Like the above poster said. Before you go replacing the breaker, make sure to test every PSU first.
I've had something similiar happen. The breaker kept blowing and I assumed it was a bad breaker. However after switching the rigs to another breaker the same thing happened AND after a few attempts I heard a VERY VERY LOUD BOOOOM!.
And basically it was some internal short with 1 PSU. I think the first few times the current protection shut it off and then it didn't work, so then the breaker shut it off and then finally some huge capacitor on the PSU basically exploded like a bomb, scared the crap out of me and took probably 2 days or so to get rid of the smell.
So just test your other rigs first and make sure its not a PSU that has gone bad.
This also might be a factor, I have the house maxed out and anymore and I blow the main 200 amp breaker, I have rigs in the basement also. I have $.049 electricity so I'm still mining all I can. I was thinking about have a new line run to the garage from the telephone pole but I'm not sure how much that will cost.