Testing a Motor

You can for an high voltage test also..

Did you notice if the original bearings are electrically isolated?

We don't want them above or below earth potential. after all, I hope they are stuck in an insulated end plate, and also insulated from the main rotor, otherwise the world would ...well ....explode or something...............

Has to be a problem that I have never heard of...?

but, always eager to learn.

Mark N,

A 24 hour "light load" test run.

A "growler" test on the rotor if it hasn't been put back into the stator yet.

HeHe never done a Growler test since I was an apprentice!

How do you do it with a squirrel cage rotor?
(that what the OP asked)

Everything so far sounds good. Mechanically, you can also push both shaft ends up/down/left/right to check for excessive play, using a dial indicator.

Most mechanical defects should be seen when replacing bearings, both with the condition of the bearings being replaced and the condition of the bearing landings, also the bearing fit should not be loose in some cases heat is required for fitting. When the motor is complete some lift will probably be seen on the shaft, this is determined by the size of motor and bearing type speed clearances which can be quite noticeable (high speed bearings). As suggested an unloaded test run is the best method, checking the temperature and vibration levels.

If you know the motor is intended for VFD duty, it may require specialized bearings and run testing at minimum and maximum rated speeds.

A no load current can be of help if you have previous or nameplate record of the same.

I reckon you just about have it.

Q. Why did you have to replace bearings, planned maitenance.

Check that the Fitter has aligned his pump or load correctly..! If he is the man to connect up. A flexible coupling can only do so much.

In case the bearing replacement is done with conventional method means that use of improper tool and not of standard bearing fitting kit , we should must check the viberation test of the motor of drive end , rear end , foundation and on the middle of motors. It will be more useful if there is the origional results for comparision , otherwise to maintain with in the standard can be checked from manufacturer .

A.K.Sharma

Windings Insulation test against the Body.

Windings resistance.

Visual Checks before replacing the bearings: Any markings on the windings indicating rubbing against the rotor before bearing replacement. These Insulation scratches might not show during testing but will develop rapidly when in use to a winding failure...

No load test run to check for vibration and bearing noise.

When connected back on the equipment, Load testing for the same as above plus current loading to compare with the nameplate and previous records if available. Monitor for temperature rise specially near the bearing housings to check the condition of the bearings and their seatings.

Finally, the Original Reason for the Failure (if early failure) must be diagnosed and corrected.

For a 3phase induction motor with squirel cage rotor, there is no Crawler test as suggested. But if the motor is of a big size (>= 10 HP) you might want to check the rotor/shaft for any play between the laminations and the shaft (none should be there) or any damages to it...

Cheee, we realy are getting excited now.

# ea x 3 phase. the resistance is equal

Insulation >100k

Spins freely.

wire the bastard in, and switch it on.

lets not get to carried away

Refer to your reply #15: YOU seem to be carried away... Bearing potential above or below ...?? exploding the motor... He will just trip his CB...

The Op is asking for advice from experience and either you help or just let it be.

NEMA has some very comprehensive guides for electric motors, including testing.

dpends upon the rating.On smaller motors IR value and simple no load running may do.On large machines u have to do additional tests suh tan Delta and compare with original test records, PI value , capcitance test and so on. Regards

Depending on how much time you wish to spend with it,

I would look at Insulation Resistance, (Dielectric Absorption OR Polarization Index) done with DC of course.

Phase to Phase Inductance and Resistance to the microhenry/ohm.

and since the motor has been apart for bearings, Rotor Influence Check for out of roundness... done first, since the other tests will possibly polarize the rotor.

once running do the online battery as well as Vibration tests...

"HeHe never done a Growler test since I was an apprentice!

How do you do it with a squirrel cage rotor?

(that what the OP asked)"

"...on a 3 phase induction motor"

Oops, missed that detail. <sheepish grin>