2018 11 Paper: Karapiro G2 Class 4 Overhaul

The Kaplan turbine-driven generating unit No. 2 at Karapiro hydroelectric power station underwent a major overhaul from September 2014 to October 2015. After the overhaul it ran satisfactorily for two years, but in December 2018 a fault affected the “stift” that operates the distributing valve of the blade servomotor, resulting in a catastrophic failure of the valve spool (by shearing off under torsional stress). The repair was effected by the Owner’s governor engineer, assisted by two mechanical fitters, without entirely dismantling the turbine hub; it took five months and during the repair work, in addition to
identifying the cause of the fault, a number of shortcomings of the major overhaul were identified, in spite of Quality Assurance provisions in the contract awarded to a large and experienced Contractor. The Quality Assurance clauses were not effective to their full extent as regards the maintenance
procedures and workmanship, largely because the Quality Control of the Contractor and the Owner had not been implemented rigorously throughout the entire duration of the overhaul.
This paper describes the root cause of the fault, the various remedial options considered, the findings discovered during the remedial option selected to fix the fault, and the lessons learnt, amongst which the vital importance of Quality Control was the most prominent.

  • Author: Giuseppe Grilli, Tony Cserney
  • Exchange: 2018 - Albury AGL
  • Company: Hydropower Engineering, Mercury
  • Topic: Asset Condition, Generator, Governor, Kaplan, Quality, Refurbishment, Runner, Turbine
  • Key Words: Asset, Hydraulics, Maintenance, Rehabilitation, Repair, generator