Using space transformation for exact diagnostic of induction motor stator faults

Abstract

Space transformation transfers 3 phase currents to one space (Parkpsilas) vector. Frequency component of space vector magnitude MagP2fl at 2fl is the basic diagnostic symptom. In the paper the analysis of possible cause of 3-phase current system unbalance due to stator faults are discussed and it is shown, that stator faults induce amplitude, phase or harmonic distortion unbalance. By comparing the measured and computed values of MagP2fl only for one of three cause of unbalance we can ascertain the contribution of individual influences to overall unbalance. MagP2fl is influenced both by stator faults and unfortunately also the overall state of 3-phase feeding system which itself can be unbalanced and causes additional error. Experiments were made at motors with artificially evoked faults of various sizes and severity simulating short winding in phase and simulating increasing stator winding resistance and their relations to values of MagP2fl examined for various motor loads. The influence of fed system on MagP2fl was searched by measurement the same stator faults for mains fed and inverter fed motors and correction for unbalanced fed system was proposed to ensure exact determination of diagnostic symptom. For the determination of degree of fault severity and for the comparison of stator fault for various induction motors the normalization coefficient is proposed.