Cause analysis and control of large expansion difference in steam turbine unit start up

Thermal expansion control during steam turbine start up is a critical safety challenge. This study investigates excessive thermal expansion in Dong fang Steam Turbine Factory's N300-16.7/537/537-8-type sub critical double-cylinder condensing turbines. Through systematic analysis of expansion mechanisms, interrelationships between high-, medium-, and low-pressure cylinder expansions, and factors including rotor-cylinder temperature differentials, shaft seal parameters, and inter-layer heating origins, we conducted quantitative analysis of expansion trends across operational conditions. The proposed cold/hot start control methodologies effectively resolved significant thermal expansion issues during both initial and subsequent start ups. These findings provide essential engineering guidance for enhancing start up safety, reducing downtime, and improving economic efficiency in steam turbine operations.