Message Board Thread - "Scanning Bus Duct"

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Scanning Bus Duct John B 4/1/2008
What do I need to know to scan bus duct effectively? It isn't practical to open swing jacks with machines running ane people working below. Can useful information be gathered by scanning the bus from the floor? Are there special techniques or tips I need to know? My working assumption is that most jacks should be at the same temperature as the bus, and any temperature rise is worth investigating because of the large air space that must be heated to warm the outside.
 
Re:Scanning Bus Duct Doctir bob 4/1/2008
You are right about the air acting as a thermal insulator. Experiments we have done at ITC show there can be a factor of 25 between the temperature rise on a bus bar inside a bus duct and the temperature rise on the bus duct surface. The attached image of a simulated problem shows the temperature rise internally was 537 F, but on the surface only 22 F. We simulated the problem with a soldering iron tip hose clamped to the bus bar with a thermocouple attached to get internal tempearature. From a paper "Common misconceptions in infrared thermography condition based maintenance applications" published in the 2000 InfraMation Proceedings.

Short answer is any temperature rise on the bus duct surface due to internal anomalies should be investigated. Watch out for duct heaters--they're supposed to be hot.
 
Re:Scanning Bus Duct John B 4/4/2008
Doctir bob wrote:
right about the air acting as a thermal insulator. Experiments we have done at ITC show there can be a factor of 25 between the temperature rise on a bus bar inside a bus duct and the temperature rise on the bus duct surface. The attached image of a simulated problem shows the temperature rise internally was 537 F, but on the surface only 22 F. We simulated the problem with a soldering iron tip hose clamped to the bus bar with a thermocouple attached to get internal tempearature. From a paper "Common misconceptions in infrared thermography condition based maintenance applications" published in the 2000 InfraMation Proceedings.

Short answer is any temperature rise on the bus duct surface due to internal anomalies should be investigated. Watch out for duct heaters--they're supposed to be hot.
Thanks. Nice to know I had the right idea. I have seen, and discounted, some cute heating effects from ventilation blowers and bus mounted transformers. They're not hard to identify.
Is there any temp rise that could be considered harmless, in the absence of external heating? Say, one or two degrees? I usually compare the jacks with the bus right next to them for a "normal" value.
 
Re:Scanning Bus Duct John B 4/16/2008
Doctir bob wrote:
right about the air acting as a thermal insulator. Experiments we have done at ITC show there can be a factor of 25 between the temperature rise on a bus bar inside a bus duct and the temperature rise on the bus duct surface. The attached image of a simulated problem shows the temperature rise internally was 537 F, but on the surface only 22 F. We simulated the problem with a soldering iron tip hose clamped to the bus bar with a thermocouple attached to get internal tempearature. From a paper "Common misconceptions in infrared thermography condition based maintenance applications" published in the 2000 InfraMation Proceedings.

Short answer is any temperature rise on the bus duct surface due to internal anomalies should be investigated. Watch out for duct heaters--they're supposed to be hot.
To satisfy NFP70, is it necessary to use certified thermographers? I'm thinking the answer must be "yes."
 
Re:Scanning Bus Duct Laland 4/18/2008
Also, in scanning bus duct, do consider on your evaluation the inductive heating of the bus. Inductive heating can provide high temperature on the duct but not on the bus.
 
Re:Scanning Bus Duct CES 5/9/2008
I scan bus duct from the floor using a 2X telephoto lens. When I detect a rise of even a few degrees, I report it to the customer for investigation.

I once detected a rise of about 10 degrees on a duct. Two days later before the customer checked it, the bus failed catastrophically.
 


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