With the Mumbai Metropolitan Region Development Authority (MMRDA) keen on an overhead wire electrification (OHE) system for the underground Colaba-Bandra-Seepz metro III corridor, the cost of the project is likely to rise.
For the OHE system, the tunnels will have to be 15-20% wider than in case of the third rail system used for most metro underground projects in the world.
Under the third rail system, electricity is provided using an additional rail along the metro tracks, for which the tunnel diameter can be 5.2m.
PRK Murthy, chief of transport and communication department, MMRDA, said, “The decision to opt for the OHE system has been taken based on the recommendations of our interim consultants.
It will hike the cost a little. The Delhi metro, too, has used the system for their corridors.”
“For the third rail system, we will have to construct sub-stations after every km. This could lead to energy losses.
The equipment for the OHE system can be installed in trains along the corridor,” he said.
The MMRDA expects 42,000 people to use the corridor during peak hours, by 2031.
While the OHE system that runs on alternating current (AC) will help the metro trains operate smoothly even during peak time, the third rail system that runs on direct current (DC) may not be able to handle the load, claimed MMRDA.
Experts, however, have a different opinion. Anil Jangid, director, LEAP Infraasys Pvt Ltd, who was part of the committee constituted by the Union Ministry of Urban Development to study standardisation and indigenisation of traction system in metro system, said, “The third rail system can handle up to 80,000 people during peak hours.
A metro service in China is handling 90,000 people during peak hours with the system. Even though the capital cost for third rail is higher than the OHE system, it is energy efficient.”
Another member of the committee said that the maintenance of the third rail system is cheaper compared to the OHE system.
According to the statistics provided by the committee members, about 95% of metro services in the world operate on DC system, 60% of underground metro services operate on the third rail DC system.