During the start-up and commissioning process of a supercritical 660 MW unit steam turbine

the lowspeed warm-up time was over long

the load and reheat steam pressure in the initial load process fluctuated abnormally

and multiple protection actions of the reheater caused several serious accidents like tripping.Investigation on these problems shows that

low start-up parameter

high setting value of X7 criterion

dismatch of the high and medium pressure regulating valve opening ratio

and imperfection of the control logic in distributed control system(DCS) and turbine digital electro-hydraulic control system(DEH) were main reasons for the above problems.Through parameter adjustment

X7 standard optimization

control strategy optimization and logic depth investigation

effective preventive measures for the problems were put forward.After start again

the turbine empty load test

loading test and one-time through 168 hours full load continuous trial operation were all successfully completed.The research can provide experience and reference for start-up and commissioning of the same type of steam turbine in newly built power plants.