Cause of rail breakdown in Singapore still not known: LTA

The cause of Tuesday night's rail breakdown - the first time both the North-South and East-West Lines have been affected simultaneously - is still unknown although train services are back to running on normal schedules at full speed and at normal peak-hour intervals.

The Land Transport Authority (LTA) said it was difficult to isolate the fault because of the size and complexity of the rail system, and more time is needed to isolate the fault.

At a media briefing on Wednesday morning, it was revealed that three key areas were checked following the service disruptions - the trains, the tracks, and the power substations.

"At this juncture we have found no anomalies. So far, we have not encountered power trips,'' said LTA chief executive Chew Men Leong.

Mr Chew added there was no reason to suspect sabotage at this point in time.

Operator SMRT Corp said the massive breakdown was a "stark reminder'' that the journey to bring higher rail reliability is "a difficult one''.

"The system seems to be running smoothly now,'' said chief executive Desmond Kuek.

According to SMRT, the disruption began on Tuesday at 5.59pm with a traction power trip. Four minutes later, 20 counts of traction power trip occurred at multiple locations across the network but commuter services were maintained as the trips could be reset remotely from SMRT's operations control centre.

It was only at 6.52 pm that things went awry with the first occurrence of a traction power tripping that could not be manually reset because of the magnitude of the tripping and five trains stalled between stations.

At 7.06 pm, following two more occurrence of traction power tripping which could not be reset, the decision was made to detrain all passengers at train platforms and suspend service for safety reasons. Less than half an hour later, free bus services were activated system-wide with investigations underway to diagnose the fault or faults.

It was decided at 8.10pm that batch testing of trains would be conducted to identify whether the power trip was train and/or track-related.

At 9pm, after batch testing on the East-West Line ended, train service was re-started in degraded mode.

There were further sporadic occurrences of tripping throughout the night but they were resettable.

As of Wednesday morning, SMRT said 92 of 115 trains were inspected, while the 94 per cent of the North-South and East-West Lines' power system checked. The rest will be completed on Wednesday night.

Still, SMRT said it was not sure whether the root cause of the problem had been resolved and would have to further examine all the data collected so far.

"We are taking some time to get to the bottom of this,'' said Mr Kuek.

Tuesday's breakdown of the two heavily used lines during the evening peak period probably affected hundreds of thousands of commuters but SMRT said it was unable to give an estimate.