Determining HP-IP Turbine Seal Leakage

This paper presents a new method for determining turbine shaft seal leakages. Specifically the seals are those which flow from the High Pressure (HP) turbine to the Intermediate Pressure (IP) turbine when these machines share the same cylinder. This work began with the well-known Booth/Kautzmann Method, also known as an “Influence Test”. The work was instigated given that routine success of Booth/Kautzmann has not always been assured. This work promotes two major modifications. First, an improvement is advocated in which the contribution from seal flows is weighted based on source energies; i.e., use of a strictly defined thermodynamic boundary. This applies to isentropes and exergy differences. However, the use of weighted isentropes does not guarantee that Booth/Kautzmann will always work. Second, the use of a convergence parameter is advocated which normalizes the influence of differing Reheat flows. This convergence parameter leads to a consistently computed seal flow which is quite suitable for routine monitoring. The new technique has a remarkable ability to detect inconsistent data. Four case studies are presented: two conventional North American designs in which the HP seal is placed between the Governing Stage shell and 2nd HP stage group (termed the “Dummy Seal” or “N2 Packing” leakage); and two European designs in which the HP seal is exposed to turbine inlet conditions. Although several of these studies produced sharp convergences using Booth/ Kautzmann with weighted isentropes, this work places doubt on their reliability. Comments are offered on the technique’s use, data reduction procedures and on further development. A sample spreadsheet has been made available for use by power engineers.