Infrared Scan Pad-Mount Transformer

[wirenut1980]

Hello! I work for a utility and one of our customers had IR images taken of internal equipment and utility equipment in the area. One image brought to my attention was of a primary (12kV) elbow on a pad mount transformer that is loop fed. The image showed "A" phase elbow at 84.4 degrees F, "B" phase elbow at about 73 degrees F, and "C" phase elbow at about 70 degrees F.

Is there some kind of standard or document that speaks to how high is too high for the temperature? Or is it more just about one phase being hotter than the others, indicating a bad connection?

Thanks in advance guys and gals!

 

[Last Leg]

Off the top of my head - each component of the system, including the wire insulation, should have a temperature rating and the temperature should not exceed any of the ratings, lest failure of the system occur. That doesn't sound very high to me though. Was this guy just playing around or did he commit to an oppinion?

 

[wirenut1980]

It did not seem very high to me either. Our transformers are rated 65 degrees C, but I was not sure if that applied to the connections as well.

The guy doing the scans pretty much gave all the possibilities of what could cause a high temperature reading, but did not commit to it being a problem. He noted that the plastic/rubber of the bushing may be masking the thermal image and may be more serious than the photo illustrates.

I'll probably have my guys change out what they can with that connection, but not sure what the cause may be if there is a problem.

 

[jim dungar]

Our transformers are rated 65 degrees C, but I was not sure if that applied to the connections as well.

You are describing the allowable temperature rise above ambient, not the actual operating temperature.

Beware of comparing IR readings without knowing the amount of current flowing through the device. Differences between phases are often caused by unbalanced loading rather than by poor connections.

 

[mivey]

It does not sound like much to worry about to me. I like to look for hot spots at the bend of the elbow as there is a tendency for the rod to be loose or to not have been properly torqued in to start with.

 

[beanland]

Infrared

Infrared

Those temperatures seem to indicate that everything is OK. 15kV wire is rated for 90C (194F) conductor temperature. So are the elbows. These elbows do not indicate any overheating.

It is possible there is unequal loading causing the unequal temperature. It could also be radiation from another source warming one elbow. Or, better airflow on those that are cooler. It could also be that the pin on one is not as tight in the compression lug or in the socket as the others. The load break insert could have a poor connection to the well. But, the difference is a small portion of the rating of the device, nothing serious.

It might be something to watch but action is probably not warranted. Think of a car engine with 150-160-155 compression; you do not rebuild it just because there is some variation (maybe because it is a 4 cylinder and one went missing!).

 

[zog]

It did not seem very high to me either. Our transformers are rated 65 degrees C, but I was not sure if that applied to the connections as well.

The guy doing the scans pretty much gave all the possibilities of what could cause a high temperature reading, but did not commit to it being a problem. He noted that the plastic/rubber of the bushing may be masking the thermal image and may be more serious than the photo illustrates.

I'll probably have my guys change out what they can with that connection, but not sure what the cause may be if there is a problem.

ANSI/NETA has values for rise above ambient and differences between similar connections. But without load data, they are pretty much worthless. But, it does not sound like a serious issue. (Assuming your temps posted in F is right)

Is this IR guy from a certified testing company? Following any standards? What level IR certification does he hold if any? Issues like this should be provided in a detailed report with recommened actions based on standards.

 

[beanland]

Clean and tighten

Clean and tighten

"I'll probably have my guys change out what they can with that connection"

I suggest de-energize, disconnect, clean, inspect, reassemble. If there are problem parts, replace them. Otherwise, clean and tighten may be all that is needed.