The frequency of an AC machine is expressed by the formula:
F = (P * N) / 120
where F = Frequency, in hertz
P = the number of poles of the generator rotor
N = the speed of the generator rotor (in RPM)
When synchronous generators (alternators) are connected in parallel with each other on an AC grid, they are all operating at a speed that is directly proportional to the frequency of the AC grid. No generator can go faster or slower than the speed which is proportional to the frequency.
When the generator rotor is locked in synchronous speed with other generators on a large grid it is effectively a "brake" preventing any increase in speed which would normally be the result of an increase in fuel.....
