Discussions under way on changing third-rail system
By Christopher Tan, The Straits Times, 22 May 2012
RAIL operator SMRT is discussing with the Land Transport Authority the need to replace the ageing third-rail system in the North-South and East-West MRT network.
The third rail supplies electricity to trains and SMRT said the current design makes it vulnerable to high stress at spots where sections of the rail are joined.
SMRT chief engineer Ng Chong Joo told The Straits Times on the sidelines of the Committee of Inquiry yesterday that replacing the third rail would be part of a multi-million-dollar plan to upgrade the rail system to make it more reliable.
Collapsed sections of the third rail caused the massive disruptions on Dec 15 and 17 last year that triggered the public inquiry.
The LTA told The Straits Times that talks to replace the third rail were 'a very recent development', and that more study needed to be done to determine if a complete change is needed.
The spotlight has been on the third-rail support assembly, in particular the metal claws that hold the third rail in place.
But cracks have also been found on the rail too.
Mr Ng told the inquiry that cracks were discovered as early as 2010 and these cracks had also led to rail sagging.
Asked if SMRT had done any analysis on third-rail cracks, he said 'no'. He said, however, that 'detailed analysis' would be done if there was a flaw found on the running rail (the rail the trains run on) - even if it was something minute, such as a weld failure.
He said this was because a running rail failure will have 'catastrophic results' whereas a failed third rail was a 'reliability issue'.
Mr Ng made this comparison no fewer than five times during the whole day he was on the witness stand. He revealed that the LTA's transit audit team was also more concerned about the condition of the running rail and required four-monthly reports. He said there was no such requirement for the third rail.
Professor Lim Mong King from the Nanyang Technological University's School of Mechanical and Aerospace Engineering asked whether reliability was important.
'Yes, it's important,' said Mr Ng. 'But in a system, there are so many components, so we manage the system according to priority.'
Asked if the third rail had a fixed lifespan, Mr Ng said the indicative figure was 35 years, but in areas such as high-speed ramps, it had a far shorter life.
He told the court 11km to 12km of third rail going around curves - another high-wear area - is likely to be changed in 'the next couple of years'. He said Singapore's MRT network was 'unique' as it had 'a lot of curves'.
Quizzed on the issue of dropped third-rail claws, Mr Ng said MRTC - the LTA's predecessor - had rejected a more secure claw design back in the 1980s.
Even so, he said SMRT had managed the problem well, citing that the annualised average number of dropped claws had fallen from 84 in 1995 to 16 before last December's incidents.
SMRT has decided to change all the claws on the North-South and East-West lines to ones far more resistant to dislodgement.
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