Leica Absolute Tracker AT401 with SpatialAnalyzer

Based at Sion in the Swiss mountains, HYDRO Exploitation SA is a service provider that specialises in the operation of electrical installations and hydroelectric facilities.

The company has around 450 employees and currently operates facilities with an output equal to approximately 22% of Swiss hydroelectric capacity. Together, these facilities produce nearly 16% of Switzerland’s hydroelectric power.

The employees of HYDRO Exploitation SA possess a great deal of experience in the operation of hydroelectric facilities. Their company brings together engineers, technicians, project managers and operating personnel in the power generation plants so that their experience can be used to undertake restoration, renewal and optimisation of other installations. Amongst the employees is David Rey, geomatics engineer at the centre of the civil engineering unit.

To measure the geometry of machine shafts – the main rotation axle of a machine – and the injectors, water inlet planes and equipment positions, HYDRO Exploitation SA has, since 2011, been the proud owner of a Leica Absolute Tracker AT401 that is operated using the SpatialAnalyzer software.

The AT401 allows HYDRO Exploitation SA to perform highlyaccurate, remote three-dimensional measurements over long distances. This tool allowed David Rey’s team to improve upon data that was previously available solely as vertical data (shaft altitude with a certain accuracy level) and provide three-dimensional data. The 3D results allow a much more relevant analysis of the geometry of power-generation machinery in cooperation with the mechanical engineers.

Thanks to this tool, HYDRO Exploitation SA has been able to provide its services much more quickly and accurately than it could previously using a conventional method. With this new measuring technique, the company can fulfil heightened mechanical maintenance requirements and has also been able to win new mandates.

Electra-Massa SA, located at Bitsch, is one of the new customers now relying on HYDRO Exploitation SA for highaccuracy 3D measurements since its acquisition of the AT401. This storage power plant, constructed in 1964 and commissioned in 1969 has a total power of 340 MW. The electrical power generation is provided by three Pelton sets driven by the melt water from the Aletsch glacier via the Gebidem dam, located 750 m above the plant. The 55 m3/s of water passing through the turbines of the Bitsch plant contain between 10 and 13 kg of sand, which is an hourly mean of nearly 40 tonnes. As a result, approximately every ten years, the four injectors of the three existing sets are demounted, reconditioned, repaired and refitted.

Thanks to its portability, David Rey can easily use the AT401 laser tracker from Hexagon Manufacturing Intelligence to take a series of different measurements around the injectors.

With the injectors removed, the first step is to use the laser tracker to measure the shape of the outlet orifice and from it derive a possible difference in shape. In theory this shape should be circular, but according to the local technicians it tends to have an oval shape. The following is an example for one of the injectors:

In this graphical representation, the measured shape is oval and is compared to the circular shape; corrections are therefore required.

Once this measurement has been performed, the work involves build-up welding and then machining of the outlet orifice so that it once again has a perfect shape that complies with the mechanical tolerances.

“The AT401 from Hexagon Manufacturing Intelligence provides a real additional technology with significantly greater quantity and quality of data,” explains David Rey. “What’s more, traceability is made easy by the functionalities of the SpatialAnalyzer software. In fact, each measurement automatically creates a data report.”

Once the four outlet orifices have had their shape defects corrected and the injectors have been reconditioned, reassembly can start.

The second measurement stage uses the laser tracker to monitor the position of the injectors relative to the Pelton wheel. This wheel, invented by Lester Allan Pelton in 1879, is a disc equipped with buckets shaped like half nutshells around its perimeter. It transforms the potential energy of the water into the kinetic energy that drives the electricity generator. The point of impact of the water jet must be within a certain tolerance to ensure optimum efficiency and minimum wear of the wheel. This tolerance is directly related to the width of the bucket in question.

The speed and accuracy of the laser tracker allow David Rey and his team to obtain an optimum number of reliable measurements in the minimum amount of time.

Electra-Massa SA is extremely satisfied with the quality and reliability of the data presented, allowing the development of a long-term collaboration. Thus the AT401 is an important factor in the trust that exists between HYDRO Exploitation SA and its customers.

The acquisition of the laser tracker has acted as a turning point in the analysis and measurement of mechanical parts.

Thanks to its speed, portability, accuracy and reliability, the Leica Absolute Tracker AT401 allows David Rey’s team to collect new data, improve their traceability, save time and money, and likewise to optimally satisfy the requirements of mechanical engineers.