#9PM9Minutes – Behind the scenes

What it takes to bring electricity to your homes? How difficult, really, is it to maintain this supply while the entire nation decides to switch off their lights and put them back on exactly at the same moment?

Ever since our Prime Minister’s (second) appeal for this act of solidarity during these trying times went live, there has been a growing interest in finding answers to these questions. And since this happens to be my field of work and I was out there, experiencing those 9 minutes in my station, let me be your layman’s guide to all things Grid!

The basics

Let’s understand what do we mean by Grid.

Power Grid constitutes the entire infrastructure that connects the consumer (your home) to the producer (the generator). There are lines, transformers, and a ton of more components to the grid, but it’s not important to get there today.

What is important though, to understand why we stress so much on its stability. For each equipment in this grid – from those giant turbines in generation plant to the small transformer outside your home – to run as it is expected to, the frequency at which it is run needs to be maintained. For some countries it is 60 Hz, for us it is 50 Hz.

This frequency is maintained when the generators produce exactly the amount which you consume. Of course, these exact figures are a little difficult to maintain at a large scale. But regardless of what happens, we cannot afford to deviate sharply from this range. Even for a nanosecond.

We’ve seen its repercussions in the past And there have been adequate systems put in place just to ensure the stability.

There is a whole world of power trading (which I suggest you look up if you’ve been pretty interested about this topic at this point), but what you should know here is that it’s a closely regulated sector with various autonomous bodies involved. Among them, POSOCO (Power System Operation Corporation) plays a mediator between the regulators and Generation, Transmission and Distribution companies. POSOCO plays a major role in our main story so keep this as a note.

One Nation, One Grid

If you are even remotely involved with power sector, you’ll hear this term quite often. What it means is, the entire nation is synchronized to one common grid. So a Hydro plant situated in a remote north-eastern area can supply electricity to a far-flung home in the southern part. Every electrical equipment is connected to another in one common network.

This is the major reason why power engineers have a lot more faith in its stability today. Since India is a power surplus nation (we have the capacity to generate more than we consume), we can get away with large generation units shutting down due to malfunction, because we have multiple sources available at any point.

05.04.2020- A unique case

The main takeaway till now should be – the generation should always meet the demand. So what made the engineers worry about this event?

  • In Power Trading, the supply and demand are scheduled based on 15-minute slots spread throughout the day. This means, for each of the 96 slots, the Distribution Companies (DISCOM) puts forward its prediction in demand, and Load Dispatch centers (owned by POSOCO) coordinates with the generation utilities and instructs to generate as per the schedule given.
    • The event is 9 minutes long, and hence does not even cover 1 whole slot of 15 minutes. How would the DISCOM factor in this major change in load in its prediction?
  • We have similar events like the Earth Hour where we see this dip in consumption for a particular period. But that cannot be used as a reference to predict the drop in this case as –

a) Like I mentioned in the previous point, prediction and scheduling for 4 full slots is simpler than predicting for 3/5th of 1 slot.
b) I don’t need to tell you the massive difference in the scale with which Earth Hour is observed and what this one would have.

  • Due to the inherent nature of thermal plants, we can neither shut them down (they need to produce a token amount called a technical minimum to keep it operational) nor tweak its generation at a minute scale. Which means, we cannot control 62% of our entire generation capacity dynamically. Add to that the limitations of Solar, which won’t work at night for obvious reasons.
  • We only had Hydros, Gas and Wind Generations which needed to be timed very well.

The Action Plan

For all these stakeholders, this situation was no less than a war, and the preparedness was treated as such. The National Load Dispatch Centre (yes, handled by POSOCO) chalked out the plan. The plan was then broken down for each region/state and from there – to each DISCOM and Transmission Utility. Demand was predicted at the regional levels, and the plans for generation were sent accordingly.

Every station and every generation unit were instructed to make sure their protection systems are robust and there is an alternate arrangement for auxiliary supply in case the station goes into shutdown. For any station/generation unit, maintaining its auxiliary supply is as important as dealing with the electricity itself.

During this period, voltages are also expected to shoot up, which is again bad news. To compensate for that, appropriate settings (read: tap changing) are done on critical transformers across the system.

Consumers were made aware to not switch off any other loads apart from lights. The load drop, in that case, would have been massive, and it would have posed a serious threat to the grid.

It’s Show Time!

The frequency curve

With all the procedures in place, our move started little prior to the main showdown. At around 08:45 PM, the frequency was brought dangerously close to its lower limit (around 49.7 Hz), so that when the demand drops and frequency takes a steep climb, we can restrict its higher figure.

When the clock struck 09:00 PM, you see the load dropping like a series of dominos, and the frequency takes off at the same instant. But thanks to our brilliant pilots, the flight takes course within its permissible limits.

As an example, the load curve for Delhi is shown. You can extrapolate the same for nationwide demand.

The route to normalcy post 09:09 PM was just as smooth. During the entire period, no abnormality was noted across the entire national grid.

There was a prediction of 12GW loss during this period, but it ended up being 32GW (27% drop from 117.3 GW). And the stability still did not budge. In fact, if it were a normal day, no one would even notice the change in parameters, as the system showed no signs of strain.

This is a testament to the minor improvements brought in the system throughout the years, and the precautions taken to tackle the worst scenarios – which made this simple task of switching your lights remain simple for the system as well!<

For the geeks – If you ever felt like checking the frequency of the supply at your home (Remember, it’s the exact same frequency the whole nation will be having), click here for a simple DIY .