Most servos above a few hundred watts are mains powered.


NEMA simply refers to the motor mounting dimensions, and is an older imperial based standard (the 34, means 3.4inches)

You can get NEMA sized servos, but they're not common, instead most modern servos typically use metric frame sizes, 40, 60, 80 etc, with the number referring to the overall size of the mounting square.
An 80 frame motor mount is a bit smaller than a NEMA34 (~85mm), but has far more performance.

I only picked 1000W servo as an example. If maximum performance isn't your goal, 750W would likely be acceptable.

To give an idea of the performance difference, a 750W 3000RPM servo will produce a constant torque of roughly 2.4Nm, and a peak torque of 7Nm. It will deliver that torque from a standstill, all the way to it's rated 3000RPM.
A suitably sized NEMA34 motor will on paper produce over 10Nm, however by a few hundred RPM, that torque will have significantly dropped, and by a 1000RPM will be lucky to produce more than a couple Nm, which will limit the possible acceleration at speed.

The NEMA34 would likely have to be direct drive to maximise it's performance, whereas the servo can be geared (also gives more flexibility with mounting position) to give more torque with less speed. With the example above, at 2:1, you'd get 4.8Nm, and 14Nm, and get that all the way to 1500RPM, which means machine acceleration will be significantly improved.