SINGAPORE: A main contractor of the Land Transport Authority (LTA) will replace 150km of power cables and more than 100 circuit breaker components along the Tuas West Extension, after some faulty parts led to a disruption of train services on Oct 14.
More than 120,000 commuters along the North-South, East-West and Circle lines were affected by the evening peak-hour disruption.
READ: Train services resume on North-South, East-West, Circle lines after disruption due to power fault
Releasing its report on the incident on Wednesday (Oct 28), LTA said the disruption was caused by the "occurrence of concurrent faults", starting with a faulty power cable on the Tuas West Extension.
This would not have caused a disruption if the circuit breaker had kicked in, but it malfunctioned, said LTA.
To facilitate the replacement of all the circuit breaker components, called trip coils, some MRT stations will close early from November. Work on this is expected to be completed by the end of the year.
As for the new cables, LTA said they will take some time to arrive. The authority will therefore schedule early closures or late openings on weekends or full Sunday closures for “limited periods” next year to facilitate the replacement work.
There are no details yet on the stations that will be affected by the closures.
In its report, LTA said that power cables on the Tuas West Extension had encountered similar malfunctions on four other occasions between 2018 and 2020.
However, they did not cause train disruptions as the circuit breakers worked in those instances.
SMRT has also suspended an employee and his supervisor for an error committed in the chain of events leading to the disruption.
The train operator had said on Oct 15 that the disruption was caused by a breakdown in the insulation of a power cable along the Tuas West Extension, as well as an attempt to restore power to two MRT lines without first isolating the fault.
The Tuas West Extension is a 7.5km-long extension on the western end of the East-West Line, comprising Gul Circle, Tuas Crescent, Tuas West Road and Tuas West Link stations.
A circuit breaker at the Tuas West Road station should have kicked in to isolate the fault but failed to do so, SMRT said then. LTA explained on Wednesday that this was caused by a faulty trip coil in the circuit breaker.
When the circuit breaker did not function, LTA said a secondary protection mechanism kicked in and isolated a larger electrical sector as a precaution, cutting off power supply from a substation that serves a section of the North-South East-West Line (NSEWL).
An SMRT staff member then tried to draw power from a different substation that also supplies power to the Circle Line (CCL). However, this should only have been done if the initial cable fault was isolated.
SMRT CEO Neo Kian Hong said the staff member’s actions “caused a trip on the Circle Line”, adding that the transport operator is "deeply sorry" for the disruption that took place when many commuters were getting home "after a long day".
“Our power staff misread the graphics display and thought that the fault had been isolated and proceeded to draw power from Buona Vista (substation),” he said.
“The power staff and his supervisor have been suspended from their duties. They will be required to undergo retraining and recertification before they can resume duties.”
As the cable fault had not been isolated, a safety mechanism kicked in to protect the CCL’s power system, disrupting supply to parts of the line.
15 TRAINS STALLED
The disruption affected services from Woodlands to Jurong East on the North-South Line, Queenstown to Gul Circle on the East-West Line, as well as HarbourFront to Serangoon on the CCL.
Fifteen trains stalled in total.
“After 40 minutes into the disruption, SMRT assessed that the power supply for the NSEWL and CCL could not be restored quickly,” LTA said.
“It proceeded to detrain commuters from 12 stalled trains along the NSEWL and three stalled trains along the CCL.”
Some commuters had to walk on tracks to make their way back to the station, while bus stops were packed with commuters looking for alternative ways to continue their journey.
LTA said SMRT employees walked along the tracks to reach the stalled trains and guided commuters to the nearest station.
“Detrainment on the three affected trains along the CCL was safely completed within 20 minutes,” LTA said.
“Detrainment operations for 11 out of 12 stalled trains on the NSEWL concluded at 8.42pm.
“Due to inclement weather and lightning risk, de-trainment for the last NSEWL train near Bukit Batok station had to be suspended and was only completed at 9.43pm.”
LTA said train services on the CCL and NSEWL were progressively restored at about 8.43pm and 10.34pm, respectively.
MORE PUBLIC ANNOUNCEMENTS NEEDED?
The disruption on the NSEWL lasted about three-and-a-half hours from 6.58pm to 10.34pm, LTA said, affecting about 110,000 commuters.
The disruption on the Circle Line (CCL) lasted about an hour from 7.34pm to 8.43pm, affecting about 13,000 commuters.
Of these, LTA said about 6,775 commuters had to disembark from stalled NSEWL and CCL trains.
LTA noted feedback on the need for more updates on the situation leading up to the point passengers needed to alight on the tracks “for better awareness and preparedness”.
“Regular public announcements on service disruption were made to all stations and trains throughout the network,” it said.
“Information related to the incidents were also provided to commuters via the various signage on the stations, SMRT Connect App and Twitter messages.”
Site investigations conducted after service hours on Oct 15 found that a section of the cables located about 500m from Tuas Link station was burnt through, LTA said.
“The faulty trip coil and faulty cables have since been replaced,” LTA said.
Maintenance teams also combed through all the stations on the Tuas West Extension to ensure all the trip coils in the circuit breakers were functioning.
“Two other trip coils were found to exhibit inconsistent performance and were immediately replaced on Oct 15,” LTA said.
“The faulty trip coils have been sent for further forensic examination.”
Alstom, the contractor that supplied the power cables and trip coils for the Tuas West Extension, is also investigating why the power cables had burnt through.
But this is not the first time the power cables had malfunctioned.
Since service on the Tuas West Extension started in 2017, LTA said there had been four instances at different locations involving faults in the upper layer of the power cables.
“These instances did not lead to any service disruption because the circuit breaker kicked in as intended and isolated the faults,” LTA said.
“LTA treated this as a matter of significant concern and raised the issue with the main contractor Alstom in January 2020.”
LTA added that Alstom had agreed to replace the upper of two layers of power cables at the Tuas West Extension, with replacement works scheduled to commence this month.
Investigations into one of the power cable failures in 2018 found that a metallic screen made of copper had affected the internal insulation layer. It is thought that a similar fault could have occurred in the Oct 14 disruption.
LTA said previous batches of the cables, which are of similar design and by the same manufacturer, have been used in other parts of the MRT network. These cables have not seen similar faults so far.
“The Tuas West Extension circuit breakers are of an established design and are widely used in the power industry,” it added.
In light of the Oct 14 disruption, LTA said all the power cables and trip coils along the Tuas West Extension will be replaced to “provide additional assurance that power cable faults will not lead to another service disruption”.
Alstom will bear the cost of replacing these parts and supply power cables with thicker metallic screens and a more resistant internal structure.
While the cables are being replaced, LTA said SMRT will increase the frequency of checks on the trip coils and circuit breakers.
“This includes visual checks of the trip coil health status every 10 days, and mechanical testing every six months instead of 12 months,” it said.
“SMRT will also enhance their standard operating procedures for power recovery so that similar errors of judgment will not recur,” LTA added.
“Once again, we apologise for the inconvenience caused to commuters that evening. LTA, SMRT and Alstom will work together to address the underlying issues to minimise the risk of a reoccurrence.”
Ms Fang Ling, Asia-Pacific senior vice-president at Alstom, also apologised for the “inconvenience caused to Singapore commuters”.
“In line with our absolute commitment to operational safety and as a precautionary measure, we are replacing all the power cables with a higher specification, and circuit breaker trip coils in the safest and quickest manner possible,” she said.