Coil Resistance of an Induction Motor

If you wish to test the stators in your motor, use a megohmmeter that applies high voltage (very low current) to the coils, and can be used to test for insulation breakdown, resistance to ground, phase to phase leakage and short circuits.

A megohmmeter can be rented or purchased. Just be very careful when using it. Read and observe all instructions in the manual.

Here is a link to one digital meter, there are plenty to choose from.

If it checks out good, I would spray the coils with Glyptal insulating enamel to further increase the life of the motor.

https://www.amazon.com/Klein-Tools-ET600-Megohmmeter-Insulation/dp/B07ZZX5TK8/ref=sr_1_1?adgrpid=1227055287094674&dib=eyJ2IjoiMSJ9.GLB_bRhSHC6W7t3Y60T4n7jFtIdYQO0_sdyNnCIJtNy_FjhStOf_mS_Y9OZVSwvBSkhsX1IAfMrEJ67aWaTCx0QGxnpln-oglgO7AJnTeYKKZ8UOh4SOqpFXkzi2NWRiOL0DkS-MdNawvVCEwKdtLOQNpiAG-JmYnS4mZbN8OcskydParOBKmh0vVn-0Rkj8qi8UwAWQKNDaCTqtTfY43KF7-QCWl5ftDZegDv94Zfk.yeMc8cgY3zWhj-YiOlDcqYgJNFJfru8uR-NGDXONdWA&dib_tag=se&hvadid=76691122019342&hvbmt=bp&hvdev=c&hvlocphy=83156&hvnetw=s&hvqmt=e&hvtargid=kwd-76691190336036%3Aloc-190&hydadcr=13420_13505134&keywords=megohmmeter&msclkid=0a3fdf2bbe1c13519300b87a956936b7&qid=1733372884&sr=8-1&th=1

Yep done that, line to ground is ok. My concern is line to line resistance ia only 1.7 ohm, its consistent btw with the other lines.

My worry is if this is the original value of resistance in the coil. Drive diagmostic tool showed Over current motor and overload resistors.

It has no factory data available of standard Line to Line coil resistance.

So I cant somehow justify if these coils needs rewinding.

I read somewhere that resistance of this induction motors is in range 0.33 to 2 ohms and value i got from.measure pass in between.

Very hard to justify cost of rewinding.

If it checks out good, I would spray the coils with Glyptal insulating enamel to further increase the life of the motor"

Spraying the coils with Glyptal insulating enamel paint may possibly be a good practice, but will only be truly effective after the coils are thoroughly cleaned and dried in an oven.. Doing so will definitely enhance the insulations...

It goes without saying that the coils be cleaned and dried properly before applying Glyptal.

Glyptal has been used for many years to enhance insulation and was a standard operation when rebuilding any motor, regardless of size.

Even drowned water logged motors can be revived after drying properly and spraying with Glyptal.

Gee thanks man.

Some more info on how to check stators in the field is to use a piece of banding material about a foot long, taped on the end you will handle. Apply 1/2 voltage to the stator and pass the band around the inside of the stator. If it growls, you have a bad spot there. A hack saw blade can also be used like this if you grind off the pitch of the teeth to get a slick surface on the blade.

They used to make a hand held growler that was a 120 vac plug-in with it's own coil and would do the same thing, but a hack saw blade is cheaper and readily available in large numbers. It could be used on non energized stators.

Another way is to take a single ball from a ball bearing, (1/2 inch diameter ball is ok bigger is better) and put it inside of a horizontally oriented stator and give it a small bump in the direction you want it to go, and it will circulate around inside the stator. If it drops off or hesitates, you have found a bad spot.

The oven vacuum method is the professional way to dry stators, but in the field the equipment is not always available.

A 100 watt incandescent build inside of a vertically oriented stator will also dry out the stator, and applying a low voltage to the stator will also aid in driving the internal moisture. 120volts is usually ok for a 600 volt motor. Alternate the coil connections to get all coils in the circuit Keep the bulb from direct contact with the stator. 24 hours is typical drying time .It sounds slow but when you have hundreds of motors from a flood damaged industry, it is much quicker to do many at once than one or two at the time in an oven.

If water damaged, replace all bearings with doubled shielded, double sealed bearings. Suffix (2RS.)Keeps grease in, contaminants out. A shielded bearing (ZZ suffix) keeps some grease in and some contaminants out, but not as well as a 2RS bearing.

Of course, after thorough cleaning and drying coating with Glyptal or similar is required.

<...1.7 ohms...> sounds about right. It is an AC motor and the reactance of the <...coils...> needs to come into play when the motor is up to speed. Compare this reading with other similar motors and see what they give in response.

Proposal:

1. Connect the motor in question, with no mechanical load applied, to a test rig designed and rated to carry <...15.6A....> under the applicable national standard; in the UK, for example, BS7671 applies.
2. Set the motor overload protection device on the test rig to <...15.6A...>.
3. Having taken all appropriate precautions to protect other CR4 users and passers-by, energise the motor, see what happens and take note.
4. De-energise the motor, connect the mechanical load, re-energise and see what happens.
5. Report back on this thread.

#3 Having taken all appropriate precautions to protect other CR4 users and passers-by, energise the motor, see what happens and take note.

Nah can't do can't do that either, system is block by drive software.

I think I have an idea now.

With resistors overload and motor over current seems like a busted drive IGBT if you would agree.

<...can't do that...>

What - run the motor on a test rig? How abstruse.

<...drive IGBT...agree...>

That wasn't mentioned in the original post, and agreement is unnecessary in this forum.

Yeah man, do not have the convenience to do the test rig.

Its ok i got it.

Inability and inconvenience are not the same thing.

I got to check the resistors. Thanks guys.

<...1.7 ohms...> sounds about right. It is an AC motor and the reactance of the <...coils...> needs to come into play when the motor is up to speed.

Agreed. And also BackEMF when the motor is energized and up to speed.

The coil resistance is better measured with an AC multi test meter. I have one that tests the coil resistance at 100 and 1KHz. It can also test the inductance of each coil as well as the capacitance to ground. You are looking to see that the values are close.

With drying a motor in an oven, I use 70 deg C and measure before the motor is placed in the oven and then after it reaches temp, you may see a dip in the Mohms as any moisture is driven out but it will rapidly rise.

Once the resistance is high and stable varnish the motor with a suitable insulating varnish, a poly urethane is good while it is hot so the varnish runs into the in stator winding space. We used to vacuum impregnate the windings in a chamber but the pole face and mounting surface cleanup was tedious.

Put a coating of hi temp grease on the surfaces that do not need coating. It will be much easier to remove afterwards.

It's just a big load of inductance.

If the <...coil resistance...> is <...1.7 ohms...> across each coil, then the chances are that it is a good 'un.

Hence the proposal #4⇑.

Does the facility own a spare motor? One could compare the two.

I got it, very useful data.