This is known as a dragline excavator. They are used in open pit mines and can be used for dredging coastlines etc. Intrestingly, they usually run on electric (something like 13KV or like that if I recall correctly.) This means that often a purpose built power station is employed to provide the power. From talking to a human, I learned that often the coal is used to also run the power station on site. The fuel operating costs for such a large machine like this are actually pretty minimal, all things considered. The best thing, is the way they move, they basically walk because they are so heavy, and there is all sort of cunning things this device can do, but not all at one time. I learned that when it sets up on certain turf, it makes what is known as a bench, and this can sometimes fail (aka "bench fail") which is usually very bad news and extremely time consuming, not to mention highly dangerous for the crew involved.