This paper presents a mathematical model to obtaina failure indicator of stator faults based on the negativesequence component of the electric current. The modelcan be used in online diagnosis systems to separate theeffects of voltage unbalance factor and the constructiveasymmetries of the machine. Results of the application ofthe model were validated trough laboratory tests madeinto a specially modified motor and results were applied tosuccess diagnosis of two motors of higher electrical power.As a main result of the work, a low computationalmodel was obtained to diagnose a quick evolution failurethat can evolve quickly to a thermal collapse of the statorwinding with consequent repair costs.