The startup sequence first depends on manually switching circuits across the region because no power can be assumed, so trucks are rolling to hundreds of substa

The startup sequence first depends on manually switching circuits across the region because no power can be assumed, so trucks are rolling to hundreds of substations and generator switchyards. Then, coordinating with emergency phones and radios as available, manually switching in loads and self-startable generators into electrical islands in a careful balance to not re-trip everything again due to voltage collapse or frequency excursions. When a single generator synchronizes to a normally operating wide area grid, the relative power balance is so huge that if the generator is not close enough to matching the phasors it will get pulled into sync as long as it's close enough to not trip offline again to avoid damage. With only a few generators on line, and very narrow extra capacity and loads, the margin of error is much smaller. This must be done methodically and carefully for every generator in the black start plan, and it must be done with the majority of the region not having power so transportation, communication, possibly fuel services for the generators, and basic services like food and water and toilets are also impacted. Everything is going to be slow. Some plants also have ramp up and startup cycles that can take most of a day to produce close to their nameplate capacity, and most of them require a significant external power source to run. Coal plants require lots of moving machines that load and process and pulverize the coal and complex steam pressure control systems that don't go from 0 to 100 at a whim; Nuclear plant cooldowns after a trip can be days, and startup again may require another day or two as well. Modern combined cycle gas plants are relatively easy by comparison but still require several hundred KW of available station servicing external power to start the unit and usually take a few hours of careful checks to go from cold to ready to sync. It would probably only take a few days to get most of the ERCOT region back on line, but a full restoration would definitely take weeks as much of the work can't even begin until the big generators in key locations are all up and stable, and most of the efforts can't realistically proceed until the cause of the blackout has been resolved, e.g. no pumps for the gas lines, those generators can't start anyway.