Comparison of Scott and Leblanc transformers for supplying unbalanced electric railway demands

Abstract

Abstract This paper presents a comparison of Scott and Leblanc transformers for supplying unbalanced electric railway demands mainly from the point of view of voltage imbalance. Feeding traction loads from the public power system may lead to some voltage imbalance on the latter and consequently affect the operation of its power supply system and other equipment connected with it. A Scott connection transforming a three-phase to a two-phase supply (or two single-phase supplies) can reduce the degree of the voltage imbalance due to large unbalanced railway demands and therefore is adopted in some railway power supply systems, particularly in systems with small short-circuit capacity. A Leblanc connection has the same effect but has not gained the same popularity as the Scott connection and is by no means so well known. The equivalent loads and formulas for estimating the voltage imbalance for these two connections are derived and compared in this paper. The results are of value to engineers and consultants working in the field to make a correct selection during periods of planning and design.