Interesting case
Interesting case
(OP)
A 660kw induction motor when stopped after large vibration during service, has shown damage to bearing .When the shaft was attended (welding was carried out at damaged area of bearing seat) and bearing were replaced, the motor was re-assembled after rotor balancing was carried out.
Now there is seen a very special problem of large scale vibration when motor crosses the 2200 rpm speed. This vibration goes on increaing as the speed gets up. All these tests are carried out at shop floor at no load.
What could be the reason and remedy of such probelm
Now there is seen a very special problem of large scale vibration when motor crosses the 2200 rpm speed. This vibration goes on increaing as the speed gets up. All these tests are carried out at shop floor at no load.
What could be the reason and remedy of such probelm





RE: Interesting case
Please give the rated speed of the motor and supply frequency. Have u done the balancing at rated speed or at 2200 rpm. Have you checked the rotor bars. Loose rotor bars (I assume it is a squirrel cage motor)can give u such vibrations at subsynchronous speeds. Please also give the bearing details.
--irdrop
RE: Interesting case
RE: Interesting case
What is the frequency of the vibration observed in the shop? How about the frequency of the vibration observed in the field?
Horizontal or vertical motor? Vibration equal at both ends? Vibration equal in both radial directions? Any axial vibration?
Does the vibration change with voltage (constant speed)? o power-down?
The speed dependence at first suggested a resonance but maybe not since you say vib continued to increase.
There seems two obvious broad scenario's:
1 - some original problem created high vibration which damaged the bearing... bearing replaced and original problem remains.
2 - the shaft repair caused the problem. Is it possible there was residual stress created which produced a shaft bend. Runout checked? Perhaps there is some problem with bearing seating on the repaired area. Just thinking out loud.
RE: Interesting case
RE: Interesting case
1 undercut and NDT
2 Ample preheat
3 Proper welding with correct filler materials
4 Post heat to stress relieve
5 Machine to proof welding
6 NDT welded sections
7 Final machine, ensure rotor iron is concentric to journals and to coupling diameters
RE: Interesting case