GESDIM Ingenieros - Vigo
Replacing the stator in a Francis-style hydroelectric turbine using a new procedure with laser measuring equipment.

Replacing the stator using laser measuring equipment

The Francis Style hydroelectric turbines, in simple terms, are driven by water falling from a great height which turns the blades of an impeller at great speed, transforming potential energy into kinetic energy. The impeller is joined to a spindle by means of an axle. The spindle turns inside a stator transforming the kinetic energy of the impeller into electricity.

To function correctly and take advantage of the driving force of the water, the axle of the turbine must be correctly centred so as not to cause wear to the support elements. It is also important that the stator-spindle set remains perfectly centred, as the separation between them, called the air gap, is controlled by opposite forces, one repelling (magnetic force) and the other attracting (centripetal force). If the air gap is uniform, the two forces counteract each other; otherwise, it may cause vibrations which will affect performance.



The standard method for replacing the stator requires the complete disassembly of the turbine. Later, to centre and realign, we need to use as a reference the vertical plumb line (for the alignment) and the position of the labyrinth (to centre). The disassembling, centring and assembling processes of the turbine pieces take various weeks and require qualified staff.

Any reduction in repair times would provide an important economic benefit, as the plant must maintain the ecological flow of the river. Therefore, during the days when the plant is not operational, the water must still be released, although it does not pass through the turbine and, therefore, does not generate electricity.


The aim of the new procedure is to determine the position of the original stator prior to its removal, so that afterwards the new stator can be placed in that position, without changing the centre of the turbine.


As indicated, the position of the original stator needed to be determined prior to its removal. To do this, we measure the upper spider (the upper bearing support bracket which also supports the entire weight of the set), which is joined to the stator and upon which the centreline bearing is assembled.

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