Power Plant Earth Leakage

There's this fault in the power station where I work. When 3.3kv is fed to a board, the current on the earth line is less than 1A, but the moment you begin to load, the earth leakage current begins to increase such that when you load an electric motor of 1050kw 3.3kv, there's a leakage current of 15A. When you load another of such motor it increases to 42A, and continues like that as you continue to load. There was a fire outbreak about 5 years ago. I don't know if it is related to this, I am counting on your inputs. Thank you.