After more than a week since the biggest MRT breakdown in Singapore history, a massive investigation involving hundreds of man-hours spent trying to identify the cause of the breakdowns has borne fruit for SMRT – according to its spokesperson, inspectors have narrowed down the likely cause of the Jul 7 disruption to faulty insulation of the third rail.

“Intensive, round-the-clock investigations and re-enactments of the incident point to the likelihood that the insulation of the third rail could have affected the supply of traction power which in turn, led to the tripping of the Touch Voltage Protection Relay among multiple stretches of the NSEWL,” SMRT said.

The relays, which are part of the original design of the NSEWL power network, are designed as a safety measure to protect commuters from unacceptable touch voltage, SMRT added.

SMRT had earlier said there were multiple power trips along the line, in the lead up to the peak-hour disruption across two of Singapore’s oldest MRT lines. About 250,000 commuters were affected during the 3.5 hour disruption. Some said the trains they were on stalled for up to half an hour, with no air-conditioning.

SMRT said it has “spared no effort” to investigate the cause of the powers. Over nine days, it has inspected 200km of train tracks on both bounds of the NSEWL, and all 67 power substations that support the lines. It has also checked 115 MRT trains that were used on Jul 7 and an additional 26 trains parked at depots.

Over the last weekend, a team from SMRT re-enacted the incident on the NSEWL in bid to trace the cause of the power trips, and ruled out two earlier suspected causes of the power trips – two track voltage balancing cables and a relay in a power substation.

SMRT said it has approached international operators, including London Underground, for a rail operator’s views on our preliminary assessment of the incident.

The Land Transport Authority (LTA) has engaged a team of independent experts from Sweden and Japan to look into the power supply infrastructure and railway trackside installations.

SMRT said it will work with LTA to segment the network of cables that supply power to the NSEWL to add resilience to the rail network. It is also refreshing trackside components.

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