AT power supply system of electrified railway

The invention relates to an AT power supply system of an electrified railway, which comprises the following: an output end of a 55Kv traction transformator submargin of a traction substation is connected with contact wires of a railway traction network, the other output end thereof is connected with negative feeder of the railway traction network; autotransformers are set in the railway traction network every 10-20 km, the autotransformer near to the traction transformator is 5-15 km away from the traction transformator; one end of the autotransformer is connected with the contact wire of the railway traction network, a midpoint thereof is connected with rails, and the other end is connected with negative feeder of the railway traction network. The output of the traction transformator is not provided with an autotransformer, thus reducing investment; no midpoint tap is mounted on the traction transformator so as to avoid arranging rail return feeder for the traction substation, thus simplifying manufacturing