Keywords: rail transportation, power systems, harmonic analysis, voltage unbalance, power quality, harmonics, impact evaluation, single-phase traction load, voltage fluctuations, light flicker, flicker indicators, electric utility substation, electric railway systems, electrical transmission grid
Harmonics impacts evaluation for single-phase traction load
A planned electric utility substation supplying the single-phase traction load at New Haven, CT, USA was evaluated with regard to several important aspects of power quality. Harmonics: the trains are non-linear and time-varying loads. Harmonic current levels were measured at a nearby single-phase traction substation, which serves the same line as the future New Haven substation. These results show that the third harmonic current and the total demand distortion (TDD) exceed the limits recommended in IEEE Standard 519-1992, IEEE (1993), hereafter referred to as IEEE 519. Voltage unbalance: the traction load is supplied by two 15-MVA single-phase transformers, each connected across phases A–C of the 115-kV line. Measurement results at a nearby 115-kV substation indicate a voltage unbalance of less than 1%, which is well within acceptable limits. Calculations for the New Haven substation location similarly show a voltage unbalance of less than 1%, with a 15-MVA load. Voltage fluctuations: the variable traction load can introduce flicker, a voltage fluctuation, which produces annoying visual changes in the intensity of electric lights. The measurement results at the nearby 115-kV substation show both the short-term (Pst) and long-term (Plt) flicker indicators are well below the recommended limits of 1.0 and 0.8, respectively.