Simulation Of Electrified Railway Traction Power Supply System

Because of a series of advantages such as large transport capacity, high driving speed, low energy consumption, low operating costs as well as good working conditions, the electric locomotive has gradually replaced steam locomotive, diesel locomotive, and has become the main development direction of railway transport. However, the use of a large number of electric locomotives, bring new problems to the electric power system.Most of the electric locomotives, used in our country's existing electrified railway, are Shaoshan series single-phase AC-DC drive electric locomotives, which are kinds of typical rectifier loads. While drawing base frequency current from the electric power system, the electric locomotive will also inject a large number of harmonic current and negative sequence current into the system during operation, which leads to the system voltage waveform distortion and brings adverse impact to the system as well its users. Therefore, it is necessary to study the electric power system harmonic problems caused by the electrified railway traction load.In this paper, the simulation model of the traction power supply system is constructed, then, the impact of the electrified railway traction load on the power system is analyzed based on the simulation. The details are as follows:(1) The simulation models for five kinds of commonly used traction transformers wired in different types including single-phase wiring, Yn/d11 wiring, V/v wiring, impedance matching balanced wiring and Scott wiring are established. The simulation results under constant resistive load conditions verify the correctness of the proposed model.(2) The simulation model for the electric locomotive based on SS6 B type is established. A set of custom modules, according to characteristics of locomotive traction control function and the relationship between the trigger angle and the rectifier circuit are set up to solve the thyristor trigger angle. A dynamic simulation of the electric locomotive at different class position, different speed is achieved. The work of the rectifier circuit correspond to the electric locomotive at five different class position, different speed is simulated. Through the waveform analysis and the comparison between the theoretical calculations and the simulation output, the validity of the locomotive model is verified. An FFT analysis of the locomotive current is conducted,and the RMS value of the fundamental and harmonic current injecting into the traction network is obtained.(3) The simulation model for the traction power supply system is established. The harmonic current and the negative sequence current injecting into the electric power system, produced by the traction load under different power supply mode (i.e. different traction transformer wiring), are obtained based on the simulation. The power quality of 110kV system including THD (short for the total harmonic distortion), HRU (short for harmonic ratio of voltage) and imbalance degree are analyzed. Simulation for the power supply system under symmetrical load (each power supply arm has one locomotive, and the two locomotives of the two arms run at the same class position and speed) and asymmetric load conditions is conducted. It is concluded that the total voltage harmonic distortion and the imbalance degree at the system side caused by traction load is getting smaller with the transformer wired in this order: single-phase wiring, Yn/d11 wiring, V/v wiring, impedance matching balanced wiring and Scott wiring.(4) The measured waveform of a single-phase wiring traction substation in Shanxi region is analyzed. The 110kV line's total voltage harmonic distortion and the voltage imbalance degree, as well as its 3rd, 5th, 7th harmonic voltage ratio have all exceeded the national standards limits. The comparison between the simulation data and the measured data shows that the simulation data is reasonable.(5) Both the simulation data and the measured data show that the traction loads can bring the electrical power system adverse effects. Therefore, the improvement measures are proposed. The simulation combined with the filtering measure is conducted for the single-phase wiring power supply system. The simulation results show that the 3rd, 5th, 7th and 9th harmonic current are significantly reduced after the filter device is connected. The total voltage harmonic distortion and the harmonic ratio also meet the requirements of the national standards.In this paper, the upwards five kinds of traction power supply system wired in different type are analyzed in details. The simulation results provide a theoretical basis for further research on the effects and the improvement measures of the traction loads.