Australia has traditionally had government led national infrastructure to achieve span and system uniformity, followed on by waves of privatisation to varying degrees - for roads, power, telecommunications, etc.

It's a large (mainland USA in area equivilant) area with sparse dense pockets of population.

W.Australia has a fully independent power grid, I suspect the Northern Territory is the same. The East Coast (where the vast majority of population resides) has inter connected State grids .. including (recently) Tasmania, an island state with a great deal of hydro electricity and gas reserves.

https://en.wikipedia.org/wiki/Basslink

There's a federal road network, lesser roads are state roads, smaller roads are managed by local councils.