Return Circuit, Earthing, EMC
The combination of mechanical, electrical, and electronic aspects come together in the return circuit, earthing and electromagnetic compatibility
Apart from their mechanical guidance function tracks also serve the return of traction current. As a result of the expansion of high-speed traffic and increasing transport in densely populated areas special measures are necessary to guarantee safety to persons and protection of equipment. The introduction of modern information technology raises questions regarding electromagnetic compatibility (EMC).
Apart from their mechanical guidance function, the tracks also serve to return the traction current. They are thus part of the complete electrical traction system. As a result of the galvanic, inductive and capacitance effects of the electrical conductors in the traction electricity circuit, unwanted effects may arise in the railway system, which could lead to inadmissible touch voltages or induced longitudinal voltages in parallel facilities or structures. Safety and protection of both people and facilities must be ensured.
In the case of d.c. railway systems, controlling stray currents is of vital importance. Measures have to be taken that securely eliminate the possibility of hazards and influences and that protect adjacent equipment. Special attention must be paid, for example, to the electrical characteristics of the tracks and the metallic equipment attached to it.
As a result of the expansion of high-speed traffic and increasing the transport provided in densely populated areas (for example when railway rolling stock crosses over onto tram rails) d.c. and a.c. supplies come into direct contact with each other or are operated in parallel. Owing to significant differences in the way return circuits are dealt with and the fact that voltages and currents of different frequencies with varying levels of harmonic distortion come into contact, special solutions have to be developed and implemented.
Special measures are necessary to guarantee safety to persons and protect equipment with regard to overhead contact lines and current collectors. These concern not only the electrical equipment, but also structural elements that conduct electricity, such as steel supports and reinforcement in concrete structures, fences and barriers, cable canals and covers, as well as water supply and waste pipes. Regular close coordination with the expert personnel involved and affected is necessary. The measures taken for a.c. and d.c. railway systems differ. Special expertise is indispensible for the engineering work required in connection with this.
The introduction of modern information technology and systems for feeding power into a.c. and d.c. railway systems has raised questions regarding the electromagnetic compatibility (EMC) of equipment. Special measures allow the influences to be minimized and the hazards eliminated.
KEMA has developed a special software tool IMAFEB/ELEFEB to calculate these effects. The KEMA staff is highly specialised to answer all possible questions regarding return circuit, earthing and EMC.