SMRT Disruption on 17 December 2015: Preliminary Investigation

After a major disruption on 17 December 2015, SMRT engineers work through the night to determine what were the major causes. Detailed investigations could take several weeks or longer to conclude but we are determined to provide an initial assessment of the situation as soon as possible after the incident. In this entry, we are sharing the results of the preliminary investigation with you, so that you may have a better understanding of what happened and the actions taken to get train service back online. 

JKN-PNRDisruption between Joo Koon and Pioneer

At around 7:35pm on 17 December 15, a power trip caused a train travelling between Joo Koon and Pioneer to stall. Initial efforts to restore power failed and eventually, the train had to be towed away before normal service could resume. Here are the initial findings of the incident based on preliminary investigations. Investigations are still ongoing and as new evidence is uncovered, we may update further.

Details of Recovery Efforts

Four attempts to restore power by resetting the breakers failed. Power was restored at about 9:13pm only after the stalled train’s current collector shoes – devices that draw current from the third rail – were lowered and electrical continuity between train and third rail was broken. This procedure isolated the train from the power supply.

With power restored to the circuit, the affected train was subsequently towed away by a rescue train and normal service could resume.

Preliminary Investigations

For incidents that are of this scale and complexity, engineers with different expertise have to be activated to find out what caused the problem, recover the defect and restore service safely and expeditiously.

For this case, SMRT Electrical Engineers checked the status of the substations at Joo Koon (JKN) and Pioneer (PNR). They found slight burn marks at the main breaker contacts which is a normal occurrence as a result of the tripping.

Breaker Contacts

Data loggers that were installed recently indicated a spike around 7:35pm on 17 Dec, which gave engineers greater cause to investigate further. They discovered that the power trip was likely due to a shorting between train or trackside equipment to the running rail.

Concurrently, SMRT train engineers also checked the various parts and subsystems on the stalled train. They discovered mild burn marks on a cable in the air conditioning compressor in one of the cars of the affected train. The severity of the burn marks is important and further investigations on the marks are still underway as to what could cause them.

Cable Chaffing

The other subsystems including the Current Collector Shoe, Auxiliary Power System, Engine and Propulsion System and all fuses were also inspected and no other anomaly was found.

Finally, Track infrastructure engineers inspected the track and third rail where the affected train stalled thoroughly. No anomaly was found.

Tying it all up

The preliminary assessment resulted in the following evidence,

  • Power could only be restored after isolating the affected train from the power system.
  • The data logger shows an overload situation from the trackside.
  • Burn marks were found on the air con compressor of the affected train. However, the burn marks are considered mild and does not suggest a large current surge that would cause the power trip that occurred on 17 Dec.

While the preliminary investigations from the first eight hours following the incident have uncovered much, further investigation is still required to establish the root cause.

SMRT Engineers from the various fields will continue to run tests and inspect each subsystem to uncover the full picture for the 17 December incident.

– Low Chin Hun, Vice-President, Operations Maintenance

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