Of Electrified Railway Liaocheng Grid

Electric railway is one important direction of railway construction in the world with the characteristics of high speed, strong carriage capability, long power support distance, energy conversation, low cost and good traction performance. With respect to the power system, the electric railway is special load with nonlinearity, and volatility. Massive harmonic and negative-sequence current is produced in power system, which is harm to power quality. Especially in the modern society with economic growth and High science and technology development, these negative effects become worse as the high requirement to power quality.The electrification of Beijing-Colon Railway is in connection with Liaocheng subsystem by Yangmiao traction substation and Shifo traction substation. It is necessary to study the effects of electric railway in Liaocheng subsystem in order to improve the electric railway efficiency.First, this paper presents the supply system and operation mode of electric railway. The mechanism of harmonic and negative currents in electric railway is illustrated in detail. Based on the standard indexes of power quality, proper methods are determined to analyzing the harmonic and negative currents, which is helpful to the quantization of electric railway effects.Corresponding to the practical Liaocheng subsystem, the main connections of Yangmiao traction substation and Shifo traction substation are introduced. In order to analyze the effects of electric railway in Liaocheng subsystem, the simulation model is established with considering short circuit capacity of traction substation based on commercial software of PSCAD. Comparisons of harmonic and negative-sequence currents in different cases are presented and the quantization of power quality are carried out based the given analysis methods. According to the characteristics of Liaocheng subsystem and the main connections of electric railway, several reasonable measurements are presents, such as the high-voltage power system in connection with traction substation, railway special transformer, back-to-back power supply mode and the application of SVC. These measurements are proved to be able to improve the power quality.The types of relay protection setting in electric railway are given according to the characteristics of practical. The equivalent model of V-V connection transformer in traction substation is established, which is effective to simulate the short circuit in low-voltage side of transformer. Combining with composite sequence nets figure and, the measurement impedance values of protective relaying equipment are calculated. Based on these impedance values, the principles are given in determining the practical relay protection settings.