Minnesota Power provides electricity to a 26,000-square-mile electric service territory located in northeastern Minnesota. Minnesota Power supplies retail electric service to 131,000 customers and wholesale electric service to 16 municipalities. They have electric transmission and distribution lines of 500 kilovolt (eight miles), 230 kilovolt (606 miles), 161 kilovolt (43 miles), 138 kilovolt (66 miles), 115 kilovolt (1,259 miles) and less than 115 kilovolt (6,550 miles). They own and operate 178 substations with a total capacity of 8,550 megavolt amperes. Minnesota Power's transmission network is interconnected with the transmission grid to promote reliability and is part of a larger regional transmission organization called the Midwest Independent System Operator.