15 tons, as in 30,000 pounds? What size inverter is this? The biggest we make is 933kW (1250HP) at 6600V, and it is 11,000lbs including the phase shifting transformer for 18 pulse. Yours would be 3x as large!
Are you sure you are describing this correctly? If so, are you sure your substation floor can bear that added weight? Have you calculated the massive amount of air conditioning that will GE required to put that in a small enclosed space?
Generally something this massive has a building designed around it, not stuffed into an existing sub station enclosure.
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