Study On The All-Parallel Direct Traction Power Supply System

At present, the direct power supply and the AT power supply are the main styles of the existing railways. All-parallel AT power supply can effectively reduce the energy loss and improve the voltage level of the traction network. Therefore, it is necessary to research on the all-parallel direct power supply and it is also meaningful to find a good effective method to reduce the energy loss with less investment.Based on the principle of direct power supply, this paper deduces the equivalent model of the single line way of direct power supply system with return line and the double lines way of all-parallel direct power supply system with return line, and also deduces the calculations of the short circuit impedance, current distribution and voltage loss.This paper mainly aims at the double lines way of all-parallel direct power supply system, and builds the model via the Platform of Matlab/Simulink. It demonstrates the correctness of the equivalent model through the simulation results of the short circuit impedance. Then it analyzes the all-parallel method through two aspects of traction network voltage loss and current-carrying capacity. Firstly it analyzes the relationship between different parallel-position or different parallel-number and the traction network voltage loss through the simulation in the case of different load. And then using one parallel-number at centre as an example, it analyzes the relationship between the percentage of each current in traction network and different parallel-position in the case of different load.This paper analyzes the reason that the original protection scheme may be failure to the traction network fault of all-parallel direct power supply system and also points out the shortage of the existing protection scheme. Based on the characteristics of short current and normal current, also combined with the current-rising-rate (di/dt) protection and current increment ((?)I) protection, this paper put forward a novel protection scheme that sets a protection which based on discrimination of current characteristic quantity at the parallel-station, and then put forward the novel protection process with different short position, finally gives the setting principle of each protection.At last, it builds the model via the Platform of Matlab/Simulink and calculats the set value of each protection in the new scheme. The simulation result shows that the novel protection scheme is feasible.