Key takeaway: the replacement time for transformers is very nontrivial:<p><i>The country's roughly 2,000 very large transformers are expensive to build, often costing millions of dollars each, and hard to replace. Each is custom made and weighs up to 500,000 pounds, and "I can only build 10 units a month," said Dennis Blake, general manager of Pennsylvania Transformer in Pittsburgh, one of seven U.S. manufacturers. The utility industry keeps some spares on hand.</i><p>Attacks at a number of sites could cripple electricity distribution infrastructure across large areas of the US for months, and force utilities to prioritize repairs among widely disparate locations: if Washington, NYC, San Jose, and Minneapolis are all wiped out, are you going to protect the government, banking and financial sector, high tech, or a large population who will freeze or roast without power?