Replacement of MRT Circle Line Power Cables

Sir, based on preliminary investigations, the disruption on 25 October this year was caused by a faulty power cable at Promenade station that disrupted the power supply to the trains. The incident that took place in September last year, when Circle Line trains were disrupted for about four hours, was also due to a faulty power cable.

The Circle Line power cables were designed and put through site tests in accordance with international specifications. However, investigations after the September 2011 incident found that the insulation of some of the cables could have been damaged during installation. During laboratory tests after the September 2011 incident, some of the cables were also found to have manufacturing defects at microscopic levels, which could not have been detected during earlier site tests. Furthermore, exposure to water in the cable pit had caused these cables to deteriorate at a faster rate than expected.

Following the completion of LTA's detailed investigation of the September 2011 incident in June this year, LTA and the contractor had already planned for a cable replacement programme which would commence in January 2013. The replacement programme is expected to take 18 months to complete, as we have to replace over 1,000 cables totalling some 120 km in cable length, and given the constraints of only three to four engineering hours each day. LTA is working with the contractor and SMRT to try to shorten the duration of the cable replacement programme, with a properly-executed planned disruption of Circle Line services to provide for extended engineering hours for these replacement works.

For Circle Line stations located in areas where the water table is high and which may be more susceptible to water seepage, LTA is working with SMRT and the contractor to replace existing cables with higher grade cables to suit the site conditions. Where faulty cables are replaced with cables of similar grade, the replacement cost will be borne by the contractor at an estimated cost of $12 million. LTA will bear only the incremental cost of higher grade cables and expects the amount to be $2 million to $3 million.

In the interim, before the replacement is completed, LTA will work with SMRT to conduct more frequent checks, particularly at locations where the risk of exposure to water or moisture is higher.

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I thank the Minister of State for the answers. I would like to find out, given that the Circle Line is only three years old, there have been various problems, particularly revolving around the cables. After the studies, was it determined that, perhaps, it was a design fault in the specification or was it the contractors that had failed in providing the correct kind of cables that had caused these problems? And what are the kinds of lessons that we can learn in the future lines that we are building, particularly the Downtown Line and the Thomson Line?

Mr Speaker, Sir, I thank the Member for his questions. The laboratory tests following the Dakota incident revealed certain manufacturing defects in some batches of the Circle Line (CCL) power cables, as well as damages in some cables sustained during the installation process. So, some of the defects were due to manufacturing defects, and some occurred during the installation process that created these damages.

But I would like to assure him that not all the CCL cables are defective. Nevertheless, for greater assurance of service reliability, LTA and SMRT have already embarked on a cable replacement programme to replace all the CCL power cables that are on the tracks. So, that is the first item that we are going to follow up on.

Mr Yee has asked about the lessons learnt and what we are going to do about it. I think one important lesson learnt is that during the manufacturing, the factory tests are conducted on cable samples based on quantity in accordance with international standards. So, there may well be cases where the cables with manufacturing defects go undetected and they still clear the factory tests. And, so, there is a possibility that cables may have component defects at the microscopic level which cannot be detected through factory tests or through the site tests even after installation. Such defects can be picked up through laboratory tests which are designed to determine the root cause of the cable failure.

Manufacturing defects may, however, cause the cables to deteriorate at a faster rate than expected when coupled with damages to the cables caused during installation and exposure to water in the cable pits. And these may eventually lead to cable faults. Stepping up the frequency of checks, therefore, will be important in helping to provide early indication of cable deterioration. And, so, the frequency of the checks has increased – it used to be once in six months. We have now increased it to once in three months, and we are looking at how we can increase it to once every month. So, that is another important lesson learnt.

Now, as to what else we might do, for example, with the rest of the Downtown Line and the Thomson Line, LTA is reviewing whether higher grade cables should be used for future projects, as well as the installation methods, so as to minimise the defects that could be caused during installation.

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Sir, just to follow up on this issue. There was a report in the papers which stated that at some parts of the tunnel, there was flooding up to a metre which also contributed to this problem. Can I just confirm with the Ministry whether there is any plan also to conduct a thorough check of these tunnels to ensure that this flooding does not become a larger safety concern beyond the issue of cable and cable damage?

Mr Speaker, I thank the Member for his question. It goes back to the question of water tables. And the water tables for a number of stations – Dhoby Ghaut, Bras Basah, Esplanade, Promenade, Bayfront and Nicoll Highway – are higher as compared to other stations. As a result of which, these stations may be more susceptible to water seepage. So, the water seepage is due to the high water tables.

What we are doing is that we are installing water pumps to drain out the water which may accumulate in the cable pits in these stations. We have also required SMRT to regularly monitor the cable pits, to ensure that any accumulated water is removed expeditiously and that they remain relatively dry at most times. So, that is something that is on-going.

Now, for the Downtown Line, we are already installing the cables in such a way as to place them in a cable trough to protect them from exposure to water, and to minimise the exposure to water. This is also actually quite useful for the installation works and also for cable inspection. These lessons are very useful and we will continue to draw from them as we implement other lines.

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