Analysis of voltage unbalance and mitigation of circulating power in bilateral co-phase traction system

Abstract

The primary aim of this paper is to analyse and mitigate the problems inherent in adopting bilateral co-phase traction network on Indian Railways. The reason for adopting bilateral co-phase traction network is to enhance regenerative braking energy (RBE) utilization in the railway traction network. There are two inherent problems in adopting bilateral co-phase traction configuration. First, it may lead to increase in the Voltage Unbalance factor (VUF) as single-phase loading by trains is effectively doubled across the same phases. Second, and more importantly, it may lead to flow of circulating power, under no load conditions, where power shall flow from leading voltage traction sub-station to lagging voltage traction sub-station. This may offset any advantage due to improved RBE utilization. This paper demonstrates through simulation, using realistic data from Indian Railways, that VUF stays within limits for bi-lateral traction configuration. It is important to mention that improved RBE utilization also plays a role in reducing VUF when there is no feedback of RBE to the grid. For the second problem, this paper takes inspiration from a control scheme existing in literature to adapt it to the proposed scenario. This scheme shows that it is possible to limit the power angle within 0.5˚ and thereby minimising circulating power.