Control of Utility System Unbalance Caused by Single-Phase Electric Traction

In an electrified railroad the traction power is delivered to the catenary system by substations spaced along the route which, in turn, receive their supply from electric utility transmission systems. As the traction load is single-phase, the substations must be designed so that a minimum unbalance is caused on the utility three-phase system. First a brief overview is given of the unbalance theory, effects, limits, and protection. Secondly, a summary is provided of candidate designs to limit unbalance with a comparison of their effects on the utility system.