Modelling and analysis of 18-pulse rectification system for DC traction power substation

Abstract

Eighteen-pulse rectifier had been proposed to replace the conventional twelve-pulse rectifier as it may further minimize the ac and dc harmonics distortions. This paper presents a simulation study of implementing an eighteen-pulse rectification system for future dc traction power substation. A phase-shifting transformer with angle displacement of 0,-20, and +20 degrees and three unit of six-pulse diode rectifier are modelled and validated via simulation. The preliminary results had confirmed that this 18-pulse rectification system managed to keep the utility grid voltage and current distortion indexes at about 2% without employing any harmonic filters. However, approximately 1 MVar reactive power must be compensated. Thus, passive harmonics filters are proposed. Three major power quality improvements are observed via simulation after implementing these filters. Firstly, the instantaneous reactive power is kept within the bands of ± 0.12 MVar. Next, an approximate unity power factor can be seen from the grid system. Lastly, the grid voltage and current waveforms distortion are complied with IEEE standard for both normal and contingency operating condition.