AC Systems at Mains Frequency

The structure of the power supply system is conditioned to limit the unbalances it creates on the high‐voltage network from the withdrawal of energy in single‐phase electric traction of 25 kV‐50 Hz, and to give maximum operational continuity to traction power substations (TPSSs). During the first French 50 Hz single‐phase electrification, the unbalance problem was solved by implementing the Scott connection for the substation. This chapter presents the diagram of a substation with two transformers with V connections, assuming that the TPSS is powered by two primary independent three phases, each protected by an automatic triple‐pole switch. It then discusses the study of power flow in the system, which involves verifying the actual distribution of the current between the various branches of the 2 × 25 kV system, in the free sections and in those occupied by trains.