Potong Pasir station replaces its rectifier transformers earlier to avoid failures

SINGAPORE – In the dead of night when most people were asleep, work was being done to install essential equipment ahead of schedule at Potong Pasir MRT station.

The job was to replace a rectifier transformer, which had been in use for 22 years. The device steps down the voltage to the right level, and converts alternating current (AC), from the electrical supply, to direct current (DC), which is used by the trains.

Another rectifier transformer had been replaced the week before.

The replacement required coordination among 50 people – engineers, technicians and contractors – working over three days to install the massive equipment, which weighed 14 tonnes and measured 3m by 3m by 2.7m.

Potong Pasir station, operated by SBS Transit, is the first station on the 22km-long North East Line (NEL) to have its rectifier transformers replaced. These have a shelf life of 25 to 30 years.

Working after train service ended on Oct 25, workers first unbolted and loaded the ageing transformer onto a service wagon heading back to a train depot.

On Oct 26, a newly tested rectifier transformer was carefully loaded and rolled to its new home.

In the final stage, 12 hours after the transformer had been bolted to the ground, it was tested before commissioning it for operation.

According to the Land Transport Authority (LTA), the renewal of the rectifier transformers at Potong Pasir station was a “pre-emptive replacement”.

Mr Esmond Pang, deputy director of power supply at LTA, told The Straits Times: “The proactive replacement of the NEL’s power assets is a crucial investment in system reliability and commuter safety.

“With the renewal, we aim to enhance the commuter experience by preventing service interruptions and ensuring a more dependable journey for commuters.”

Over the next three years, other stations along NEL will see similar replacements.

Mr Koh Boon Yeow, head of NEL and Sengkang-Punggol Light Rapid Transit at SBS Transit, said replacing the transformers earlier helps maintain their reliability.

Mr Koh told ST: “You know, it’s just like renovation of a house... It’s better if you start to change out some of the old components just before they fail.”

Even after the new transformer is bolted down in the small room, more tests are required.

SBS Transit’s Mr Dennis Tan, head of maintenance (rail power), said they include high voltage tests, connectivity tests, insulation tests, ratio tests and cable checks.

Mr Tan said a new transformer requires 17,000 litres of oil for cooling and insulation.

After the Singapore-made transformer passes all the tests, it is warmed up and observed for several hours before being put into service.

As the removal of the old transformer and the installation of its replacement have to be done between the time when service ends at about midnight and when it begins at 5.42am, timing is critical, said Mr Koh.

“The greatest risk for me is not being able to bring the transformer into the room,” said Mr Koh.

“Once you have problems, then that’s it, it will affect revenue. Our work hours are very short.”

In September, a new task force was formed

that included senior leaders from LTA, SMRT and SBS Transit, following at least 15 delays and interruptions across the MRT and LRT networks in three months.

The task force will review the recent service disruptions to identify components that may require replacement, upgrading or increased maintenance.

It will also review if the renewal programme for NEL’s power system can be brought forward.

The NEL and Sengkang-Punggol LRT

system experienced a major electrical outage lasting several hours on Aug 12. This was followed by a power fault on the Sengkang-Punggol LRT on Aug 15.

Correction note: This story has been corrected to say that a new transformer requires 17,000 litres of oil for cooling and insulation.