Large blackouts can be particularly devastating and happen much more frequently than a normal distribution predicts.
The impact of a blackout exponentially increases with the duration of the blackout, and the duration of restoration decreases exponentially with the availability of initial sources of power. For several time-critical loads, quick restoration (minutes rather than hours or even days) is crucial. Blackstart generators, which can be started without any connection to the grid, are a key element in restoring service after a widespread outage. These initial sources of power include pump-storage hydropower, which can take 5-10 minutes to start, to certain types of combustion turbines, which take on the order of hours.
For a limited outage, restoration can be rapid, which will then allow sufficient time for repair to bring the system to full operability, although there may be a challenge for subsurface cables in metropolitan areas. On the other hand, in widespread outages, restoration itself may be a significant barrier, as was the case in the 1965 and 2003 Northeast blackouts. Natural disasters, however, can also lead to significant issues of repair—after Hurricanes Rita and Katrina, full repair of the electric power system took several years (NAS)
Restoring a system from a blackout required a very careful choreography of re-energizing transmission lines from generators that were still online inside the blacked-out area, from systems from outside the blacked-out area, restoring station power to off-line generating units so they could be restarted, synchronizing the generators to the interconnection, and then constantly balancing generation and demand as additional generating units and additional customer demands are restored to service.
Many may not realize it takes days to bring nuclear and coal fired power plants back on-line, so restoring power was done with gas-fired plants normally used for peak periods to cover baseload needs normally coal and nuclear-powered. The diversity of our energy systems proved invaluable (CR).
Restarting the grid after the 2003 power outage was especially difficult.
The blackout shutdown over 100 power plants, including 22 nuclear reactors, cutoff power for 50 million people in 8 states and Canada, including much of the Northeast corridor and the core of the American financial network, and showed just how vulnerable our tightly knit network of generators, transmission lines, and other critical infrastructure is.
The dependence of major infrastructural systems on the continued supply of electrical energy, and of oil and gas, is well recognized. Telecommunications, information technology, and the Internet, as well as food and water supplies, homes and worksites, are dependent on electricity; numerous commercial and transportation facilities are also dependent on natural gas and refined oil products.
NAS. 2012. Terrorism and the Electric Power Delivery System. National Academy of Science
NAS. 2013. The Resilience of the Electric Power Delivery System in Response to Terrorism and Natural Disasters. National Academy of Science
CR. September 4 & 23, 2003. Implications of power blackouts for the nation’s cybersecurity and critical infrastructure protection. Congressional Record, House of Representatives. Serial No. 108–23. Christopher Cox, California, Chairman select committee on homeland security