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Transformer power sources of welding arc of industrial frequency alternating current generate into the mains the level of higher current harmonics, which is by an order of magnitude lower by the value of the coefficient of general harmonic distortion, than that of the inverter power sources. Here, their high electromagnetic compatibility with other equipment of the mains is achieved. Moreover, they are much easier to maintain and more reliable. Harmonic composition of current during AC welding was calculated at application of pulsed devices of arc stabilization. It is shown that application of stabilizing pulses with the polarity opposite to that of arc current, is more advantageous that the use of pulses with the polarity coinciding with that of arc current. Advantages as to welding process effectiveness and smaller generation of higher current harmonics are also observed. [ABSTRACT FROM AUTHOR]