From a student

We have an underground cable problem (1 metre depth). How can we check if it is ground water that is causing the problem or if it is the cable itself. There are 7 cables in close proximity and could this also be the problem. We want to use thermography to find if

(a) there is a water problem or (b) if there is a cable problem and if it is a cable which one.

Reply

It is not really possible to use thermography for this. The cable is shorting out and creating heat for a very short period of time. The solution is to do electrical testing on it, it should be possibly to locate the fault with the right test equipment. To be honest if the cable has failed, you could locate the problem and repair it, but you are gambling on the fact that it is not damaged elsewhere. I would just replace it as this is probably what they will end up doing anyway.

A thermal camera sees the radiated energy coming from an object, to be visible, there must be a difference in the intensity of the radiated energies of the both the object of interest and the other objects surrounding it. From a practical point of view this means that a cable problem must generate heat in order to be detectable with infrared. Not all electrical problems generate heat, and in the case of a short circuit on a cable, the heat is only present momentarily.

Electric cables buried at a depth of 1 metre need to generate a substantial amount of heat to be observable on the surface with infrared, the exact depth at which a cable can be detected will depend on a number of factors including; load, size of cable, mass of cable, soil type, soil conditions etc. etc..

Using infrared to try to pinpoint the exact location of a short circuit on a cable buried 1 metre down is really working beyond the limits of possibility with infrared.

Low delta

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