Geometry Recovery of a Francis Runner Prototype at Site

Geometry recovery of a turbine runner can be of prime importance in at least two cases: upgrading of an old power plant and field repair of a runner. Considering the importance of the field geometry recovery, we have decided to compare three methods of measurement, on a Francis runner with a 4.4 m outlet outer diameter. The first method of geometry measurements is the classical template technique, consisting in drafting both horizontal and slanted sections of the runner blade-to-blade passage. The instrument used for the second method is a 3D Laser interferometer. The last method is based on a portable coordinates measurement arm with 6 degrees offreedom. The aim of the paper is to describe the procedure and the use of each method, and to compare them from the point of view of their accuracy and their flexibility in the field. As a conclusion, it will be explained why the recovery method with the portable arm seems to be the most advantageous for us.