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Contact bounce is a common phenomenon in the closing process of electromagnetic relays, which seriously affects the electrical contact reliability of the system. The whole closing process of flexible spring components consists of the free movement stage and the contact bounce stage, which increases the complexity of analyzing the electrical contact behaviors of electromagnetic relays. In this study, a novel nonlinear dynamic model of the flexible spring components in electromagnetic relays is established to analyze the physical mechanism of the electrical contact bounce. Considering the electromagnetic effect, flexible deformation, contact collision, and welding force, the proposed mathematical model can capture the dynamic closing process accurately and collect bounce parameters efficiently. The Kelvin–Voigt viscoelastic contact model is employed to evaluate the nonlinear contact force between the static and movable contacts. Based on the Galerkin method, the nonlinear equations of motion for the movable spring within electromagnetic relays are formulated. A series of experimental work are designed to measure the typical waveforms of displacements of the movable contact and currents in the coil during the closing process of the movable spring. Furthermore, the theoretical results are validated by comparing with the experimental data. The dependences of some key factors, including the structural, material, and electrical contact parameters on the contact bounce characteristics, are investigated explicitly. The theoretical results attest that the proposed model can accurately predict the dynamic behaviors of the movable spring, and the contact bounce can be effectively suppressed by adjusting the parameters of the flexible spring component. [ABSTRACT FROM AUTHOR]

Contact bounce is a common phenomenon in the closing process of the electromagnetic relay under capacitive loads. The investigations on the contact characteristics are mainly conducted by experimental methods. However, the experimental method is extremely complicated and time-consuming in structural design, and it cannot clearly reveal the mechanism of contact bounce. Therefore, a new theoretical model is proposed to investigate the dynamic characteristics of the electromagnetic relay under capacitive loads. The model allows for simulating dynamic process and collecting bounce parameters in a simple and effective way compared with conventional simulation and experimental methods. The physical mechanism of contact bounce for the electromagnetic relay is presented. The nonlinear contact force between the fixed and moving contacts is evaluated according to the Kelvin–Voigt viscoelastic contact model. The equations of motion considering the coupling of electromagnetic and mechanical fields are established. The theoretical results obtained in this study are validated by comparison with experimental data. The influences of the structural parameters, coil current, surge current, and contact resistance on the contact bounce are analyzed. The numerical results well demonstrate that the contact bounce can be effectively weakened by adjusting the parameters of contact spring and the mass of the moving contact. [ABSTRACT FROM AUTHOR]

The importance of high-power relays used to interrupt dc current has been significantly growing recently. In their arc chambers filled with nitrogen or its mixtures, bridge-type contacts with permanent magnets are major measures widely used for arc extinguish. Arc dwelling for a short duration after arc ignition, until its voltage increases rapidly, plays a crucial role in contact erosion. In this paper, arc dwelling time in a nitrogen environment during the entire bridge-type contacts interruption process of a resistive dc circuit is studied both experimentally and numerically. A multiphysics model coupled with the fluid flow, the temperature, the current density, as well as the E- and M-fields was built based on the magnetohydrodynamics theory for the arc chamber. The model was solved in COMSOL. The external resistive electric circuit was connected to the model, and the electric field in the arc was solved by adopting a floating potential. The detailed arc dwelling process is presented and preliminarily discussed according to the calculated temperature and current density distribution sequences. The calculated arc voltage shows good agreement with experimental results. Furthermore, the influence mechanism of breaking velocity on arc dwelling is analyzed by arc voltage. In this sense, the arc dwelling time could be shortened by increasing the breaking velocity within the reasonable extent. [ABSTRACT FROM AUTHOR]

Electrical lifespan prediction is one of the key problems for the designers of switching apparatus. It is of great necessity to develop empirical correlations between the design parameters and the electrical lifespan. In this paper, a novel method using the arc erosion mass as the prediction variable is proposed to predict the electrical lifespan of high-voltage direct-current (HVDC) relays. The arc current waveforms are measured, and the arc erosion mass during each breaking operation is calculated based on the relationship between the arc current and the arc erosion rate. The arc erosion mass is accumulated until it reaches a threshold value, which is determined by the electrical lifespan experimental results using HVDC products. It is found that the arc erosion mass linearly accumulates with the lifespan, which is very convenient in the electrical lifespan prediction. Experiments are carried out with a parameter-adjustable device similar to the actual HVDC relay structure. Effects of two key design parameters, the arc-blowing magnetic field flux density and the contact breaking speed, of the electrical lifespan are investigated. The magnetic field flux density is changed in the range from 40 to 80 mT, and the breaking speed is varied from 0.85 to 1.3 m/s. The relationships between the lifespan and the magnetic field flux density as well as the breaking speed are regressively constructed. It is shown that the developed relationships can be used for HVDC relay electrical lifespan prediction. [ABSTRACT FROM PUBLISHER]

DC power relay is a key electromechanical component widely used in electrical vehicles, photovoltaics, as well as more-electric aircrafts for energy managing, power conversion, and distribution. As the voltage and current increase due to relay switches, arc discharge becomes an unavoidable and significant issue during the operation of the dc high-power relay. Bridge-type contact and external permanent magnets are spontaneously employed in its arc chamber to accelerate the quenching of arc. In this paper, the complicated arc discharge plasma in a dc power relay has been investigated by using both experimental and numerical approaches. Initially, arc dwell and arc restriking characteristics during the arc motion phase are presented by analyzing the voltage and current waveforms and arc images acquired in carefully designed breaking experiments. The arc driven by a transverse magnetic field with a variety of flux densities and the influence of flux densities on arc voltage and dwell are preliminarily discussed based on the experimental results. Then, to reveal the arc physics and to determine the influence of transverse magnetic field on arc motion characteristics, a simplified model based on the magnetohydrodynamic (MHD) theory is built and three cases with different magnetic field are calculated. The simulated arc behaviors including distributions of the temperature and current density are presented. The mechanism underlying the influence of transverse magnetic field on the arc motion is analyzed according to arc root transfer and arc voltage variation. In addition, to understand the formation of the arc restriking, the critical breakdown electric-field strength inside the arc gap is also calculated based on streamer breakdown theory. The parameters in the space occupied by earlier arcs, as predicted by the MHD simulations, are used in the breakdown calculation. Results show that the critical breakdown voltage reduces remarkably along with growth of the operating voltage and breaking current, and the arc dwell time can be reduced by strengthening the external magnetic field within a reasonable extent. [ABSTRACT FROM PUBLISHER]

Two mass erosion mechanisms or mass loss modes for electrodes during the repetitive arcing processes should be responsible for the failure of electromagnetic relays, and there are evaporation erosion and sputter erosion. Of these two, the evaporation erosion is believed to be the main failure mechanism for the electrodes used in low-current relays. Unfortunately, there is still no straight-forward model to predict the characteristics of the evaporation process on the electrodes. In this paper, heat transfer and fluid dynamics in the molten pool in silver contacts are coupled with the gas dynamics in the vicinity of arc spot to determine the evaporation rate due to static arc. The influences of input parameters, such as arc current and material properties, on the evaporation rate are analyzed. Of all those parameters, boiling point and thermal conductivity of the electrode are found to be the most significant influences on the evaporation rate. The transfer direction of mass due to electrode evaporation is discussed on the assumption of zero net material loss, and it is found to be directly related to the current and heat flux from the arc to the electrodes. The method used in this paper to evaluate the evaporation erosion characteristics can serve for strategies to alleviate evaporation erosion for relay electrodes. [ABSTRACT FROM AUTHOR]

Composite contacts used for dc relays can help reduce their cost and the amount of precious metals used in their construction. Because of their electrical properties, silver metal oxide-copper (AgMeO–Cu) composite contacts are widely used; however, at heavy loads, the bonding strength of the composite contact will change due to the influence of uneven temperature and stress distributions, which may even cause failure in the form of oxide layer peeling. Here, typical AgSnO2In2O3–Cu composite contacts are studied. A 3-D finite-element simulation model that considers contact making, arcing, and breaking was established to calculate the contact temperature and thermal stress after any operation cycle. The model can be used to determine the variation of the contact temperature and thermal stress distributions versus operation time during an electrical life cycle test. For different AgMeO layer thicknesses (0.25 and 0.38 mm), the temperature and thermal stress distribution of composite contact’s bonding area were calculated under different current load levels: 30, 45, and 60 A, while the load voltage is a constant 17 V. Results show that the thickness of the AgMeO layer has a significant effect on the temperature and stress distribution of the bonding area in the moveable contact and the composite contacts may more easily curl and crack with an increment of the AgMeO layer thickness under the same current condition. The simulation results agree well with the experimental data and the relative error is less than 10%. The validity of the model and method was verified. The numerical model in the paper may be used to analyze a composite contact’s properties and is therefore useful for design optimization and the selection of composite contact materials. [ABSTRACT FROM PUBLISHER]