Homopolar Rotor Slot Harmonics for Inter-Turn Fault Detection in Induction Motors

Stator faults detection under normal operation is one of the most important open problems in Induction Motors (IMs): they start as Inter-Turn Faults (ITFs) and rapidly evolve into catastrophic failures, being one of the major causes of shutdown. Hence, continuous monitoring is essential for early detection. Regarding this, line current analysis is preferred due to ease of equipment installation. In this paper, a new ITF indicator is proposed: amplitude of the homopolar Rotor Slot Harmonics (RSHs); those that form a homopolar system in a symmetrical machine. These harmonics are proven as always highly sensitive, opposite to previously used RSHs, which appear as sensitive or completely insensitive, depending on the motor analyzed. It is shown how ITF detection can be reliably solved using homopolar RSHs: they dramatically rise under early ITFs. To achieve generality, a theoretical analysis is conducted to deduce which are these RSHs as a function of the number of bars per pole pairs of the IM. Moreover, the proposed approach automatically selects and detects these harmonics, and ensures robustness against load, eccentricity and voltage unbalance variations. Efficacy of this approach is confirmed through finite element simulations of three IMs covering all cases and laboratory tests.