The purpose of this paper is to demonstrate and analyse transition events that occur when the loaded transformer is turned on and off within the welding device. The purpose of the welder is to provide a high quality and stable voltage during the ignition of the arc, and often during the ignition of the arc the transformer comes from its no-load state to the work-load state, depending on the diameter of the electrode that the arc melts. The welding currents of the MIG/MAG (Metal Inert/Active Gas) process are not less than 100 A, about 350 A, at a voltage of the arc of 35 V (DC). In this paper, the MATLAB/PSB programme package is used to analyse the no-load inrush currents and the loaded inrush currents of welding transformers. Current and voltage waveforms were recorded on the primary side of the transformer, as well as the harmonic content of the transformer primary currents, with indicator calculation of the current waveform distortion -THDi.