NEL, Sengkang-Punggol LRT disruption: LTA, SBS Transit working to avoid repeat of rare 'double fault' scenario

CNA

4 days ago

SINGAPORE: The Land Transport Authority (LTA) and SBS Transit are working on eliminating a recurrence of the "double fault" scenario that affected the North-East Line (NEL) and Sengkang-Punggol LRT.
Such a scenario is "rare", LTA and SBS Transit said in a joint statement on Saturday (Aug 16).
On Tuesday, the power fault incidents disrupted services on the NEL for about three hours and Sengkang-Punggol LRT for about five hours.
Services on the Sengkang-Punggol LRT were again disrupted on Friday for about four hours.
THE POWER FAULTS
The Sengkang Depot Substation has two interconnected switchboards which serve as backups for each other, said LTA and SBS Transit. Two faults were encountered at the voltage transformer for Switchboard 2 on Aug 12, read the statement.
The first involved a high current surge due to a fault in the voltage transformer, while the second was a dislodged cable connecting to the voltage transformer.
In a normal situation, the first fault would have triggered the fuse in the voltage transformer and cut off electric current, said LTA and SBS Transit.
"However, in this situation, the dislodged cable came into contact with the metallic surface of the voltage transformer panel and allowed electric current to continue to flow, despite the fuse having been blown," they said.
As a result, the high current surge damaged Switchboard 2.
As the two switchboards were connected, the high current surge from the fault caused Switchboard 1 to disconnect from the system to avoid damage.
With Switchboard 2 damaged and Switchboard 1 disconnected, power supply to parts of the NEL and the SPLRT was cut off.
LTA and SBS Transit noted that services on NEL and Sengkang-Punggol LRT were "progressively restored" on the same day using a backup power supply.
However, Switchboard 2 could not be repaired immediately "due to the extensive damage".
"As Switchboard 1 was protected from damage, it was reconnected to allow normal service to resume the next morning," according to the statement.
POWER CABLE FAULT
A power cable fault occurred between Farmway and Kupang stations on the Sengkang LRT on Friday, said LTA and SBS Transit.
"The power cable fault caused the entire network to lose power," they added.
Switchboard 2 at Sengkang Depot Substation, which could have been used to provide backup power, was still out of service from the incident on Tuesday, they said, adding that service progressively resumed in the afternoon after power was restored.
LTA and SBS Transit are still investigating the cause of the cable fault, said the authorities.
Their engineers are also testing the cables along the entire Sengkang-Punggol LRT network to assess their condition.
These tests on around 28km of cables is expected to be completed by Aug 23 as they can only be carried out during engineering hours, said LTA and SBS Transit.