Abstract: The existing method of measuring intermediate pressure(IP) balance piston seal leakage by temperature variation test exists some errors and cannot achieve on-line monitoring. The errors of the temperature variation test method are analyzed, and the detailed variable condition calculations which considering IP balance piston seal leakage for a 300 MW steam turbine are performed. The results show that the IP turbine efficiency is basically not influenced by reheated steam flow, IP balance piston seal leakage and reheat steam temperature. The new calculation methods of balance piston seal clearance, IP balance piston seal leakage and IP turbine efficiency are put forward which based on the balance piston seal clearance and IP turbine efficiency are equivalent at two adjacent working conditions. By the detailed variable condition calculations results and temperature variation test results, the effectiveness of the new calculation methods is proved. The IP balance piston seal clearance, IP balance piston seal leakage flow, reheated steam flow and IP turbine efficiency for a steam turbine in a certain period are computed.

Key words: intermediate pressure(IP) balance piston, on-line monitoring, seal clearance, steam turbine