On Nov 10, 2009, a massive power failure blacked out Brazil’s two largest cities and other parts of Latin America’s biggest nation leaving millions of people in the dark. Transmission connecting the large Itaipu dam to Brazil and Paraguay apparently tripped disconnecting some 17,000 megawatts of power. I was on Copacabana Beach years ago for a training course and can only imagine the disruption that the outage may have caused. A blackout in a major city is not a fun time.
But blackouts are interesting to study. More often than not, the initiating cause is something innocuous, such as the infamous overgrown trees in the 2003 Northeastern US-Canada blackout. (An announcement just came out that the 2007 Brazil blackout that was blamed on hackers was due to sooty insulators!) So when the news report says, “A storm near the hydro dam apparently uprooted some trees that caused the blackout,” I am inclined to consider that the trees hit some transmission lines which could have led to the isolation of Itaipu. That’s not so far-fetched. You never know what a failure-bunching event such as the major storm that hit Itaipu could do to redundancy and good planning practice. Reliability is only as good as the next blackout!
By happenstance, this event occurred when we were conducting our HVDC course in Albany. So this picture of the Itaipu transmission lines came in handy. A bipole high-voltage DC (direct-current) line is on the right; while two double-circuit AC (alternating current) lines are on the left. They’re too far apart to fall down on each other so most likely more than one failure occurred from separate incidents but these failures were “bunched” or overlapping in time due to the heavy storm at the time.
Frequently asked questions
Are transmission systems designed to withstand this type of failure bunching?
Generally not. Loss of one line is the general practice for design criteria, and this appears to be at least the loss of two lines with the subsequent, dependent failure of the third line.
Can transmission systems be designed to withstand this type of event?
Yes, but at some cost penalty. A planner can add double or triple redundancy to the transmission path, and locate the lines so that there is reduced exposure to the same weather pattern, all at a price. A more common practice is not to provide withstand capability for the extreme event, but to design the system so that any outages will be short and manageable. This is accomplished by providing reserve, backup and startup generation capacity for the large load centers, and isolating any faults quickly and efficiently through system protection equipment, among others.
Would wind power have helped avoid this blackout?
If located at Itaipu, wind generators would have dropped off as soon as the wind picked up above about 25 mph. If located near the urban centers, such as Rio de Janeiro and Sao Paulo, they could have provided backup power if there was wind blowing at the time.
Can this blackout happen again during the next Summer Olympics?
Objectively, the likelihood remains small. But viewed subjectively, if an improbable event happens once, it can happen again. The engineering answer would thus depend on whether you would consider yourself a scientist or a populist.