Monitoring Central Gland Leakage on Combined HP-IP Casing Steam Turbines

Steam turbine generators, the mainstay of electricity production, are increasingly required to run for well beyond their intended lifetime. As opening up machines for inspection is expensive, owners need to consider all relevant information in making the decision. Deposits on blades and erosion of internal clearances reduce machine efficiency and output, and can be detected and monitored using condition monitoring by performance analysis. Data obtained before and after overhaul also reveals whether any restorative work achieved the expected improvements in performance. Many large machines, including an increasing number in Australia, are of the compact combined High Pressure-Intermediate Pressure opposed-flow casing design. Increasing internal steam leakage from entry into the high pressure section to the intermediate pressure entry section has a large effect on output and efficiency. This flow through the central gland packing cannot be measured directly. Using a case study, this paper describes a method of estimating it by test that is sufficient for routine condition monitoring. The test explained observed poor performance that had led to extensive modifications to the boiler.