A method to calculate circulating currents in the bars, especially double Roebel bars of the stator winding of synchronous machines is presented, different physical modeling is discussed, and results of calculations and measurements are explained. In synchronous machines, especially in large turbogenerators with direct water cooling of the stator winding, the bars consist often of two simple Roebel bars integrated in a double bar (twin bar). In these bars, circulating currents produce local losses which may lead to an overheating of the cooling medium. Double Roebel bars with cross transpositions avoid such overheating.