Temperature exhaust from rolling turbine to taking initial load with exhaust hood spray the upper limit is 52C, and 80C is high alarm and 107C turbine should be trip.
In this case it would be better to continuo to accelerate the turbine and observe the tendency of the vacuum to increase. This way the vacuum limit of 0.12bara should be check again when the initial load is reached.
The vacuum should not decrease to the alarm value 0.17bara after initial load.
If low vacuum alarms occur during operation, the cause must be immediately investigated and repaired. The atmospheric relief diaphragm on the low pressure casing is design to blow apart if steam in the casing reaches 0.34barg and all steam at 1.03barg or greater pressure relieved to ensure that the turbine low pressure casing and condenser are not over pressurized.
The reason the Turbine should trip if the Condenser vacuum got bad is The Turbine is going to damage caused by torsion from LP Turbine rotation is against to rotation of HP and IP Turbine.
The maximum vacuum is about 0.036bara because of the strength of the casing construction in the exhaust hood. Vacuum operation above this limit may deform the bearing housing projected in the low pressure exhaust hood and changes the vibration level.
The vibration recorder must be observed closely during low load operation. The upper vacuum limit should be determined on the basis of moisture at the turbine last stage buckets. Since the moisture at the last stage is function of reheat pressure and temperature, figure above can be used for consultation. The limit of moisture at the last stage is about 16% because of the bucket erosion rate.
Curves show the relation between reheat steam condition and turbine exhaust pressure to get 12% wetness of saturated steam at the last stage buckets.
Any of two factors among reheat steam pressure, reheat steam temperature and exhaust pressure should be controlled so that the 16% wetness line is not exceed.
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