What caused one of the world's largest power blackouts in history? And is it the first of many? E&T investigates.
As far as power failures go, few can match the dubious record set by Brazil last year. On the night of 10 November, nearly 70 million people were left in the dark - some of them for up to five hours - in an incident that is still being investigated by national authorities.
The massive blackout affected not only 18 of Brazil's 27 states, but also the entire population of Paraguay. São Paulo and Rio de Janeiro, Brazil's two largest urban areas, were among hundreds of cities and towns that were unexpectedly plunged into darkness.
So what happened? From the outset, it appeared clear that the blame lay with the Brazilian electricity sector - more specifically with Itaipu, the world's second-largest hydroelectric power station.
However, it was quickly established that there was nothing wrong with the dam itself. Earlier that afternoon, the power station had provisionally interrupted the transmission of energy for 25 minutes in response to a weather alert. But at the time of the incident (2213 local time), the company running Itaipu insisted the plant was operating normally.
Instead, the source of the problem was traced back to a section of the transmission lines that carry energy from Itaipu to São Paulo. A series of nearly simultaneous short-circuits in the proximity of the Itabera substation was identified as the apparent reason why three 750kV transmission lines were cut.
In total, 28.8GW were temporarily lost from the Brazilian grid and 980MW from its Paraguayan counterpart. A significant portion of that power loss can be directly attributed to the disconnection of Itaipu. The bi-national plant has an installed capacity of 14GW, which provide approximately 20 per cent of Brazil's and 90 per cent of Paraguay's electricity.
Power grid hackers?
In Brazil, where millions of homes remained in the dark for up to five hours, two different developments (one involving a local meteorologist, the other one an American TV network) led some sectors of the media to speculate that maybe there was more to the incident than the official hypothesis seemed to suggest.
Osmar Pinto, a weather expert at Brazil's National Institute for Space Research, was highly sceptical of the possibility of thunderbolts having damaged the affected transmission lines, as the only lightning strikes that satellite imagery proved existed in the Itabera area at the time were hitting the ground at least 10km away from the problem area.
Besides, as Pinto pointed out, there was nothing that made that particular storm different from most other storms regularly affecting that area of the country. According to his calculations, those strikes were hitting the ground at an average of once every two minutes - nothing that the transmission infrastructure would not have been able to tackle.
The other development that helped raise question marks was a report that CBS had broadcast in the US just three days before the blackout. In the TV station's '60 Minutes' programme, it was claimed there was evidence that previous power outages in Brazil had been the result of hacker attacks. Was this just a new case?
The Brazilian National Electricity System Operator (ONS) released a statement insisting that it was impossible for a hacker to penetrate the network used for the real-time operation of the grid. Such a critical IT network is completely isolated from the open Internet, the ONS explained. Any necessary remote operational instructions are transmitted as voice commands via private telephone lines.
Nonetheless, president Luiz Inácio Lula da Silva ordered a full investigation to determine the exact causes of the blackout, and whether human error could have played a part. Compiled by the ONS with input from close to 70 engineers working for the private and public companies that would have been directly involved in the incident, the official perturbation analysis report was about to be made public at the time of writing.
Blame it on the rain
Judging by a preliminary version of the report (details of which were revealed by Hermes Chipp, the director general of the ONS in a November press conference), bad weather will still be accused of having played a role in the incident. However, the report is also likely to confirm that there was negligence on the part of Furnas, the private company which owns the Itaipu-to-São Paulo transmission lines.
While the preliminary report couldn't rule out lightning strikes as the initial source of the short-circuits, the analysis of data obtained from equipment installed at certain substations suggests that an insulator at one of the pylons operated by Furnas might have failed following the accumulation of rainwater.
Regardless of the initial trigger, the incident caused phase B of one of the transmission lines to collapse. Just 13.5ms later, a separate short-circuit was registered at phase A of a second line. And 3.2ms later, yet another short-circuit disconnected a third line.
The extremely short lapse of time separating the three events suggests that the disconnection of the first line might have overloaded the two others, triggering a chain reaction.
Double and triple occurrences are not that infrequent. In almost ten years between 2000 and 2009, the Brazilian grid had previously experienced nine triple and ten double short-circuit incidents in the same lines, without any of them triggering a blackout. According to Chipp, this was because in all those cases the interval between any two short-circuits was between three and five seconds.
The lines need at least one second between short-circuits to be able to recover. With just a few milliseconds separating a succession of three events, Chipp says this particular blackout was as freak as it was inevitable: 'No system is designed to support the planning ahead of contingencies with such extremely remote probabilities. In order to do that, I would need to build a second - and maybe a third - set of alternative transmission lines to offer the optimum level of redundancy,' says Chipp.
So, could this ever happen again? The answer is: yes. If the final report into the incident concludes that a faulty insulator was at the heart of the problem, then Furnas will be fined and asked to provide a technical solution, such as the installation of 'insulator umbrellas' to protect these devices from the rain.
The government itself has already acknowledged that it can't promise Brazilians that there won't be temporary interruptions to their electricity supply caused by unforeseen circumstances. What it can promise, president Lula has insisted, is that none of the electricity rationing measures that people were frequently forced to put up with during much of 2001 and 2002 will be reinstated in the future.
The blackouts that Brazil suffered then were directly linked to a lack of generation capacity. But the government has since adopted a very aggressive infrastructure development policy that has seen the commissioning of numerous new thermal power stations.
In terms of transmission infrastructure alone, Lula claims that, in just seven years, his administration has invested the equivalent of 30 per cent of what Brazil had invested in the previous 123 years.
He's not exaggerating. When he came to power in 2002, the country's high-voltage transmission lines covered about 67,000km. Today, that figure is 89,200km. Making sure that this growing network is always 'on' will be an entirely different challenge.