The Cebu Power Plant is a 2 x 103MW nominal coal fired electricity generating station. The turbine manufacturer is Fuji Electric. The turbine was manufactured in Kawasaki, Japan. The turbine design is based on a design originally licensed from Siemens.
Following a planned maintenance outage, unit 2 was restarted and synchronized to the grid on 7 July 2012. The turbine unit was tripped automatically on 8 July 2012 by DCS protection logic due to an instrumentation issue on the plant. Technicians were deployed to rectify the defect meanwhile the unit 2 boiler was banked at minimum output with steam bypassed to the condenser in anticipation of a quick restart. Unit 2 turbine main stop valve was opened and speed up under steam was initiated. The turbine run-up was aborted at 1,200rpm due to excessive vibration measured on the #2 and #3 bearings.
Thorndon Cook Power staff was engaged by Crawford & Co (Manila) to carry out a root cause analysis of the turbine rotor bow failure.
Inspection of components (rotor and turbine casings).
Discussion with plant personnel including event chronology and unit operating history.
Review of turbine drawings and steam cycle P&IDs.
Formulation of potential root causes based on experience at other plants.
Analysis of key parameters before and during the incident.
Check of key parameters in normal operation for comparison with the incident.
Further targeted data analysis to confirm probable root cause.
On the basis of available information (equipment inspection, personnel reports, operating data), the most likely incident scenario was suggested. Recommendation was made for the remediation of rotor bowing, and the review of control system logic and steam permissions for hot reheat start.