Experimental Research on Electromechanical Properties of Multiple Contact Surfaces Copper Bulks under Normal Cyclic Loading and Variable Temperature.

Limei Liu,Keyang Wang,Wurui Ta,Yuanwen Gao,Yang Liu,Jiangtao Yan

doi:10.3390/ma12233883

Abstract

Contact resistance is key for stable operation of electrical contact equipment, and can also be extensively applied. For Tokomak devices in fusion reactors, contact resistance of the superconductor magnet system strongly relates to the alternating current (AC) loss of the cable; the cable is assembled using a certain number of contacting superconducting tapes coated with copper layers on both sides. The contact resistance of a metal solid surface is affected by many factors. In this work, the contact resistance of copper surface samples was studied experimentally under variable normal cyclic load, temperature and number of contact surfaces. This is consistent with real-world working conditions, as the structure of superconducting cables can be changed, and such cables are used under cyclic electromagnetic forces in temperatures which range from room to working temperature. Experimental results showed that contact resistance decreased rapidly with an increase of load. Further, when temperature was varied from 77 to 373 K, the load–unload contact resistance lag decreased. When the number of contact surfaces was increased, contact resistance increased. Finally, a fitted formula describing the relationship between contact resistance and cyclic times, temperature and number of contact interfaces was determined. This formula can be used to predict variation trends of contact resistance in complex environments and provide more accurate contact resistance parameters for calculating the AC loss of superconducting cables.

Highlights

Electrical contact resistance is key to stable operation of electrical equipment
Relative contact resistance curves obtained under the given normal loads during (a) the first, second, third, fifth, eighth and tenth cyclic loadings; (b) the first cycle only; (c) the second cycle first, second, third, fifth, eighth cyclic loadings; (b) the first cycle only; (c) the second cycle only; and (d) the fifth, eighthand and tenth tenth cycles
Results of and Resistancecontact under resistance oxidized hardened, thereby the action of the same normal force, the fact that the unloading contact resistance was less than the loading contactapplications, resistance indicates that the actual conductive area are during unloading used was greater

Summary

Introduction

Electrical contact resistance is key to stable operation of electrical equipment. It is extensively applied in various fields, including in the creation of resistance spots on metal elements [1,2,3], making force sensors in micro-electromechanical systems [4], making gas sensors using contact between semiconductors [5], detecting critical points in the contact area of connectors [6], and obtaining a lubrication contact diagnosis between contact surfaces [7].Used especially in the superconductor magnet system of Tokomak devices in fusion reactors, a new generation of non-insulated REBCO (Rare Earth-Barium-Copper Oxide) tape, which possesses a layer of copper coated on both sides, has been shown to have strong mechanical properties and high critical current density. Electrical contact resistance is key to stable operation of electrical equipment. It is extensively applied in various fields, including in the creation of resistance spots on metal elements [1,2,3], making force sensors in micro-electromechanical systems [4], making gas sensors using contact between semiconductors [5], detecting critical points in the contact area of connectors [6], and obtaining a lubrication contact diagnosis between contact surfaces [7]. When a non-insulated REBCO magnet works, internal current flows. Materials 2019, 12, 3883 current flows between the tapes. Transverse contact resistance between the tapes is a key parameter of the internal alternating current (AC) loss of the magnet. Transverse a keythe parameter the internal calculated effectively when thecontact contactresistance resistancebetween betweenthe thetapes tapesisunder action ofofcyclic load is alternating current (AC)

Results

Discussion

Conclusion