| Analysis and Calculation of Short-circuit fault for urban rail transit was used to improve the ability of safe operation of traction power supply system and was the basis for protection and control technology.First of all, the model of DC traction power supply system was established in this paper. Rectifier unit was equivalent to a voltage source with internal resistance and steady-state short-circuit current was calculated with using the external characteristics of rectifier unit.Analysis and calculation of transient short-circuit current, close-up short-circuit faults are characterized by a high rate of current and a high prospective peak fault current. It is significant to research the close-up short circuit transients on DC supplied railways. In this paper, approximate expression of the dc short-circuit current for close-up fault was derived. Then the accuracy of calculation methods was verified by modeling. Calculating Remote short circuit fault current, one must consider that the electrical parameters vary with current. The series resistance and inductance of steel rails varies with frequency owing to the skin effect because they are large magnetic conductors. In this paper, the equivalent cylindrical conductor model has been proposed to calculate transient impedance of track circuits. External inductance reflected effects of the external magnetic field surrounding track was consisted of magnetic field of external to the rail cross-linking with the current. When the geometrical arrangement of the track and the external installation environment was determined, external inductance also was determined. In the remote fault case, the impedance of the contact line and rails together tends to limit both the rate of rise of current and the peak current. The peak fault current were disappeared with increase of the fault distance. It was shown that a simple DC power source model of rectifier was appropriate for remote fault current calculation and the detailed model was not used.
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