Using nuclear-powered steam to turn turbines, Siemens needs the measurements of its blades as precise as possible to avoid losing steam energy. Siemens turned to the Omnitrac, with its weight of less than 20 pounds and its precision, to power its facility.
API Omnitrac Laser Tracker at Siemens AG in Mülheim an der Ruhr, Germany
The most modern and the largest nuclear power station of the world with an output of 1.600 MWatts relies on Germany technology. At Siemens blades are installed to the rotor and measured in the housing during the final assembly of turbine manufacturing. With a difference of just tenths of a millimeter, this is a balancing act between optimal efficiency and necessary safety margin between blades and housings.
The steam turbine which is more than 12 m long and has a diameter of 6.7 meters is waiting for the final cross section before distribution to the nuclear power station Olkiluoto 3 in Finland. The free standing blades of the low pressure turbines are aligned to tenths of a millimeter despite their mass and weight. “The deciding factor of these rows of blades is their distance to the housing”, describes Stefan Hoeyng, Plant Engineer for final assembly of the steam turbine at Siemens AG Power Generation. The gap between turbines and housings must be kept as small as possible, as the larger the distance, the more steam passes through and this lowers the efficiency. The turbine blades are under no circumstances allowed to come in the contact with the housing as this causes damage.
Better efficiency with the employment of Laser Trackers
During final assembly large disks are shrunk and inserted into the groove of the blade on the rotor. Olkiluoto´s low-pressure turbine has a blade weight of about 320 kg. If the rotor is bladed, it is loaded in the force shelter with excess rotation speed, in order to obtain an appearance of compression. Subsequently, the free standing blades are measured. “The more exact a measurement system is, the smaller the tolerances for the distance between blades are and the housing can be laid out which improves efficiency”, explains Stefan Hoeyng. An accuracy of at least 1/10 mm was therefore the requirement with the new measurement system. After some tests, they decided on the API Omnitrac, thanks to its ease of use and lightweight portability at just 8,5 kg. If the housings are to be measured in the final assembly, the Laser Tracker must reach heights of 3-5 meters and an lightweight system is a lot easier to handle in such tasks. It is planned that the Laser Tracker will be additionally used on the construction sites. For example when there are measurement revisions in the power station housings.
Custom-made measurement software
Additionally Siemens have a specialized and easy to use software to measure turbines. The Laser Tracker can also be used by skilled employees, who are not trained research employees. “If I would like to measure distances and geometry with the 3D coordinate system, then I need to understand the system perfectly and be able to work with it every day, otherwise I will have too many errors”, states Stefan Hoeyng. A strict program sequence leads the user step by step in the measurement task. Metrology, an open measurement software also supplied from API delivers the basics. In close cooperation with Siemens, API has developed a measurement routine, where the measurement is checked with logical examinations and cycle requests whilst being measured.
Collaboration with system suppliers
As Stefan Höyng explains, Siemens have already provided internally measurement procedures, however not to this extent and in such detail. Therefore, API´s offer to deliver the hardware, software and programming, contributed to the final decision to purchase. “In principle I needed something to practice with in order to be able to use the Laser Tracker to recapture the laser beam, but this is not difficult with the software operation”, adds Steffen Linnemann, API Account Manager. The measurement project was released internally for this measurement. The measurement system is suitable for the task if different operators work with the system and want to reproduce different blades or acceptable values. The Laser Tracker fulfilled these requirements to one hundred per cent. Therefore, it is officially used together with the custom-made software for blade measurement.
Better results in less time
Documentation and indication of the single blades takes place automatically. This was one of the main requirement specifications for the custom designed software. The Laser Tracker is in employment at Siemens since February 2006 and measured values were reproducible with measurement analyses.
Wide range of employment
Laser Trackers are not only used for the measurement of the blades. The Laser Tracker is a great tool if you need to measure axial distances or diameters in a housing. With a height of 36 cm it is small enough to position exactly where you want it, and with its rotating ranges of +/- 320 degrees horizontally and +80 to -60 degrees vertically, the Laser Tracker is also suitable for measuring large objects from long range. The Omnitrac is certified with a range of 60 meters and at Siemens it captures with an accuracy of 10 ppm to NIST – a distance of 40 meters. As Stefan Hoeyng explains, the Laser Tracker has no boundaries. Siemens are very happy with their Laser Tracker and are already thinking about purchasing the API Intelliprobe V2 hand held sensor in the near future. Contact with API will continue to remain very close, even more so with the continuous growing presence of API in Europe and the opening of the German office in Mannheim in 2007.