Reliable Detection of Broken Bar Fault through Negative Sequence of Stray Flux in Induction Motors

As well-known, the broken bar fault affects the harmonic content of the stator current and airgap & stray flux. This paper proposes to detect broken bar fault through negative sequence stray flux spectrum in induction motors (IMs). For this purpose, three stray flux data which have 120o relative phase differences are collected from the vicinity of IMs. Then, stray flux space vector is calculated and analyzed at low frequency range when the motor is operated as both healthy and broken bar  cases. It is shown that there are some effective signals such as –((fs-fr)±2sfs) to detect broken bar fault in negative sequence stray flux spectrum while only sidebands of fundamental signatures rise up in positive sequence stray flux spectrum. Comparative 2D finite-element simulations results including current space vector prove that the negative sequence stray flux spectrum can yields more effective results than classical stator current and stray flux analysis in induction motors.