Starting Wednesday, the electric cooperative United Power will officially cut the cord from Tri-State Generation and Transmission, the multi-state utility that has kept the electrons flowing to the Brighton-based company for about 70 years. The departure follows years of conflicts between the cooperative and Tri-State over the power supplier’s rates, what critics considered an over-reliance on coal and restrictions on how much power members like United Power could generate on their own. United Power, Tri-State’s largest member, sued Tri-State over the addition of new members it believed were being used to stack the deck for Tri-State leaders.