how do they find out where an underground electrical cable that are encased in concrete pipes has developed a fault or gotten cut and needs fixing?
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You realise there’s a fault when electricity doesn’t come out the other end like it should do.
You can find the fault through a few ways. Walking the line might reveal a very obvious point, like someone has dug up the ground or something.
You can put a signal down the cable, watch for its reflection (it bounces off where the cable fault is) and, since you know the speed of the signal and the properties of the cable, you can make a good guess for the location of the fault. You then go out to the approximate area and look.
You can dig near the approximate area and see if there’s anything obvious underground. Damaged cables have a specific type of burn smell that can be detected.
You can put a signal down the cable and use detection equipment to follow it. When the signal stops you’ve found the break.
Sometimes it’s just a known cable with a dodgy connection buried, and you happen to know that connection failed every few years so you go dig it up again on a hunch.
There are two common faults, open circuit (a break) and short circuit (the cable ends touch each other). Different techniques can be used for each.
They make multimeters (volt/amp meter) that tests continuity. Basically just let’s you know if electricity makes it from point a to point b. About 99% of the time if something is wrong, all we have to do is ask around about if anything weird or new has happened in the area recently(ie: “I was cutting the grass and heard a loud gunshot from under the blades”, or “we recently had an underground water line put in from here to here”) and that solves the mystery.
I’ll give you a small scale example.
I’m an electrician for a small company.
We have a break locator tool which is meant for direct burial conductors in soil.
There is a signal generator which one clamp clips onto a conductor at either end of a termination point and the other lead is clamped onto a long screw driver that I push into the soil.
The signal is a high voltage dc pulse. It will send high voltage DC (2400V) down the conductor and if it is broken, and the soil moisture content is high enough the signal will return through the earth back through the screw driver and negative lead.
The second part of the tool is an inverted I shaped tool with two probes which I push into the earth. There’s a small signal detector with a needle that tells me if the break is to the left or right of where I pushed the probe tool into the ground.
Once the tool stops indicating left or right, and the needle on the gauge stays in the center then that is likely where the break is located.
I know that there is much fancier equipment out there than what I use, but that’s my experience.
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