Power switchboard failure led to disruption in NEL, Sengkang-Punggol LRT services: SBS Transit

SINGAPORE – The three-hour

disruption

of train services on the North East Line (NEL)

on Aug 12 was caused by a failure of the power switchboard at the NEL depot’s substation.

Preliminary investigations found that the failure caused a flashover – an unintended electrical discharge – in one of the voltage transformers used to regulate the power supply, said SBS Transit group chief executive Jeffrey Sim in a statement on Aug 12.

This led to a power trip in both the main and backup power supplies as part of the power protection mechanism, he added.

A voltage transformer reduces a high voltage to a lower, safer level, while a power switchboard distributes power from electric sources to several smaller circuits.

The trip at 11am crippled services on the NEL along an 11-station stretch between Farrer Park and Punggol Coast, as well as the entire Sengkang-Punggol LRT.

Mr Sim said engineers from SBS Transit and the Land Transport Authority (LTA) will be working to restore power to the affected substation at the NEL depot in Sengkang after the end of rail service.

The Sengkang and Punggol LRT services were operating on a single track each on the evening of Aug 12, until services were fully reinstated at 9.20pm, said SBS Transit in a Facebook post.

Mr Sim said the faulty voltage transformer at the NEL depot substation could not be repaired immediately after the power trip, so SBS Transit decided to draw power from its other substation at Dhoby Ghaut.

Engineers carried out extensive checks to ensure that the fault would not affect operational stations on the NEL, he added.

Train services then progressively restarted at affected stations as power was restored, before fully resuming across all NEL stations from 2.10pm.

As for the LRT system, Mr Sim said recovery works had to be carried out in stages to ensure a steady increase in electrical load, and prevent another power trip.

He noted that both the NEL and Sengkang-Punggol LRT were relying on one shared substation, with the NEL depot substation down.

A complete restart of the signalling and power systems, followed by checks of those and the LRT trains, had to be carried out to ensure safety, Mr Sim said.

Service on the Sengkang LRT resumed at 3.34pm, while trains started plying the Punggol LRT again at 4.04pm.

Mr Sim said SBS Transit decided to run Sengkang-Punggol LRT services on a single track from both the eastern and western loops during the evening peak period to avoid stressing the power supply from the single substation.

He apologised to affected commuters, and said the operator will work closely with LTA to prevent a repeat of the incident.

In a Facebook post, LTA said about 350 staff from LTA and SBS Transit, on top of regular station staff, were deployed to the affected stations to guide commuters. It added that the NEL has been running an average of 4 million train-km between delays of more than five minutes.

“LTA will investigate the cause of the power fault and SBS Transit’s recovery efforts,” the authority said.