A composite generator-network-demand planning method is needed today.It requires connection of large capacity generators into220kV regional networks where the loading is relatively small.This method will help to cope with the increasing short circuit currents at500kV networks，and to develop a smart grid capable of with standing nature disasters.In order to solve over-frequency stability problem of large generator in a small network，this paper presents a method of speed governor state transition control based on signal of power flow transfers.The method can quickly and precisely regulate power of generator unit following abrupt changes of an isolated grid.It can increase over-frequency stability margin of speed governor at steam turbine unit from9%to50%.The performance of speed governor at hydropower unit can also be significantly increased.The control system is decentralized robust and compatible with other systems.It can effectively maintain the operation of the remaining power networks with residual generation capacity after the overall system is damaged by natural disasters.Case studies are given to show the effectiveness of the proposed methods.