LV Squirrel Cage Induction Motor

Stick a dry paper wick (toilet paper) into an opening. If the paper comes out damp then there is water in the motor. If there is no opening then there likely is no water.

Now, if that valid answer is not what you were looking for I recommend that you be as specific as you possibly can about the amount of water you think this motor has been exposed to. (An actual calibrated volume of water is not necessary. A simple description of the circumstance that got it wet will help.) I would also recommend you tell us why you are concerned about having moisture on this motor. Now a squirrel cage induction motor must work with an AC voltage, I'm curious what you consider to be Low Voltage (LV); 24VAC, 60VAC, 120VAC, 480VAC or any other mystery numbers.

Megger^®

As Tornado suggest use a Megger tester to check the insulation resistance to earth and between windings.

The quickest test is just turn it on, if it goes bang, it's knackered, if it runs it's OK. Basic rough a*sed way around it!

it is a 415v motor with heaters, heaters were tripped for some time and now, I believe there is some moisture.I did read that a polarizing index will give you an idea if there is moisture in the motor but on a 1000v megger the reading stayed on0.3M ohm for 10 minutes

Is that phase to phase or phase to ground

Meggering the motor with 500 v megger will reveal the IR value . but a lower ir value may be due to entry of dust/contaminants also PI value is mostly used for HIGH VOLTAGE EQUIPMENTS For drying the motor and improving the IR value pl connect the motor windings in series and feed power from a single phase variac ( without exceeding the motor rated current or variac ampere rating( which ever is lower))

phase to ground

Can you put about 50V on each of the windings, it would get some heat in the windings and dry them without doing any damage.

I'm an old school rough a*sed engineer some of a methods may seem crude but they usually work!

One of the founders of the CR4 old farts!

I love tony's answer.. switch it on, if it goes bang... its buggered.

however, I have had motor running with no problem in water up to the shaft. Providing the connctions are NOT wet, it would run OK.

now a megger tests the winding insulation, if your reading is correct, then it would seem that water/mositure has corupted the insulation and you need to either dry out the motor and re-test. Have you tried running the motor off-load to warm it up?

The answer of 50volts per phase is a good answer, 3 ph 110v will dry it quicker if you are limited on time with no adverse effects on teh windings.

Or rewind and make sure that the winding heaters are installed and working.

I would guess that you are using this motor in an area of high humitiy?

you could try WD40...

I agree with you. GE, Century, Marathon motors generally spec an 'air over' motor good if winding to winding readings are within 1% of each other AND 10M ohm or greater to ground. There is always the old fix: leave it out in the sun and check it again!

If the megger read 0.3MΩ then the windings are definitely wet. You need a reading in excess of 1.5MΩ to be able to try and connect-run the motor.

As suggested, dry the windings by injecting a low AC voltage, making sure that the current does not exceed half the name plate rating of the motor (Variac or some resistance ...) for ~ 1h then check again the insulation to ground (body of the motor). You can blow hot air into the motor to remove the moisture at the same time, otherwise, condensation will happen when the winding cools down.

What is the type of insulation? If it is epoxy then it will not absorb moisture. In that case low IR could be due to surface contamination. Generally IR value as measured with higher voltage megger will show a lower value as compared to the measured value with lower voltage megger. In such case it would be necessary to clean the winding surface to get good IT value.

If the winding insulation is hygroscopic, then attempt dry out by any method as suggested by others keeping end cover open allowing moisture to get out of the motor. Measure the IR value at some time interval and plot time verses IR till curve becomes flat. Initially the IR will drop and then as drying progresses, it will increase.

dear I have seen even motors with 0.5 M ohms burnt when started and Motor with 0.3 M ohms run when started without any failure of winding. basic rule 1 M ohm +voltage rating in KV - for 415 volts motors it should be 1.5 M ohms however, when you are in doubt and when the IR value is in single digit , isolate the phase windings and see which phase winding is less in IR. If all the 3 phase windings are less in IR then go for heating. in case only one winding is less in IR , then it is preferred to open the motor

If any of you have worked on a site with over 2000 drives. Rough a*sed engineering saves time and money. OK I could go to the stores and get a 2500HP motor off the shelf if needed. But a quick flick of the start switch saves a lot of time testing!

To be honest most motor faults turn out to be mechanical, but it's always the electrical bod that has to sort it out!

If there is moisture content in the insulation, it will show poor IR value when tested by Insulation Tester/ Meggar and it is already discussed. From practical experience it is seen that under this condition, due to presence of moisture, contamination of dirts, and other foriengn materials,for environment reasons, cell formation is occured, and measurement of low DC millivolt( cell voltage) between say, winding to motor body indicates presence of moisture. After de-moisturiation,and improvement of IR value this cell voltage is drastically reduced.

I believe your cell concept needs opening of the motor body and measure. in practical in plant that is not possible due to limited constraints and manpower shortage,shortage of skilled contract manpower. you have to try out maximum,without dismantling motor