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The massive grid failure in India affected over 19 states with 600 million people. With so many speculations as to the reasons for the failure, we decided to talk to engineers working at the load dispatch centers on the ground to get a firsthand understanding of what really happened.
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· What happened: Two states allegedly overdrew power beyond their allocation while grid frequency was falling to dangerous levels. The "NEW" grid (which interconnects the Northern, Eastern, Northeastern and Western grids) tripped and cascaded to the Northern and Eastern grids. The Western grid managed to survive by rapidly reducing demand and managing its existing supply and islanding from the NEW grid.
· Why did it happen? There was a mismatch between demand and supply. The fragile safety mechanisms (relays) seemed to have failed under pressure from having to meet rising demand from the agricultural sector due to weak monsoons and mismanagement by regional dispatch centers. This year the monsoons have been weak and delayed in India, and the lack of precipitation is felt especially acutely in some northern states that have economies dependent on agriculture. The sowing of sugarcane has started in some states and there is high demand for power for irrigation.
· Why did it take so long to restore power? The generation that tripped had to be restored in phases and matched with the system. Also, the Northern grid is highly dependent on thermal power supply (coal). Hydropower generates a small percentage of power for the Northern grid, but the below-average precipitation from monsoon season has pushed hydropower generation to even lower levels. Once thermal power stations are shut off due to this kind of tripping, it normally takes at least six to eight hours to come back online because they have to be cooled and stabilized, whereas hydropower plants can come back online immediately. Because the Northern grid is largely dependent on coal and nuclear power plants, it takes much longer to restore when tripped.
· Could this historic blackout have been avoided? Yes. This was a clear case of mismanagement by the regional load dispatch centers which were negligent or did not see the warning signals. There is a critical need to have safety mechanisms that automatically shut off load when frequencies drop down to dangerous levels. For example, the Southern grid has deployed an ‘Under Frequency (UF) Load’ mechanism which will not allow states to draw more power from the grid when the frequency dips below 49.5 cycles. There is also a System Protection Scheme (SPS) in the Southern grid where the load feeder in the grid systems will trip when there is a problem but the main grid will be safe and stable. The Northern grid also has such systems in place (UF and SPS) but they are generally not implemented due to non-technical and political issues. Per the Indian Electricity Grid Code (IEGC), the area of responsibility on maintaining the grid is clearly defined on regional load dispatch instructions to be followed by SLDCs.
