Power-less: More transmission towers collapse as winds turn ferocious

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Updated: July 29, 2019 4:38:32 PM

A senior PGCIL official told FE that “upgrading all 2.75 lakh existing towers of the company based on the probabilities of high-wind events warrants significant due diligence”. 

Power less, transmission towers collapse, power transmission sector, electricity transmission towers, Power Grid Corporation, Essel Infra, L&T, Adani TransmissionThe BIS standards vary across the six different wind zones in the country.

Here is more proof of climate change’s enormous economic cost. Altered wind patterns across the Indian
sub-continent, which the scientific community, too, hasn’t sufficiently forewarned of, is wreaking havoc on the country’s power transmission sector, with the towers collapsing at a much faster rate in recent years.

While over 90% of tower collapses are believed to be due to high-speed wind, as many as 473 towers failed between 2012 and 2016, compared with 142 in the previous five-year period. Replying to a question raised in Parliament, power minister RK Singh recently said as many as 52 electricity transmission towers collapsed between October 2016 and March 2018 and high-velocity wind was behind the failure of 39 of these towers, which came apart within five years of commissioning.

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While most of the collapsed towers were owned by the state-run Power Grid Corporation of India (PGCIL), several structures built by Sterlite Power, L&T, Adani Transmission and Essel Infra also failed. Of the 615 towers that collapsed across the country since 2007, 263 fell under one specific wind zone (Zone 4).

A senior PGCIL official told FE that “upgrading all 2.75 lakh existing towers of the company based on the
probabilities of high-wind events warrants significant due diligence”.  The cost of transmission towers ranges between Rs 10 lakh and Rs 70 lakh. On top of that, laying new lines would cost around Rs 1.5 crore-Rs 3.5 crore per kilometre. Replacing parts of existing towers to strengthen them also warrants long shutdowns of critical power systems.

Transmission lines and towers are designed and constructed according to the specifications (IS-802 and IS-875) prescribed by the Bureau of Indian Standards (BIS). The BIS standards vary across the six different wind zones in the country.

Though BIS has revised the National Buildings Code (NBC) in view of the increase in wind speed in some zones, it is yet to correspondingly update the standards for transmission towers. So, the towers in many areas continue to be designed to sustain only slower winds.

According to sources, the Central Electricity Authority (CEA) had requested BIS to include the revised wind map in the tower benchmark standards in 2017, but the latter is yet to take a call on this. Ironically, unless the BIS changes in its norms, PGCIL, which is the both the largest player in transmission infrastructure and sort of regulator of standards for itself and other players, can’t update the bidding norms for setting up towers in different geographies in the country.

Some recent studies conducted by the Structural Engineering Research Centre under the Council of Scientific and Industrial Research have confirmed that climate change has caused wind intensity to change in some parts of the country. PGCIL and other transmission utilities have come on record that heavy storms are the reasons for the increasing number of towers failures.

The problem is complicated because localised high-intensity wind events last for very short durations and are contained in small areas, making it difficult for meteorological equipment to record actual wind speed data for the days when the towers failed.

Also, wind movements occurring within 10 metre of the general ground level—where wind gusts gain more speed—is nearly impossible to record.

Till 2016, government reports on tower failures had pointed that “the probability of such occurrences (high-speed wind events) is low and the tower design will be uneconomical if such situation is considered in the design. Nevertheless, the latest report released in June has dropped this disclaimer, signifying that climate change cannot be overlooked anymore.

A CEA committee of experts has also suggested that “changing climactic condition/wind patter should be deeply studied with the help of wind experts in India”.

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