Causes

Heavy rains and strong winds caused three transformers on a key high-voltage transmission line to short circuit, cutting the line and automatically causing the complete loss of 14 GW of power and the shutdown of the Itaipu Dam for the first time in its 25-year history.^[7][8] The power cut, which Brazilian officials said affected 18 of the country's 26 states, brought chaos to cities including São Paulo, Rio de Janeiro, Belo Horizonte, Campo Grande and Vitória.^[9]

Media such as Slashdot^[10] and 60 Minutes reported^[11] that the outage was the work of hackers. However, in December, 2010, a leaked US diplomatic cable suggested otherwise and indicated that the longest outage was 6 hours, in São Paulo, and details interim reports on what failures caused the outage, and responses under consideration.^[11]

President Luiz Inácio Lula da Silva arranged an emergency commission to enquire into the cause of the blackout.^[12] The blackout also unleashed a political stir as the Minister of Energy has been summoned to testify before Congress.^[13]

Paraguay

The Itaipu Dam is shared with Paraguay. In the immediate aftermath of its failure, interconnecting lines to Paraguay's other large powerplant, the Yacyreta Dam (in the border with Argentina), also failed. All of the country's territory was affected by the blackout.^[14][15]

Brazil

Entirely affected states ^{[citation needed]}

• São Paulo
• Rio de Janeiro
• Mato Grosso do Sul
• Espírito Santo

Partially affected states

• Rio Grande do Sul
• Santa Catarina
• Paraná
• Minas Gerais
• Mato Grosso
• Goiás
• Rondônia
• Acre
• Bahia
• Sergipe
• Alagoas
• Pernambuco
• Paraíba
• Rio Grande do Norte