7 July NSEWL disruption investigation updates

Work on improving the robustness of the network of power cables, switches and substations that provides traction power to trains on the North-South East-West Line (NSEWL) has been put on the fast track following the 7 July 2015 power fault that disrupted train services on Singapore’s oldest MRT line.


1. What is SMRT doing to prevent an incident similar to 7/7 from happening again?

Work on improving the robustness of the network of power cables, switches and substations that provides traction power to trains on the NSEWL have been put on the fast track.

SMRT will work with LTA to segment the network of cables that supply power to the NSEWL where possible. This improvement will mean that a power fault on one part of the line will be unlikely to disrupt travel on other parts of the network. This is to be done even as trackside components are renewed.

The 7/7 NSEWL disruption underscores the urgency for SMRT engineering staff to renew NSEWL power-related infrastructure and also highlights the importance of condition monitoring efforts initiated by us a year ago.


2. How did the NSEWL break down?

SMRT has narrowed down the likely cause of the 7/7 disruption to the insulation of the third rail.

This insulation is part of the trackside infrastructure that is used to protect power cables that supply electricity to the third rail. Investigations point to the likelihood that the insulation of third rail could have affected the supply of traction power which in turn led to the tripping of the Touch Voltage Protection Relay (known by its code 64P) along multiple stretches of the NSEWL.


3. What is 64P and why did it have an impact on the decision to halt train services?

To protect the safety of commuters, the 64P relays are designed as a safety measure to mitigate the possibility of unacceptable touch voltage.

During the 7/7 disruption, the decision was made to halt train services temporarily to investigate the cause of the relays being tripped. It was these trips that resulted in loss of power that affected the train motors, air-conditioning and cabin lighting.

This decision was made to avoid a situation where a power trip would leave trains stalled in tunnels or on viaducts, which would then force commuters to detrain on track.


4. What was done to investigate the incident?

SMRT spared no effort to investigate the cause of power trips. The full and comprehensive investigation over the past nine days covered the following areas:

  • 200 km of train tracks on both bounds of the NSEWL;
  • All 67 power substations that support the NSEWL; and
  • All 115 MRT trains that were used on 7 July, and 26 additional trains at train depots.

On 11 and 12 July, the team re-enacted the incident on the NSEWL in an effort to trace the cause of the power trips. The re-enactment helped investigators rule out two earlier suspected possibilities for the power trips – two track voltage balancing cables and a relay in a power substation. This led the engineering staff to focus investigation works on the insulation of the third rail as the possible cause.

SMRT approached international operators, including London Underground, for a rail operator’s views on our preliminary assessment of the incident. This is part of SMRT’s pledge for an independent consultation into the 7 July incident, which is essential for the Company to learn from the incident and deal with it decisively to strengthen the safety and reliability of the NSEWL.

SMRT has also engaged retired staff to assist.  Two of them were part of the Mass Rapid Transit Corporation team involved in the development of the power network in the early years.  They will assist with concurrent investigative works and mitigation efforts, including the project to segregate the power network of the North-South from the East-West lines.

In the meantime, as the joint investigations by SMRT and LTA continue over the weekend to determine the root cause conclusively, with the support of the appointed external consultants, SMRT is taking all possible precautionary and preventive measures to safeguard the system in terms of safety and service reliability.


The full press release can be read on the SMRT Corporate website.

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