Winding Temperature with Infrared Thermometer

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fifty60

fifty60

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Can you use an infrared thermometer to determine the winding temperatures of a three phase motor?
 
TEFC means 'Totally Enclosed Fan Cooled'. It is supposed to be reasonably sealed so you won't have any way to view the windings to get the temperature.

By 'open end bell' I assume some thing like an 'Open Drip Proof' motor, one with airflow holes in the frame or end bells.

For research you could drill holes in the frame to visualize the windings....

-Jon
 
I don't know of any way to extrapolate winding temperature through a motor frame. The absolute best you could do would be to say that you know that the windings are hotter than any maximum case temperature, but unless you are seeing alarmingly high case temperatures that's not helpful.

Most large motors I would expect to have internal RTD or thermistors which would be far more accurate than any thermography.

While you could use this for bearing temperatures, I'd argue that vibration analysis is a far more effective indicator of potential problems. If you're worried about electrical overheating I think your best bet would be ensuring you're running below FLA and ensuring that cooling fans are working properly and that air passages are clear.
 
If this is an experiment rather than an operational monitoring application, you could stop the motor and make a DC resistance measurement on the windings.
The results will be crude compared to an actual RTC, and will require a precision (4-point) resistance measurement. But it would be better than nothing.
 
I read 82 cold (at ambient 24 C) ohms and then 85 ohms after the motor was finished operating. The motor only operates for around 13 minutes, then shuts off for several hours if not days. It is a continuous duty motor, so I don't think it is overheating.

When I plug the numbers into the heat rise equation I get a heat rise of about 10 C. Sounds right. The FLA is still not over the nameplate value.

It is a 380V 50Hz motor operating at 415V 50 Hz. It tripped an overload but it appears the installer simply set the overload too low. I adjusted it properly, to temps via the resistance method, and do not detect any problems...
 
You cannot determine wdg temp from a motor frame or closed housing since the actual wdgs cannot be accessed with the laser temp. The method I was referring to was for much older motors or very large motors where you could see the wdgs. You can determine the wdg temp using the current but, you need to know all the constants of the motor first. There are eqns in IEEE and IEC stds that will help you with this. There are also protective relays that do this as well (SEL, GE, ABB, etc.).
 
fifty60 said:
I read 82 cold (at ambient 24 C) ohms and then 85 ohms after the motor was finished operating. The motor only operates for around 13 minutes, then shuts off for several hours if not days. It is a continuous duty motor, so I don't think it is overheating.

When I plug the numbers into the heat rise equation I get a heat rise of about 10 C. Sounds right. The FLA is still not over the nameplate value.

It is a 380V 50Hz motor operating at 415V 50 Hz. It tripped an overload but it appears the installer simply set the overload too low. I adjusted it properly, to temps via the resistance method, and do not detect any problems...
Click to expand...

That seems quite high. What's the motor hp size?
 
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