Tools for Diagnosing Case Deflections and Alignment on a Power Utility Combustion Turbine

This paper discusses development, installation, and analysis of instrumentation systems for reliably measuring casing, thermal distortion, and alignment deviation on a large combustion turbine in power utility service. A variety of redundant measurement systems were installed to document casing distortion during the cooldown period after firing. The operating principles of each measurement system are described and presented with the rationale developed for installing and locating sensors. A vertical deflection sensor used for casing bow and bearing misalignment measurement is highlighted in the paper to illustrate its potential for use in other investigations. Additional sensors used include an array of shaft proximity probes, blade tip proximity probes, thermocouples, and axial growth probes. A measurement system for casing ovalization was developed using LVDTs mounted from a thermally stabilized ring. An automated data acquisition system was developed and installed to facilitate the recording of turbine cool-down events over the complete operating season without the need for constant on-site attention. Preliminary results define the turbine cylinder bow and ovalization response during the cool-down event following normal unit operation and correlated casing distortions with thermal gradients.