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Attempt to compare the different voltage systems

Plus (minus) signs mark (dis-) advantages of the system in this feature.

But the number of signs is not proportional to (dis-)advantage: "++" only means more favourable. Because most features are not comparable it's nonsence to sum up the signs!
Table by Jean-Franηois Bourdin


voltage system 750V1 1,5kV2 3kV3 15 kV4
16 2/3Hz
25 kV5
50/60Hz
50 kV
50/60Hz
"DB"6 "SJ"7 1x8 2x9
"fault" reason result
third rail impossible high voltage operation + +10 – – – – – –
third rail required high current
>voltage drop
indirect –11 + + + + + + +
difficult track maintenance third rail costs – + + + + + + +
heavy catenary high current costs –– – + + + + +
limited power low current operation ––––12 –– – + + + + +
contact interruptions third rail operation – + + + + + + +
limited speed third rail operation ––––
(160 km/h)13
+ + + + + + +
high current operation ––
(220 km/h)14
–
(250 km/h)15
+ + + + +
number of feeder stations16 voltage drop costs –––– –– – + + + ++ ++
feeder stations with converter:
direct current
costs – – – + + +
commutator:
special frequency
costs + –
seperate power generation special frequency costs + + + – + + + +
seperate high-voltage circuit special frequency costs + + + – + + + +
lenght of feeder lines number of feeder stations costs –––– –– – + + + ++ ++
transformers in vehicles alternating current space, costs + + + –17 – –
alternating current &
low frequency
–– ––
impedancy alternating current costs + + + – – –– –– ––
interchange18 with the public network using regenerative brakes direct current19 costs – – –
seperate network (–) + + + +
larger insulation clearances high voltage costs ++ ++ + – – – – ––


  1. Includes currencies between 600V and 900V.
  2. Includes currencies higher than 1200V.
  3. Includes currencies up to 3,6kV.
  4. Includes frequencies like 20Hz and 25Hz (a fraction of the common frequency)
  5. 50Hz or 60Hz depending on the common frequency. The current is 25kV almost everywhere. Two exceptions: The Japanese metric gauge network (20kV) and the network of the RWE Rheinbraun (6 kV) near Cologne.
  6. As an theoretical example using an independent high-voltage circuit, whereas a mixture with the "SJ"-solution is possible.
  7. As an theoretical example using an public high-voltage circuit, whereas a mixture with the "DB"-solution is possible.
  8. customary electrification
  9. electrification
  10. Chambéry-Modane (1,5kV) was a exception of long standing.
  11. Only valid for main lines.
  12. Eurostar on conventional track south of London.
  13. Lines London-Waterloo-Dover and London-Waterloo-Southampton.
  14. On the old line Tours-Bordeaux. With 270 km/h under a 1,5kV catenary the southbound end of the TGV-Atlantique line is a real exception.
  15. High-speed line from Rome to Florence.
  16. Depends on a high degree on the electrified network (how many adjacent substations can deliver the needed power in case of a breakdown) and the position of the feeder stations (in some cases it's cheaper to build them next to high-voltage circuit)
  17. One exception: RWE Rheinbraun used (still uses?) locomotives without transformers, whose rotating convertors were (are?) directly connected to the catenary (6kV).
  18. Exchange with the ordinary high-voltage network if no train is around.
  19. Traction substations have to be equipped with thyristors.

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