Rotating Element Bearing Diagnostics in a Nuclear Power Plant: Comparing Vibration and Torque Techniques

Planning for an upcoming refueling shutdown at Limerick Nuclear Power Station, sixteen vane axial fans were analyzed to determine which ones need maintenance. Vibration and torque signature technologies were employed. Vibration technology is the standard bearing diagnostic approach; however, the need of physical proximity limits the usability to low radiation areas. Lacking this drawback, torque signature is being investigated as an alternate diagnostic approach. Experts analyzed newly acquired air gap torque signatures, and pre-existing vibration signatures independently of one another. Both techniques concluded the same four fans needed maintenance due to bearing signatures, since both technologies supported that the motor bearings were in the very early stages of degradation probably due to grease problems. These four fans have been scheduled for predictive maintenance repair during the upcoming plant shutdown.