Tolerance for temperature rise in cable sealing end

[nraju]

We recently conducted an infrared thermography test on our outdoor cable sealing ends. In one of the phases, the temperature was found to be 7.2 degrees Centigrade more than the corresponding phase in an adjacent cable sealing end. Currents in both the CSEs were found to be the same, but I would like to know possible reasons for this temperature rise. Is it pointing to a potential partial discharge inside? Also, is there any international standard on the allowable tolerance for temperature rise for CSE bushings? For instance, above how many degrees is it considered serious enough to shut down the generator?

 

[prc]

A loose connection in the current carrying path is to be suspected.

 

[ausphil]

1. prc's suggestion
2. low insulating fluid level in the sealing end
3. poor sheath connection producing heat from induced current.
4. high surface leakage current over the outside of the sealing end

My gut feeling is that partial discharge is not producing a temperature rise of 7deg on the outside of the sealing end. There is not sufficient energy caused by partial discharge to generate that amount of heat. If it was PD, I would expect that it would have failed prior to raising the surface temperature by that much.

You might want to try to determine the source of the heat in the infra-red image. If you can localise the initial source, you can narrow down what the component is, and hence the issue. Adjust the settings to remove all but the hottest temperatures.

With #3 above, you might be able to measure the sheath current to see if there are any differences from the other phases.

ausphil

 

[cgrodzinski]

What is the voltage of the circuit?