The Elephant and the Flea - Living with Traction Return Currents
Paul Szacsvay
Why is it the Signal Engineer's problem?
The nature of the problem
Voltage and Current Levels
Issues common to all
- Interference to signalling
- Immunisation of track circuits
- Traction return continuity
- Supply substation connections
Issues peculiar to DC traction
- High current levels
- Simple circuits, all supplies in parallel
- Current balancing
- Tying-in between tracks
- Thermal effects
- Longitudinal voltage drops
- Isolation from earth
- Electrolysis
Issues peculiar to AC Traction
- High voltage levels, lower currents
- Complex arrangements - 25-0-25, autotransformer
- Earthing of rails and trackside signalling equipment
- Immunisation of trackside signalling equipment
- Managing electromagnetic induction
Impacts on equipment design
- AC immunisation
- DC blocking.
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