The traditional overspeed protection control(OPC) uner operation state of isolated power grid may make the govener valve of steam turbine to be frequently actuated due to large fluctuation in rotation speed of the steam turbine

affecting the stability of frequency in power grid.For this

taking the reheated steam turbine as example

a mathematical model for emulating the multiregional single machine infinite system has been established

the influence of different set values of OPC upon the stability of frequency in power grid under operation state of isolated power grid has been emulated

the measures of suitably enhancing the set value of OPC during the time of decoupling the units being put forward

and adding three control modes

i.e.synchronizing

decoupling

and isolated grid operation

into the control logic of OPC.