SINGAPORE — A cut into the internal insulation layer of cables between Tuas Link and Tuas West Road stations and rust developing on a critical component of the trip coil caused the massive three-line rail breakdown last October.
These findings were revealed by the Land Transport Authority (LTA) in a press release on Wednesday (17 March), following a forensic investigation into the incident which stalled the North-South, East-West, and Circle lines for over three hours.
The LTA, together with main contractor Alstom, found that the metallic screen layer in the damaged power cables was defective and had cut into the cables’ internal insulation layer, resulting in a short circuit.
This was likely due to an inherent manufacturing defect or mishandling during installation, said the LTA.
As a precautionary measure, Alstom had previously committed to replacing the affected power cables with higher specification cables, it added.
Cable replacement works have commenced, with full Sunday closures taking place at selected stations along the East-West Line from 14 March until 23 May to speed up the works.
The joint investigation also revealed that the trip coil failure was caused by rust developing on the surface of the plunger rod, likely formed due to inadequate protective coating of the plunger rod for a particular manufacturing batch.
This had prevented the movement of the plunger rod, causing the trip coil to malfunction and fail to isolate the fault, resulting in the train service disruption, said the LTA.
The authority said it has worked with Alstom to design and manufacture new trip coils that are more rust-resistant.
Once the newly designed trip coils are manufactured, all 113 trip coils which Alstom had already changed out last year will be replaced, it added.
"To further mitigate the risk of a future recurrence, the humidity setting within the circuit breakers will also be lowered, so as to reduce the ambient humidity and minimise the risk of rusting. In the interim, SMRT has stepped up the frequency of their maintenance checks for the trip coils," said the LTA.
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