What is rated speed and rated frequency, and what is their relationship ？ 

Rated rotating speed (Ne) refers to the rotating speed of the generator to maintain the frequency of alternating current to be 50Hz or 60 Hz, and its unit is round/minute(r/m).

Rated frequency (Fe) refers to the periods permitted by alternating current and must be changed in one second in the alternating current circuit. We have products with rated frequency of 50Hz and 60Hz. 

For example, the rated frequency of the household incandescent bulb is 50Hz, and if the frequency is below the rated frequency, the bulb will seriously flick and irritate people's eyes; if the generator is below the rated power, the rotating speed will slow down.

The formula of rotating speed and frequency of the generator 
n=60f/p 
n—— rotating speed of the generator(round/minute);
60—— per minute (seconds)
f——frequency(Hz)
p——number of pole pairs of the rotating magnetic field of the generator 
When the frequency remains the same, the rotating magnetic field of the generator is only related to the magnetic pole pair number. The more the magnetic pole pairs are, the slower the rotating speed of rotating magnetic field is.