Low-cost revamping of the Rothenbrunnen power plant

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Courtesy of Inspecteam Hydro

Introduction
At the Rothenbrunnen powerplant of Kraftwerke Zereraila AG (KWZ) all Pelton runners were replaced between 1999 and 2000, using the solution of FRAVIT's „forged Pelton runners' . Thanks to the successful replacement of the runners, KWZ avoided the high cost of complete refurbishment of the turbines: the new runners fit with the existing turbines, i.e. casing, injector, etc.
Several advantages in comparison with cast Pelton runners was decisive for this choice:

  • the forged material has better characteristics than cast
  • complete checking of the forged disk can be performed with much more ease and efficiency
  • the numerically controlled (CNC) machining makes high precision possible in the realisation of the bucket profile; this has an important effect on the turbine efficiency and on the rotation of the runner
  • the better material characteristics also influence maintenance and its costs. Less wear, less likelihood of cracks, lack of the typical porosities of the cast runners, which have to be welded: all these elements lead to economic advantages, which for the 30 years typical lifetime of a Pelton runner can be quite significant.

In the Power Plant the efficiency has been increased of 2.1% on average. Only with the increase in production these runners can be amortised in less than the half of the lifetime. This data have been verified by thermodynamic efficiency measurement.

After 8000 working hours no sign of cavitation is visible. The low wear confirms the expectations concerning the forged material. Moreover, by means of a continuous measurement we have confirmed that the efficiency shows no worsening.

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