Monash University Gippsland School of Engineering This paper was originally presented at the 52nd Conference of the Machinery Failure Prevention Society, Virginia Beach, April 1998 In machines with an HP-IP opposed-flow casing, increased N2 packing internal steam leakage can occur from the high pressure turbine section into the intermediate pressure section has a large effect on output and efficiency. The application of a simple test method for estimating this leakage explained observed poor performance on two sets. Key Words: condition monitoring; optimisation; plant performance; predictive maintenance; steam turbines; testing; N2 packing Where a machine is taken from service, coastdown and running up through shaft bending critical speeds can allow momentary rubbing at the internal seals. The resulting enlarged flow area can reduce the internal efficiency, such that less energy is extracted from the steam. This also results from internal leakage within a casing which allows steam to bypass blading stages. These effects are particularly evident on the turbine design with both High Pressure and Intermediate Pressure sections in the one casing, with flow in opposite directions. Retractable packings have been developed by manufacturers and after-market suppliers. These avoid shaft rubbing as they do not close into their normal clearances until the machine is near operating speed, having passed through the bending critical speed or speeds. Vibration analysis can detect the occurrence of such shaft rubbing and other conditions of the rotor line, but cannot detect the extent of internal wear or deposition. It is well suited for other quite different failure modes, such as when blades or parts of them come off and cause consequential damage. As with the application of all condition monitoring, the rule is to choose techniques to match the likely failure/wearout modes. As steam turbines are critical machines, all the main techniques have their place. Performance analysis
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