Thanks "slow-poke", I also had no idea that DC power was being used for power transmission anywhere like that either. I am always amazed about some things like this ( and many others) the size, the "power " being generated and being used, and in this case being converted back and forth AC to DC. And to say nothing of finding out about "grounding" currents/fields going deep into the earth and back again, I thought that was a kind of "surface" 10 ft.+- deep thing.
We had a ground grid put in around the sewage plant I worked at. The plant was in a slightly deep narrow valley, a concrete batch plant was right beside side but about 20ft. higher on a bank, with the towers and high tanks, it was a bit of a lightening magnet. After a number of near strikes that took out pieces of control equipment which would result in thousands of dollars of reprogramming and replacing parts and having to operate some of the plants equipment manually, or run, operate with work arounds. I was also having trouble with why we didn't have more grounding around the plant. An earlier electrician had told me it was all built to spec. I basicly said bull $&$@, might be spec, but no way it could handle anything from a near hit load.
I talked to an older electrician about this when he was doing some other work for us, and after looking things over he felt that the plant was a very large grid above ground that had power wire, sensor wires, etc. running many places, laying in metal trays, metal walkways and railings, metal piping, and so on.
The result, a go over of the grounding, adding extra tie points, and in earth/dirt grid put in at other end of plant with a somewhat "large" cable going to it. This seemed to prevent our previous problems very well.
A few years later the concrete plant was moved out, which also helped.
Luckily, we never had a direct hit.
