1. The function of upper limit of synchronizer is to prevent the synchronizer opening from exceeding the normal value due to the changing of steam parameters such as pressure, temperature and vacuum during operating, if there is no upper limit on the synchronizer, then when the steam turbine suddenly loses load, the danger of overspeed of galloping of steam turbine will be caused. 

2. The function of lower limit of the synchronizer is to ensure that the units can work reliably in parallel or disconnect when the frequency of the power grid is reduced.