PROBLEM TO BE SOLVED: To provide a device for controlling the changeover of power supplies for AC electric railroads capable of limiting overcurrent at the time when a changeover switch at the terminal station side is closed.
SOLUTION: This device is provided with a starting station side changeover switch 4 and a terminal station side changeover switch 5 connected parallel at a neutral section 3 where different power supplies are matched comprising a starting station side power supply 1 and a terminal station side power supply 2. By feeding power to a transformer provided inside an electric car 6 from either of these power supplies 1, 2 by alternately changing these changeover switches 4, 5, this device makes it possible to drive an auxiliary electric motor connected to the transformer. In this case, when the electric car is on the line of the neutral section 3, residual flux of the transformer inside the electric car 6 immediately before the changeover of the power supplies and its stable flux after the changeover are each calculated. A flux calculating means 10 is also provided which gives a closing command to the terminal station side changeover switch 5 when the difference between the calculated values is within a permissible range.