Oct 26 disruption along NEL caused by melted wires which snapped

Oct 26 disruption along NEL caused by melted wires which snapped
Stranded commuters waiting for the train at Hougang MRT station on October 13, 2015 after a power fault disruption services along the North-East Line.
PHOTO: The Straits Times

SINGAPORE - The Land Transport Authority (LTA) and SBS Transit have determined the causes of the Oct 13 and 26 disruptions along the North-East Line (NEL).

On Oct 13, train services were down for more than 1 1/2 hours during the morning peak period, with blackouts reported at several stations.

Investigations have revealed that this was due to a power fault triggered by a malfunction of a component in the electrical switchgear at a substation that supplied electricity to power the trains running between Farrer Park and Hougang stations.

"This caused the main circuit breaker to trip. As a result of the trip, power was diverted to a backup breaker which also tripped," the LTA and SBS Transit said in a joint statement today (Nov 27).

They added that they have since determined that the original manufacturer protection setting of the backup breaker was overly conservative, and, as an interim measure, have increased its protection setting to cater for the projected maximum load of the network, which the electrical network is able to support safely.

The Oct 26 disruption, which also occurred during the morning peak period, was caused by a slip-up during the testing of a new train.

The train damaged the overhead catenary system (OCS), which supplies power to trains, when it was returning to the depot via one of the reception tracks.

The train was being manually driven from the mainline back to the depot when the driver saw sparks from above the train and stopped the train immediately, the LTA and SBS Transit said.

"The train stopped at a stretch where the mainline and depot OCS wires overlap, resulting in arcing between the mainline and the depot OCS wires. The sustained arcing caused the OCS wires to melt, which eventually snapped," they added.

Arcing occurs at this overlap point because of the voltage difference between the mainline and depot OCS. But the LTA and SBS Transit said that this is not a problem during normal operations as the NEL trains are driverless and will not stop at this overlap point to cause sustained arcing.

"Power to the mainline tracks between Hougang and Buangkok stations (both bounds) was switched off to facilitate urgent repair works. This affected the launching of trains to the mainline, and hence the disruption to NEL services. Power to the rest of the mainline and depot was not affected," the LTA and SBS Transit said.

As an interim measure, SBS Transit has marked all overlap zones on the reception tracks to indicate these as non-stopping zones.

The public transport operator is working together with the LTA enhance the power system and the design of the OCS to help prevent disruptions similar to those on Oct 13 and 26.

huizhen@sph.com.sg

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