The influence of rotating machine design standards on the design of traction supplies

Railway traction loads, because they are single-phase, produce unbalanced currents which in turn cause unbalanced voltages in the supply system. Outages due to equipment failure or maintenance increase this unbalance. Of most concern is the effect of unbalanced voltages on three-phase rotating electrical machines which is examined by the author. The loads however draw fluctuating currents with the highest levels only occurring for relatively infrequent short periods and this needs to be considered in arriving at an economic solution to the problem. It is shown that the predominant effects are rotor and stator heating and that the performance limits are a function of time of application as well as absolute level