[nagr22]

Since the time our PM announced the 9 min lights off, I can see few people are worried about a possible grid failure whereas the remaining people are dismissing it off with a reasoning that we all switch off our lights every night so whats the big deal? I thought I would explain the technicalities of the power grid in layman terms in this post so that the forum members can be in peace.

TLDR: This 9 minute event does have an effect on the grid and the power engineers are capable of managing it. There will most likely be no failure of the power grid as long as people dont go overboard and switch off their mains. Please, only switch off the lights!

Now coming to the details, in simpler terms the power grid consists of power generators and load centers. There are 3 important parameters of the grid which are important for safe operation - Voltage, Frequency and Synchronization.

Voltage and frequency depends on the speed of the generators. Generator speed is dependent on the match between the power input to the generator (coal, hydro power etc) and the load. If the load power is greater than the power fed to the generator, the generator speed tends to drop and the grid voltage and frequency also start dropping. This is sensed by the generator's speed governor which immediately increases the power input to the generator (burns more coal/releases more water etc) and tries to balance the produced power of the generator with the load demand. If the load drops, the speed of the generator tends to increase and the governor reduces the speed by removing some of the coal/ reducing the water flow. Let us keep this understanding in mind.

Base Load, Peak Load and Intermediate Load:

The electrical load demand of the nation varies with many factors like time of the day, day of the year (season, festivals) etc. Demand tends to be lower at nights (reason why some countries offer discount at night) with a few spikes at different times of the day. A typical plot of load demand in a 24 hour duration looks like this:

Image courtesy

We can see that there is a portion of the load which remains the same irrespective of time of day. This is called base load. This consists of all the utilities that are powered on throughout the day like centralized HVAC, refrigerators, CCTVs, industrial load (those which run 24x7) etc.

There are certain loads which are transient in nature but draw significant amount of power and cause a temporary surge in the load demand. Such loads are called peak loads. Examples include turning on the water heaters in the morning for short duration, using iron box etc.

At certain times of the day, the base load itself becomes high and remains high for a longer duration. For example, many IT industries start their offices at 8 AM which adds a sudden spike in the load demand that stays till 6 pm. Such loads are called intermediate loads.

Types of Power Generation:
Not all generators can produce Base load and Peak load. This allocation depends on the dynamics of the generator i.e., how quickly can the generator scale up or ramp down during the transition from base load - intermediate - peak.

Base load power plants
Power plants like coal get their energy from pressurized steam which is obtained by burning coal. If a coal plant were to produce more energy, it requires more coal to be burnt. Coal takes a significant time to catch fire and come to required temperature. It cannot respond to fast changes in load demand. Sometimes it may take days for a coal plant to come online! Similarly, if the load demand on a coal plant were to drop suddenly, it has to stop burning some of the coal otherwise the steam boiler may explode due to high pressure! It is not easy to stop the coal burn at the same speed as switching off the heater at your home!
For the above reasons, coal and nuclear power plants are generally used as based load power plants which are scheduled to generate the expected base load for a given day.

Peak load power plants
Hydro power plants use a stream of water to run a turbine which in-turn produce electricity. By controlling the valves of the water channel, one can quickly start/stop/adjust water flow according the load. Hence hydro power plants are used as peak load power plants.

Similarly, natural gas or diesel power plants can also respond to sudden variation in load demand and can adjust their output by varying a throttle like in a ICE car.

Peak load power plants can be used as base load power plants but not vice versa.

Intermediate load generation
Intermediate loads are the sudden transitions in the base load demand. Whenever such a transition occurs, the increase in load is initially supplied by the peak load stations while in parallel, the thermal plants are slowly ramped up to to meet the new base load. Similarly when the base load is expected to drop at a certain time of the day, the thermal plants start ramping down well in advance and in parallel the peak load stations take up the excess load so that when the intermediate load suddenly drops, the peak load stations can respond quickly and cut off themselves from the grid.

Load Planning and Scheduling
Load planning and scheduling is the process of predicting the load curve for a given day and scheduling the base and peak load stations accordingly so that we get seamless power supply. If the load demand is more than the prediction, there will be load shedding and if demand is less than predicted, the peak load stations do not have to work. A problem occurs when the load demand is such that it is even less than the base load scheduled for the day.

Suppose the base load predicted for a day is 10 GW and a coal station has been scheduled such that 'x' kg of coal is burnt per hour to produce that power. If for some reason the load drops to 9.9GW, there are protective devices called reactors (think of a flywheel) which absorb this extra energy and stabilize the grid. But of the load drops to 8GW, some of the thermal plants must be removed from the grid and depending on for how long they have to be removed, the consequences can be bad. While it is not as bad as a total grid failure, removing a coal power plant off the grid for too long will require it to be put off (coal burning stopped) which will cause that plant to stay offline for a long time (coal needs a lot of time to start burning again). So when the load demand becomes 10 GW again, we may not have additional power stations to take up that load which will lead to load shedding for a few hours in some areas services by that plant.
If the drop in load demand is planned well, the engineers can plan and schedule the coal plants for 8GW and supplement the remaining 2GW with hydro or gas power plants, there will be no issues.

Summary:
Since the 9 minute lights off event is a well planned event, there is nothing to worry as the engineers in the electricity department would have already planned and scheduled their generators to cater for this anticipated load fluctuation. But please, Switch off lights only and DO NOT turn off the mains.

Please note that I have made many simplifications in order for the content to be easily understood by everybody irrespective of whether they are an electrical engineer or not.

Additional Reading:
The phenomenon of sudden load fluctuations and their effect on the grid is a well researched and understood subject. A very interesting phenomenon has been observed in the United Kingdom where the national cable network is BBC which makes the advertisement breaks to get synchronized. Because of this, all the Brits at once tend to make tea (well, they are Brits what did you expect? ) and use their toilets which puts a huge stress on their power grid. This especially severe during popular soaps or Tennis matches where there can be a sudden twist any time and the engineers cannot predict when there will be a commercial break or when the Brits will be angry on a soap actor and turn off their TV's! One can read about it here.

Some more details about how India's power industry is planning to handle tonight's power off event can be read here

Mod Note: A Very Good topic to debate on the concepts of Power Systems. Definitely needs a separate thread.

[Safety is Param]

On the power fluctuation and load variation front, enclosing couple of docs received from my engg. batch friends who are currently placed at various power stations across India (20+ yrs. experience)

Advisory for Lighting load switch off on 05Apr2020_NLDC.pdf

[padmrajravi]

I understand that with a bit of planning and effort by the electrical engineers and government bodies, the diya show can be pulled off without any problems. But do we really need all this planning at this juncture when all our efforts should be in fighting the pandemic? There are many ways in which we can show respect to the health workers without the grid engineers having to go through all these planning and precautions. Just lighting some Diyas without switching off lights would also serve the purpose right? Another short-sighted call that needs a lot of extra effort and with no real benefit.

[venkyhere]

There are two parts to this :
1) transient change or "kick"
2) steady state change

1) Transient :
An inductor (windings in a transformer) doesn't like current getting chopped off suddenly and it will rapidly shed stored magnetic energy and try to restore (unsuccessfully) the same current flow, which will cause a massive voltage surge across the windings of the inductor - this is the fundamental simple reason.
Sudden load-shedding all at once, will cause massive "kick" (voltage surge) in all sub-station transformers (different for different phases), which can pass on this "kick" to feeder transformers, and further on, via HT lines, to national grid, which in turn can transfer this "kick" to power generation plants. The risk is real - that's why the instruction to NOT switch off all loads in all households, so that the 'chopped off current' is not a high number.
Discharge capacitors installed at the mouth of transformers at substations (leaf level) and feeder stations (twig level), are purposefully designed and installed, to withstand inductance kicks. Question is not whether such leaf-level surge protection mechanisms are in place. Question is what was their 'estimated' surge protection capacity while designing and installing them. Mostly they must have made realistic load-shed estimates (rainfall, thunderstorms, cyclones, peak load conditions during the day) and multiplied by an industry standard safety factor. Whether it will be enough to handle the MASSIVE surge that "could" happen at the precise time - because something of this proportion is beyond the wildest dream of any power network design. Designing and installing for this level of surge is prohibitively and needlessly expensive. The problem boils down to : Say the total cascaded surge produced is going to be X%. And some Y% of it will be blunted by the capacitor network at leaf-leaf, leaf & twig hierarchies. Still some X-Y surge will pass onto the branches, the trunk (the national HT grid) ; and make its way to the roots (the power stations all over the country). Whether the X-Y can be handled by the rotor speed governors (otherwise 50Hz will go for a toss beyond recoverable limits and lead to a catastrophe) in non-coal based power plants, is the final question.

2) steady state :
The speed at which the rotor of the massive generator of the power plant is running, is critical to the 50Hz frequency of the power available at home ; and it is critical for the 50Hz to be perfectly in sync, in all power stations that are producing electricity. Otherwise no such thing as a 'grid' can even exist. So, protecting the generators at all costs, from producing erroneous frequency, is critical. Whenever load changes occur to the grid predictably - time of the day, scheduled on/off a large factory etc ; control systems will manage the ferocity with which non-coal plants are operating, and maybe even disconnect/reconnect them, depending on the size of the load change. This is a much slower (relatively) action of the control system, where the power generation plants get their operating point corrected to a new one, so that the frequency of generation stays clean. However, this banks heavily on (1) to work well.


(1) is like the flywheel that sits between the crank and the gearbox in a car, in between gear changes. (2) is like the fuel adjustment that eventually happens (mechanically or via ECU) for the gear change.

Hoping that control systems installed for control/monitoring of our power grid is "prepared" well in advance for this "switch off" activity that is going to happen. As of now, the info that we get from power grid corporation is that they are 'well and comfortably prepared, protocols are in place'.

My hope is for the surge itself to be kept 'less harmful' by :
1) hopefully people have got the message to ONLY switch off lights and nothing else
2) people having their watches/clocks/decision-to-peek-at-neighbors-and-decide-whether-its-time to be slightly staggered w.r.t each other ; and if 10 crore switch off at 9pm, another 10 crore switch off at 9:01pm, and another 10 crore at 9:02pm, that itself will help.

On balance, this is creating a problem, then finding a solution for it, and assuring everyone that the problem is solved. Like picking up a snake from the jungle and putting on your lap, just because your dear friend is a snake antivenom expert. "Light some diyas" would have been enough without ever mentioning any phrase like "switch off"

[nagr22]

Originally Posted by nagr22

Additional Reading:

Adding to the above post, one can view the below documentary to understand what happens behind the scenes when such unprecedented changes occur to the load.

https://www.youtube.com/watch?v=slDAvewWfrA

Someone asked me why cant these events be automated and why does it require manual intervention. The reason for that is quite complex. Our power grids are a shared resource with generating stations located in a different geography than that of the load center. The load to a major city can actually be fed by generators present in some other state and could even be in a different country! For instance, India imports huge amounts of hydro electricity from Bhutan and Nepal and in tonight's case, hydro electricity is a critical resource to manage the surge! The State Load Despatch Centers(SLDC) which manage such surges might find conflicts and challenges in deciding to which load centre should a generator's power be directed to.
For instance, let us say that a power plant in Sharavathi Valley is supplying power to both Mumbai as well as Bangalore and it is capable of providing 10GW at max. If both Mumbai and Bangalore demand 12GW together, now the challenge arises as to whom should I cater? The last time I checked, such rules are still in the grey area and because of that reason there is no automated program which can take decisions under such situations. There is a huge layer of politics and profits involved behind taking such decisions. It only gets more complex when you are buying power from another country! I hope for tonight our state governments are all in sync and have a proper protocol in place to share and manage the load. I am predicting at least 1 instance of political drama between two states whose power department is managed by different parties. I only hope they dont do anything silly

[Miyata]

On the power grid stability issue: Guess the bigger issue could be the following - Now that a panic has been set loose about possible grid stability issue and its potential (negative) impact on our home appliances/electronics, many people across the country would be worried and might turn off all their appliances to ride out this 30-min of uncertainty/instability.

Off and by itself, issue of frequency increasing above 50Hz with a sudden dip in power demand is fairly easily handled - happens all over the world.

But this lack of proper communication from authorities and the panic associated with it is what could lead to any disruption - there is no way to model how many folks will suddenly switch off all of their home appliances to ride out this "possible instability."

This is the same misinformation and also lack of trust on the authorities that causes panic buying and hoarding - guess our folks issuing orders just don't learn or just don't care!

Come 8:55pm this evening, it's quite possible, to use the analogy of our car, one wheel COULD suddenly start moving at a different speed wrt other three wheels. Hope the driver is skilled enough to keep the car stable!

[ampere]

The load variation and demand is one part. Grid stability also depends a lot on the type of load. A Power Distribution System is deemed like an infinite source where one can draw any type of current (active or re-active) for constant voltage.

Higher the inductive load (read large scale industrial drives) swing the power factor to lower active power which shows up on the meter reading (VI Cos phi). Hence the mandate to maintain power factor within a prescribed limit. This also is an important aspect to maintain grid stability.

[diyguy]

Originally Posted by poloman

So in effect if houses switch off only lights it may hardly be a blip in the grid.

No offense but going by your calculation and halving the wattage number, if 40% of the households follow through, it would amount to 5GW drop in power demand for those 9 mins. Is that a blip?

[Dinesh_Malhotra]

Originally Posted by diyguy

No offense but going by your calculation and halving the wattage number, if 40% of the households follow through, it would amount to 5GW drop in power demand for those 9 mins. Is that a blip?

Looking at people posting here in support of power shutdown, the supporting references for this melodrama are the following with counter explanation:

1. Earth hour

I don't know anyone around me who even understands what is earth hour, but there are plenty around, who do follow what our respected PM says. This will occur with outcomes one is not sure of

2. Don't we switch off the lights at night?

Yes, we do and that's accounted for when electrical supply chains are established. That's basic right? But, nobody was/is prepared for this. Why believe me? See how people across management level in discoms are running helter and skelter to make it a success. If it's so easy, why aren't they relaxed. Why are they worried? Why are they saying that this is unprecedented and we don't know for sure what might happen? I don't understand the panic in them. Do they all too belong to govt bashers tribe?

3. Relax, you're just petrified. Why are you not verifying before posting?

I am relaxed but worried. Yes, one can be in the same state at one time. I am calmer than usual in fact. That allows me to read, comprehend and make simple understandings of complex issues. That way, I can uplift myself, make some contribution in the society and ask questions when as and when necessary. We are allowed to do that right?


Lastly, isn't it also the reality that safety of our health workers, our defenses against COVID-19 and our approach to the whole virus scene is filled more with irony and comic relief than real applications of solutions?

This feels like a movie. A cheap slap stick comedy movie. Where fun engulfs reality and even in death people could be seen laughing and cheering.

[poloman]

Originally Posted by diyguy

No offense but going by your calculation and halving the wattage number, if 40% of the households follow through, it would amount to 5GW drop in power demand for those 9 mins. Is that a blip?

5GW of 125GW is 4% deviation. Let us wait and argue whether this is a major load deviation for a robust grid after 9:10 PM today.
Repeat: I am not following this. Going by the response in forum, not many as well.

[diyguy]

Originally Posted by poloman

Let us wait and argue whether this is a major load deviation for a robust grid after 9:10 PM today.

I am not concerned about the grid but my home electronics which can get damaged by grid related fluctuations. So I intend being off grid for this duration and maybe a bit longer for it to stabilize.

[nagr22]

Originally Posted by diyguy

I am not concerned about the grid but my home electronics which can get damaged by grid related fluctuations. So I intend being off grid for this duration and maybe a bit longer for it to stabilize.

No offence but this is exactly the kind of behaviour which can cause trouble if done en masse. I can understand your concern about power surge and even the authorities know it and that's why they are asking the public to ONLY switch off the lights. By staying off the grid, you are contributing to the exact scenario of which you are worried about.

[diyguy]

Originally Posted by nagr22

By staying off the grid, you are contributing to the exact scenario of which you are worried about.

I know, but I cannot risk any of our devices going bad and not being able to fix them due to the lock down. I have a borewell pump that runs automatically by level sensors. I shudder to think if it goes bad what I would do till shops open for me to be able to repair it. We have no other water source and the pump had some issues a few months back. We relied on can water for a few days. Same with sensitive inverter acs and more at home. Why should I risk the TVs and other electronics which will burn a hole in my pocket and cause a lot of discomfort in these times if I cannot get them fixed?

[poloman]

Originally Posted by nagr22

No offence but this is exactly the kind of behaviour which can cause trouble if done en masse. I can understand your concern about power surge and even the authorities know it and that's why they are asking the public to ONLY switch off the lights. By staying off the grid, you are contributing to the exact scenario of which you are worried about.

This was exactly the proponents of grid doomsday wanted. A lot of paranoia is being spread among public which may worsen the scenario. If houses and housing societies switch off their main circuit breaker, then this can get really unpredictable.

This in any way was a needless exercise. This should have been done on the day we come out of lock down as a symbolic gesture.

[ritz3645]

My Electronic Engineering friend had connected a high capacity capacitor used in farm motor pumps, at the input end of electricity at home. It helps as a surge protector. This was done long time back and is still there.