en High Voltage Engineering High Voltage Engineering Research Paper Research Paper <p style="text-align: justify;">Specific and sensitive operation of circuit breakers makes an individual position for them in power networks. Circuit breakers are at the central gravity of variations and execution operations. Therefore, an optimum operation is the main reason to investigate about new gases to be used in MV and HV circuit breakers instead of <em>SF₆</em>. The arc process has enormous complexity because of hydrodynamic and electromagnetic combination equations, and that is the exact reason why most of the previous simulations were processed in two-dimension analysis. But, in this paper a three-dimension simulation with sufficient results has been fully discussed. Different evaluations on the other gases have taken under study in order to find a suitable substitute instead of <em>SF₆</em> gas, which can also bring an optimum operation for the breakers and can be even friendly with the environment. The simulations have been carried out based on the finite element method (FEM) and magneto-hydrodynamic equations. A three-dimension model under the transient state has been chosen in the simulations to find a feasible substitute for <em>SF₆</em> gas. The main factors of the analysis are threefold as follows: arc temperature on the different regions, the cooling ability and arc resistance. <em>CO₂</em>, <em>CF₃I</em> and <em>N₂</em> are nominated to substitute the <em>SF₆</em> gas and their effects on cooling ability, nozzle evaporation, contacts erosion and arc resistance will be discussed.</p> <p></p> Magnetohydrodynamic (MHD) Equations,Finite Element Method (FEM),Cooling Ability,Substitute Gas, 257 265 http://ijeee.iust.ac.ir/browse.php?a_code=A-10-1825-2&slc_lang=en&sid=1 V. Abbasi v_abbasi@kut.ac.ir 180031947532846005650 180031947532846005650 Yes Department of Electrical Engineering, Faculty of Energy, Kermanshah University of Technology, Kermanshah, Iran L. Hassanvand l-hasanvand@kut.ac.ir 180031947532846005651 180031947532846005651 No Department of Electrical Engineering, Faculty of Energy, Kermanshah University of Technology, Kermanshah, Iran A. Gholami gholami@iust.ac.ir 180031947532846005652 180031947532846005652 No Electrical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, Iran