We have Siemens SST5-3000 steam turbine. Its a HP Turbine and IP/LP turbine which are in opposite direction in terms of steam flow.
What is the purpose of seal steam at IP/LP turbine exhaust which is under vacuum?
Can i have PID of seal steam system? i may be able to answer this question after having PID at least.
Think about a large steam turbine (Tandem compound), condenser with reheat steam system. This type of turbine, before entering steam at HP/IP blade, shaft need to seal with steam, otherwise, all steam will go out from the bearing of HP/IP turbine shaft. After entering steam, the labyrinth seal may expand from both side of HP/IP shaft. So after entering there is no risk of steam leakage from HP/IP bearing. But its highly recommended to put always seal steam, cause, if no seal steam exist, main steam may get contact with bearing, which leads to increase lube oil temperature.
At LP steam turbine, the both bearing side of shaft, there may create some vacuum, which may lead to pull air in the LP turbine, even in condenser. Which may lead to reduce condenser vacuum, which is never desired at ST running condition.
So, Seal steam is very important fact for ST.