The blackout being suffered by Legazpi City, Manito town and some areas of Sto. Domingo town started on Wednesday morning after the 35-year-old 20-MVA transformer of the Bitano sub-station conked out.
Imported during the Martial Law years, (during the implementation of establishing electric cooperatives in the country) in 1979, it was originally bought as a second-hand equipment in 1991 and commissioned at the former Culliat sub-station in Daraga town.
It was then transferred to the Bitano sub-station in year 2000 for the replacement of a damaged unit.
Based on records, since its installation, the 20-MVA Wagner power transformer has not gone into a major repair or rehabilitation but only maintenance works such as correction of hot spots, injection of nitrogen and oil leak repairs — the latest of which is the maintenance done by the Gigantic Electrical and Mechanical Contractors Inc. (GEMCO) in July 2012.
The maintenance covered hot oil flushing of the core and winding, vacuum and filtering of oil, cleaning and painting works, re-gasketting, cleaning and re-aligning of gears and latching of the off-load tap-changer.
Latest report based on the testing conducted by GEMCO (Gigantic Electrical and Mechanical Contractors Inc.) in July 2012 showed that the tests such as insulation resistance, transformer turns ratio, winding resistance, polarization index excitation and dielectric breakdown voltage tests were acceptable, except for the insulation power factor test for the secondary bushing which did not meet the minimum passing criteria of the National Grid Corp. of the Philippines.
For it to be re-energized and connected to the grid, after the maintenance work of GEMCO, National Grid Corporation of the Philippines had Aleco submit a waiver in the event that the 20-MVA transformer would become defective due to cause of low insulation of the secondary bushing.
For the past two years, the 20-MVA power transformer has been loaded with 13.33-15.06-MVA, according to records. (from PNA report backgrounder by Floreño G. Solmirano)