Safe Distance from Overhead Voltage

Ground level should be good for pedestrians.

The FAA would be the agency to advise of minimum separation of aircraft above the lines, probably 500 feet AGL.

It depends on the application and the standard.

For example.

Are the standards the same, "Down Under"?

Your question is too broad, it depends upon your country, its regulations, the type of lines you are working on, and the type of work you are doing. For example in the US utilities routinely do live-line maintenance on overhead distribution lines where there is an approved set of insulation blankets/barriers over the live lines between the workers and the lines. The crew is also working in a cherry-picker bucket truck which is isolated from ground to further minimize the risk. The clearance under those circumstances is the thickness of the insulating barriers. Provide more info, get better answers.