15 kV AC railway electrification
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The 15 kV, 16.7 Hz AC railway electrification system is used in Germany, Austria, Switzerland, Sweden and Norway. The high voltage enables high power transmission with low losses powering traction motors available since the beginning of the 20th century. Railway electrification in late 20th century tended to use 25 kV, 50 Hz AC systems which has become the preferred standard for new railway electrifications but extensions of the existing 15 kV networks are not completely unlikely.
Due to high conversion costs and little advantages it is unlikely that existing 15 kV, 16.7 Hz systems will be converted to 25 kV, 50 Hz.
History
The earliest electrification of railways used DC series-wound motors. Starting at 600 V these power trains were able to be pushed to a voltage of 1,500 V - railway electrification of 3 kV puts two of these DC motors in series. This is still a relatively low voltage to allow for long and heavy trains to be pulled so that research was performed on other traction motors that could be run with higher voltage. The AC 50 Hz power grid (60 Hz in the US) was already established at the beginning of the 20th century, however the universal motors AC motor type had flashover problems in the motor brushgear. Tests showed that the problems were reduced at lower frequencies, in particular the reduction of the reactive impedance of motor windings and the eddy current losses in non-laminated magnetic pole-pieces originally designed to work with DC. In the German-speaking countries it was decided to start high-voltage electrification running at exactly one third of the frequency of the national power grid being 50 Hz making for 16⅔ Hertz. The 15 kV AC power can be transformed to the motor voltage needed for a specific drive power.
In Austria, Switzerland and Germany (except Mecklenburg-Western Pomerania and Saxony-Anhalt), the railway power grid is run by separate power plants. For these countries, 16⅔ Hz is equivalent to 1,000 rpm in a two-pole electrical generator. The first generators were synchronous alternate current generators or synchronous transformers; however, with the introduction of modern double fed induction generators, there was a bad side-effect of inducing a low DC power from the control current. Since this led to problems overheating the pole, it was decided to move the frequency of these generators slightly off the ⅓ frequency - the choice of 16.7 Hertz is completely arbitrary (it was just required to have the new frequency within the input tolerance of the traction motors that did already exist). Austria, Switzerland and Southern Germany switched to the new nominal frequency beginning on 16 October 1995 at 12:00 CET for their power plants.[1][2] Note that regional electrified sections run by synchronous generators keep their frequency of 16⅔ Hz just as Sweden and Norway still run their railway networks at 16⅔ Hz throughout.
One of the disadvantages of 16.7 Hz locomotives as compared to 50 Hz or 60 Hz locomotives is the heavier transformer required to reduce the overhead line voltage to that used by the motors and their speed control gear. Low frequency transformers need to have heavier magnetic cores and larger windings for the same level of power conversion. (See effect of frequency on the design of transformers.) The heavier transformers also lead to higher axle loads than for those of a higher frequency. This, in turn, leads to increased track wear and increases the need for more frequent track maintenance. The Czech Railways encountered the problem of the reduced power handling of lower frequency transformers when they rebuilt some 25 kV AC, 50 Hz locomotives (series 340) to operate on 15 kV AC, 16.7 Hz lines. As a result of using the same transformer cores (originally designed for 50 Hz) at the lower frequency, the transformers had to be de-rated to one third of their original power handling capability, thereby reducing the available tractive effort by the same amount (to around 1,000 kW).
There are no longer any technical reasons for not using 50 Hz systems - the disadvantage of needing to create a separate supply infrastructure has inhibited the spread of the concept beyond the original five countries. Other countries that started their railway electrification process later used 50 Hz systems (or 60 Hz systems in the US) early on. Newer electrification in Europe is mostly 25 kV AC at 50 Hz. Switching to this voltage/frequency is inhibited by some minor problems: on the network side, all insulators of overhead lines need to be checked to allow for the higher voltage and the distance to bridges and other structures needs to be increased slightly. This is now standard for new overhead lines as well as for modernizing old installations.
Simple European standardization with an alignment of voltage/frequency across Europe is not necessarily cost-effective since trans-border transport is more limited by the differing national standards in other areas. To equip an electric locomotive with a transformer for two or more input voltages is cheap compared to the cost of installing multiple train protection systems and to run them through the approval procedure to get access to the railway network in other countries. However, some new high-speed lines to neighbouring countries are already intended to be built to 25 kV (e.g. in Austria to Eastern Europe). Newer locomotives are always built with asynchronous motor control systems that have no problem with a range of input frequencies including DC. However the Deutsche Bahn train operator does still use older models from the standard electric locomotive series - even though some are now as much as 50 years old. As soon as these obsolescent models are decommissioned, it will be easier to standardise, but this may take a few decades to happen. Meanwhile, the Deutsche Bahn tends to order train sets that are capable of running multiple electrification systems.
Distribution networks
In Germany (except Mecklenburg-Western Pomerania and Saxony-Anhalt), Austria and Switzerland, there are special power grids for single phase AC current at 16.7 Hz; the voltage of these grids is 110 kV in Germany and Austria and 132 kV in Switzerland. This system is called centralized railway energy supply.
In Sweden, Norway, Mecklenburg-Western Pomerania and Saxony-Anhalt, there are no special single phase power grids. The energy is taken directly from the three phase grid (110 kV at 50 Hz), converted to low frequency single phase and fed into the overhead line. This system is called decentralized railway energy supply.
Generation and conversion
There are two possibilities to supply the centralized system with electricity: either the energy is provided by a special power plant that generates 110 kV (or 132 kV in the Swiss system) AC at 16.7 Hz or the energy is taken from the national power grid (e.g. 110 kV, 50 Hz) and converted into 55-0-55 kV (or 66-0-66 kV) AC at 16.7 Hz by rotary machines or AC/AC converters. The 0 V point is connected to earth through an inductance so that each conductor of the single phase AC power line has a voltage of 55 kV (or 66 kV) with respect to earth potential. This is similar to split-phase electric power systems and results in a balanced line transmission. The inductance through which the earthing is done is designed to limit earth currents in cases of faults on the line. At the transformer substations, the voltage is transformed from 110 kV (or 132 kV) AC to 15 kV AC and the energy is fed into the overhead line.
Asynchronous converters
The frequency of 16.7 Hz depends on the necessity to avoid synchronism in parts of the rotary machine, which consists principally of a three phase asynchronous motor and a single phase synchronous generator. Since synchronism sets in at a frequency of 16⅔ Hz (according to the technical details) in the single phase system, the frequency of the centralized system was set to 16.7 Hz.
Power plants providing 110 kV, 16.7 Hz, are either dedicated to generating this specific single phase AC or have special generators for the purpose, such as the Neckarwestheim nuclear power plant or the Walchensee hydroelectric power station.
Synchronous converters
The power for the decentralized system is taken directly from the national power grid and directly transformed and converted into 15 kV, 16⅔ Hz by synchronous-synchronous-converters or static converters. Both systems need additional transformers. The converters consist of a three-phase synchronous motor and a single-phase synchronous generator. The decentralized system in the north-east of Germany was established by the Deutsche Reichsbahn in the 1980s, because there was no centralized system available in these areas.
Facilities for 15 kV AC railway electrification in Germany, Austria and Switzerland
Germany, Austria and Switzerland operate the largest interconnected 15 kV AC system, which uses central generation, central and decentral converter plants.
Germany
Substations
In these facilities electricity is transformed down from 110 kV-level of DB to 15 kV. There is no conversion or generation of power.
Switching stations
Switching stations without power conversion, generation or feeding in overhead wire
| Facility | Coordinates |
|---|---|
| Neckarwestheim | 49°2′34″N 9°12′6″E / 49.04278°N 9.20167°E |
| Nenndorf | 53°22′35″N 9°54′13″E / 53.37639°N 9.90361°E |
| Nitzahn | 52°27′35″N 12°20′45″E / 52.45972°N 12.34583°E |
| Schönarts | 49°57′46″N 9°49′08″E / 49.96278°N 9.81889°E |
Central converter plants
In these facilities AC from public grid is transformed into single phase AC and fed into traction current grid. At some facilities, power is also fed to overhead wire. Conversion is made by machines or in electronic way.
![[1]](http://www.elektrische-bahnen.de/history/images/DR_elektr_Netz_1943.jpg){kind=link}
Decentral converter plants
In these facilities AC from public grid is transformed into single phase AC and fed only in overhead wire. Conversion is made by machines or by electronic means.
Power plants
Border crossing powerlines
Germany - Austria
| Leitung | Coordinates |
|---|---|
| Walchenseekraftwerk - Zirl | 47°23′55″N 11°15′53″E / 47.39861°N 11.26472°E |
| Traunstein - Steinsdorf | 47°53′20″N 12°58′25″E / 47.88889°N 12.97361°E |
Former inner German border
| Leitung | Coordinates |
|---|---|
| Lehrte - Heeren | 52°24′48″N 10°59′34″E / 52.41333°N 10.99278°E |
| Bebra - Weimar | 51°00′29″N 10°12′13″E / 51.00806°N 10.20361°E |
| Steinfeld am Wald - Saalfeld | 50°27′52″N 11°25′07″E / 50.46444°N 11.41861°E |
Switzerland
Substations
In these facilities electricity is transformed down from 132 kV|66 kV-level of SSB to 15 kV. There is no conversion or generation of power.
Central converter plants
In these facilities AC from public grid is transformed into single phase AC and fed into traction current grid. At some facilities, power is also fed in overhead wire. Conversion is made by machines or on electronic way.
| Facility | Year of inauguration | Maximum transmission rate | Technology Used | Coordinates |
|---|---|---|---|---|
| Bever (RhB) | Rotary Converter | 46°32′52″N 9°53′17″E / 46.54778°N 9.88806°E | ||
| Landquart (RhB) | Rotary Converter | 46°58′28″N 9°33′6″E / 46.97444°N 9.55167°E | ||
| Giubiasco | Rotary Converter | 46°10′32″N 9°0′9″E / 46.17556°N 9.00250°E | ||
| Kerzers | Rotary Converter | 46°58′27″N 7°11′25″E / 46.97417°N 7.19028°E | ||
| Massaboden | Rotary Converter | 46°19′55″N 8°0′42″E / 46.33194°N 8.01167°E | ||
| Rupperswil | Rotary Converter | 47°24′21″N 8°6′19″E / 47.40583°N 8.10528°E | ||
| Seebach | Rotary Converter | 47°25′20″N 8°33′17″E / 47.42222°N 8.55472°E | ||
| Wimmis | Rotary Converter | 46°40′51″N 7°39′23″E / 46.68083°N 7.65639°E |
Switching stations
Switching stations without power conversion, generation or feeding in overhead wire
| Facility | Coordinates |
|---|---|
| Zollikofen | 47°0′45″N 7°27′53″E / 47.01250°N 7.46472°E |
Power plants
| Facility | Year of inauguration | Maximum Power |
Technology Used | Coordinates |
|---|---|---|---|---|
| Amsteg | 1922 | 55 MW | Hydroelectric Power Plant | 46°46′4″N 8°40′18″E / 46.76778°N 8.67167°E |
| Le Châtelard VS | Hydroelectric Power Plant | 46°3′41″N 6°57′29″E / 46.06139°N 6.95806°E | ||
| Etzelwerk | Hydroelectric Power Plant | 47°11′42″N 8°48′42″E / 47.19500°N 8.81167°E | ||
| Göschenen | Hydroelectric Power Plant | 46°40′2″N 8°35′3″E / 46.66722°N 8.58417°E | ||
| Klosters | Hydroelectric Power Plant | 46°51′39″N 9°53′44″E / 46.86083°N 9.89556°E | ||
| Gösgen | 51,3 MW | Hydroelectric Power Plant | 47°22′8″N 7°58′47″E / 47.36889°N 7.97972°E | |
| Massaboden | 1916 | 7,2 MW | Hydroelectric Power Plant | 46°19′55″N 8°0′42″E / 46.33194°N 8.01167°E |
| Mühleberg | 1921 | 45 MW | Hydroelectric Power Plant | 46°58′9″N 7°17′4″E / 46.96917°N 7.28444°E |
| Ritom | 1920 | Hydroelectric Power Plant | 46°31′2″N 8°40′33″E / 46.51722°N 8.67583°E | |
| Rupperswil | 1945 | Hydroelectric Power Plant | 47°24′42″N 8°6′52″E / 47.41167°N 8.11444°E | |
| Vernayaz | Hydroelectric Power Plant | 46°8′3″N 7°2′10″E / 46.13417°N 7.03611°E | ||
| Wassen | Hydroelectric Power Plant | 46°42′56″N 8°36′36″E / 46.71556°N 8.61000°E |
Border crossings
Germany-Switzerland
| Leitung | Coordinates |
|---|---|
| Holdingen - Muttenz | 47°34′53″N 07°36′14″E / 47.58139°N 7.60389°E |
| Singen - Etzwilen | 47°42′49″N 08°49′52″E / 47.71361°N 8.83111°E |
Austria
Substations
In these facilities electricity is transformed down from 110 kV-level of OBB to 15 kV. There is no conversion or generation of power.
Central converter plants
In these facilities, AC from the public grid is transformed into single phase AC and fed into the traction current grid. At some facilities, power is also fed to overhead wires. Conversion may be performed mechanically or electronically.
| Facility | Year of inauguration | Power | Maximum transmission rate | Coordinates |
|---|---|---|---|---|
| Auhof | 1956 | 90 MW | 48°12′00″N 16°14′12″E / 48.20000°N 16.23667°E | |
| Bergern | 1983 | 48°13′3″N 15°16′17″E / 48.21750°N 15.27139°E | ||
| Haiming | 1995 | 47°14′47″N 10°52′27″E / 47.24639°N 10.87417°E | ||
| Kledering | 1989 | 48°8′21″N 16°25′56″E / 48.13917°N 16.43222°E | ||
| Sankt Michael | 1975 | 47°21′27″N 15°0′9″E / 47.35750°N 15.00250°E |
Power plants
| Facility | Year of inauguration | Power | Type of power plant | Coordinates |
|---|---|---|---|---|
| Annabrücke | 20 MW | Hydroelectric Power Plant | 46°33′39″N 14°28′46″E / 46.56083°N 14.47944°E | |
| Braz | 1954 | 20 MW | Hydroelectric Power Plant | 47°8′0″N 9°56′45″E / 47.13333°N 9.94583°E |
| Enzigerboden | 20 MW | Hydroelectric Power Plant | 47°10′10″N 12°37′36″E / 47.16944°N 12.62667°E | |
| Fulpmes | 1983 | 15 MW | Hydroelectric Power Plant | 47°9′30″N 11°21′29″E / 47.15833°N 11.35806°E |
| Obervellach | Hydroelectric Power Plant | 46°56′13″N 13°11′29″E / 46.93694°N 13.19139°E | ||
| Schaltposten Schönberg | Hydroelectric Power Plant | 47°12′02″N 11°23′29″E / 47.20056°N 11.39139°E | ||
| Sankt Pantaleon | Hydroelectric Power Plant | 48°13′29″N 14°31′50″E / 48.22472°N 14.53056°E | ||
| Schneiderau | Hydroelectric Power Plant | 47°11′50″N 12°36′28″E / 47.19722°N 12.60778°E | ||
| Spullersee | 1925 | 36 MW | Hydroelectric Power Plant | 47°7′58″N 10°3′16″E / 47.13278°N 10.05444°E |
| Steeg | 1910 | Hydroelectric Power Plant (only direct fed of overhead wire) | 47°36′29″N 13°37′57″E / 47.60806°N 13.63250°E | |
| Uttendorf | Hydroelectric Power Plant | 47°15′43″N 12°34′3″E / 47.26194°N 12.56750°E | ||
| Weyer | Hydroelectric Power Plant | 47°51′07″N 14°38′19″E / 47.85194°N 14.63861°E |
See also
- Electric power supply system of railways in Norway
- Electric power supply system of railways in Sweden
- List of installations for 15kV AC railway electrification in Germany, Austria and Switzerland
- List of current systems for electric rail traction
- Category:15 kV AC locomotives
- 25 Hz Power Transmission System
- 25 kV AC railway electrification
- Traction power network
References
- ^ Bahnstromsystem (German) railway electrification systems
- ^ C. Linder (2002), "Umstellung der Sollfrequenz im zentralen Bahnstromnetz von 16⅔ Hz auf 16,70 Hz (English: Switching the frequency in train electric power supply network from 16 2/3 Hz to 16,70 Hz)", Elektrische Bahnen (in German), vol. Book 12, Munich: Oldenbourg-Industrieverlag, ISSN 0013-5437