Rapid load variations can cause abrupt changes in the utility voltage, so-called voltage flicker. The voltage flicker may result in light flickering and, in extreme cases, damage to electronic equipment. Electrified railroads are just one example where such rapid load variation occurs as trains accelerate, decelerate, and encounter and leave grades. For balanced loads, the voltage flicker is easily determined using per-phase analysis. AC electrification system substations operating at a commercial frequency, however, are supplied from only two phases of utility three-phase transmission system. In order to calculate the voltage flicker for such an unbalanced system, symmetrical component method needs to be used. In this paper, a procedure is developed for evaluating the effects of short-time traction load variation onto utility system. Applying the symmetrical component method, voltage flicker equations are developed for loads connected to A-B, B-C, and C-A phases of a three-phase utility system. Using a specially-developed software simulating the train and electrification system performance, loads at the traction power substation transformers are calculated in one-second intervals. Subsequently, voltages at the utility busbars are calculated for each interval, and the voltage variation from interval to interval is expressed in percent. The calculated voltage flicker is then compared to the utility accepted limits. Based on this comparison, the capability of the utility power system to support the traction loads can be assessed and the suitability of the proposed line taps for the traction power substations evaluated.
Voltage flicker calculations for single-phase AC railroad electrification systems
2003-01-01
826199 byte
Conference paper
Electronic Resource
English
Voltage Flicker Calculations for Single-Phase AC Railroad Electrification Systems [IEEE]
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