THooper
Electrical
- Jul 19, 2001
- 90
We have recently acquired an SKF Microlog. We are to the point that we understand the microlog and the soft wear that goes with it. We are now starting to learn how to interpret the data.
We recently rebuilt a 1250 hp, 1750 rpm, 2300 volt motor. The bearing arrangement is a NU228 in the drive end and opposite drive is a stacked arrangement with a 6226 on the inside and a NU226 on the outside. The ball bearing is strictly for momentary thrust and has no housing fit.
We like to test run our motors on half voltage and listen for any mechanical problems as the motor comes up in speed. So we started the motor on 950 volts. When the motor came up to speed we took vibration readings and felt that they would be accurate. All of the velocity readings were around .05 ips to .02 ips. However the acceleration was at 44 G's on the drive and 56 G's on the idle.
I felt that the problem with the high G's was the rotor hunting for magnetic center and with the lower voltage being applied to the windings of motor, the roller bearings will not see the total radial load that is applied by the rotor.
We then ran the motor on full vac, 2300 and the end rush current put a heavy strain on our facility power. When the new readings were taken the G's were down to 5 and 6.
I haven't been able to convince anyone of my theory at our shop, and I don't fully understand why this went from 56 G's down to 6 G's.
Any suggestions would be appreciated.
We recently rebuilt a 1250 hp, 1750 rpm, 2300 volt motor. The bearing arrangement is a NU228 in the drive end and opposite drive is a stacked arrangement with a 6226 on the inside and a NU226 on the outside. The ball bearing is strictly for momentary thrust and has no housing fit.
We like to test run our motors on half voltage and listen for any mechanical problems as the motor comes up in speed. So we started the motor on 950 volts. When the motor came up to speed we took vibration readings and felt that they would be accurate. All of the velocity readings were around .05 ips to .02 ips. However the acceleration was at 44 G's on the drive and 56 G's on the idle.
I felt that the problem with the high G's was the rotor hunting for magnetic center and with the lower voltage being applied to the windings of motor, the roller bearings will not see the total radial load that is applied by the rotor.
We then ran the motor on full vac, 2300 and the end rush current put a heavy strain on our facility power. When the new readings were taken the G's were down to 5 and 6.
I haven't been able to convince anyone of my theory at our shop, and I don't fully understand why this went from 56 G's down to 6 G's.
Any suggestions would be appreciated.
