Electrification - Circuit Diagrams
Shown below are three schematic circuit diagrams for electrification systems used on IR. These show the power flow from the 25kV AC catenary through the locomotive. Also see the traction power supply feeding schematic for the details of the circuit between the regional high-voltage grid and the 25kV catenary. For more information on this and related topics, see the FAQ sections on electric traction and electric locomotives.
The first figure shows a simple feeding system. Catenary current Ic is returned as rail current IR and earth currents IE.
The second figure shows the use of booster transformers to force return current through a separate return conductor instead of through the rails or earth. Insulated rail joints ensure that currents flow in the rails only in occupied track sections. Inductive interference is reduced since the return wire is close to and parallel to the catenary.
The third figure shows an auto-transfomer system (also known as the 3-wire system or 2x25kV system). Inductive interference is reduced as the negative phase feeder and catenary carry equal but opposite currents and are close to each other and parallel. The supply voltage to the locos can be kept close to the 25kV figure by tap changers on the autotransformers. (Note: In the autotransformer case the currents drawn do not have to be symmetric across the autotransformers on the left and right of the loco -- they can vary, as long the currents add up to half the current drawn by the loco.)