SMRT:Water dripping caused massive train breakdown on July 7

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Cause of massive NSEWL train disruption in July identified, says SMRT
To address issues with the network's third rail, which supplies electrical power to trains, all insulators will be replaced by Q1 of 2017, while data loggers will be installed at substations along the line within two months. The transport operator has also looked for leaks in the train tunnels.



SINGAPORE: SMRT has attributed the Jul 7 disruption of the North-South and East-West MRT lines (NSEWL) to "weak electrical resistance" of the train network's third rail insulator.

The third rail supplies electrical power to trains.

A confluence of factors triggered the incident, SMRT said in a media briefing at the Land Transport Authority (LTA) headquarters on Wednesday (Jul 29), including water dripping onto the third rail cover in an MRT tunnel between Tanjong Pagar and Raffles Place.

These were the conclusions of a team of independent experts from Sweden's Parsons Brinckerhoff and Meidensha Corporation of Japan, who were recruited by LTA to look into the power supply infrastructure and railway trackside installations.

The process involved checks on 200km of tracks and other components, as well as inspections of all 141 trains and their logs from the day of the incident.

To address the issue, it has started replacing all third rail insulators, a process which should be completed by the first quarter of 2017. The insulators which have shown signs of electrical resistance weakness - for example, on a stretch near Commonwealth - will be replaced first, SMRT said.

To monitor the condition of the insulators, data loggers will be installed at all 47 traction power substations on the NSEWL within the next two months, the transport operator said.

A joint LTA-SMRT team will monitor the progress of the changes.

"We have reviewed all existing work instructions and we're satisfied that they have been complied with. Arising from the Jul 7 incident, we will be taking very firm steps to review and improve all work instructions to tighten (checks on) the most vulnerable spots in the system," said SMRT CEO Desmond Kuek. Also at the press conference were LTA CEO Chew Men Leong, LTA deputy CEO for infratstructure and development Chua Chong Keng and MD for SMRT Trains Lee Ling Wee.

"INTERMITTENT TRIPPING AT MULTIPLE LOCATIONS"

On the evening rush hour of Jul 7, train services on the NSEWL were disrupted for at least 3.5 hours, leaving some 250,000 passengers stranded as they jostled for free bus services.

After both lines were back up and running, free travel along the NSEWL continued until service resumed normally the next day.

"The disruption was caused by intermittent tripping of the rail power system at multiple locations, due to the lower electrical resistance pathway at a third rail insulator," SMRT said in a press statement.

"However, the weak resistance of an insulator can allow electricity to flow through the insulator to the ground, resulting in a higher than normal voltage difference between the running rail (the surface on which the train wheels run and through which the electricity returns to the source to complete the circuit) and the ground."

This - exacerbated by the movement of the trains - resulted in the activation of the a safety mechanism known as 64P, or the Touch Voltage Protection Relay, at multiple locations in the network, tripping the power system, SMRT said.

In the stretch of tunnel between Tanjong Pagar and Raffles Place, tests on sample residue collected from the third rail cover indicated mineral deposits with high chloride content, SMRT said, pointing to a leak in the tunnel. "The presence of chloride on the insulator, coupled with a wet environment, would have significantly reduced the effectiveness of the insulator."

A patrol office on the Saturday before the incident had spotted the leak and classified it as "non-urgent" at the time, said Mr Lee. However, there was a downpour the night before the Tuesday breakdown, he noted.

SMRT has since combed the tunnels to ensure there are no other leaks with water dripping onto trackside installations.

"We thank our commuters for their patience and understanding over the incident. We continue to adopt a zero-defect attitude, learning from each and every incident that takes place and we're committed to ensuring a high level of safety and reliability in our system," Mr Kuek stated.

SMRT CEO: SORRY

In an earlier press conference on Jul 8, Mr Kuek apologised to affected commuters, with LTA CEO Chew Men Leong recognising that it was a serious breakdown and that authorities "will continue to check on systems".

SMRT's managing director of trains Lee Ling Wee acknowledged on Channel 5's Talking Point seven days after the disruption that the train operator "doesn't have the organic capacity to cope with this level of disruption", pointing to the sheer volume of commuters descending on the concourse when services stopped.

He said he hoped for the matter to be addressed at a national level.

Both Prime Minister Lee Hsien Loong and Transport Minister Lui Tuck Yew expressed concern about the disruptions, with the Prime Minister saying he wanted the relevant authorities to "identify and resolve the faults quickly, to prevent further inconvenience to commuters".


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