Have any of you ever made any link between a motor running a bit hot and having a 2x line frequency signal?

I have a motor with both features, and considering that it is a possible indication of soft foot, ie stressed frame; could a stressed frame put suffucient pressure on bearings, shaft ect to create enough heat to heat the overall temp of the motor.

Actually, now that I have written it out as an idea, it seems less likely, but I would still like to hear if anyone has ever associated heat with a 7200 signal.

You probbaly should be looking closely at the 7200 cpm frequency to be sure if it is not 2X of running speed. Also quantify any sidebands around 1X and 2X of line (if any).

Stator problems such as stator eccentricity, shorted laminations and loose iron generally produce high seismic vibration (> 0.05 - 0.10 in/sec pk) at 2 times line frequency (2*fline). Stator eccentricity results in an uneven stationary air gap and can be caused by soft foot conditions that distort the casing. Air gap variances exceeding 5% usually warrant inspection.Note: high resolution or zoom spectra, in conjunction with logarithmic amplitude scaling, may be necessary to accurately diagnose stator and rotor related problems other than the above. Also, high frequency ranges, up to 120 times fshaft may be required to analyze rotor bar passage frequency information.

Phasing problems resulting from loose or intermittent connections typically result in vibration at 2 times line frequency (2*fline) with sidebands at one-third line frequency (1/3 *fline).

I am familiar with the problems associated with 2x line, I was just wondering if anyone has witnessed 7200 linked to heat..

Just thinking out loud here. Maybe Pete will have some comments...

One reason for high 120 Hz levels is loose laminations in the stator. I would suspect that loose laminations would reduce efficiency resulting in a termperature increase.

Jon
Spintelligent Labs

I have been knee deep in peakvue readings for the last six months. 2X line freq is showing up everywhere. Would someone tell me what the basics of this 2X line freq means? THANKS.

As everybody seems to agree, 2xLF is standard for stator related problems. To specifically answer you question, I would think that if a stator had high resistance connections or shorted turns, this may provide a basis for 120 Hz and excessive/uneven heating.
I have caught ueven heating of motor stators and successfully attributed it to rotor bar problems. It would be interesting to see a thermagram of the stator under load.
As a quick check, I would verify my phase voltages and currents and calculate an imbalance for each parameter. An MCE test would also be helpful here.
Hope this was some kind of help to you, good luck....

I'd say there are a lot of possible connections between the two symptoms in theory.

The one other thing I would add: High or unbalanaced voltage (or miswiring) can cause excess core heating and can also cause twice line frequency (due to higher flux).

Motor running hot is sometimes tough to judge. Some motors run hot, particularly near or above full load. As you know, surface temperature might be in the neighborhood of 10C below winding temperature. Continuous average winding temperature ratings I think are 120C for class B; 145C for class F; and 165C for class H (not including hot spot allowance).

You can determine the load by measuring with clamp-on ammeter or also estimate the load based on the slip (which you can estimate from your vibration spectra). For example if nameplate speed is 1780rpm and actual speed is 1790 rpm, then load is roughly 50%. If there is indication of a conitnous motor overload, that might be a reason for concern either due to possibility of tripping on overload, or possibility of long-term thermal degradation. But I normally wouldn't be concerned just based on surface temperature (unless there is some abnormal pattern for example excess heating from the bearing).

Thanks Pete, helpful as usual.