PJM Interconnection said Thursday that its board of directors has approved more than 130 upgrades worth nearly $2 billion to the transmission grid it manages. The Valley Forge, Pa.-based grid operator and power wholesaler said the upgrades are necessary because of plans by generation companies on its grid to retire nearly 14,000 megawatts of generation capacity between May 2012 and the end of 2015. The capacity being retired consists mostly of older, coal-burning power plants, which are dirty and