The total reduction in all-India demand during the lights out at 9 p.m. on Sunday was 31,089 MW, which is more than 25% of the demand on a typical Sunday, according to the Power System Operation Corporation Limited (POSOCO). The lowest demand recorded was 85,799 MW at 9:10 p.m. after which the demand started picking up and settled at 1,14,400 MW at 10:10 p.m. Grid frequencies varied from 50.26 Hz to 49.70 Hz. In the run-up to the event, POSOCO had expected a demand variation of 12,000 to 14,000 MW over a shorter period of time.
POSOCO data showed regional variations in the demand dip from 8:45 p.m. to 9:10 p.m. The dip was 30% in the northern region, 32% in western region, 17% in the south, 39% in the east and 40% in the north-east.
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Just as the power managers had planned, the generation from hydro power plants toed the dip and surge pattern of lighting loads. Hydro generation was maximised by 8:45 p.m. to 25,559 MW. From then it was reduced to 8,016 MW at 9:10 p.m. This meant the 75% reduction in hydro generation achieved in 25 minutes took on the bulk of demand variations. Simultaneously, a reduction of 10,950 MW was achieved through thermal (6,992 MW), gas (1,951 MW), and wind (2,007 MW) between 8:45 p.m. and 9:10 p.m.
Advance actions such as switching off transmission lines and taking reactors in service were undertaken to keep voltages and line loads within permissible limits, POSOCO said in a release, adding that the event was managed smoothly without any untoward incident.
Hydro and gas-powered plants can support fast changes in load. Gas turbines can ramp up or ramp down rather quickly and, world over, they are often used to support the grid supplied with fluctuating wind power. Similarly, water can be stored in dams and reservoirs and can be released in a planned manner to achieve a sharp increase or decrease in hydro power. Coal plants have a more limited ability to handle sharp load variations. Nuclear plants even lesser.
On Sunday, the changes in load, though swift, happened over a more prolonged period of time than the 2 to 4 minutes expected by power managers. The coming back to normal took longer, probably indicating that people eased out of the lights out more gradually than expected. They took longer to switch on their house lights, likely spending more time on rooftops and balconies.
The exercise showed that the Indian grid could handle large load changes if done in a planned way. Blackouts are a different matter and typically happen unplanned. Blackouts at one place can spread to other places when power plants that are not designed to take sharp load changes are forced to take those changes.
(The author is an independent journalist)
