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?