THE blackout on Tuesday that hit large parts of Singapore and affected close to 147,000 customers was caused by the power generating units of Sembcorp Cogen and Senoko Energy tripping.
The Energy Market Authority (EMA) said in a statement on Wednesday afternoon that it was working with the two power generation companies and their equipment suppliers to establish why the units tripped.
EMA said preliminary findings showed that one of the power generating units at Sembcorp had tripped.
"The stability of the power system requires the electricity supply to constantly meet electricity demand. When a power generating unit trips, the other units in operation will increase their electricity supply automatically," EMA explained.
Later, one of the power generating units owned by Senoko also tripped while it was ramping up additional supply.
The tripping of both power generating units resulted in insufficient electricity supply to meet demand.
Protection devices in the power system automatically disconnected electricity to about 146,500 consumers to "rebalance the system", the authority said.
In order to restore electricity supply, EMA instructed other standby power generating units to provide additional electricity supply.
These included unaffected units from Senoko and YTL PowerSeraya.
"The restoration of electricity supply was done in a controlled manner to ensure the electricity system remained stable. As electricity generation increased, supply to consumers was progressively restored over 38 minutes," it added.
Tuesday's power disruption happened at 1.18am and electricity supply was restored at 1.56am. SP said that 19 areas in Singapore were affected, from Bishan to Boon Lay.
There are seven companies which generate power and feed it to the national grid. While SP manages the grid, it does not own these companies.
EMA added that investigations are still ongoing and that it would look into additional measures that can be put in place to minimise the recurrence of such incidents.
"We thank the public for their patience and understanding for the inconvenience caused," EMA said.
THE STRAITS TIMES