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Insufficient output and rising pressure after governing stage of a 630 MW supercritical unit occurred only 18 month after the first outage. Though analysis based on measured parameters, fouling existed in governing stage and the first stage group. By virtue of linearization of formula and decoupling the impacts to thermal characteristic parameters, the quantified deposition degree was obtained. The fouling reason was determined by scale sample analysis, and the solution was proposed by quantitative calculation. The problem was successfully solved with boiler pickling, turbine cascade jet-beading and pulsing minimum oxygen to inhibit flow accelerated corrosion. A steam quality detection method was also proposed as the installation of measurement point after governing stage of supercritical unit. These treatments provided building and operation experience for 1000MW ultra-supercritical turbine and the same type of equipments.

The fouling on flow path of steam turbine would lead to the changes of thermal parameters and significantly deteriorated efficiency. In this paper, a qualitative analysis of fouling on flow path based on measured parameters was described for the preliminary diagnosis, and the zooming thermoeconomic diagnosis model combined with the equivalent flow area diagnosis model was proposed to diagnose the specific location of fault. Then the flow performance of a 630 MW supercritical unit was analyzed, and the possible fouling stages were also discussed according to the thermoeconomic diagnosis and quantitative analysis. The result of diagnosis was consistent with the situation of uncovering cylinder, which indicated that though the actual system was complex, the coupling multiple faults of flow path could be diagnosed by combining the above diagnosis models.

With a long natural cooling time after a shutdown of steam turbine restricting its available coefficient, this paper presented the analysis and application of a forced cooling process to sub-critical steam turbine. The radiating mechanism of natural cooling was analyzed theoretically, and the required amount of cooling air was calculated for a WH 600MW steam turbine. Moreover, the cooling rate with no life loss principle was determined by the method of quantitative calculation and numerical analysis, together with safety analysis. The research discussed the control strategy of practical application according with steam turbine characteristic and applied to operation, which provided theoretical guidance for the optimization of cooling condition.