1. High-speed synchronous generator:
Since most generators are coaxially connected to the main engine, thermal power plants use high-speed steam turbines as the main engines, so turbine generators use usually a high speed. 2-pole motor, its speed reaches 3000 rpm (3600 rpm when the network frequency is 60 Hz). Nuclear power plants mainly use 4-pole motors with a speed of 1500 rpm (1800 rpm when the grid frequency is 60 Hz).
2. Low-speed synchronous generator:
Most are driven by hydraulic turbines or low-speed diesel engines. The number of magnetic poles of the motor varies from 4 poles to 60 poles or more. The corresponding rotation speed is 1500 to 100 rpm and below. Due to the low rotational speed, salient pole rotors with demanding requirementsndres in materials and manufacturing processes are generally used.