Type of machine : Three Phase Sq. Cage Induction Motor
Rating :- 900 kW_6P_6.6kV
Type of cooling :- CACA
Problem : Noise (very high - touched 100 db) and vibration (upto 20 mm/second)
Description of problem : It is not clear whether it is mechanical or electrical noise.As soon as the motor runs on no load ,vibration and noise increases with speed.
Slot combinations used are 54-Stator & 70-Rotor.
Problems found : 1. Air gap eccentricity is violated 2. Waviness of body.
I would like to know what the motor is going through electrically & mechanically and solutions to it will be highly appreciated.

Hi Nirav,
Could you check the presence of electrical noise by cutting off the supply and see the influence on acoustic noise ?
What do you mean by waviness of body ?
Considering your slot numbers you might have a resonance due to slotting (wave order 0) or saturation (wave order 4). If this is due to a resonance with magnetic forces, the noise should decrease after resonance.

Dear Sir

Thank you for the response.

We have checked the machine after cutting off the supply and found that the noise still persists.It can be predicted that noise is purely windage noise.But talking about vibrations,those are very high.
By waviness of body , I meant the non uniformity of the body, I doubt that there is heavy magnetic pull which are affecting the vibrations(maybe i am wrong).
Noise can be controlled by varying diameter of fan but vibrations are the serious issues.

As already commented check whether the noise is due to mechanical or electrical by checking noise with and without power supply to motor . Without power supply I mean switching off of power supply when the motor is running and measuring the noise. Is it the first motor made with this stator . If so check the resonance of stator . No of papers are available for checking the resonance. you can also use ANSYS for the same. If it is mechanical then check whether the is stator rotor rubbing or any mechanical loose part on rotor . Of course air gap eccentricity can give rise to noise . Bad fitting of stator into the housing I mean loose fit can also give rise to noise .

You might have a vortex that is created between the blades and the frame. In this case you can try to move the blades further away from the frame.
Sometimes the rotor slots also act like some kind of fan blades if the rotor bore radius is not smooth. To check if the fan is really responsible for noise you can make a noise spectrum and check that the frequency is proportional to the blade number.

Check the no of blades in fan . If it is even it can be one reason for noise. Shrink fit of stator will reduce vibration and hence noise. Good fit for parts on rotor reduces vibration with speed .