Simulation Method Study Of Short-term Tolerance Ability Of Electromechanical Relay Used Inwatt-hour Meter

Short-term tolerance ability is a very important index for evaluating electrical performance and reliability of electromechanical relay used in watt-hour meter. And simulation method is an auxiliary technique used in virtual prototype design and failure mechanism analysis. In this paper, the simulation method specially for short-term tolerance ability, that is thermal-stability and electro dynamical-stability of typical electromechanical relay, is present explicitly by using COMSOL Multiphysics commercial software.Firstly, the basic feature, the thermal source and conduction route are provided, and then the temperature distribution and associated influencing factors are illustrated separately. Further, the geometry model of relay is simplified reasonably. The relative thermal-electrical-fluid coupled physics field is built, and the effects of boundary conditions and body force on steady thermal field are analyzed. The optimal simulation model is determined by considering computation accuracy, computation time and consuming computing resources.Secondly, effects of electrical load, curvature radius of contact and spring material on the maximum steady temperature are analyzed with the use of above mentioned simulation method. The relationship between shock current waveforms(including rectangular wave, sinusoidal wave and triangular wave) and transient temperature rise of contact is investigated explicitly. Particularly, effects of spring thickness, width and size parameters of contact on the temperature rise response are also provided.Thirdly, the spherical-flat model and conductive bridge model of contact are built separately, and the calculation results of Holm force are also compared. The fundamental mathematical model is obtained basing on the physics nature of Holm force. The Holm force resulted from the single centralized a-spot is calculated and future the effects of elliptical shape, rectangular shape, circular shape, annular shape and circuit shape on Holm force are researched. The beneficial methods for increasing spring electrodynamic force are given. Basing on the contact force moment, the Lorentz moment of movable spring and the moment of contact force, the minimal contact force for preventing shocking current is present. Finally, the minimal shock current, which could repulse the normally closed contact pairs, is found experimentally.This research not only can provide theory foundation for the optimization design of electromechanical relay used in watt-hour meter, but also can be applied to the design of the general switching apparatus with mechanical contacts.