Severity Class. & Qualitative / Quantitative Inspection 1

[charleseee]

1. Is it possible to set up a standard classification of severity in infrared electrical inspection?
For example, the phase to phase temperature difference is 1-20¢J (Minor), 21-45¢J (Important), 46-90¢J (Serious), 91-Above (Critical).
2. What factors do I need to consider when deciding whether I am going to do a qualitative inspection or a quantitative inspection?
3. I am doing an infrared inspection on the joints (about 800 joints) of busbar, I believe I am doing a qualitative inspection. Because I assume all of the good condition joints are all in a liner (same) temperature under same loading, if any abnormally heat which over the liner temperature would regard as an exception, am I right?

 

[CRS1]

1. I would STRONGLY recommend against any absolute severity classification based on temperature. Small temperature differences may be extremely meaningful, depending on load/emmissivity, etc. Also, in many cases, you reaslly don't know the real temperatures, which may be far different from those you see on the camera because of low emmisivity, convective cooling, etc.
2. Qualitative inspection is generally regarded as an inspection that focuses on identifying problems, whereas a quantitative inspection is involved in determining the actual, rather than apparent temperatures.
3. Yes, because you are looking for apparent differences rather than assigning absolute actual temperature values.

 

[mvcjr]

Hi!

In our case we do qualitative and quantitative inspections at the same time. I work in an electric distribution utility.

By quantitative inspection, we inspect joints and compare it with similar joints nearby to determine whether it is operating abnormally (different from the rest). But we also take note of the temperature of the abnormal joint to aid in prioritizing repair schedules. In prioritizing schedules we not only take into account the temperature but also the importance of the circuit to the rest of the system, i.e., a hotspot at the source side of the feeder has more weight than a hotspot at the end side of the feeder even if their temperatures are the same.

God bless!

 

[gsfitzsr]

Both responses above are great advice.

It seems there is a big discussion about what is good and what is bad when surveying electrical connections.

I recenlty called my local utility when I found a pole mounted transformer connection feeding a supermarket 75degF hotter than the other. They told me they don't get concerned unless its 100degF or higher deltaT. Since these are low E materials I know the actual temp was probably over 200F. Their response confused me, but then I don't have to maintain thousands of transformers.

You will have to decide for yourself what is acceptable or not in your facility. Be conservative until you can justify relaxing your criteria.

 

[JKEngineer]

A comment on gsfitzsr's experience with the local utility:

If the 75degF delta that was observed already had the emissivity of the materials in it, then it was not 200F. If an emissivity of 1.0 was used in the camera, as is often the case in qualitative surveys, then the observed 75F was not the actual rise. What did the utility think it was being told? Did it know that the 75F was under-reported as being measured with e=1, or did it think it was being given an emissivity compensated number? (If that was the case.)



Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com

 

[tucan]

charleseee,
Any temp diff at joints is important, even as little as 5C.