Twenty-eight months after two successive grid collapses triggered cascading outages across most of northern and eastern India, the country’s grid manager has red-flagged at least half-a-dozen hotspots in the nation’s grid infrastructure that continue to be vulnerable to high voltage tower collapses.
The lack of system protection schemes at these locations to mitigate the resulting unplanned outages and systemic shock puts at risk major power generation complexes at locations that include Singrauli, Rihand, Vindhyachal, Korba, Ramagundam, Dadri, Sipat, Mundra and Sasan, which depend on high capacity 400 kV and 765 kV AC transmission corridors for power evacuation, according to a July 2014 report by grid manager POSOCO.
The 765 kV double-circuit transmission towers carry power to the tune of 4,000-5,000 MW and collapse of a single tower could lead to a cascading grid failure, unless special protection schemes are in place or the transmission system is made robust to handle such a huge loss of power.
The July POSOCO report points out that the Central Electricity Authority or CEA — the apex transmission planning body — had revised the transmission planning security criteria in January 2013 in the wake of the July 2012 twin blackouts. The revised criteria required that the grid should remain stable in case of two contingencies in the same area such as tripping of two transmission lines or the collapse of a tower carrying two circuits.
Those suggestions, as highlighted by POSOCO in its July report and reiterated in an October 2014 report, are “yet to be fully implemented”, even as it has buttressed the fact that a tower collapse has to be considered a “credible contingency”. In the interim, exceptional events that could have impacted the stability of the grid include outage of 6,000-6,500 MW generation at two mega stations at Mundra (Adani Power Mundra and Tata’s CGPL) in the last week of August 2014 due to a combination of technical and commercial reasons.
A government official involved in the exercise said that there has been “a lag in planning and implementing the new transmission schemes matching with the rapid setting up of generating stations by the private sector and the increase in demand in the southern parts of the country, which has resulted in chronic transmission congestion in many parts of the country”.
However, PGCIL officials maintained that such an eventuality is “unlikely”. “These 765 kV double circuit towers have been designed keeping in mind the maximum wind speed encountered in the region in the past 150 years, so chances are less that they will collapse. Besides, we have one of the largest grids in the world, and a single tower collapsing might not have a major impact. If 4 or 5 towers go out, then it is a different matter,” said RN Nayak, CMD, PGCIL.
Senior government officials point out that ‘N-2’ type contingency planning is expensive, making cost a major roadblock in the process, but it is becoming necessary to avoid congestion.
According to Anish De, partner, Infrastructure and Government Services, KPMG India, the Indian power system will continue to remain vulnerable till there is a deeper network of 765 kV double circuit towers. Currently, these form about 6 per cent of the transmission network.