A method and apparatus are provided for differential protection of a three phase electric connection of an electric system. The apparatus includes means for determining a value of an operate quantity, which operate quantity is based on a difference between current quantities at a first point and a second point of the electric connection, and means for detecting a fault in the electric connection between the first point and the second point if the value of the operate quantity exceeds a value of a predetermined threshold quantity. The operate quantity is based on a difference of residual currents at the first point and the second point, or a quantity indicative thereof, and a coefficient indicative of an angle between a residual voltage of the electric connection and the difference of residual currents at the first point and the second point.