The synchronous motor of 1250 HP, 4 kV to 60 Hz of high performance and constant speed, corrects the power factor and drives the ball mill operating in the "Concentration" sub-process carried out in the Magnetic Plant of San Nicolás in the company Minera – Metalúrgica Shougang Hierro Perú S.A. The mill is called "milling medium" and uses 2" diameter carbon steel balls to obtain final products of iron ore with a diameter of 0.074 mm to 0.4 mm. In this subprocess, secondary milling is carried out, which consists in crushing and rectifying the ore. The interruptions in the productive process generated by operational problems in the synchronous motor, originate from the humid, highly corrosive and particulate contamination of the ore and are concentrated in the armature and field windings, constantly lowering the insulation resistance of these. Currently scheduled corrective maintenance...