Grid management is an increasingly complex and critical task , rarely appreciated by common electricity consumers. Maintaining grid frequency is a critical aspect of power system operations, and POSOCO, the national, regional & state load despatch centres work in coordination with power generators and distribution companies to maintain frequency within a narrow range of 49.5-50.2 Hertz. The demand and supply of electricity needs to be synchronized at all times and if this fine balance is not maintained, the results could be catastrophic. 2012 blackouts were result of such an instance which affected 62 crore individuals across the country.
Prime Minister Narendra Modi’s call for solidarity in fight against COVID-19 on 5 th of April, at 9 PM for 9 Minutes, sent the grid operating machinery into tizzy. Concerns were voiced by power institutions across the country but in a remarkable display of coordinated planning, resilience of our power grid and seamless execution, the grid operators managed a massive demand drop of approximately 32 GW in a span of 25 minutes. While India took heed of the Prime Minister’s call, our grid operators flung into unprecedented action, ensuring that one of the key lifelines of our nation is not disrupted in these difficult times. POSOCO, along with regional and state load dispatch centres deserve all the adulation for this remarkable feat.
Power grid operator POSOCO flung into action to prepare for the possible scenarios soon after the PM’s call for solidarity. Estimates were drawn for possible demand variation. After accessing demand from preceding Sunday, receiving inputs from State Load Dispatch Centres and demand estimation for lighting loads for all households across India, it was estimated that the electricity demand may drop by 12-14 GW during the event.
Given the high ramp capacity, i.e. capacity to increase or decrease generation at a high rate, hydro and gas-based generation assets were scheduled to be in action. Total 118 gas-based and hydropower plants with capacity to provide flexibility of 19,392 MW were identified. 7 Nos. of 765 kV stations and 19 Nos. of 400 kV of EHT sub-stations were identified where voltage could have risen beyond permissible limits. Elaborate mock exercises were conducted and safety protocols rehearsed prior to the event.
On the eve of the scheduled event, hydropower power was conserved, to be swung later into action. Coal and Gas plants met most of the demand during the evening hours. By 8:30 PM, thermal assets had been ramped down and hydro generation was peaked to meet the immediate demand. With this, at 8:30 pm, the operators were ready to ramp down generation based on signals for electricity demand.
What happened after that is a historic milestone – far more than the estimates of POSOCO, a massive 32 GW of fall in electricity demand was managed in a short time span of just 49 minutes. Following typical late evening demand pattern, the demand was already on a decline at 8:30 PM. By 8:55 PM, electricity demand had already fallen by 4.5 GW, thereafter falling sharply by another 11.6 GW in a span of next 5 minutes. Electricity demand bottomed at 85.8 GW, recording a sharp decline of approximately 16 GW in a span of 9 minutes. Without a doubt, hydro power played the leading role, with gas generation providing the support for maintaining grid frequency. However, it is to be noted that thermal assets also played a key role as their capacity ramped down by 9.5 GW during the event. What makes this feat even more noteworthy is that average power demand has fallen by almost 30 per cent since the beginning of the lockdown, implying the electricity generation assets were already operating in sub-par conditions. Possibly, about 4 GW of demand was managed through this and wind curtailment since hydro and thermal assets accounted for 27.7 GW of the decrease in power generation corresponding to a demand reduction of 32 GW.
Electricity demand began to gradually pickup after 9:10 PM, and finally settled around 112 GW by 10:00 PM. Hydro generation was back down during the period, while thermal plants were ramped back up to meet the electricity demand. During the course of event, an unprecedented cumulative ramp rate of 4.1 GW was recorded for the power grid. While hydro assets recorded a peak ramp rate of 2.7 GW per minute, even the thermal assets recorded a peak ramp rate of 1.1 GW per minute.