The resistance welding transformer is designed for resistance welding with alternating current of mild steels up to 2.0 mm thick. The transformer is designed for operation in closed specially equipped rooms with natural ventilation at an ambient temperature of 0 ° to plus 40 ° C, relative humidity of no more than 80% at a temperature of plus 25 ° C. The air in the room should not contain flammable and combustible liquids, flammable dust and active chemicals.