What Really Happened During the 2003 Blackout?

Ten minutes after missing Hanna-Juniper, the Star-South Canton line was disconnected when it too struck a tree and shorted out. It was actually the third time that day that the line had been disconnected, but it was equipped with circuit breakers called reclosers that would automatically energize the line if the fault was cleared. But the third time was the charm, and Star-South Canton stumbled and was left out. Of course, FirstEnergy didn't know about the first two trips because they didn't see an alarm, and they didn't know about this one either. They had begun sending teams to the substations to put troops on the ground and try to control the situation, but by this time it was too late.

With Star-South Canton offline, flows on the lower capacity 138 kV lines to Cleveland increased significantly. It wasn't long before they too began to log out one after another. Over the next half hour, sixteen 138 kV transmission lines failed, all due to sagging enough to touch something below the line. At this point, voltages had dropped enough that some of the load in northern Ohio was disconnected, but not all. The last remaining 345 kV line to Cleveland from the south came from the Sammis Power Station. Sudden changes in current flow through the system now had this line operating at 120% of its rated capacity.

Seeing such an abnormal and sudden increase in current, relays on the Star-Sammis line assumed a fault had occurred and disconnected the last remaining major link to the Cleveland area at 4:05 p.m., just one hour after the first incident. After that, the rest of the system fell apart. With no remaining connections to the Cleveland area from the south, bulk power flowing through the grid attempted to find a new path to this urban center.  The first surges moved north toward Michigan, shooting lines and separating even more areas of the network. Then the area was isolated to the east.

With no way to reach Cleveland, Toledo, or Detroit from the south, west, or north, a huge surge of energy flowed east toward Pennsylvania, New York, and then Ontario, counterclockwise around the Lake Erie, which generated a major change of course. energy flow in the network. Along the way, relays meant to protect equipment from damage saw these unusual changes in power flows as faults and tripped transmission lines and generators offline. Relays are sophisticated instruments that monitor the network for faults and activate circuit breakers when one is detected. Most relay systems are built with levels of redundancy so that lines remain isolated during a fault, even if one or more relays malfunction.  One type of redundancy is remote backup, where separate relays have overlapping protection zones.

If the relay closest to the fault (called Zone 1) does not trip, the next closest relay will detect the fault in its Zone 2 and trip the circuit breakers. Many relays have a Zone 3 that monitors further along the line. When you have a limited set of information, it can be quite difficult to know if a computer is experiencing a failure and should be disconnected from the network to prevent further damage or is simply experiencing an unusual set of circumstances that protection engineers may not have been aware of. consider. anticipated. This is especially true when the fault is far from where you are taking measurements.

The vast majority of lines that were disconnected in the cascade were disconnected by Zone 3 relays. That means that Zone 1 and 2 relays, for the most part, saw the changes in current and voltage on the lines. and they were not triggered because they were not outside of

what

was considered normal. However, the Zone 3 relays, being less able to discriminate between faults and unusual but non-harmful conditions, turned them off.  Once the dominoes started falling in the Ohio area, it only took about 3 minutes for a huge swath of transmission lines, generators and transformers to go offline.  It all

happened

so quickly that operators had no opportunity to implement interventions that could have mitigated the cascade.

Ultimately, enough lines were activated that the outage area became an electrical island separate from the rest of the Eastern Interconnection. But, since generation was not balanced with demands, the power frequency within the island was completely unstable and the entire area quickly collapsed. In addition to all transmission lines, at least 265 power plants with more than 508 generating units shut down. When it was all over, much of the northeastern United States and the Canadian province of Ontario were completely dark. Since there were very few actual failures during the cascade, revitalization occurred relatively quickly in most places.   Large portions of the affected area had power back before the end of the day.   Only a few places in New York and Toronto took more than a day to restore power, but the impacts were still tremendous.  More than 50 million people were affected.   Water systems lost pressure, forcing boil water advisories.

Cell service was interrupted. All the traffic lights were off. It is estimated that the

blackout

contributed to nearly 100 deaths. Three trees and a computer error caused much of North America to come to a complete standstill. If that's not a good example of the complexity of the electrical grid, I don't know

what

is. If you had asked anyone working in the energy industry on August 13 whether the entire northeastern US and Canada would suffer a catastrophic loss of service the next day, they would have said no.  People understood the fragility of the grid and there were even experts sounding the alarm about the impacts of deregulation and the vulnerability of transmission networks, but this was not a major storm.

It wasn't even a peak summer day.   It was just a series of minor contingencies that aligned perfectly to create a catastrophe. Today's power grid is quite different from that of

2003

. The bilateral report made 46 recommendations on how to improve operations and infrastructure to avoid a similar tragedy in the future, many of which have been implemented over the past nearly 20 years. But that doesn't mean there aren't challenges and fragilities in our current energy infrastructure. Current trends include more extreme weather conditions, changes in the energy portfolio as we move towards more variable generation sources such as wind and solar, increasing electrical demands and increasing communications between loads, generators and grid controllers.  Just a year ago, Texas suffered a major

blackout

related to extreme weather and the strong link between natural gas and electricity.

I have a video about that event if you want to check it out later.  I think the

2003

blackout highlights the complexity and interconnectedness of this critical resource we depend on, and I hope it helps you appreciate the engineering behind it. Thanks for watching and let me know what you think.