When D.C. Traction Systems Meet HF Disturbances: The Best of Both Worlds?

Traditionally d.c. traction systems rely on insulated running rails used for traction return current, use unscreened cabling, and do not utilize a proper earthing strategy, due to fear for stray currents. This leads to systems which are very vulnerable to disturbances due to traction harmonics, or HF phenomena such as lightning, which quite often lead to availability problems. As railway systems are legacy systems, a change over to a modern earthing philosophy, which is needed in order to reach EMC, is quite often very difficult to implement. For a green field metro line in Doha, Qatar, however it was possible to develop and implement an earthing philosophy taking care of HF disturbances and of stray currents at the same time.