SINGAPORE - A section of power cable that burnt through and a faulty circuit breaker along the Tuas West Extension were the primary cause of a massive disruption on Oct 14 that affected three MRT lines.
The Land Transport Authority (LTA) on Wednesday (Oct 28) released a report of its findings on the three-hour, 36-minute incident, which affected 123,000 commuters.
Of these, 6,500 commuters were on 12 stalled trains along the North-South and East-West Lines while 275 were on three stalled Circle Line (CCL) trains.
Here is a timeline of events on Oct 14:
6.58pm: Concurrent faults along the Tuas West Extension cause a power outage. The burnt section of 22 kilovolt (kV) cables between Tuas Link station and Tuas West Road station had triggered a power fault, which activated circuit breakers nearby. But one failed to trip and isolate the power fault as designed due to a melted trip coil.
The circuit breaker failure caused a secondary protection system to trip, cutting off power supply from the Tuas Depot substation. This affected a larger zone of stations along the North-South and East-West Lines (NSEWL).
Train service was shut down between Woodlands and Jurong East stations on the North-South Line and between Queenstown and Gul Circle stations on the East-West Line.
The outage caused 12 trains to stall on the tracks. It also affected in-train lighting and air-conditioning. The backup battery on affected trains kicked in to provide emergency lighting and ventilation.
Operator SMRT subsequently decided to draw power from the Buona Vista substation, which supplies power to the CCL.
An SMRT staff member and supervisor misread equipment at the substation and wrongly assumed the fault in Tuas had been isolated.
7.34pm: Failure to isolate the fault before drawing power led to a voltage dip at the Buona Vista substation, causing a power trip and a second outage that affects service between HarbourFront and Serangoon stations on the CCL. Three trains stall as a result.
7.38pm: SMRT decides to detrain passengers on the stalled trains as it could not restore power supply quickly. As a safety measure, electrical protection devices are installed to guard against accidental turning on of traction power. SMRT staff walk along the tracks to reach the stalled trains and help commuters.
7.53pm: Detrainment of NSEWL passengers begins.
7.59pm: Detrainment of CCL passengers begins.
8pm: Power supply is restored for CCL, but SMRT does not restore traction power along sectors where detrainment is taking place for safety reasons.
8.17pm: All stranded CCL passengers reach the nearest stations.
8.42pm: Commuters from 11 stalled trains on NSEWL reach the nearest stations.
8.43pm: Train service along CCL progressively resumes.
8.44pm: Detrainment of the last train near Bukit Batok station is temporarily halted due to rain and lightning risk, with 78 commuters still on board.
9.43pm: The 78 commuters alight at Bukit Batok station.
10.34pm: Train services are progressively restored on the NSEWL.