Advanced diagnosis of stator faults in large induction motors based on internal flux measurement

Abstract

Most of the existing electrical techniques of condition monitoring and fault diagnosis are based on stator current and/or stray flux measurement external to the motor. In this paper we propose a new diagnosis method for rotor bar faults based on flux measurements inside the main air gap of large induction motors. Theoretical analysis is presented, of both healthy motor and a motor with a broken rotor bar. Based on this, the fault detection method is proposed, which utilizes both time and space domain analysis of the air gap flux, to achieve superior rotor fault detection at early stages. The proposed method is demonstrated by extensive simulations. The method is experimentally validated using a specially instrumented laboratory scale induction motor. The prospective applications include large induction motors used in mining machines, in which internal Hall Effect Flux Sensors (HEFS) instrumentation is both feasible and justified.