Metro Rails are all set to take the centre stage of mass urban transportation in India’s fastest-growing cities. But the performance and safety of the new and fast-emerging metro rail infrastructure in India will only be as good as its supporting infrastructure and systems. Safe and reliable electrical power is at the core of keeping Metro Rails running. And Power Cables have a key role to play in keeping the safety and reliability of Metro Rail infrastructure on track.
Metro rail systems are growing across the length and breadth of India. Presently, there are 13 metro rail systems running across 678.52 kms of operational metro lines and over 540 stations. A further 557.34 kms are under construction.
Metro Rails Stations are used by millions of people every day, and the safety of such buildings is critical. As of now, the Metro Rail Stations are classified into three broad categories: Elevated, At-Grade, and Underground stations. With tough operating conditions the Metro infrastructure in general carries a high risk of electrical fires. The challenges are even more complex in the case of underground stations where smoke cannot easily pass into the open air. Power Cables are key to arresting the occurrence of electrical fire and reducing the risks, in case of an instance of fire.
Recently, an incident of fire was reported at the ongoing Metro-3 line in Mumbai Metro Rail Corporation. The incident was caused by short-circuit, damaging 12 Power Cables. While no injuries were reported, the incident highlights the risks to human safety in such facilities
Standards set the benchmark and show the way. Delhi Metro Rail Corporation (DMRC) is the biggest metro network in India, carrying over 3 million passengers per day. Over the years, cabling practices and specifications of Delhi Metro have become benchmarks for most other upcoming metro networks in India. The standards followed by DMRC, especially the use of Fire Survival (FS) cables, must be understood and followed further in ensuring the safety of underground stations.
Underground stations present complex challenges in terms of fire safety. The underground stations and tunnel areas do not allow free passage for smoke and gasses in an instance of fire.
Critical facilities in the underground stations must be kept working under fire situations.
Fire Survival (FS) cables are used to power critical facilities within underground stations and tunnels. Further on, these cables are specialised to not generate halogen gasses in fire conditions. It is recommended that Fire Retardant LSZH type cables be used in underground metro stations. British Standards BS 7846The British standards prescribe different durations and different temperatures for FS cables and circuity integrity cables. Depending upon their fire-resistance characteristics, the British standard classifies cables into 4 categories: F2, F30, F60 and F120. The minimum requirement to meet for all cables is F2 when tested under CI.17.4.2 specifications. F2 category cables must survive under 950 degrees for 3 hours. Provisions for mechanical shock and fire testing of F2 cables have also been laid down in the standard. The tests for fire, fire and water, and mechanical shocks are carried out simultaneously on F2 cables while for other categories they are conducted separately. Know the new Standard: IS 17505 (Part 1) for Fire Survival CablesThe Indian Standards for Fire Survival Cable which have been under consideration by the Bureau of Indian Standards (BIS) are now published by BIS in a Gazette notification dated 19 March 2021 - Standard Number: IS 17505 (Part 1) The standards set the specification for Thermosetting Insulated Fire Survival Cables for Fixed Installation having Low Emission of Smoke and Corrosive Gases when affected by fire for working voltages up to and including 1100 Vac and 1500 Vdc. Until now, the domestic industry, including the Metro Railways have been following the British Standard BS 7846 for fire-survival cables. Such Cables must withstand temperatures up to 950°C for at least three hours. This is to ensure that emergency services continue to stay operational to ensure a safe passage. With the publication of IS 17505 (Part I), the new standards can now be used as a benchmark by manufacturers and users. This Indian Standard IS 17505 (Part 1) has been developed keeping in mind the specific needs of the Indian industry and are aligned with other international specifications like BS 7846/IEC 60331 As of now, the Delhi Metro uses FS-type XLPE insulated, armored copper conductor cables as per BS7846 standard for emergency services. In near future, the Indian Standard for Fire Survival Cables IS 17505 (Part 1) will have to be followed for emergency and other critical applications with high fire risks. Code requirements for the selection of cablesRegulations laid down in the NFPA 130 (2017) are followed in the selection of FS cables for underground stations. Key requirements with regard to such FS cables are:
|
Read the .PDF Version Here |