Motor Electric Issues?

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tankfarms

Member
My inspector just showed me some vibration data on a motor when it's solo run. See attached. The concern is that the 2x line frequency spike (as it indicates an electrical issue). I verified some basic electrical parameters and found nothing abnormal. Both votlages and currents are all balanced. Motor with load (pump) runs at about 130 amps each phase balanced. The following is the motor info:

700HP, 2400V, FLA=160amps, 3-PH, 3600RPM

Just curious to know how to further verify the problem (if any) of this 2x line frequency spike; what kinda tests can be done to indentify any potential issues? Thanks.
 
J

jtp

Member
Location
Iowa
Motor Vibration

Motor Vibration

Do you have any information from the manufacturer or your motor rebuilder on what is acceptable? What is the vibration at the same measuring points when under load? This may be O.K. Do you have any historical data? Is this spike a recent event? Does this frequency tend to spike? How recent was the motor rebuilt?

Sometimes predictive maintenance data is feel based on your experience. What does it sound like in your highly trained acoustical intake device (ear) or how does it feel?

Keep an optical intake device (eye) on it and if it trends higher, consider a rebuild.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101208-1131 EST

You likely havee a mechanical problem.

A single weight put on the side of a shaft will give you a once per revolution unbalance. Your motor RPM is 3600 RPM so once per revolution is 1/60 second. The fundamental of the line frequency. As well as an unbalanced load, a non-parallel set of bearings, causes a once per revolution variation.

Ovality of bearings causes a twice per revolution variation. In your case a double frequency vibration.

Cage velocity of ball or roller bearings is about 1/2.3 per revolution of the shaft.

Roller or ball problems will be much higher than twice per revolution.

Likely a compound unbalance problem.

But as stated by jtp check with the manufacturer as to a possible cause or if this is normal.

.
 
T

tankfarms

Member
Thanks for both of your advice. This is one of these "are we over reacting" or "real problem" issues. It's a US brand motor, not sure where to go to get support/mfg. info for this.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101208-1206 EST

Do some Internet searching.

One I found was
http://goliath.ecnext.com/coms2/gi_0199-391347/The-relationship-of-vibration-to.html
But the figures were omitted and I did not read it closely to see if there was any real useful information beside broad generalities.

May be go to your library and see what is available.

The search string I used was
twice per revolution vibration problems in a pump

Maybe
diagnosis of double frequency vibration problems
would be more productive.

Rather than the motor manufacturer it may be more useful to talk to the pump manufacturer.

.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
One more possibility:
Broken rotor bars exhibit vibrations at even multiples of the fundamental. Uncouple the load. If the vibration persists, it's probably that or a motor bearing as Gar suggested. If it goes away, it's in the load. That at least narrows the field of things to look for.

Link
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
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