Balancing of Electric Motors
Balancing of Electric Motors
(OP)
HI. We are currently commencing the overall program on out compressor motors on our locomotives. As part of the scope of work, we are replacing the bearings on the motor side. My question is, should the motor now be balanced or can the motor be assembled and placed in service without being balanced? Is their a specific RPM rating which states that: motors exceeding a certain RPM should be balanced or is it the norm that all motors, irrespective of their RPM rating, should be balanced? What would the long term effects of an unbalnced motor be?





RE: Balancing of Electric Motors
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RE: Balancing of Electric Motors
RE: Balancing of Electric Motors
http://www.skfcm.com/service/support2/New%20Library/CM3...
for: Trim Balancing
RE: Balancing of Electric Motors
As both the intertia of the armature and the speed are greater, so the need for balancing becomes greater.
Another factor to consider is with what type of equipment the motor will used. This is expressed in what is referred to as "Balancing Quality Grades" expressed as "G" numbers, running from G0.4 (very well balanced, e.g. gyroscopes) to G4000 (somewhat balanced, e.g. crankshaft drives of slow, rigidly mounted marine diesel engines, with uneven # of cylinders).
For reference, take a look at Fundmentals of Balancing, published by Schenck Trevel Corp., Deer Park, L.I., NY, 2nd edition, March 1983. ppgs, 46 - 47. Here you will find the "G" table, and chart showing what levels of unbalance can be tolerated for various speeds, and various "G" grades. These are also commonly found in both instruction manuals for balancing equipment, and included in vibration analysis course textbooks.
Hope this helps!!
RE: Balancing of Electric Motors
Don't rely on vibration monitoring to check unbalance. Vibration level is related to the stiffness of the mounting.
RE: Balancing of Electric Motors
I think for in-house work, it is not as common to require a balance check. For example we replace bearings on NEMA frame motors without balancing and we do in-place split sleeve bearing replacement without removing rotor or balancing. We rely on solo-run installed in-place before coupling to identify problems. I agree with jc this is not a perfect way to find unbalance. If we find a problem at that point we may or may not be able to balance in-place.
I think it is a matter of effort vs payback. Depends in part on where the motor will be worked, will rotor be pulled... how easy to get it to the shop, do you have your own shop or have to send it out for balance, etc.
So far we have taken the shortcut and no balance and never gotten in trouble.
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RE: Balancing of Electric Motors
RE: Balancing of Electric Motors
Wear & tear can be only at the bearing support point.
Whether the rotor has bulged due to hot spots?
Whether any stotor - rotor rubbing has taken place ?
Whether rotor bar has broken?
If any unbalance is detected in a rotor , the root cause is to be analysed and rectified before balancing is done. Simply balancing does not help as the rotor developes unbalance only when there is an unwanted stress in the rotor.
RE: Balancing of Electric Motors
You should also call for balancing of the rotors at the same time. This is helpful because you get a chance to visually see the the condition of both the rotor and the stator, at which point you can determine if any preventive repairs are necessary or not.
Yes, a balnced rotor will help your motor live longer and work smoother, quieter and be more efficient.
I design, manufacture, test and maintain motors, hopefully that adds some weight to my point of view.
RE: Balancing of Electric Motors