Surge load experiment design and results analysis of relay
Due to the transient overvoltage or overcurrent when relay's contacts switch different loads, the relay's contacts are damaged by transient arc erosion of electrical-over-stress, which influences the reliability of relay seriously. Firstly, according to the life test requirements of one type of electromagnetic relay with permanent magnets, the load circuit and the testing program are designed, which has characteristic of adjustable surge current time. Secondly, the contacts' breaking arc and closing bounce under 2A resistive load, 5A resistive load and surge load are analyzed. The influence of surge load on relay's electrical life is studied with increasing of test cycles. Finally, based on the testing data, the optimal design of relay has been modified and the results have been analyzed, which is helpful for improving the life of the relay.
Influence of arc duration and current on contact welding in low power switches
A model test switch has been developed to investigate the influence of kinetic parameters (as contact velocity and contact force) on contact welding under conditions prevailing in relays, micro switches etc. Both frequency and intensity of the statistically scattered weld forces increased with increasing arc duration and current. Pre-strike and bounce arcs show identical results under corresponding conditions. Therefore, the configuration of the load circuit determining the actual arc current curve essentially influences the weld force values.
Electrical contact phenomena during impact
The authors outline the theory of impact as it applies to electrical contacts. The concept of the coefficient of restitution is evaluated as a means of modeling the events at impact. The events occurring during the impact of electrical contacts are vital to the long-term reliability of the contacts; so design parameters are considered in terms of their influence upon the dynamics of impact and bounce. Experimental studies are presented which include the measurement of impact forces, impact time, and both current and voltage characteristics. The influence of preimpact arcing is evaluated in the medium current range, and is shown to have an effect on the events occurring during the first impact. A mathematical model is proposed for electrical contact bounce, but it is shown that reducing the arcing may not always reduce contact wear.<<ETX>>