Thermodynamic model of HP–IP leakage and IP turbine efficiency

In this paper, temperature variation method and numerical calculation method are both presented for the calculation of the HP–IP steam leakage through midspan packing (N2 packing), which is called N2 leakage for short, and an error analysis mathematical model about the impact of measured parameters error on N2 leakage rate is established. The two methods have been both applied to a 600 MW supercritical steam turbine’s N2 leakage rate estimation, and the results show that numerical calculation method can estimate N2 leakage rate as accurately as temperature variation method, and the chief parameters which affect the accuracy of N2 leakage rate are hot reheat temperature and IP turbine exhaust temperature. Taking the leakage from HP turbine exhaust balance piston to IP turbine exhaust zone (N1 leakage) quantity into account, which has great influence on N2 leakage calculation precision, combined with N2 leakage, IP turbine efficiency is calculated exactly, and the result indicates that: Compared to N1 leakage, N2 leakage is the main factor which affects the IP efficiency.