Tuesday's 38-minute blackout which affected 146,797 customers from Boon Lay to Bedok was caused by the power-generating units of Sembcorp Cogen and Senoko Energy tripping.
The Energy Market Authority (EMA) said in a statement yesterday that it was working with the two power-generation companies and their equipment suppliers to find out why the units tripped.
Preliminary findings showed that one of the units at Sembcorp had tripped first. The company's spokesman told The Straits Times that the unit is on Jurong Island. Later, one of the power-generating units owned by Senoko also tripped while it was ramping up additional supply.
"When a power-generating unit trips, the other units in operation will increase their electricity supply automatically," EMA explained.
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 customers 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.
ENERGY MARKET AUTHORITY
"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.
Energy utilities provider SP Group said that 19 areas in Singapore were affected, including Boon Lay, Choa Chu Kang, Pandan Loop, Geylang, Tanjong Rhu, Mountbatten, Bedok, Thomson, Mandai, Admiralty, Sembawang and Woodlands.
Mr Bernard Esselinckx, Senoko Energy's president and chief executive officer, said the company is working closely with its equipment supplier and EMA to review the incident.
"We are relieved that we managed to support the restoration of electricity promptly within 38 minutes with our other units," he said.
Sembcorp's spokesman said: "We have called in technical specialists from our equipment suppliers and are working with them to investigate the cause of the trip."
Experts said a number of reasons could be behind the power trips, but added that the situation could have been worse.
Professor Choo Fook Hoong, co-director of Nanyang Technological University's Energy Research Institute, said: "Overloading could be possible, but this is less likely given it was the middle of the night... It is difficult to say for now, but faulty equipment or supply problems are two possible causes."
Mr Teo Chor Kok, a fellow of The Institution of Engineers, Singapore, added that supply, mechanical and overheating issues could have caused the trips.
"The trips protect the generator when such issues arise. While they cannot be completely avoided, they can be mitigated by regular checks and maintenance," he said.
Mr Teo, who has 38 years of experience in electrical engineering, thought that Tuesday's outage was handled well.
"It could have potentially led to the collapse of the entire system had it not been for safeguards put in place by the EMA to keep the situation contained," he said.
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. The seven are: PacificLight Power, Tuas Power Generation, Senoko Energy, YTL PowerSeraya, Tuaspring, Keppel Merlimau Cogen and Sembcorp Cogen.
EMA, which is responsible for the reliable supply of electricity to consumers, added that investigations are ongoing, and it will look into extra measures to minimise the recurrence of such incidents.
"We thank the public for their patience and understanding for the inconvenience caused," it said.
• Additional reporting by Ng Huiwen