SINGAPORE: A lapse in protocol led to the disruption of train services on the Circle Line for nearly two hours on Sep 17royal panalo, transport operator SMRT said on Thursday (Sep 26).

The disruption happened during the evening peak-hours, affecting scores of commuters.

In a Facebook post on Thursday, SMRT provided an update on its investigations into two Circle Line disruptions last week.

This comes amid a disruption on the East-West Line that shut down regular train services between Boon Lay and Queenstown stations. It began on Wednesday and has carried over to Thursday.

SEP 17 INCIDENT

On Sep 17, a circuit breaker on the traction safety shutdown system (TSSS) - one of the key systems that monitors the safe operation of trains - on the Circle Line tripped.

SMRT's maintenance team reset the circuit breaker, but had concerns that the fault might reoccur and disrupt the withdrawal of trains to the depot later in the day.

To prevent this, the team intended to go one step further by replacing the main circuit breaker that had tripped, named MCB37.

Before proceeding with this, they powered down the TSSS cubicle as a safety precaution. But this caused another circuit breaker, named MCB33, to trip.

It led to a loss of traction power across the entire Circle Line.

This second circuit breaker is part of a fail-safe design intended to trigger a line-wide power shutdown when necessary for operational and commuter safety, SMRT said.

"Our standard protocol requires the maintenance team to seek clearance from the head of Circle Line operations before conducting corrective maintenance during service hours," the rail operator said.

"This step ensures that maintenance in a live system is carefully controlled. Unfortunately, in their eagerness to rectify the fault, the team overlooked this critical step."

According to SMRT's standard operating procedureroyal panalo, such corrective actions should have been carried out during engineering hours, when train services are not running.

A SMRT staff member puts up a sign at Buona Vista MRT station warning of longer travel time on the Circle Line on Sep 17, 2024. (Photo: CNA)

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