> Paper No 414 < 1 Analysis of Voltage Unbalance on Korean Railway System

Abstract—The railway characteristic, which is concerned, as most utilities is unbalance produced by the large single-phase loads. This paper presents two power quality issues in electrified railway, voltage unbalance and harmonics. For a useful method to estimate voltage unbalance, power simulation procedure is added to the conventional formula. The proposed method can be practically used and easily applied to evaluation of voltage unbalance indices. For a new model to analyze harmonics in 2×25kV traction power supply system including inverted feeder, contact line, rails and auto-transformer, the system model based on eight-port representation is derived which is an extension of two-port network theory. In order to verify the proposed approach, we have analyzed and tested real traction power feeding system focused on the amplification of harmonic current. The calculation results from the proposed approach and the measurement data from the test are widely discussed in the paper. Index Terms—Voltage unbalance, Four-port network model