Re: 300 MW
300 MW for a few minutes is insignificant. Australia does have some measure of power distribution between states, so the problem of consistent power generation is distributed somewhat. Their stupid moves towards solar and wind generation have made giant UPS efforts like these necessary.
Pretty soon they'll realise that their insane "green" generation schemes aren't going to work. They'll find that their commerce is crippled by the intermittency that they'll suffer (the Californians have just realised this and are about to do something about it by commissioning the construction of several nukes!).
A paper has recently been presented to the UK government, laying out the utter stupidity of their "green" power proposals, and amply demonstrating that this government has little time in which to dither around "deciding" what to do.
Unless significant amounts of generation capacity is added to the grid very soon, the UK will have rolling power cuts (that's why your "Smart Meter" has a remotely controllable contactor inside it). The closure of most of the old nuke stations has precipitated this collapse in power infrastructure, and no number of worthless bird mincing windmills and solar arrays are going to make up the energy shortfall.
The UK doesn't have the engineering capacity or a sufficiently educated populace to deal with the problem any more. The UK government will have to hire in expensive "talent" from elsewhere. It really is a shambles!