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SINGAPORE: A prime contractor for the Land Transportation Authority (LTA) will replace 150 km of electrical cables and more than 100 circuit breaker components along the Western Tuas Extension, after some defective parts caused an interruption to the services of trains on October 14.
More than 120,000 commuters along the North-South, East-West and Circle lines were affected.
READ: Train services resume on North-South, East-West, Circle lines after disruption due to power failure
Releasing its report on the incident on Wednesday (Oct 28), LTA said the outage was caused by the “occurrence of concurrent faults,” beginning with a faulty power cord in the West Tuas Extension.
This would not have caused an interruption if the circuit breaker had tripped, but it malfunctioned, LTA said.
To facilitate the replacement of all breaker components, called trip coils, some MRT stations will close in early November. Work on this is expected to be finished by the end of the year.
As for the new cables, LTA said they will take some time to arrive. Therefore, the authority will schedule early closings or late openings on weekends or full closings on Sundays during “limited periods” next year to facilitate replacement work.
There are no details yet on the stations that will be affected by the closures.
Timeline: how a power failure caused an hour-long outage on three MRT lines on October 14
In its report, LTA said that the power cables at Tuas West Extension had encountered similar failures four other times between 2018 and 2020.
However, they did not cause any interruptions on the train as the circuit breakers worked in those cases.
SMRT has also suspended an employee and his supervisor for a mistake made in the chain of events that led to the interruption.
WHAT HAPPENED
The train operator had said on October 15 that the outage was caused by a failure in the insulation of a power cable along the Western Tuas Extension, as well as an attempt to restore power to two MRT lines without first isolate the fault.
The Tuas West Extension is a 7.5 km long extension at the western end of the East-West Line, comprising the Gul Circle, Tuas Crescent, Tuas West Road and Tuas West Link stations.
A circuit breaker at the Tuas West Road station should have tripped to isolate the fault, but it didn’t, SMRT said at the time. LTA explained Wednesday that this was caused by a faulty trip coil in the circuit breaker.
A passenger receives orientation at the Buona Vista MRT station after a power failure disrupted train services on several lines on October 14, 2020 (Photo: Christy Yip).
When the circuit breaker failed, LTA said a secondary protective mechanism was activated and isolated a larger power sector as a precaution, cutting off power to a substation that serves a section of the North-Southeast-West Line (NSEWL ).
Then a SMRT staff member attempted to obtain 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 “triggered a trip on the Circle Line.”
“Our power personnel misread the graphic display and thought the fault had been isolated and proceeded to draw power from the Buona Vista (substation),” he said.
“The energy staff and their supervisor have been suspended from their duties. They will be required to undergo retraining and recertification before they can resume their duties. ”
As the cable fault had not been isolated, a safety mechanism was activated to protect the CCL’s power system, interrupting supply to parts of the line.
WALKING THE TRACKS
The outage occurred during the afternoon rush hour. It affected train 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.
“After 40 minutes of the outage, SMRT assessed that the power supply for NSEWL and CCL could not be restored quickly,” LTA said.
“Passengers were unlocked from 12 trains stopped along the NSEWL and three trains stopped along the CCL.”
Some commuters had to walk on the tracks to return to the station, while the bus stops were packed with commuters looking for alternative ways to continue their journey.
The LTA said SMRT staff walked along the tracks to reach the stopped trains to check on the well-being of the passengers and guided the passengers to the nearest station.
“Detraining on the three affected trains along the CCL was safely completed in 20 minutes,” LTA said.
“De-training operations for 11 of the 12 trains stopped at the NSEWL concluded at 8.42 pm.
“Due to inclement weather and the risk of lightning, the detraining of the last NSEWL train near Bukit Batok station had to be suspended and was only completed at 9.43 pm.”
LTA said train services on CCL and NSEWL were progressively restored around 8.43pm and 10.34pm, respectively.
MORE PUBLIC ANNOUNCEMENTS NEEDED?
The outage at the NSEWL lasted about three and a half hours from 6.58 p.m. to 10.34 p.m., LTA said, and affected about 110,000 commuters.
The disruption on the Circle Line (CCL) lasted approximately one hour from 7.34pm to 8.43pm and affected some 13,000 commuters.
Of these, LTA said that around 6,775 travelers had to disembark from stopped NSEWL and CCL trains.
LTA noted comments requesting more updates that would lead to passengers having to get off the tracks “for better awareness and preparation.”
“Regular public announcements were made about the interruption of service at all stations and trains on the network,” he said.
“Information related to the incidents was also provided to travelers through the various posters at the stations, the SMRT Connect app and Twitter messages.”
DEFECTIVE PIECES
Site investigations conducted after hours on October 15 found that a section of the cables located about 500 meters from the Tuas Link station burned, LTA said.
“The faulty trip coil and faulty cables have since been replaced,” LTA said.
Maintenance crews also checked all stations at Tuas West Extension to make sure all trip coils on circuit breakers were working.
“Two other trip coils were found to exhibit inconsistent performance and were immediately replaced on October 15,” LTA said.
“The faulty firing coils have been sent for further forensic examination.”
Alstom, the contractor that supplied the power cables and trip coils for the West Tuas Extension, is also investigating why the power cables had burned out.
But this is not the first time that power cables have failed.
Since service began at Tuas West Extension in 2017, LTA said there have been four cases at different locations involving faults in the top layer of power cables.
“These cases did not cause any service interruptions because the circuit breaker tripped as intended and isolated the faults,” LTA said.
“LTA treated this as a matter of great concern and raised the issue with prime contractor Alstom in January 2020.”
LTA added that Alstom had agreed to replace the top of two layers of electrical cables at Tuas West Extension, and that replacement works are scheduled to begin this month.
Investigations into one of the power cable failures in 2018 found that a metallic rope made of copper had affected the internal insulation layer. A similar failure is believed to have occurred in the October 14 outage.
LTA said that previous batches of cables, which are of similar design and from the same manufacturer, have been used in other parts of the MRT network. These cables have not seen similar failures so far.
“Tuas West Extension circuit breakers have an established design and are widely used in the power industry,” he added.
SYSTEM CHECK
In light of the Oct. 14 outage, LTA said that all power cables and trip coils along the West Tuas Extension will be replaced to “provide additional assurance that power cable failures will not will lead to another service interruption. “
Alstom will bear the cost of replacing these parts and will supply power cables with thicker metallic strands and a stronger internal structure.
While the cables are being replaced, LTA said that SMRT will increase the frequency of checks on trip coils and circuit breakers.
“This includes visual checks of the health of the firing coil every 10 days and mechanical tests every six months instead of 12 months,” he said.
“SMRT will also improve its standard operating procedures for energy recovery so that similar errors in judgment are not repeated,” added LTA.
“Once again, we apologize for the inconvenience caused to the travelers that night. LTA, SMRT and Alstom will work together to address the underlying issues and minimize the risk of their recurrence. “
Ms. Fang Ling, Senior Vice President of Asia Pacific at Alstom, also apologized for the “inconvenience caused to Singapore travelers.”
“In line with our absolute commitment to operational safety and as a precautionary measure, we are replacing all power cables with a higher specification and breaker trip coils as safely and quickly as possible,” he said.
