pilot-or industrial-scale use.Thus,there is a strong and urgent need to structure COFs into monolithic materials.Herein,a facile strategy was developed to prepare COFs@alginate composite beads.Three composite beads comprising different COFs including TpPa-1(2,4,6-triformylphloroglucinol(Tp) and p-phenylenediamine(Pa-1)as monomers),TpDb(Tp and 2,5-diaminobenzonitrile(Db)as monomers) and TpTt(Tp and 1,3,5-triazine-2,4,6-triamine(Tt) as monomers) with controlled COF loading and product size have been facilely achieved via this strategy,validating the applicability of this method.Furthermore,the representative TpDb@alginate composite beads showed good adsorption performance of uranium(VI) in aqueous solution with high adsorption capacity(635 mg·g^(-1)),good interference immunity and recyclability.This work offers a practical approach for incorporation of COFs into polymer matrix,which can serve as potential adsorbents for radioactive wastewater treatment.