When the Lights Went Off

POSOCO successfully manages the load during the nine-minute event on April 5

Amidst the Covid-19 nationwide lockdown, the prime minister of India appealed to the citizens of India to switch off their lights and express solidarity by lighting earthen lamps or torches on April 5, 2020, at 9 p.m. for nine minutes. The anticipated reduction in all-India demand during this event was estimated at 12-14 GW. Prior to the event, there were concerns that this sudden fluctuation in demand could result in grid instability and blackouts in many states. However, the load despatcher, Power System Operation Corporation Limited (POSOCO), which oversees grid stability, successfully managed the drop in load. It remained in constant touch with all the state discoms and regional load despatchcentres for proper planning and management of the event. Since it was a pre-planned event, measures were adopted to ensure that the grid was not affected.

Event analysis

Responding to questions on social media on whether all household appliances had to be switched off for the safety of the equipment or if additional devices had to be switched on, the Ministry of Power clarified that only lights had to be switched off. As per POSOCO, the total reduction in all-India demand recorded during the event was 31,089 MW. The all-India demand started reducing from 8:45 p.m. and a minimum demand of 85,799 MW was recorded at 9:10 p.m. Subsequently, from 9:10 p.m., the demand started picking up and settled at around 114,400 MW at 10:10 p.m.

Grid frequency is a critical aspect of power system operations. It must be kept close to 50 Hz as per global standards. India’s grid code calls for grid frequency to be in the range of 49.5-50.2 Hz. Any sudden change in the demand pattern impacts grid frequency. Grid frequency during the event was in the range of 49.70-50.26 Hz, with the maximum frequency recorded at 9:08 p.m. and the minimum frequency at 8:49 p.m. This means that the voltage was kept stable.

Hydropower stations played a key role as they provided the flexibility to quickly ramp up and down generation as they take the least time to switch on or off. Hydropower generation across the country was maximised by 8:45 p.m., and generation reduction of 17,543 MW (from 25,559 MW to 8,016 MW) was achieved with these resources between 8:45 p.m. and 9:10 p.m. (matching with the demand reduction of 31,089 MW during the same period). Hydro generation was again ramped up from 8,016 MW to 19,012 MW from 9:10 p.m. to 9:27 p.m. to meet the increase in demand after the event. A generation reduction of 10,950 MW was achieved through thermal (6,992 MW), gas (1,951 MW) and wind (2,007 MW) sources between 8:45 p.m. and 9:10 p.m.

Advance actions such as switching off transmission lines, taking reactors in service and changing SVC, STATCOM and HVDC set points were taken prior to the event to keep voltages and line loadings within permissible limits.

Conclusion

Overall, POSOCO successfully managed this unprecedented challenge without any untoward incident and the event went smoothly with the support and cooperation of all stakeholders. The power system parameters were maintained within limits. Such an unprecedented ramp-down and build-up of electricity load within a small window of nine minutes has not been seen anywhere in the world on such a scale. After the grid collapse of July 2012, which raised questions on India’s electricity grid management, the April 5 event marked a landmark moment in India’s electricity grid management story.

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