Analysis And Optimal Design Of AC Contactor’s Thermal Characteristics

AC contactor plays a key role in power transmission and equipment control.As the complexity of the electrical equipments increases continuously, therequirements for the performances and reliability of contactors are getting higherand higher. The AC contactor studied in this paper has some practical problems inapplication, such as high temperature rise, contact welding, insufficient electricallife and so on. These problems require analysis and optimum design of its thermalcharacteristics.Firstly, the eddy-current and hysteresis loss of iron core in the electromagneticsystem are calculated. The temperature distribution of iron core is obtained by theelectromagnetic-thermal coupled finite element simulation by using the multi-fieldsimulation function of ANSYS software. The Newton law of heat transfermechanism is applied to calculate the power loss and the maximum temperature ofthe coil in the close situation. The results are verified by experiments.Secondly, based on the contact theory of rough surfaces, the mathematicalmodel of the contact is established due to the surface measurement and the statisticsanalysis. Specially, the average distance, the number of contact spot and the realcontact area under certain pressure are calculated. This contact model is applied onthe formula of contact resistance, the mathematical model of which is consequentlyachieved. By means of the equivalent model of contact resistance, a3-Delectromagnetic-thermal coupled simulation is carried out to obtain the contacttemperature rise, which is also verified by experiments. The further analysis focuson the influence laws of the contact pressure, the current and the contact size on thecontact temperature rise.Based on the work in the former chapters, the mathematical model of thermalfield and finite element model in the software ANSYS for the whole AC contactorare established. Moreover, the heat transfer mechanism of the internal gas isdetermined and the convection heat coefficients of external surfaces are calculatedusing the experiment correlations based on the dimensional analysis and similarprinciples respectively. With these parameters, the simulation is performed and thesimulation results provides the temperature distribution of the entire AC contactorand its key parts, which is verified by the experiment data obtained by the infraredthermography. The thermal characteristics of AC contactor under the environmentof high and low temperature are studied. The results confirm the tolerance of theproduct to the high and lower temperature impacts. Finally, by analyzing the influence factors of the contactor’s thermalcharacteristics, this paper proposes three improvement schemes. After comparisons,the final scheme is replacing the coil to a kind of laminated silicon steel, and at thesame time, changing the material of leading-out terminal rod to another materialwith higher heat conductivity. This improvement can reduce the eddy-current lossand the contact temperature rise, enhance the heat dissipation performance andbetter redistribute the temperature field, which all contribute to increase thereliability of this product. This work achieves better design of the AC contactor,and satisfies the customer’s requirements.