content: Mw is a function of how much current is being drawn. The amount that can be carried across hv lines is limited by the maximum current the cables and equipment can safely carry. To supply it you need to know the maximum output of what you want to power, the maximum possible output of your power supply, then you work out what you need to carry between them. This is dependant on a bunch of shit, safe distance between cables, insulation, environmental factors (above or below ground, below means no cooling, above means load bearing, wind, ice, etc)