SUBMITTED BY: Kevin Ritchie
TITLE: Vibration Analyst
EQUIPMENT: MR Steam Turbine Material Accelerator
TECHNOLOGIES USED: Vibration, UE, IR
PROBLEM DESCRIPTION:
After completing installation of a fresh 2250 hp motor on the Fructose MR, initial quality check vibration readings showed a significant .17g spike at 2X line frequency (120hz) in the gse spectrum. This is indicative of rotor-stator rotation eccentricity. There was also a 1X spike in the ips spectrum but it has been attributed to cold alignment of the motor to the gearbox and the need to re-align at operating temperature to correct for thermal growth variations.
INVESTIGATION:
During the quality check after replacing a 2250HP 4160VAC motor we discovered a high X1 and 120hz set of spikes in the spectrum. X1 is balance or alignment and the 120hz is indicative of stator eccentricity.
CONCLUSION:
Temporary fix was to remove the access cover plates to the floor anchor bolts which extend from front to back on both sides of the motor and allow the forced air an exit path thus eliminating the positive pressure within the motor. This condition was discovered when the repair technician tried to access the mounting bolts to address the hot alignment/balance requirement and correct the X1 spike indication and we just happened to be there at the same time taking a verifying spectrum for the motor and discovered that when the unit was vented, the 120HZ eccentricity spike in the spectrum disappeared. Permanent fix is to redesign the cooling duct feeds and allow proper ventilation exhaust.
VALUE TO CUSTOMER:
Prevented replacement of a $80,000+ motor due to indicated rotor-stator eccentricity
