Single-phase-to-ground fault protection based on zero-sequence current ratio coefficient for low-resistance grounding distribution network

Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs.

Electrical transport properties of cerium doped Bi_(2)Te_(3)thin films grown by molecular beam epitaxy

Introducing magnetism into topological insulators(TIs)can tune the topological surface states and produce exotic physical effects.Rare earth elements are considered as important dopant candidates,due to their large magnetic moments from heavily shielded 4f electrons.As the first element with just one 4f electron,cerium(Ce)offers an ideal platform for exploring the doping effect of f-electron in TIs.Here in this work,we have grown cerium-doped topological insulator Bi_(2)Te_(3)thin films on an Al_(2)O_(3)(0001)substrate by molecular beam epitaxy(MBE).Electronic transport measurements revealed the Kondo effect,weak anti-localization(WAL)effect and suppression of surface conducting channels by Ce doping.Our research shows the funda-mental doping effects of Ce in Bi_(2)Te_(3)thin films,and demonstrates that such a system could be a good platform for further re-search.

Adjustable indentation and vibration isolation performances of nacre-like metamaterial

Along with the living environment,organisms have evolved structures that adapt to specific environments and have better mechanical properties.Bioinspired materials learn from nature and improve their mechanical properties by imitating the structure of living organisms.Based on the 4D printed shape memory polymer and the bioinspired design method,this research proposes a soft and hard phase hybrid bioinspired metamaterial with shape memory effect and programmable mechanical properties.Compared with traditional nacre-like materials,bioinspired materials have adjustable characteristics of mechanical properties,impact resistance,and low-frequency vibration isolation.First,based on the constitutive relation of SMP(Shape memory polymer)material and its numerical simu-lation,an intelligent bioinspired metamaterial is designed.Subsequently,the mechanical properties and vibration isola-tion behavior and adjustability performance of multi-scale bioinspired metamaterials are explained by experiments.Finally,the adjustable functional mechanism of the deforma-tion and vibration isolation of the bioinspired metamaterial is described.The research of these bioinspired metamaterials has broad application prospects in the fields of impact protection and low-frequency vibration absorption.