We have had Genrator Bus Duct failures. We are thinking that we can use IR to detect potential faults. Has anyone had success in inspection of these ducts using IR?

Infrared thermography is a very effective technique for some conditions on isophase bus ducts. It can show unusual circulating current patterns. Depending on the design and the defect, there can be hotspots created by at the joints between bus duct sections, at the grounding jumpers, and very commonly at either generator or transformer end, particularly under the middle phase low voltage bushing enclosure of the generator stepup transformer. You might also detect anomalies with the forced cooling pattern including incorrect damper positions.

Of course there are other degrading conditions associated with the isophase bus that you won't see. Those include fatigue cracking of the laminated flex strips at the low voltage bushing terminations, and problems with the internal bus support insulators.

Don,
Be aware that most shiney metal, such as buses, will reflect the temperature of ambient items around it giving a false IR value. Shiney metals have low emissivity and high reflectance values which make them hard to get accurate IR readings on. A good trick is to put electrical tape on strategic locations. Electrical tape has an ideal transmitance value for conducting IR.

J-

The bus duct is painted. Flat gray at our plant. Kind of ugly, but a nice high emissivity target.

The bus wouldn't be accessible for a camera unless you have the special I.R. windows installed.

Oops! What kind of failures does bus DUCT have?

All of E-petes suggestions are great. To see the actual bus joints you need to install IR transparent windows; IR viewports are probably not sufficient due to air flow issues that would be compromised by onpening them.

Even with an IR window, however, you want, as Wally suggests, to make sure the busbar itself (the duct is not the problem!) has some sort of high-emissivity marking on it. That is where things get tricky as there is no good guidance for how to proceed. Insulating tape wrapped around the busbar near the joints should work well if you can get your engineering staff to approve it (and I see no reason why they should not).

Even with the window and the high-emissivity targets, the airflow through the bus will cool any problem joints making it more difficult to detect them in their early stages of failure.

I have also seen instances of the air flow being impeded by something as simple as plugged air filters. This can result in critical overheating of the bus and/or an already abnormally heating joint.

In my experience the circulating currents can shift position as can the hotspots on the grounding jumpers. These can also reach suprizingly hot temperatures (100-200C+)!

I have experienced scanning a bus duct of which hotspots (80 degrees C) were found on the bus duct. The hotspot were at the screw joint of the bus duct Underneath those hot spot is the bus bar joint. However, when we open the bottom portion of the bus duct, there was no hotspot on the bus bar joint. taking a scan from the inside of the bus duct, the hotsport can be seen. We dound out that the hotspot on the bus duct was due to electromagnetic induction (if my term is correct. They replaced the bolt on the bus duct joint with stainless steel and the hotspot were gone.

Hi guys,

We were also using IR Thrmography for checking our Bus bars and other electrical panels..We can find some interesting faults just by comparing similar busbars even though you were not using the correct emissivity..

Check the attached file.. We got an image of a hot bus bar in our plant..

Have a nice day!!

Thermography_Report_ISPC-R1-PDB__8_25-11-07.pdf (212 Kb, 43 downloads) Bus bar

Hi Jenish,

Do you consider if the load`s current is unbalanced in your bus bar?
In our checks in plant we think is very important that factor to evaluate any problem with differents temperatures.

Best regards
Cristian