Extract 5W low voltage power from 3000W high voltage source
There are parts that will easily withstand a 600VDC input. TI has a reference design of a converter that will handle 800V input and produce a 25V/0.25A (6W) output that could easily be used to create your 3.3V required power. 



I do suggest that you consider shopping for such a converter on the market though- making the transformer will require some technique for safety as well as functionality and will not be very cost-effective for a one-off (sourcing custom magnetics in small quantity seldom is). 

Note that the ratio of 600V:3.3V or even 24V is way beyond what you can reasonably expect to achieve without a transformer or tapped inductor (about 10:1 as a rule of thumb), and that probably means you need a custom magnetic component unless you want to do it in a bunch of stages.