Thermal-fluid coupled calculation is an effective way to simulate the temperature rise and heat dissipation process of switchgear. But there are still problems such as huge calculation and low accuracy need to be solved. This paper discusses the optimization methods of the thermal-fluid coupled field for the switchgear from grid controlling, boundary conditions, and heat source calculation. First, the mesh adaption method based on posterior error estimation is proposed to achieve efficient mesh refinement with less redundancy. The final mesh size is only 32.3% of that obtained with the traditional global-refining method. Then, an external flow model is built to obtain the convective heat transfer coefficient of the enclosure, replacing the process of artificial choosing. The results show that the convective heat transfer coefficient at the enclosure under natural convection is 0.4 W/(m 2 • • C) ∼1.4 W/(m 2 • • C). Afterwards the eddy current field is used to solve the heat generation in the switchgear. The heat sources are coupled to the thermalfluid calculation so that the influence of current non-uniformity, contact heat, and eddy loss is considered. At last, the methods are applied to the steady-state temperature rise simulation of KYN28A-12kV/630A switchgear and the results are compared with the test data. The maximum relative error between simulation and experimental results is 3.43%, which proves the validity of the mentioned methods. INDEX TERMS Convective heat transfer coefficient, posterior error estimation, switchgear, thermal-fluid coupled simulation.
In order to meet the requirements of corrosion resistance of the grounding material and thermal stability of the grounding material of the transmission line towers, under the condition of power frequency current and high-frequency lightning current scattering into the ground in the case of short-circuit fault and lightning strikes, a kind of high-current capability flexible graphite grounding material was developed. The corrosion resistance of the flexible graphite grounding material and the steel type grounding material was compared by the soil simulation solution corrosion tests. The contact performance with different soils of the two materials was analyzed by the actual contact resistance measurement test. The thermal stability and the impulse current effective length of this grounding material were studied by means of simulation calculation. The results show that the high-current capability flexible graphite grounding material has a strong anticorrosion characteristic, whose reliable service life can exceed 30 years. Compared to the round steel grounding material, the contact resistance with the soil can be reduced by approximately 30%, and the impulse current effective length can be increased by about 30%. INDEX TERMS Flexible graphite grounding material, corrosion resistant characteristic, contact resistance, thermal stability, impulse current effective length.
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