There is not enough information in the article to actually understand what they mean. Spinning the generator a bit faster or slower is not the problem. They sho

There is not enough information in the article to actually understand what they mean. Spinning the generator a bit faster or slower is not the problem. They should always be operated within their limits, so that is not the problem. The problem is that when one region is overloaded it loses synchronization with the rest of the grid and that causes issues. Before that happens some regions are shut off (local controlled blackout), the grid is split up and some power plants even go offline. In general it's like this: * Generators in the whole grid need to be synced up (frequency identical and phase difference small). * If the generators in one area cannot keep up with the load in that area the frequency drops a bit (phase is shifted back). * Powerlines transmit power from areas with more generation capacity (where phase is ahead) to areas lacking capacity (phase in the lacking area is pushed ahead and frequencies remain identical). * Powerlines have limited capacity. * If the transmitted power is not enough to satisfy demand in that area the generators slow down more (phase gets further behind). * If one area gets out of phase too much it would lose frequency completely and there would be catastrophic failure in powerlines, transformers, generators, switches etc.. * To prevent catastrophic failure all areas agree on a small band of frequency variation inside which the regulation mechanisms work. * If the frequency falls below that the grid disconnects into islands. * The islands will either go dark completely (and power plants in those areas shut off) or they will have an oversupply of electricity (with these power plants reducing production). * Regions with an oversupply go back to nominal frequency, sync up and reconnect. Then bit by bit the other areas are connected.