Recently I have started to design a character in Mutants and Masterminds third edition, and have hit a snag. We start at power level 8, so could I only take 8 ranks in any power, or could I go as far as I want, providing, of course, I have the sufficient points. Is it possible to get powers at a rank beyond your power level? I can't find the rule in the SRD in the powers section, and nobody online is having the same issue.
There are basically two sorts of powers, PL(Power Level)-limited ones and non-PL-limited ones. The first are anything that impacts a PL-limited trait such as an attack bonus, an attack rank, a defense bonus, a save bonus, or a skill check. Basically, no power can be bought that would put you over PL. That's simple enough, right? Any power that does not impact PL, such as something that gives you a higher rank of Movement, or gives you additional senses, or Immunity, is not limited by PL.
Note that tradeoffs mean that even PL-limited powers could have higher ranks than your PL. For example, a PL 8 character could have Damage 10 (Ranged) as long as his ranged attack bonus with that power is +6 or lower.
And, of course, the GM can decide that any given trait is limited. They are perfectly within their rights to veto Speed 20, or Regeneration 30.
I do not know if 3E explicitly noted it, but in 2E those ranks are supposed to be hard limits, so you can't over-buy to protect against a Weaken effect or to be able to shift caps on the fly.
Can you acquire additional ranks in a power level limited power (e.g. Blast or Protection) if those ranks are ignored for power level purposes, that is, they don’t add to limited traits like save DC or bonus, and the ranks are just used to resist things like Drain effects?
This is a GM call. The official answer is that power level limits are “hard” limits: if a power would push a trait beyond the limit, you can’t even spend power points on it. However, power level is intended as more of a guideline than a hardand-fast rule, and Gamemasters should feel free to bend or waive it as they see fit. Generally speaking, allowing ineffective “virtual” ranks in a power over the PL limit is pretty harmless, given the player is paying full price for a pretty limited benefit (particularly considering that making any power immune to effects like Drain costs only 1 point for the Innate power feat).