Impact on grid if entire country turns off all electrical appliances within few seconds and then turns them on within few seconds

Question

This is not a hypothetical question but a real one. My country (India) will be turning off all their lights at 9 PM local time on 5th April. They will keep it off for 10 minutes and then turn it back on at 9:10 PM. This has been requested by prime minister amidst coronavirus outbreak in order to challenge the darkness that is looming over the country. Some people have raised concerns that this might cause a grid failure because of sudden disconnect and reconnect of a lot of load.

I understand that there will be a lot of people who won't bother much and will continue with their daily lives. At the same time, there will be a lot of people who will turn off everything and not just lights.

So, assuming that 90 % (it should be far less than 90 % but I wanted to know about worst case scenario) of the load is disconnected across the entire country within a span of 10 seconds and then re-connected again within a span of 10 seconds, what would be the impact on electrical grid and power generation plants? Will it cause any failure in grid or power plants?

Answer 1

The article explains it fairly well.

In Uttar Pradesh, India’s most-populated state, the local utility plans to switch off electricity in phases to stop the surge in voltage from threatening the state’s power grid and equipment, U.P. Power Transmission Corp. said in a letter sent to generators. The country plans to switch off some of its hydropower generation capacity to deal with the sudden dip in demand, Sahai said. The power ministry, in a statement, said adequate arrangements had been made to handle the variation in demand.

While the load reduction will be rapid it will not be instantaneous. Most people will switch off their lights but leave fridges, pumps, and other loads running and I would be surprised if the load reduction was not spread over a couple of minutes.

As mentioned in the article, hydro can be switched off fairly quickly, solar will already be off so it will be a matter of venting steam on the rest of the generators to maintain the grid frequency. Presumably wind generation can be switched off as required.