On the basis of overspeed protection control(OPC)function and its characteristics of the unit with high pressure cylinder start-up mode which was designed by Nanjing Keyuan Automatic Corporation Limited

the OPC function during the unit load rejection test was investigated.Moreover

the estimative method of OPC recovery time was put forward.The value of OPC reset time Tr related to the minimum speed of the turbine and the OPC action times after the unit load rejection.Rapid relief of reheat steam pressure could reduce the OPC action times.The result of load rejection test on a subcritical 300 MW unit showed that

the DEH could meet the requirements of turbine speed control.If selecting the OPC reset time Tr that the unit speed idled to2 900r/min to reset the OPC

the peak value of the second time turbine speed raise would be lower

and the speed control effect would be better.