The electrical contact resistance of cambered surface contact is systematically studied by analytical solution and finite-element simulation. Two representative cambered surface contacts, namely sphere-plane contact and cylinder-plane contact are built and the distributions of electrical current lines profile and isopotential are compared explicitly. Subsequently, the effects of size parameters of cambered surface and mechanical load on contact resistance are evaluated over a large range of aspect ratios. Furthermore, dissimilarity between sphere-plane contact and cylinder-plane contact is deduced.

Higher contact resistance not only increases power consumption and temperature rise but also causes undesirable interconnectivity between electrode materials, which further influences the electrical lifespan and reliability of switching devices. However, relevant studies on the relationship between contact resistance and load force, and on the reduction of contact resistance by controlling the micro-structure of rough surfaces, especially for electrode materials with larger S_q (root mean square) values, are very limited. In this study, the contact resistance calculation method, based on classical Holm theory in combination with the elastic and plastic deformation, was reviewed. Then, typical curves of measured contact resistance and load force were analyzed and compared with the calculation results for smooth surfaces. Furthermore, experimental results for electrodes with bright and matt surfaces were compared. It was found that the average contact resistance of samples with matt surfaces was 0.162 mΩ for a load force of 5 N, which decreased by 18.52% compared to that of the bright surface. The standard deviation of the contact resistance greatly decreased to 0.008 mΩ for samples with matt surfaces, which indicated that the matt electrode surface could effectively produce low and stable contact resistance. In addition, the influences of the numbers and sizes of contact a-spots on the relationship between contact resistance and load force were investigated. It was found that denser asperities with smaller curvature radii for the matt surface were beneficial for lower contact resistance, even for the electrode material with larger S_q values. Finally, an empirical model of the contact resistance with error bands based on the experimental results was established and verified.

Electrical connectors play an indispensable role in electrical and electronic systems. The frequently occurred intermittent failure events seriously affect the reliability of application systems. In this article, the repetitive mechanical insertion and withdrawal experiment of electrical connector is carried out by using our designed test rig and the intermittent failure phenomena recurs. The typical waveforms of contact resistance and force during the mating operation are presented. The variation laws of static contact resistance and dynamic contact resistance under intermittent failure condition are counted and analyzed. And the dynamic contact resistance is proven to be a suitable sensitive parameter to characterize the intermittent failure event. Based on the mathematical model, variation of surface morphology, and element analysis, the failure mechanism of electrical connectors under repetitive operation is proposed.

The electrical arc erosion behavior extremely limits the lifespan of electromechanical switching devices. Observation the gradual evolution of arc erosion is highly beneficial for to understand the arc ignition and the contact degradation. In this paper, the erosion of contact materials is simulated and visualized in-situ with the recorded 2D microscopic images. A novel method for erosion area identification is proposed with the combination of difference image method and mathematical morphology operations. The variation in erosion area as a function of switching current cycles is demonstrated, and the center of erosion zone migrates continuously during the endurance experiment is determined. Finally, three types of arc erosion regimes (centralized arc erosion, separated arc erosion and commutated arc erosion) are revealed, but also the associated occurrence probabilities during 1,000 cycles are provided.

Multiple breaks are favorable for arc extinguishment of relays switching heavy load. However, the existed asynchronous mechanical separation of contact pairs and associated unbalanced arcing behavior limit the electrical lifetime to some extent. In this article, the typical contact voltage and contact current waveforms of double breaks within power relays are presented. Based on the variations in bounce energy, contact resistance, and arc energy as a function of switching cycles, the effect of contact gap on the electrical lifetime of power relays is analyzed explicitly. Furthermore, the failure process of power relays with two bridges is characterized by the recorded breaking time difference of bridges. The observed significant asynchronous breaking phenomena in the end of electrical lifetime experiments attribute to the contact welding failure of power relays.