Computer-based methods for induced-voltage calculations in AC railways

Calculations of induced voltage in metallic lineside cables have traditionally been made using simple methods based upon the explicit solution of transmission line equations. These methods were developed about 40 years ago with an emphasis on lead-sheathed cables which were in continuous contact with the ground. The authors review the limitations of the classical approach and conclude that in-section induced voltages are significantly overstated by this approach. An alternative computer-based approach is presented which is more appropriate for modern cables, with insulated outer sheaths, which are normally earthed by discrete earth-rod connections along the cable. This new approach, which is illustrated with reference to CAD techniques developed for autotransformer and booster-supplied AC railways, should permit a more realistic and economic approach to specifying screening requirements for copper cables. Examples of the use of the developed software for assessing induced voltages in the electrified 2×25 kV North Island Main Trunk in New Zealand are also presented