Aratiatia G2 Runner Overhaul

We assisted MB Century in the overhaul of one of Mighty River Power’s Francis Turbines at Aratiatia. ¬†Aratiatia is a hydro station about 13km downstream from Taupo on the Waikato river. The equipment used at the hydro station suffers adversely from erosion due to harsh particles in the river water.
Some of the equipment used at the hydro station was recently repaired by AIE:
  • The turbine runner was cracked, had cavitation damage and was badly eroded
  • Sealing diameters were machined then weld overlaid with a wear resistant material
  • Wicket gate sealing strips were weld overlaid. Erosion damage was repaired and the sealing faces were completely re-aligned by CNC machining
  • A new fabricated Bottom Ring was manufactured in our Okuma CNC machining centre using erosion resistant materials. The ring was 4.5 metres in diameter with 20 accurately spaced holes in a PCD around the centre for the wicket gate locations
A lot of effort went into the transportation of the runner and the shaft from the Hydro Station to our premises. By not removing the shaft from the runner, our customer was able to reduce the workload. The risk of alignment issues was also reduced.

The runner weighed almost 40 tonnes, but we were able to manoeuvre the runner through the AIE workshop without a problem thanks to the two 25 tonne overhead Gantry cranes in the fitting and fabrication areas. We also utilised our special purposes lathe to turn the runner in our workshop.