3-line MRT disruption: Inherent manufacturing defect or installation mishandling likely caused power cables to fail

SINGAPORE: An inherent manufacturing defect or mishandling during installation had likely caused power cables to fail, resulting in last October's three-line MRT disruption that affected more than 120,000 commuters.

Transport Minister Ong Ye Kung on Wednesday (Mar 17) announced the Land Transport Authority's findings into the Oct 14 disruption that halted train services on the North-South Line between Woodlands and Jurong East stations, the East-West Line between Queenstown and Gul Circle stations and the Circle Line between Serangoon and Harbourfront stations.

Passengers had to leave stalled trains and walk on tracks to nearby stations. Bus stops were also packed as commuters rushed to continue their journeys by bus.

The disruption affected 15 trains and 123,000 commuters.

READ: MRT disruption on Oct 14 prompts system overhaul, with early weekend closures from November

READ: Timeline: How a power fault caused an hours-long disruption on three MRT lines on Oct 14

Speaking at the groundbreaking ceremony for the Integrated Train Testing Centre (ITTC), Mr Ong said that a concurrent failure of the power cables and trip coils along the Tuas West extension had caused the disruption.

An inherent manufacturing defect or mishandling during installation then caused a cut in the insulation layer, which resulted in a short circuit, he said.

Meanwhile, the trip coils failed because one of the components - a plunger - had rusted.

"The plunger moves to enable the circuit breaker to kick in when there is a fault. However, the rust on the plunger obstructed the plunger’s movement and this caused the circuit breaker to malfunction," said Mr Ong.

He added that forensic investigations showed that inadequate protective coating, likely specific to a particular manufacturing batch, had probably caused the plunger to rust.

RECTIFYING THE FAILURES

Since December, the vendor Alstom has started replacing the 22kV power cables along Tuas West Extension with cables of higher specifications, said Mr Ong.

It started with the section along Tuas Depot Intake and Tuas Link station. To speed up the replacement, LTA had decided on full Sunday closures from Mar 14 to May 23 on selected stations along Tuas West Extension, he said. Bridging bus services will be provided during the closures.

READ: Human error compounded MRT disruptions on Oct 14: Ong Ye Kung

LTA has also changed out all the trip coils after October’s disruption, but it will replace the trip coils again with an enhanced design made of stainless steel by the third quarter of next year, Mr Ong added.

"To further ensure that that humidity does not add to the probability of rusting, LTA has also adjusted the settings on the space heaters to reduce the humidity level within circuit breakers," he said.

While waiting for the change, SMRT has increased the frequency of the maintenance regime to every three months, he added.

"When something goes wrong … very natural for us to explain ourselves, tell others we have done what we can," Mr Ong said.

"But even so, we therefore must always know we always bear collective responsibility and it is only by working together, addressing each other’s blind spots and shortcomings that we deliver a better system."