One of the challenging problems in the plasma spray technique is reproducibility of the coating quality. This problem is mainly associated with arc fluctuations, which affect the plasma jet temperature and velocity inside the plasma torch. In this study, three-dimensional numerical models are developed to study the behaviour of Ar-N-2 plasma arc inside a non-transferred torch and plasma jet. Ar-N-2 plasma arc is simulated for given arc current and gas flow rate. Different arc sizes, which correspond to given torch power, are predicted. A most feasible arc size, which corresponds to an actual physical situation of the arc inside the torch, is identified using thermodynamic principle of minimum entropy production for particular torch power. Predicted torch efficiency is comparable with measured one. Cathode and anode losses are reported. Predicted temperature and velocity profiles at the nozzle exit are used to simulate the plasma jet. Since plasma gas is mixed with cold air, plasma jet is diffused in the radial direction. Three-dimensional effect on plasma jet temperature and velocity is diminishes along the axial direction.