All power cables on Tuas West Extension to be replaced following 14 Oct service disruption

Passengers alighting stalled trains to walk on train tracks on 14 October, 2020. (SCREENCAP: Grace Guo/Facebook)
Passengers alighting stalled trains to walk on train tracks on 14 October, 2020. (SCREENCAP: Grace Guo/Facebook)

SINGAPORE — French firm Alstom will be replacing all 150km of 22 kilovolt (kV) power supply cables and breaker trip coils along the Tuas West Extension (TWE) following the major train service disruption on 14 October.

To facilitate the trip coil replacements, early closures on weekends will be implemented along the TWE starting from next month till the end of the year. Meanwhile, replacement work for the 22kV power supply cables began this month and will also see either early closures, late openings or full Sunday closures along the TWE for limited period next year.

“Alstom is deeply sorry for the inconvenience caused to Singapore commuters during the disruption of train services on the North-South, East-West and Circle lines.

“In line with our absolute commitment to operational safety, and as a precautionary measure, we are replacing all the power cables with the highest specifications and the circuit breaker trip coils in the safest and quickest manner possible,” said Alstom’s Asia-Pacific senior vice-president Ling Fang at a media briefing on Wednesday (28 October).

Land Transport Authority (LTA) chief executive Ng Lang noted that the cables along the TWE, which commenced commuter services in 2017, had showed similar faults on four previous occasions. This led to the LTA raising the issue with Alstom, the main contractor for the cabling, in January after which the company agreed to replace the upper two layers of TWE power cables, where all the faults occurred.

Alstom will bear the costs of the cable replacement. The sum involved has not been revealed.

“Our trains are a very complex system and just a small part of it not working can cause a major disruption to the whole system,” Ng said.

LTA said that site investigations the day after the incident found that a section of 22kV cables located around 500m from the Tuas Link station was “burnt through”. (PHOTO: LTA)

What happened

The three-and-a-half hour incident, which affected 123,000 commuters and left thousands trapped in stalled trains, began with a 22kV power cable fault in the electrical zone between the Tuas Link and Tuas West Road stations along the TWE. While this would not have normally caused a disruption, the circuit breaker at the Tuas West Road station malfunctioned due to a faulty trip coil.

As a result, the circuit breaker meant to isolate the cable fault within the electrical zone did not activate as designed. A secondary protection mechanism kicked in, leading to the power supply from the Tuas Depot Intake substation being cut off and disrupting the power supply to the affected section of the North South and East West Lines (NSEWL) – from Woodlands to Jurong East stations and from the Queenstown to Gul Circle stations.

To rectify the situation, a member of SMRT’s power staff made the decision to draw power from the Buona Vista Intake (BVI) substation but failed to ensure that the earlier cable fault had been isolated. This in turn led to a voltage dip at BVI, which activated the safety system that protects the Circle Line (CCL) and stopped power being supplied from the HarbourFront to Serangoon stations.

Remedial actions

In a news release, LTA said that site investigations conducted the day after the incident found that a section of 22kV cables located around 500m from the Tuas Link station was “burnt through”. LTA noted that the faulty trip coil and faulty cables have since been replaced.

The authority added that maintenance staff also combed through all the TWE stations to ensure that every circuit breaker trip coil is functional. Two trip coils were found to exhibit inconsistent performance and were replaced on 15 October. The faulty coils have also been sent for forensic examination.

“This includes visual checks of the trip coil health every 10 days, and mechanical testing every six months instead of 12 months. SMRT will also enhance their operating procedures for power recovery so that similar errors of judgement will not recur,” said LTA.

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