MOTOR BEARING DAMAGE DETECTION USING STATOR CURRENT MONITORING

This paper addresses the application of motor current spectral analysi s for the detection of rolling-element bearing damage in induction mac hines. Vibration monitoring of mechanical bearing frequencies is curre ntly used to detect the presence of a fault condition. Since these mec hanical vibrations are associated with variations in the physical air gap of the machine, the air gap flux density is modulated and stator c urrents are generated at predictable frequencies related to the electr ical supply and vibrational frequencies. This paper takes the initial step of investigating the efficacy of current monitoring for bearing f ault detection by correlating the relationship between vibration and c urrent frequencies caused by incipient bearing failures. The bearing f ailure modes are reviewed and the characteristic bearing frequencies a ssociated with the physical construction of the bearings are defined. The effects on the stator current spectrum are described and the relat ed frequencies determined. This is an important result in the formulat ion of a fault detection scheme that monitors the stator currents. Exp erimental results which show the vibration and current spectra of an i nduction machine with different bearing faults are used to verify the relationship between the vibrational and current frequencies. The test results clearly illustrate that the stator current signature can be u sed to identify the presence of a bearing fault.