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Today (April 5th, 2020) at 9:00 PM IST, people across India are expected to switch off lights for 9 minutes.

This has apparently raised concerns that there would be problems to the power-grid, due to under-utilization of power.

Can any one explain this (in layman's terms)?

a) Specifically, will the generator be overloaded and stall because the power lines will eventually be saturated and achieve the same potential as that of the generator (given that energy flows from a source of higher potential to that of a lower potential)?

b) If it is the case, is there no control to simply reduce the amount of power generated to match the consumption?

c) Or is it the sudden decrease in power consumption that is the cause for concern?

PS: There is a similar question here - Why does the frequency of power generation change when there is a change of load on the power grid?

But I'm looking for an explanation that can be understood by a layman.

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    \$\begingroup\$ I'm looking for an explanation that can be understood by a layman - for engineers there's an explanation. For laymen you'll just have to wait and see. Did you read this: Specifically, will the generator be overloaded and stall because the powerlines will eventually be saturated and achieve the same potential as that of the generator (given that energy flows from a source of higher potential to that of a lower potential)? in a science fiction book? \$\endgroup\$
    – Andy aka
    Commented Apr 5, 2020 at 14:36
  • \$\begingroup\$ That was my guess. Why is it fictional? \$\endgroup\$
    – Ravindra HV
    Commented Apr 5, 2020 at 20:17
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    \$\begingroup\$ If you switch off the light in your kitchen will your house supply be overloaded and stall because the power lines will eventually be saturated and achieve the same potential as that of the generator? (No.) If you switch off your torch/flashlight will the battery be overloaded and stall because the power lines will eventually be saturated and achieve the same potential as that of the battery? (No.) Switching off stuff reduces the load on a generator or battery. \$\endgroup\$
    – Transistor
    Commented Apr 6, 2020 at 6:41
  • \$\begingroup\$ @Transistor - Thanks. When I said load, I meant 'potential' / 'voltage'. Guess typically 'load' would refer to the flow of electricity (current) and not the potential voltage. \$\endgroup\$
    – Ravindra HV
    Commented Apr 19, 2020 at 23:19
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    \$\begingroup\$ Yes, incandescent light bulbs, heaters, cookers are resistors. \$\endgroup\$
    – Transistor
    Commented Apr 20, 2020 at 22:34

2 Answers 2

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If you are pushing a cart up a hill, you need to push harder if the cart is full of bricks and not as hard if it is empty. If the load falls off and you keep pushing with the same effort, the cart will go faster.

With electric generators, a certain amount of effort is required to turn the generator. If the load is shut off, the same effort will make it go faster. If it goes faster, the frequency and voltage will increase. Generators have regulators that sense the load and automatically reduce the effort if the load decreases. Reducing the effort of the engines, turbines etc. that turn large generators takes some time and care. That is the cause of concern. The power grid equipment and operators should be able to handle demand variation without too much concern, but they apparently are not universally trusted.

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The power grid is normally run with a safe margin between the supply and the demand.

Under normal conditions the frequency of the grid will reduce (the generators and motors will slow down) under high loads. This will also cause a natural reduction in the demand.

If this slow down is not controlled, large portions of the load will be disconnected by automatic under-frequency protection. This is severe event.

To prevent this severe event the utility will take measures to reduce the demand.

What you experienced is such a request.

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