Hi, I'm not sure someone who is separated (not yet divorced) can apply for permanent residency. I'm guessing your estranged husband is a resident or citizen but if you're separated, he probably isn't going to sponsor your residency as his spouse.
The link below will give you some other options for visa's to enter but I cant see an option to apply for permanent residency when you are separated.
https://www.border.gov.au/Trav