Using magnetometer to locate underwater power cables

I work for a high voltage testing company.
We are often called in to fault locate under water power cables. I have equipment that can tell where a fault is in the cable length.

Unfortunately after a cable has been on the ocean floor for a while it tends to go 'missing'. I've seen towed magnetometers used with varying degrees of success to locate these lost (de-energized) power cables.

Now for my real question, if I was able to flow an electric current down a buried underwater cable, would it make it more visible to a magnetometer? How much current do we think it would need? Would I need to return the current through the sea water? as presumably if I passed current down a shield and returned it up a center conductor wouldn't the magnetic field be canceled out?

All comments are welcome.



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Often the problem we come across is that there may be more than one cable lying in the area. This is especially true of oil fields, but can occur anywhere there's under water cable, as they are all generally layed along the same routes. One of the reasons for wanting to push some current through our cable of interest was to try and make it more visible than the ones we're not interested in.

We could actually use the steel armor as a conductor, if this would make a greater anomaly than using the actual cable inside.

Even if the cable is cut I can push current down the armor and use the sea water as the return path, it just requires a higher voltage supply. The only type of current that could practically be applied is DC, as the capacitance of the cable, or armor requires a lot of power to energize it.

Thanks for the info.
Mike



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