Brazilian authorities defended the reliability of the nation's electric grid after a massive power failure Tuesday darkened about half the country and revived concerns about Brazil's ability to provide energy infrastructure to match its surging economy. Blackouts hit about 800 Brazilian cities, including Rio de Janeiro and the economic hub of São Paulo, around 10 p.m. Tuesday night after three high-power transmission lines collapsed, triggering a domino effect that prompted a 14,000-megawatt hydroelectric plant to go offline, officials said. Paraguay, which shares the dam with Brazil, also suffered a major blackout. Energy Minister Edison Lobão said the outage was provoked...