The Hindu : New Delhi News : Metro achieves another feat

Online edition of India's National Newspaper
Thursday, Jul 08, 2004

New Delhi

New Delhi

Metro achieves another feat

By Our Staff Reporter

NEW DELHI, JULY 7. The Delhi Metro is on its way to becoming the first underground Metro in the world to operate on 25 kv rigid overhead electrical equipment which not only reduces electricity loss but also does away with the necessity of constructing a sub-station above every station and thereby preserves the aesthetics of the city.

Incidentally, it was the presence of a slightly larger tunnel boring machine with the contractor which led to an increase in the tunnel size and facilitated the installation of the high voltage overhead equipment. But this fortuitous happening has made a world of difference to the Delhi Metro, allowing it to overcome a handicap which has plagued Metros across the world for years.

So unlike other Metros which run either on 750 volt DC or 1,500 volt DC, both being carried by a third line running alongside the tracks, the Delhi Metro will have overhead cables carrying the current.

Though the changes sound only technical, it has several advantages. The Chief Project Manager of Metro Corridor, Mangu Singh, said most importantly the electricity loss is less due to the high voltage. Then as against the requirement for having a sub-station at every station in the case of a DC current supply, in this case one sub-station for the entire length of the line would do.

In the case of Delhi, this has done away with ugly sub-stations on the surface in areas rich in history and aesthetics. A proper design for a sub-station above every stations would have been a challenge since the underground line passes through some of the most visually appealing parts of the city which includes the University area, Walled City and Lutyens' Delhi.

Also, the AC 25 kv supply would mean better power back up for the Delhi Metro as besides its two own power sources it will be able to fall back on a special arrangement with Northern Railway in the event of a major breakdown. This has been made possible by the fact that Northern Railway also operated on a 25kv AC supply. For the purpose a special power transfer arrangement has been made at Shahdara. In fact, with the Delhi Metro running on broad gauge and 25 kv supply, it also becomes the first Metro in the world which is completely compatible with the main railway system in the country.

But despite the fact that the metro tunnels are 5.7 metres in diameter -- a good 100 mm more than what Metro actually needed -- and therefore meet the requirement of keeping a minimum safe distance between the overhead cables and the coaches due to the presence of the high voltage electricity the power supply would be needed to be cut off for all maintenance works inside the tunnels, lest the electromagnetically charged cables pull someone towards them.

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