Unexplained Hot Spot in Cable

Do yourselves a favour and replace the cable.

Afterwards take a scalpel and peel of layer by layer of the cable and document what you find.

And report back.

The noload current of transformer is always flowing, and in case of something really bad, that can heat up the cable. Do as the #1 said unless you want a potential catastrophe.

For a possible related topic, study up on "arcing ground faults."

Check for possible loose cripming of cable lugs or loose joints of busbar.

Do as #1 said and replace the cable. Replace all phases and neutral if applicable.

Internal "treeing" within the cable insulation will cause a fault. Outdoors in winter they locate the cable fault by looking for the spot without snow cover, due to the short circuit heat.

Corona on the jacket of the cable can also cause a 5-50F temperature rise, and it may only be present during damp night conditions thru 8am.

The corona is due to an insulation defect in the cable causing a locally instense electrical field.

The type of cable may also have outlived it's normal lifespan ?

If I had the pic's on this computer I could post them and show what you are describing.

Hi, Pl some details are required, What type of cables three core or single core, cable voltage rating, armored or unarmored cable, how they connected, pl check the cable insulation with respect to armored. And what protection relays you are using in the circuit.

The cable is Aluminium armored,3 core 300 sq.mm 33kV connecting the 33kV switch gear and 1600 kVA Dry type Indoor transformer 33/0.415 kV

There are other explanations, however, my guess is that your tong measuring device is missing the current that is causing the temperature rise. I think you need to use the tong over each phase individually instead of over the whole cable.

Please note that we know how to use the tong tester, and tong tester was inserted on individual phases.

Please search your topic at IEEE Xplore where there are probably several papers describing your problem.

You may wish to report back.

To have hot spots there has to be current flowing from somewhere as you have noted it disappears when the gear is out, also a cable in good condition should not have localised hot spots it should be uniform.

There has to be current flow to create the hot spot(s). There is definetely a problem with the cable, the hot spots are most likely areas of increased resistance. Replace the cable.

If you are measuring temperature gradients in a cable when no current is flowing, then maybe there is another heat source, sunlight, etc. or you may have emissivity gradients in the cable jacket that appear to be hot spots.