Abstract: In the periodical flexibility test of highpressure intercept device of 335MW steam turbine in Huadian International Zouxian Power Plant, some potential hazards of shutdown accident occurred, which include the fault of pressure transducer, the jam of electromagnetic valve, the human error and others. The highpressure intercept electromagnetic valve was redesigned, and an isolating device was added. In the flexibility test, the online safe oil system is completely isolated. Then the shutdown risk caused by hardware fault or improper operation can be avoided. 

Key words: high-pressure intercept device, isolating device, flexibility test, risk of shut-down