Operational Problems: Cold to Hot to Hotter

Turbine-generators sometimes exhibit substantial changes in vibration going from a cold startup to on-line, or when moving between load points. Such behavior results from problems beyond simple unbalance. Pedestals hanging or twisting, alignment changes due to foundation problems, and abnormal piping stresses on the cylinders are some of the possible conditions influencing the vibration.

Diagnosing such problems suggests measuring the motion of piping, pedestals and other components, but doing so on a running unit is difficult. Distances are large. There are no fixed objects to measure against in a power plant because everything moves. The measured components are also vibrating and so are potential mounting points for the usual laser or optical equipment that might be used.

Photogrammetry can accurately show the relative movement between components. Photogrammetry uses images taken with high speed (typically 9 microseconds) flash. Motion is frozen. Targets on measured components are included in many images taken at different times and places so their movement due to vibration is averaged out. Further, the high speed flash freezes any motion of the camera. It does not require a stable mount, unlike laser and optical equipment.

Even with the capabilities of photogrammetry, the large turbine world still presents measurement challenges. The size of the equipment and the limited sight distances often encountered require specialized tooling and techniques to make the required measurements with the necessary accuracy. Mechtell specializes on power plant work and has the techniques and tooling to make measurements needed for this kind of work.

Following is an example of the type of measurements that can be made. Note that all measurements are in 3 dimensions.

Turbine Location Measurement Results Due To Load Change

Turbine Bearing Vibration Changes at Different Load Points