Long Read: Why The ‘9 PM 9 Minutes’ Event Makes For An Extremely Fascinating Study In Power Grid Management
‘The 9 Minutes Lights Off’ event has turned out to be a fascinating case study for power sector professionals and enthusiasts.
For power sector professionals and enthusiasts in India, ‘The 9 Minutes Lights Off’ event on Sunday, 5 April 2020 was equivalent to a celestial event for astronomy. What made the event very unique is there is no known precedent of about 25 per cent power demand switching off and coming back up in matter of less than 20 minutes in a large and complex interconnected power grid.
The general discourse in the country was the event would result in grid failure, blackout, damage to equipment, essential medical equipment losing functionality etc.
While a lot of people supported the event as a signal of national solidarity and resolve, others questioned the need to conduct such an exercise when the country is facing a pandemic.
Though the officials and grid operators put up a brave face, there was certainly a lot of anxiety whether the event would pass off without a glitch.
While some of the concerns were valid given the unprecedented event; robust regulatory regime, strong power infrastructure, flexible generating capacity and detailed planning meant the event passed off with flying colours providing a number of lessons for the future shape of the power grid.
Electricity Grid Balancing – A Tug of War
For people not from the power sector, a good analogy of how the power grid operates is with the sport of tug of war.
In the sport, the force on rope is applied by a pull from the opposing ends. As long as the pull is equal from both the ends, the rope is in equilibrium not moving beyond the tolerance zone marked by central lines.
If suddenly a few members from one side stop exerting any pull or new members start exerting extra pull, there is disruption in balance with one side being overwhelmed and the whole set up collapsing.
Similarly, in a large integrated power grid, a state of equilibrium normally exists between the power generators and consumers.
Electricity cannot be stored. It is transported from the generator to the consumer via transmission and distribution wires on a real time basis. This transmission happens at a pre-determined electrical frequency. All generation, transmission, distribution and consumption equipment are rated to operate at this pre-determined frequency.
Like the tolerance zone marked by central lines in the sport of tug of war, Power System Operation Corporation Limited (POSCO), the national grid operator, endeavours to ensure that the power grid frequency remains within the 49.7-50.2 Hz band with a target to keep it operating around 50 Hz.
Also, the Indian grid code mandates all participants of the power grid make all possible efforts to operate within 49.9 to 50.05 Hz. Overall 75 per cent to 80 per cent of the times the power grid operates within this band. Technically, tolerance of the power grid is higher than the above mentioned frequency range.
When either the demand or supply goes out of sync; electrical frequency becomes unstable. This results in the power grid operating beyond the pre-determined levels leading to grid failure and blackouts.
Manoeuvres to stabilise the power grid by starting new power stations and/or implementing demand side management with new load profile is technically complex and time consuming.
The infamous 2012 power blackout impacting more than 700 million people in North, East and North Eastern India was essentially a result of surge in demand resulting in very low frequency and grid collapsing.
Evolution Of India Power Grid
The Indian power grid has significantly evolved and modernised in the last few years. It has augmented its ability to respond to sudden supply-demand mismatch.
Earlier, the national power grid was functioning as five separate regional power grids. It was plagued with frequency indiscipline due to inadequate regulations and weak enforcement of the same.
Since 2014, with the southern grid integrating with the rest of the national grid, India operates as ‘one nation, one grid’ with one frequency mode. This allows for better balancing of both supply and demand.
Additionally, inter regional power transmission capacity has risen to almost 78 GW. This allows for large quantum of electricity movement between regions to balance the shortfall in supply from one region to another.
The erstwhile uninterrupted interchange mechanism for load balancing has been substituted with a more effective deviation settlement mechanism (DSM) for better discipline of scheduling and forecasting.
Since 2017, POSCO operates as a separate company managing the national load dispatch centre (NLDC) and five regional load dispatch centres (RLDCs) ensuring integrated and reliable operation.
Power Sector At A Glance Leading Up To ‘The 9 Minutes Lights Off’ Event
As of 31.3.2020, all India generation capacity is 370 GW. Before the lockdown due to the pandemic, typically about 160 GW of peak demand and about 3,600 BUs of energy demand was met during the day. This fell by about 25 per cent to about 120 GW of peak demand and about 2,200 BUs of energy demand.
Typically, about 85 per cent of the electricity demand was met by thermal generation. Post the lockdown as the based load demand dropped. Due to this, coal and lignite generation being designated as base load generators are being curtailed to meet about 80 per cent of the demand to balance the grid.
Every night at around 6pm there is a surge in demand and at around 10 pm there is a drop in demand. However, the spike and dip in demand is gradual due to the staggering time duration in which people switch on and switch off their lighting and other appliances.
On 5 April 2020, at the designated time of 9 pm, a sharp spike in grid frequency was anticipated due to 12-14 GW of lighting demand expected to be switched off and drop in grid frequency 9 minutes later, when the lighting demand is switched back on. Prima facie it would appear that event was potentially riskier than mere demand surge on the grid as the whole event would unfold within a short span of 10-15 minutes.
There are key differences between a large-scale power blackout/base load reduction to the one off ‘The 9 Minutes Lights Off’ event.
It’s a planned event; this gives sufficient time for grid operators to put in place a response. Once again drawing from the tug of war analogy, timing of sudden withdrawal of force on rope at one end was known so that a similar reduction in force from the other side could be simultaneously planned.
However, one vital question remained, what is the quantum of force reduction (or demand reduction)? Like the management of reduction in base load demand, can thermal generation be backed down to manage the ‘The 9 Minutes Lights Off’ event? What are the constraints?
Technical Constraints On How Generation Is Shut Down And Restarted
Each type of generation has its own technical limitations of how it starts to generate power, reaches full capacity and synchronises with the grid.
Slow Starters: once switched off, nuclear power takes couple of days before the fuel stabilises and generation can be restarted. Coal and lignite power plants take about three-four hours to start and generate full power. An analogy is a steam engine train which takes the train few minutes before it runs on full steam.
Fast Starters: gas-based power plants can start generating full power in matter of minutes on single cycle mode. It takes a shade longer for full generation on combined cycle mode. Once the reservoir sluice gates are opened hydro power plants can instantly generate full power.
Unpredictable starters: solar power does not generate at night and is limited during cloudy environment. There needs to be favourable conditions for wind energy to generate electricity at capacity. Hence both are unreliable.
Due to the above reason, typically nuclear generation and renewable energy is operated as must run power plant. Thermal generation like coal and lignite due to their slow start times are categorised as base load generators and typically operate at above 60 per cent load factor for economic and technical reasons. Gas and hydro power plants due to their quick start are typically categorised as peak load generators and used to balance the power grid.
The Planning For ‘The 9 Minutes Lights Off’ Event
The announcement of the event was done on the 3 April 2020. A meeting of POSCO, all state load despatch centres (SLDC), power distribution companies and hydro generators was held to plan for the event.
A review of the power demand estimated the likely drop and surge of lighting demand at 12-14 GW during the event. The same was cross checked with state-wise number of household and typical consumption.
Available power generation capacity was determined by eliminating the under maintenance and fuel short generating plants. Capacity was then reviewed by fuel type and the technical constraints on how long they will take to restart.
The total generation capacity was 370 GW of which hydro power was 45 GW and gas power was 25 GW. However, certain hydro and gas power was being used for base load demand. Based on plant by plant review it was ascertained that 30.9 GW was available for maximum generation with a flexibility of 19.4 GW.
Based on the above facts, a plan was set that hydro power generation would primarily respond to the change in demand to manage the power grid. Communication was sent out to all SLDCs and hydro generators about the plan.
Key Features Of The Plan
- Hydro generation would be maximised by 20:45 hours.
- Hydro generation would then be curtailed to respond to the demand reduction post 21 hours.
- Once demand picks up after 21:09 hours, hydro generation would once again be ramped up.
- Thermal, gas and wind generation would be restricted to allow Hydro generation ramp up.
- Advance actions such as switching off transmission lines, taking reactors in service, changing SVC, STATCOM, HVDC set points etc, were taken prior to the event for keeping voltages and line loadings within permissible limits.
How Did The Actual Event Play Out?
The much-hyped and anticipated event passed off successfully in terms of people participation and without any collateral damage to the power grid operations. Power Ministry personnel, grid operators and distribution companies heaved a sigh of relief. The chief executive officer of one of the largest power distribution companies aptly commented “kasam se, ISRO chief jaisi feeling aa rahi hai” (by god, it feels like being ISRO chief) underlining the high anxiety levels sector professional were experiencing prior to the event.
However, a more granular analysis of event showed things at the backend were more dramatic than that would appear from the optics of the outcome.
So What Was The Surprise?
While the anticipated demand drop was in the range of 12-14 GW, the actual demand drop in the system between 20.57 hours and 21.07 hours turned out to be about 31 GW. This constituted 20-30 per cent reduction and subsequent increase in demand.
This meant that the system was stress-tested to a much higher degree than what was anticipated. If a 30 per cent reduction was known ab initio it would have certainly raised much bigger alarm bells for the grid operator.
What Explains The Larger Than Expected Demand Drop
Various reasons can be assigned for the higher than expected drop in demand. Lighting load could be higher than that estimated. People could have switched off all the appliances and not just the lights, load shedding etc.
While it is entirely likely that some of the above may be true to some extent, the demand drop pattern probably points out to another potential reason.
From the above chart, it appears that the expected 12-14 GW demand dropped by 21:00 hours. This can be assumed to have dropped purely on account of the public response to ‘The 9 Minute Lights Off’ event.
However, more interestingly there is a second phase of demand reduction after 21.05 hours that coincides with the frequency breaching 50.2 Hz.
Since there are no reports of major load shedding it is highly likely that other loads (including critical large scale industry still operating) may, out of precaution, switched off to protect their equipment due to frequency spike.
This hypothesis though presently is only speculative and a more detailed analysis will have to be carried out to establish it.
What Saved The Day?
Quite clearly, the pre-planned ramping up and down of identified generating plants combined with the availability of generation flexibility in hydro power withstood the higher than expected load fluctuation.
As the pre-plan analysis showed, the total available hydro plus gas generation was 30.9 GW with a flexibility of 19.4 GW. This was nearly double the expected 12-14 GW of demand drop.
How Did Various Regions Respond?
One of the striking aspects of the load pattern was the almost equal nature of response to ‘The 9 Minutes Lights Off’ event across all the regions of the country.
Almost synchronised response and reduction of demand in all the regions took away some of the balancing geographical diversity of a grid could provide. The ‘one nation, one grid’ provided the necessary intra-regional surplus transfer capacity cushion to carry out such an unprecedented event.
Key Policy And Regulatory Takeaways From ‘The 9 Minutes Lights Off’ Event
The event, its planning and the outcome has demonstrated that fundamentally the Indian power grid is technically strong. The regulatory process for grid operations is robust and has successfully passed the unintended stress test.
Ironically, a lot of hype about the potential risk on the grid in hindsight only added to the grid operators being extra vigilant and cautious.
With planned large-scale integration of renewable power particularly solar and wind power, which are inherently prone to large supply variation there is a need to further strengthen the power grid infrastructure and the regulatory management process.
Some key action areas which regulators and policy-makers will have to focus on are listed below:
- Movement Towards Smart Grid: the Power Ministry has drawn up a road map towards a smart grid project. Some developments in this regard are under way. If there was a fully functional smart grid in place it would have allowed for better demand change estimation and an automatic supply response management rather than a very human driven response.There is a need to further accelerate this programme.
- Automatic Generation Control (AGC): based on the national electricity policy, Central Electricity Regulatory Commission in 2015 provided a roadmap for ‘operationalisation of generation reserves in the country’. It mandates each region should maintain primary, secondary and tertiary generation reserves with an objective to introduce ‘spinning reserves’ in the country. This is one of the most important components to ensure power grid security, quality and reliability. While several pilot projects for establishing AGC have taken place there is an urgent need to accelerate its roll-out.
- Power Generation Mix: ‘The 9 Minute Lights Off Event’ once again reinforced the importance of an optimum power generation mix. With the increase in renewables in the generation mix, careful thought has to be weighed in developing peaking/spinning reserves. While globally there is a lot of focus on battery storage as a key enabler for large-scale adoption of solar and wind, its commercial viability is still being questioned. In the medium term, a lot of renewable power can still be adopted with hydro and gas generation being used to provide the balance and spinning reserve.
- Strengthening Of National Grid: while the southern grid has been successfully integrated into the national grid a few years ago, continuous investments will have to be made to ensure the capacity keeps pace with the increase in demand and the various generation capacities that are being built across the country. At a regional and local level transmission and distribution infrastructure have to be augmented especially given the renewable capacities being built and the vagaries of nature that put stress on such renewable generation.
- Demand Side Management: this is an area where no amount of work is insufficient. Further, effort has to be put in place to equally distribute demand by encouraging new demand to shift to areas of generation surplus. Industries must be encouraged to stagger operations so as to reduce and flatten the load curve. Work on appliance efficiency should always be ongoing. Tariff design must be reworked by introducing market mechanisms to economically incentivise demand to back down and reduce the load curve.
- Supply Side Management: balancing mechanism regulations should be strengthened with market-based incentives for generators to back down or ramp up generation through trading/tariff mechanism.
- Strengthening Communication And Digital Infrastructure: today’s world is interconnected with the latest digital protocol being used to operate and manage the power grid. Continuous efforts should be made to strengthen digital security so that this digital framework is not breached and the real time communication channel is always open for grid management.
All in all, ‘The 9 Minute Lights Off’ event has turned out to be a fascinating case study for power sector professionals and enthusiasts.
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