Hi pithpal
Can you state what kind of mine it is (opencast or underground) and what they are mining? I am working on an opencast iron ore mine on this moment but has also worked in an underground coal mine.
I agree with Tulum on many of his answers. All my answers are based on my own experience, and not necessarily the only way of doing things.
In the plants the electrical distribution is much the same as anywhere else. The different voltage levels are much depending on the size of the plant - on the mine I am now working the motors in the plant are up to 3.3kV, while in the coal plant where I have been it is just up to 400V. There are a big difference between electrical distribution in the pit/mining areas in mines and electrical distribution on other places. But the basic principles stays the same.
The distribution-method (cables, overhead lines, etc) are very temporarily. It shift almost every day, depending on where the mining activities are taking place. Overhead lines and cables for main distribution are 11kV, while trailing cables, depending on the machines, can be up to 6.6kV (400V, 525V, 3.3kV and 6.6kV)
Grounding method is normally high impedance grounding. Because there are no stationary ground point on a moving machine, it has to be grounded through the cable. Inside the trailing cables are a extra pilot wire/s - and like Tulum stated it is used with the ground wire to ensure continuity on the ground wire. This is a very important issue, because the machine must be grounded the whole time.
Due to the fact that the equipment moves continuously and is located in extreme conditions (wind, rain, sun, mud, dust etc, etc) the electrical panels are build very robustly. And like stated previously, flameproof equipment are also used sometimes, especially in underground mines (normally gold and coal mines) where there are possibilities of explosions.
Also remember - mines are not always the cleanest place to work!
Regards
[red]Failure seldom stops us, it is the fear for failure that stops us - Jack Lemmon[/red]
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