QMT Features: August 2014
Powering up
Reverse engineering is helping power companies generate up to 15% more power


Power generator Southern California Edison used Verisurf software to reverse engineer steam turbine rotor assemblies to support the installation of new and improved blades. Its engineers are now applying those lessons for other operators.

Steam turbines still generate approximately 90% of the electrical power in the United States. But most of the steam turbine power plants in use today were built over 60 years ago, long before CAD and advanced surface and fluid analysis.  So when plants are taken offline for maintenance, repair and overhaul, there is an opportunity to upgrade turbine rotors with more efficient blades that are capable of generating 8-15% more power from the same rotor configuration.  
The turbine housings are extremely large castings and the rotor assemblies have tight tolerances, which makes the design and integration of improved blades tricky. This is compounded by the fact that drawings and detailed plans for the original rotor assemblies do not exist; requiring a detailed ‘as built’ dimensional CAD model of the entire rotor – coupling face, shaft, bearings, steam seals and bladding area.

Southern California Edison created Edison ESI in 1987 specifically to support the metrology requirements of its nuclear and conventional electric power generating plants. In the beginning Edison ESI employed a team of people to capture 2D measurements using traditional hand tools (rulers, tapes, calipers, plumb-bobs), then return to their offices to assemble the hand measurements into a 2D drawing. As metrology software and supporting digital capture devices evolved, Edison EDI standardized on Verisurf Software as its application of choice. As power utilities deregulated, Edison EDI was able to offer services outside of Edison and quickly became the preferred choice among power companies worldwide to provide metrology consulting services. 
“My team and I have traveled all over the world providing ‘as built’ and ‘best fit’ data for turbine fan retrofits,” said Peter Tavis, Quality Control Inspector for Edison ESI. “Our data has always been considered to be highly accurate gaining us the reputation as the ‘go to’ source for reverse engineering of rotor assemblies.” Turbine rotor assembly tolerances are extremely tight; errors can be catastrophic.

A typical turbine fan can rotate at 3,600 RPM. At this speed the blade tips are turning at close to the speed of sound. All components, including coupling face, bearings and shaft must match the rotor exactly.
Verisurf Reverse Software can process scan or probe data to produce usable 2D or 3D manufacturing models, as well as producing the final deliverable of an intelligent CAD model. Retrofit turbine fan manufacturers are able to import the data directly into their CAD/CAM application and provide a ‘best fit’ for the new fan. The reverse engineering of the rotor assembly requires probe data as opposed to scan data, which means fewer data points but greater accuracy. Typically a Faro Platinum portable CMM is used for probing. Given the nature of the rotor assembly the final output is a 2D CAD model.
Due to location and size of steam turbines portability of the overall metrology solution is important. Since Verisurf serves has a common metrology platform, compatible with all digital measuring devices including portable CMMs and scanners, it is just a matter of selecting the right digital measuring device.www.verisurf.com
  
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Rob Tremain Photographer
www.4exposure.co.uk
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