1. When the units are running separetly, the synchronizer may be used for regulating the rotating speed, so that the unit can keep operating at rated speed under any load, in order to ensure the stability of the power supply frequency. 

2. When the units are running in parallel, the synchronizer may be used for changing the load distribution of each unit in the power grid and regulating the power grid frequency. 

3. Before the units are interconnected with the power grid, the synchrinizer may be used for regulating the rotating speed of the unit, so that the rotating speed of the unit is synchronous with the power grid and can be interconnected with the power grid, just for this reason, the mechanism of the frequency static characteristic curve is called synchronizer.