ANALYSIS MODEL FOR HARMONIC STUDY ON KOREAN RAILWAY SYSTEM

초록

In recent yaears, the AC electric railway in Korea has progressed rapidly. KTX(Korea Train Express) runs in 300 kilometers per hour. Korea has become the 5th nation to manufacture and high-speed railway technology. Up to the end of 2010, the rate of electrification will be 70%. A lot of AC electric vehicles as well as KTX will run on the AC electric railway in Korea. AC electric vehicles controlled by thyristor or PWM(Pulse Width Modulation) line side converters inject harmonic current into the feeding overhead line. As the feeding circuit is a distributed constant circuit composed of RLC, the capacitance and the inductance of the feeding circuit on the side of power system cause a parallel resonance and a amplification of harmonic current at a specific frequency.The amplified harmonic current usually brings about various problems. That is, the current harmonics makes interference in the adjacent lines of communications and the railway signaling system. Furthermore, in case it flows on the side of power system, not only overheating and vibration at the power capacitors but also wrong operation at the protective devices can occur. Therefore, the exact assessment of the harmonic current flow must be undertaken at design and planning stage for the electric traction systems. The harmonic current flows through the catenary system, we should get the line constants of the catenary system to analyze and to assess the harmonic effect on the power feeding system. First of all, the assessment of the line constants should be calculated to get the values. The catenary system is very complex with about 14 conductors. However, if we do observe the catenary system detail, we can find out the fact that some conductors are connected. We might think like one conductor electrically about physically connected some conductors. The catenary system is regarded as 5 conductors. Therefore, the line constants of 5 conductors are supposed to be calculated by the reduction method of line constants to analyze the amplification of harmonic current. From this point of view, this study presents an approach to model and to analyze Korean high-speed railway system focused on the amplification of harmonic current with the exact model of the catenary system. The system model for the harmonic studies is made by the PSCAD/EMTDC. This is the professional’s simulation tool for analyzing power systems. PSCAD is the graphical user interface and EMTDC is the simulation engine. PSCAD/EMTDC is most suitable for simulating the time domain instantaneous responses, also popularly known as electromagnetic transients of electrical systems. When run under the PSCAD graphical user interface, the PSCAD/EMTDC combination becomes a powerful means of visualizing the enormous complexity of portions of the electric railway system[1]. Aggregating subsystems composes overall system. Representation of each component by the PSCAD/EMTDC is many advantages. The catenary system, which have impedances and shunt admittances, can be easily represented. Distributed circuit parameters for the line model can be defined. The entire system can be easily modeled by the combination of each component in parallel and/or series. The proposed model is applied to Korean high-speed railway system for the harmonic studies. We have analyzed and tested this system focused on the amplification of harmonic current. The simulation results of the proposed model and the measurement data from the test are compared in this paper."