Circle Line shutdown on Sep 17: Maintenance team did not follow protocol, says SMRT
There were long queues and big crowds at Circle Line stations after train services were disrupted for nearly two hours on Sep 17.
Passengers were not allowed to enter the ticket gantries at one-north MRT station amid a shutdown in Circle Line train services. (Photo: CNA)
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SINGAPORE: A lapse in protocol led to the disruption of train services on the Circle Line for nearly two hours on Sep 17, 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 procedure, such corrective actions should have been carried out during engineering hours, when train services are not running.
SMRT added that the resumption of normal train services took longer than anticipated because of the additional time and effort needed to ensure there were no further technical issues.
"For the safety of our commuters, the operations control centre had to account for all trains before normal services could resume," SMRT said.
It added that it activated diversion plans and advised commuters to continue their journeys using other MRT lines or buses.
In-train and station announcements were made between 5.46pm and 7.30pm, except for a 12-minute break between 6.35pm and 6.47pm, when a technical glitch required a public announcement system restart, SMRT said.
All lines were operational by the end of the day.
"Throughout the night of Sep 17, SMRT engineers worked with Land Transport Authority (LTA) and OEM engineers to diagnose and resolve the issue, ensuring normal train services resumed on schedule the following morning."
SEP 18 INCIDENT
The Sep 18 incident was caused by a fire. At about 8pm on Sep 18, an SMRT team detected the fire in a TSSS cubicle at Kim Chuan Depot.
In response, the global emergency shutdown system - a built-in safety feature - was automatically activated, triggering a line-wide power shutdown.
The fire was extinguished and the Singapore Civil Defence Force (SCDF) confirmed the area was safe.
"Traction power was restored within 10 minutes, and full train services resumed at 8.15pm," SMRT said.
LTA, SMRT, and OEM engineers worked through the night to diagnose the cause, implement corrective actions, and conduct functional tests, including test runs.
The priority was to ensure safe and smooth train operations, especially during the F1 period, SMRT said.
"The damaged TSSS cubicle at Kim Chuan Depot has since been isolated from the Circle Line power network."
Operational control has been transferred to a backup operations control centre at another site.
SMRT said the cause of the fire is still under investigation.
"Meanwhile, the SMRT engineering team is working with LTA to review the overall design of the TSSS and global emergency shutdown systems," said SMRT.
It added that system improvements will be made, including enhancements to the Circle Line's signalling and PA systems, as well as fail-safe and fail-soft features.
The procurement of a replacement TSSS cubicle, with enhanced features, is being expedited, SMRT said.
