Zhou Xue

Evaporation Erosion During the Relay Contact Breaking Process Based on a Simplified Arc Model

Evaporation erosion of the contacts is one of the fundamental failure mechanisms for relays. In this paper, the evaporation erosion characteristics are investigated for the copper contact pair breaking a resistive direct current (dc) 30 V/10 A circuit in the air. Molten pool simulation of the contacts is coupled with the gas dynamics to calculate the evaporation rate. A simplified arc model is constructed to obtain the contact voltage and current variations with time for the prediction of the current density and the heat flux distributions flowing from the arc into the contacts. The evaporation rate and mass variations with time during the breaking process are presented. Experiments are carried out to verify the simulation results.

Experiment research on re-strike phenomenon occurring during high-voltage direct-current breaking process under transverse magnetic field

In high-voltage direct-current relays, transverse magnetic field is widely used to reduce the arc erosion. Experiments showed that re-strike phenomenon always occurred during the arc-blowing process, which increased the arc duration and affected the normal breaking operation. In this paper, the arc-blowing process is investigated for 300~800V, 50A resistive load and special attentions are paid on re-strike phenomenon. The re-strike type, re-strike voltage and re-strike probability under different voltages are studied with the help of the arc images and arc voltage waveforms.

Electrical lifespan prediction of high-voltage direct-current relay based on arc charge accumulation

Electrical lifespan prediction has always been one of the greatest challenges in switching apparatus. In this paper, a mathematical model based on arc charge accumulation from experiments is set up to predict the electrical lifespan of high-voltage direct-current (HVDC) relays. The electrical circuit condition is 270VDC/200A, resistive load. The contact pair is bridge-type and made of copper. Experiments are carried out with a parameter-adjustable device in similar with actual HVDC relay structure. The magnetic field flux density for arc blowing is controlled in the range of 40mT to 80mT. The arc current waveforms are acquired and the arc charge during each breaking operation is calculated. The arc charge is accumulated until it reaches threshold value, which is decided according to electrical lifespan test results of actual products. The relationship between the lifespan and the magnetic field flux density is constructed, which can be used for lifespan prediction.

Thermodynamic Properties and Transport Coefficients of Nitrogen, Hydrogen and Helium Plasma Mixed with Silver Vapor*

Species composites of Ag-N2, Ag-H2 and Ag-He plasmas in the temperature range of 3,000-20,000 K and at 1 atmospheric pressure were calculated by using the minimization of Gibbs free energy. Thermodynamic properties and transport coefficients of nitrogen, hydrogen and helium plasmas mixed with a variety of silver vapor were then calculated based on the equilibrium composites and collision integral data. The calculation procedure was verified by comparing the results obtained in this paper with the published transport coefficients on the case of pure nitrogen plasma. The influences of the silver vapor concentration on composites, thermodynamic properties and transport coefficients were finally analyzed and summarized for all the three types of plasmas. Those physical properties were important for theoretical study and numerical calculation on arc plasma generated by silver-based electrodes in those gases in sealed electromagnetic relays and contacts.