Impact of Unbalance Single-phase Traction Load to Three-phase Power System

Abstract

The two most common types of supply for mass transit systems are 1.5 kV dc and 25 kV ac. This paper will firstly brief the relative merits of dc and ac traction systems. As the ac traction system is of single phase, imbalance in three-phase supply is inevitable and is an universal problem. With reference to the local 25 kV traction system, the paper will assess the degree of imbalances and the corresponding impacts at different phase connection scenarios. Cost-effective and pragmatic measures to reduce degree of imbalance by minor but appropriate modification of existing phase connections of traction transformers 132 kV will be proposed in this paper. Consequently, generation performance and efficiency are improved, unnecessary fuel consumption is reduced as much as possible, and the extra cost imposed to consumers at large would also be reduced.