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-FranÃ§ois 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	+	+	+	+	+	+	+
limited speed	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	–	–	–			+	+	+
feeder stations with	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	–	–
transformers in vehicles	alternating current & low frequency	space, costs				––	––
impedancy	alternating current	costs	+	+	+	–	–	––	––	––
interchange¹⁸ with the public network using regenerative brakes	direct current¹⁹	costs	–	–	–
	seperate network	costs				(–)	+	+	+	+
larger insulation clearances	high voltage	costs	++	++	+	–	–	–	–	––

Includes currencies between 600V and 900V.
Includes currencies higher than 1200V.
Includes currencies up to 3,6kV.
Includes frequencies like 20Hz and 25Hz (a fraction of the common frequency)
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.
As an theoretical example using an independent high-voltage circuit, whereas a mixture with the "SJ"-solution is possible.
As an theoretical example using an public high-voltage circuit, whereas a mixture with the "DB"-solution is possible.
customary electrification
electrification
Chambéry-Modane (1,5kV) was a exception of long standing.
Only valid for main lines.
Eurostar on conventional track south of London.
Lines London-Waterloo-Dover and London-Waterloo-Southampton.
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.
High-speed line from Rome to Florence.
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)
One exception: RWE Rheinbraun used (still uses?) locomotives without transformers, whose rotating convertors were (are?) directly connected to the catenary (6kV).
Exchange with the ordinary high-voltage network if no train is around.
Traction substations have to be equipped with thyristors.

page last updated: 26. March 2018



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