The timeline provides an early picture of what happened. Most of the events that appear to have contributed to the blackout occurred during the period from about noon EDT until 4:13 p.m. EDT. Generation and transmission operating events plus scheduled interchange through the systems in the region may have affected events later in the day. The task force is studying these events beginning at 8 a.m. on August 14 to determine whether they were significant to the blackout.
Events Leading to the Blackout
12:05:44 - 1:31:34 PM – Generator trips
- 12:05:44 – Conesville Unit 5 (rating 375 MW)
- 1:14:04 – Greenwood Unit 1 (rating 785 MW)
- 1:31:34 – Eastlake Unit 5 (rating: 597 MW
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Conesville plant is in central Ohio and Greenwood plant is north of the Detroit area. Greenwood Unit 1 tripped at 1:14:04 and returned to service at 1:57. Eastlake Unit 5 is in northern Ohio along the southern shore of Lake Erie and is connected to the 345 kV transmission system. These generating unit trips (shutdowns) caused the electric power flow pattern to change over the transmission system.
2:02 PM – Transmission line disconnects in southwestern Ohio
- Stuart – Atlanta 345 kV
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This line is part of the transmission pathway from southwestern Ohio into northern Ohio. It disconnected from the system due to a brush fire under a portion of the line. Hot gases from a fire can ionize the air above a transmission line, causing the air to conduct electricity and short-circuit the conductors.
3:05:41 - 3:41:33 PM – Transmission lines disconnect between eastern Ohio and northern Ohio
- 3:05:41 – Harding-Chamberlain 345 kV
- 3:32:03 – Hanna-Juniper 345 kV
- 3:41:33 – Star-South Canton 345 kV
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These three transmission lines are part of the pathway into northern Ohio from eastern Ohio. At this time, the reason for the Harding-Chamberlain line going out of service is unknown. The Hanna-Juniper line contacted a tree, creating a short-circuit to ground that caused the line to disconnect itself. The Star-South Canton line had disconnected and reclosed twice earlier in the day, but the significance of those events is not yet clear.
With these lines disconnected, the effectiveness of the transmission path from eastern Ohio into the northern Ohio area was reduced. The electricity that had been flowing over these lines instantly began flowing over other transmission lines, including the underlying 138 kV systems, that connect northern Ohio to the grid. However, this new power flow pattern began to overload those other lines as well. As voltage was dropping, demand of about 600 MW disconnected in the northern Ohio area from industrial customers (whose motors dropped off line due to low voltage) and distribution-level customers who were disconnected automatically from the 138 and 69 kV transmission system.
3:45:33 - 4:08:58 PM – Remaining transmission lines disconnect from eastern into northern Ohio
- 3:45:33 – Canton Central-Tidd 345 kV
- 4:06:03 – Sammis-Star 345 kV
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Canton Central-Tidd disconnected at 3:45:33 and reconnected 58 seconds later. However, the Canton Central 345/138 kV transformers disconnected and did not reconnect, isolating the 138 kV system from the 345 kV support at the Canton Central substation. The Sammis-Star 345 kV line then disconnected at 4:06:03, which completely blocked the 345 kV path into northern Ohio from eastern Ohio. This left only three paths for power to flow into northern Ohio: 1) from northeastern Ohio and Pennsylvania around the southern shore of Lake Erie, 2) from southern Ohio (recall, however, that part of that pathway was severed following the Stuart-Atlanta line trip at 2:02), and 3) from eastern Michigan. This also substantially weakened northeast Ohio as a source of power to eastern Michigan, making the Detroit area more reliant on the west-east Michigan lines and the same southern and western Ohio transmis- sion lines.
During the period 3:42:49-4:08:58, multiple 138 kV lines across northern Ohio disconnected themselves. This blacked out Akron and the areas west and south.
4:08:58 - 4:10:27 PM – Transmission lines into northwestern Ohio disconnect, and generation trips in central Michigan
- 4:08:58 – Galion-Ohio Central-Muskingum 345 kV
- 4:09:06 – East Lima-Fostoria Central 345 kV
- 4:09:23-4:10:27 – Kinder Morgan (rating: 500 MW; loaded to 200 MW)
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When the Galion-Ohio Central-Muskingum and East Lima-Fostoria Central transmission lines disconnected, this blocked the transmission paths from southern and western Ohio into northern Ohio and eastern Michigan. Thus the combined northern Ohio and eastern Michigan load centers were connected only by the transmission lines from: 1) northeastern Ohio and Pennsylvania along the southern shore of Lake Erie; 2) western Michigan via the west-east lines that cross the state; and 3) Ontario. Eastern Michigan was connected to northern Ohio only by three 345 kV transmission lines near the southwestern bend of Lake Erie.
The Kinder Morgan generating unit tripped (shut down) in central Michigan (loaded to 200 MW).
Power flows became heavy from Indiana and over the west-east Michigan transmission lines to serve loads in eastern Michigan and northern Ohio.
The reduced transmission capacity serving the northern Ohio load centers resulted in the transmission voltage becoming depressed in that area as load exceeded the rapidly declining power delivery capability.
At about 4:09, the Eastern Interconnection frequency rose by 0.020 - 0.027 Hz, which represents a demand loss in the range of 700 - 950 MW.
4:10:00 - 4:10:38 PM - Transmission lines disconnect across Michigan and northern Ohio, generation trips off line in northern Michigan and northern Ohio, and northern Ohio separates from Pennsylvania
- 4:10 – Harding-Fox 345 kV
- 4:10:04 - 4:10:45 – Twenty generators along Lake Erie in northern Ohio (loaded to 2174 MW total)
- 4:10:37 – West-East Michigan 345 kV
- 4:10:38 – Midland Cogeneration Venture (loaded to 1265 MW)
- 4:10:38 – Transmission system separates northwest of Detroit
- 4:10:38 – Perry-Ashtabula-Erie West 345 kV
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Twenty generators (loaded to 2174 MW) tripped off line along Lake Erie during the period 4:10:04 - 4:10:45. The loss of this generation increased the power flows into the northern Ohio and eastern Michigan load centers on the remaining paths, which included the west-east transmission lines that cross Michigan.
The west-east Michigan 345 kV paths then disconnected at 4:10:37, leaving eastern Michigan connected by only a circuitous path around northern Michigan that disconnected one second later, and the connections to Ontario and northern Ohio. Investigators are still studying the power flows that resulted.
At 4:10:38, the Midland Cogeneration Venture (MCV), loaded to 1265 MW, tripped off line.
The MCV generation trip imposed heavier flows on the remaining transmission system, and left eastern Michigan and northern Ohio with very depressed voltages. The remaining transmission paths into the Detroit area from the northwest separated.
At 4:10:38, the Perry-Ashtabula-Erie West 345 kV transmission line tripped, severing the path into the northern Ohio area from Pennsylvania along the southern shore of Lake Erie.
The MCV generation trip imposed heavier flows on the remaining transmission system, and left eastern Michigan and northern Ohio with very depressed voltages. The remaining transmission paths into the Detroit area from the northwest separated.
At 4:10:38, the Perry-Ashtabula-Erie West 345 kV transmission line tripped, severing the path into the northern Ohio area from Pennsylvania along the southern shore of Lake Erie.
Summary of the Situation at 4:10:38
When the Perry-Ashtabula-Erie West 345 kV transmission line disconnected at 4:10:38, the entire eastern Michigan and northern Ohio load centers had little generation left available to them and the voltage was declining. The only connection between those load centers and the rest of the Eastern Interconnection was at the interface between the Michigan and Ontario systems. Also, the frequency was declining in northern Ohio in those areas that had separated from the Interconnection.When the transmission lines along the southern shore of Lake Erie disconnected, the power that had been flowing along that path immediately reversed direction and began flowing in a giant loop counterclockwise from Pennsylvania to New York to Ontario and into Michigan.
What happened in Pennsylvania, New York, Ontario, Quèbec, and Maritimes areas.
4:10:40 - 4:10:44 PM – Four transmission lines disconnect between Pennsylvania and New York
- 4:10:40 – Homer City-Watercure Roa d 345 kV
- 4:10:40 – Homer City-Stolle Road 345 kV
- 4:10:41 – South Ripley-Dunkirk 230 kV
- 4:10:44 – East Towanda-Hillside 230 kV
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Responding to the surge of energy flowing north out of Pennsylvania through New York and Ontario into Michigan, these four lines disconnected within four seconds of one another and separated Pennsylvania from New York.
At this point, the northern part of the Eastern Interconnection (which still included the rapidly dwindling load in eastern Michigan and northern Ohio) remained connected to the rest of the Interconnection at only two locations: 1) in the east through the ties between New York and New Jersey, and 2) in the west through the 230 kV transmission line between Ontario, Manitoba, and Minnesota.
Heavy power flows were moving northward over the New York-New Jersey ties.
4:10:41 PM – Transmission line disconnects and generation trips in northern Ohio
- Fostoria Central-Galion 345 kV
- Perry 1 nuclear unit (rated 1252 MW)
- Avon Lake 9 unit (rated 616 MW)
- Beaver-Davis Besse 345 kV
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The Fostoria Central-Galion line forms part of the pathway from central to northern Ohio. That path was already blocked by the combination of the Galion-Muskingum-Ohio Central line disconnecting at 4:08:58, and the East Lima-Fostoria Central line disconnecting at 4:09:06.
Perry 1 nuclear unit, located on the southern shore of Lake Erie near the border with Pennsylvania, and Avon Lake 9, located near Cleveland, tripped off line at virtually the same time.
When the Beaver-Davis Besse 345 kV line, which connects the Cleveland and Toledo areas, disconnected, it left the Cleveland area isolated from the Eastern Interconnection. Cleveland area load was disconnected first by automatic underfrequency load shedding, and finally by the disconnection of the transmission lines.
4:10:42 - 4:10:45 PM – Transmission paths disconnect in northern Ontario and New Jersey, isolating the northeast portion of the Eastern Interconnection
- 4:10:42 – Campbell unit 3 (rated 820 MW) trips
- 4:10:43 – Keith-Waterman 230 kV
- 4:10:45 – Wawa-Marathon 230 kV
- 4:10:45 – Branchburg-Ramapo 500 kV
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At 4:10:43, eastern Michigan was still connected to Ontario, but the Keith-Waterman 230 kV line that forms part of that interface disconnected.
At 4:10:45, the Ontario system separated when the Wawa-Marathon 230 kV line disconnected along the northern shore of Lake Superior. The portion of Ontario to the west of Wawa remained connected to Manitoba and Minnesota.
At the same time, the Branchburg-Ramapo 500 kV line was now the remaining link between the Eastern Interconnection and the area ultimately affected by the blackout, and that line disconnected at 4:10:45 along with the underlying 230 and 138 kV ties in New Jersey. This left the northern part of New Jersey connected to New York. Pennsylvania and the remainder of New Jersey remained connected to the Eastern Interconnection.
At this point, the Eastern Interconnection was split into two sections separated by an east-to-west line. To the north of that line was New York City, northern New Jersey, New York, New England, the Maritime provinces, eastern Michigan, the majority of Ontario, plus the Quèbec system. To the south of that line was the rest of the Eastern Interconnection, which was not affected by the blackout.
4:10:46 - 4:10:55 PM – New York splits east- to-west. New England (except southwestern Connecticut) and the Maritimes separate from New York and remain intact.
During the next nine seconds, several separations occurred between the areas in the northern section of the Eastern Interconnection.
- 4:10:46-4:10:55 – New York-New England transmission lines disconnect
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The ties between New York and New England disconnected during this period, and most of the New England area became an island with generation and demand balanced close enough that it could remain operational. However, southwestern Connecticut was separated from New England and remained tied to the New York system for about one minute. - 4:10:48 – New York transmission splits east-west.
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The transmission system in New York split along an east-west line, with northern New Jersey and southwestern Connecticut connected to the eastern part of the New York system, and Ontario and eastern Michigan connected to the western part. During the next second, Ontario and New York would separate, with 15% of the demand across New York state disconnected automatically. About 2500 MW of Ontario demand automatically disconnected as Ontario attempted to rebalance its system.4:10:50 - 4:11:57 PM – Ontario separates from New York west of Niagara Falls and west of St. Lawrence. Southwestern Connecticut separates from New York and blacks out.
- 4:10:50– The Ontario system just west of Niagara Falls and west of St. Lawrence separates from New York.
- 4:11:22 – Long Mountain - Plum Tree 345 kV
- 4:11:57 – Remaining transmission lines between Ontario and eastern Michigan separate
The Ontario-New York separation at 4:10:50 left New York’s and Ontario’s large hydro and some thermal generators at Niagara and St. Lawrence, as well as the 765 kV and direct current interties with Quèbec, connected to the New York system, supporting the demand in upstate New York just south of Lake Ontario. Three of the transmission circuits near Niagara automatically reconnected Ontario to New York at 4:10:56. Another 4500 MW of Ontario demand automatically disconnected. At 4:11:10, the Niagara lines disconnected again, and New York and Ontario again separated. Most of Ontario blacked out after this separation, leaving 22,500 MW of demand disconnected out of a total demand of about 24,000 MW. The eastern New York island blacked out with only scattered small pockets of service remaining. The western New York island continued to serve about 50% of the demand in that island.
When Long Mountain-Plum Tree (connected to Pleasant Valley substation in New York) disconnected, it left southwestern Connecticut connected to New York only through the 138 kV cable that crosses Long Island Sound. About 500 MW of southwest Connecticut demand was disconnected by automatic grid operations. Twenty-two seconds later the Long Island Sound cable disconnected, islanding southwest Connecticut and blacking it out.
4:13 PM – Cascading sequence essentially complete
The major portion of the northern section of the Eastern Interconnection (the area within the dotted line in the map above) was blacked out.
Some isolated areas of generation and load remained on line for several minutes. Some of those areas in which a close generation-demand balance could be maintained remained operational; other generators ultimately tripped off line and the areas they served were blacked out.
One relatively large island remained in operation serving about 5700 MW of demand, mostly in western New York. This service was maintained by generating stations south of Lake Ontario with Ontario generators at Niagara and St. Lawrence as well as the 765 kV and DC interties with Quèbec. This island formed the basis for restoration in both New York and Ontario.
Conclusion
This sequence of events for the August 14, 2003 blackout summarizes some of the many significant events that occurred before and during this widespread and complex system failure. It reflects events that have been identified and verified as of September 10, 2003. Much more data collection, analysis, and research must be completed before the Joint United States-Canada Power Outage Task Force will be able to state with confidence exactly what happened and why it happened. Our understanding of the events described here, and of those not yet fully catalogued, may change as the investigation progresses. The Task Force’s future reports will include a more detailed timeline, and will address the causal relationships among these events.
