I understand that a two-pole AC generator has to rotate at 3600 rpm (60 Hz USA) in order to maintain a 60 Hz frequency and higher frequencies would require these generators to spin even faster which could be problematic.
I also understand that increasing the number of poles would allow the generator to spin slower, but it would require more complexity and cost. However, are there other reasons that power grids tend to use lower frequencies?
Higher frequencies are much more affected by the inductance of the power lines. 400 Hz is fine on an aircraft, but over long distances the power factor would be extremely poor. 60 Hz was an educated guess (as I understand), but it has turned out to be about right.
What @Frog says about losses is true, however, that's not the real reason for utility frequency to be around 50-60Hz. HVDC systems have essentially no reactive losses, yet they did not really become widespread.
The choice of utility frequency is largely historical, and frequencies outside the 25-100Hz range were simply prohibitive around year 1900 from the technology point of view: 25 Hz and lower were too low for most consumer applications and required bulky generators and transformers, and 100Hz and higher frequencies could only be generated with belt-driven generators which were already being replaced by direct-coupled alternators due to higher reliability of the latter.
The frequency of the power grid is a great compromise.
Make the frequency higher and you get smaller (read: cheaper) transformers and (somewhat) smaller generators and motors. But, you get higher hysteresis loses in the transformers' cores and higher radiative loses in long power lines as well.
The above consideration about 100 years ago ended up with the conclusion that frequencies 20-100Hz are OK-ish. US engineers started using 60Hz as they liked the number for being the same for other time divisions (seconds vs minutes vs hours). European engineers (1-2 years late to the party) liked 50 Hz better for being a multiple of 5 and 2 only, just like other unit divisions they used.
Other, independent power grids use other frequencies (like Swiss railways at 16Hz) because they fit their purposes better.
Skin effect is not really a consideration as most power conductors are made out of a number of smaller wires for mechanical reasons anyway.
I believe the reason for low frequency is as your frequency gets higher the impedance, capacitive and inductive, of the network has an effect on efficiency. The reason for AC is mainly so voltage levels can easily be changed using transformers, so as to carry higher voltages over long distances to minimize copper losses in transmission lines.
If you research under water power transmission systems, you will find, in a majority of cases, they use DC because underwater cabling has a high capacitor type characteristic due to the ocean surrounding it. AC power would not be efficient.
This is a good explanation of power distribution
Skin effect gets worse as frequency goes up. Large diameter conductors would not conduct very much in the center. Hollow power wires would be difficult to imagine. Very long lines would be an appreciable portion of a wavelength. This means radiation resistance and radiation losses.
Anything over 100Hz was also getting into the audible range. Noise from electricity was far too scary for most folk.
The frequency output has physical constraints on the generator as well to what Tom has mentioned. A higher frequency = more poles on the 3phase generator and it has smaller copper coils in the winding pair.You want to achieve an optimal current output for the generator for it size.
