Standard current and voltage settings for most high-speed rail
Railway electrification systems
using
alternating current
(AC) at
25
kilovolts
(kV)
are used worldwide, especially for
high-speed rail
. It is usually supplied at the standard
utility frequency
(typically 50 or 60
Hz), which simplifies traction substations. The development of 25
kV AC electrification is closely connected with that of successfully using utility frequency.
This electrification is ideal for railways that cover long distances or carry heavy traffic. After some experimentation before
World War II
in
Hungary
and in the
Black Forest
in
Germany
, it came into widespread use in the 1950s.
One of the reasons why it was not introduced earlier was the lack of suitable small and lightweight control and rectification equipment before the development of solid-state
rectifiers
and related technology. Another reason was the increased clearance distances required where it ran under bridges and in tunnels, which would have required major
civil engineering
in order to provide the increased
clearance
to live parts. Where pre-existing
loading gauges
were more generous, this was less of an issue.
Railways using older, lower-capacity
direct current
systems have introduced or are introducing
25 kV
AC instead of
3 kV
DC/
1.5 kV
DC for their new high-speed lines.
History
[
edit
]
The first successful operational and regular use of a utility frequency system dates back to 1931, tests having run since 1922. It was developed by
Kalman Kando
in Hungary, who used
16 kV
AC at
50 Hz
, asynchronous traction, and an adjustable number of (motor) poles. The first electrified line for testing was Budapest?Dunakeszi?Alag. The first fully electrified line was Budapest?Gy?r?Hegyeshalom (part of the Budapest?Vienna line).
[1]
Although Kando's solution showed a way for the future, railway operators outside of Hungary showed a lack of interest in the design.
The first railway to use this system was completed in 1936 by the
Deutsche Reichsbahn
who electrified part of the
Hollentalbahn
between Freiburg and Neustadt installing a 20
kV
50
Hz
AC
system. This part of Germany was in the French zone of occupation after 1945. As a result of examining the German system in 1951 the
SNCF
electrified the line between
Aix-les-Bains
and
La Roche-sur-Foron
in southern France, initially at the same 20
kV but converted to 25
kV in 1953. The 25
kV system was then adopted as standard in France, but since substantial amounts of mileage south of Paris had already been electrified at 1.5
kV
DC
, SNCF also continued some major new DC electrification projects, until dual-voltage locomotives were developed in the 1960s.
[2]
[3]
The main reason why electrification using utility frequency had not been widely adopted before was the lack of reliability of
Mercury arc rectifiers
that could fit on the train. This in turn related to the requirement to use
DC series motors
, which required the current to be converted from AC to DC and for that a
rectifier
is needed. Until the early 1950s, mercury-arc rectifiers were difficult to operate even in ideal conditions and were therefore unsuitable for use in railway locomotives.
It was possible to use AC motors (and some railways did, with varying success), but they have had less than ideal characteristics for traction purposes. This is because control of speed is difficult without varying the frequency and reliance on voltage to control speed gives a torque at any given speed that is not ideal. This is why DC series motors were the most common choice for traction purposes until the 1990s, as they can be controlled by voltage, and have an almost ideal torque vs speed characteristic.
In the 1990s, high-speed trains began to use lighter, lower-maintenance
three-phase
AC induction motors. The
N700 Shinkansen
uses a three-level converter to convert
25 kV
single-phase AC to
1,520 V
AC (via transformer) to
3 kV
DC (via phase-controlled rectifier with thyristor) to a maximum
2,300 V
three-phase AC (via a
variable voltage, variable frequency
inverter using
IGBTs
with
pulse-width modulation
) to run the motors. The system works in reverse for
regenerative braking
.
The choice of
25 kV
was related to the efficiency of power transmission as a function of voltage and cost, not based on a neat and tidy ratio of the supply voltage. For a given power level, a higher voltage allows for a lower current and usually better efficiency at the greater cost for high-voltage equipment. It was found that
25 kV
was an optimal point, where a higher voltage would still improve efficiency but not by a significant amount in relation to the higher costs incurred by the need for larger insulators and greater clearance from structures.
To avoid
short circuits
, the high voltage must be protected from moisture. Weather events, such as "
the wrong type of snow
", have caused failures in the past. An example of atmospheric causes occurred in December 2009, when
four Eurostar trains broke down inside the Channel Tunnel
.
Distribution
[
edit
]
Electric power for
25 kV
AC electrification is usually taken directly from the three-phase
transmission system
. At the transmission substation, a step-down
transformer
is connected across two of the three phases of the high-voltage supply and lowers the voltage to
25 kV
. This is then fed, sometimes several kilometres away, to a railway feeder station located beside the tracks.
Switchgear
at feeder stations, and at track sectioning cabins located halfway between feeder stations, provides switching to feed the overhead line from adjacent feeder stations if one feeder station loses grid supply.
Since only two phases of the high-voltage supply are used, phase imbalance is corrected by connecting each feeder station to a different combination of phases. To avoid the train pantograph bridging together two feeder stations which may be out-of-phase with each other,
neutral sections
are provided at feeder stations and track sectioning cabins.
SVCs
are used for load balancing and voltage control.
[4]
In some cases dedicated single-phase AC power lines were built to substations with single phase AC transformers. Such lines were built to supply the French
TGV
.
[5]
Standardisation
[
edit
]
Railway electrification using
25 kV
,
50 Hz
AC has become an international standard. There are two main standards that define the voltages of the system:
- EN
50163:2004+A1:2007 ? "Railway applications. Supply voltages of traction systems"
[6]
- IEC
60850 ? "Railway Applications. Supply voltages of traction systems"
[7]
The permissible range of voltages allowed are as stated in the above standards and take into account the number of trains drawing current and their distance from the substation.
Electrification
system
|
Voltage
|
Min.
non-permanent
|
Min.
permanent
|
Nominal
|
Max.
permanent
|
Max.
non-permanent
|
25
kV
50
Hz
|
17.5
kV
|
19
kV
|
25
kV
|
27.5
kV
|
29
kV
|
This system is now part of the European Union's Trans-European railway interoperability standards (1996/48/EC "Interoperability of the Trans-European high-speed rail system" and 2001/16/EC "Interoperability of the Trans-European Conventional rail system").
Variations
[
edit
]
Systems based on this standard but with some variations have been used.
25 kV AC at 60 Hz
[
edit
]
In countries where
60 Hz
is the normal grid power frequency,
25 kV
at
60 Hz
is used for the railway electrification.
20 kV AC at 50 or 60 Hz
[
edit
]
In Japan, this is used on existing railway lines in
Tohoku Region
,
Hokuriku Region
,
Hokkaido
and
Kyushu
, of which Hokuriku and Kyushu are at 60
Hz
.
12.5 kV AC at 60 Hz
[
edit
]
Some lines in the United States have been electrified at
12.5 kV 60 Hz
or converted from
11 kV 25 Hz
to
12.5 kV 60 Hz
. Use of
60 Hz
allows direct supply from the 60
Hz utility grid yet does not require the larger wire clearance for
25 kV 60 Hz
or require dual-voltage capability for trains also operating on
11 kV 25 Hz
lines. Examples are:
12 kV at 25 Hz
[
edit
]
6.25 kV AC
[
edit
]
Early 50
Hz AC railway electrification in the United Kingdom was planned to use sections at
6.25 kV AC
where there was limited clearance under bridges and in tunnels. Rolling stock was dual-voltage with automatic switching between
25 kV
and
6.25 kV
. The
6.25 kV
sections were converted to
25 kV AC
as a result of research work that demonstrated that the distance between live and earthed equipment could be reduced from that originally thought to be necessary.
The research was done using a steam engine beneath a bridge at
Crewe
. A section of
25 kV
overhead line was gradually brought closer to the earthed metalwork of the bridge whilst being subjected to steam from the locomotive's chimney. The distance at which a flashover occurred was measured and this was used as a basis from which new clearances between overhead equipment and structures were derived.
[
citation needed
]
50 kV AC
[
edit
]
Occasionally
25 kV
is doubled to
50 kV
to obtain greater power and increase the distance between substations. Such lines are usually isolated from other lines to avoid complications from interrunning. Examples are:
2 × 25 kV autotransformer system
[
edit
]
The 2 × 25
kV
autotransformer
system is a
split-phase electric power
system which supplies 25
kV power to the trains, but transmits power at 50
kV to reduce energy losses. It should not be confused with the 50
kV system. In this system, the current is mainly carried between the overhead line and a feeder transmission line instead of the rail. The overhead line (3) and feeder (5) are on opposite phases so the voltage between them is 50
kV, while the voltage between the overhead line (3) and the running rails (4) remains at 25
kV. Periodic autotransformers (9) divert the return current from the neutral rail, step it up, and send it along the feeder line. This system being initially deployed, in 1981, on France's then new
Paris-Lyon High speed rail line
,
[10]
and has gone on to be used by
New Zealand Railways
in 1988,
[11]
Indian Railways
,
[12]
Russian Railways
, Italian High Speed Railways, UK
High Speed 1
, most of the
West Coast Main Line
and
Crossrail
,
[13]
with some parts of older lines being gradually converted,
[
citation needed
]
French lines (LGV lines and some other lines
[14]
), most Spanish high-speed rail lines,
[15]
Amtrak
and some of the Finnish and Hungarian lines.
Boosted voltage
[
edit
]
For
TGV world speed record
runs in France the voltage was temporarily boosted, to 29.5
kV
[16]
and 31
kV at different times.
[17]
25 kV on broad gauge lines
[
edit
]
25 kV on narrow gauge lines
[
edit
]
Other voltages on 50 Hz electrification
[
edit
]
Multi-system locomotives and trains
[
edit
]
Trains that can operate on more than one voltage, say 3
kV/25
kV, are established technologies. Some locomotives in Europe are capable of using four different voltage standards.
[18]
See also
[
edit
]
References
[
edit
]
- ^
Hollingsworth, J. B.; Cook, Arthur F. (1998).
The great book of trains : featuring 310 locomotives shown in more than 160 full-colour illustrations and 500 photographs
. London: Salamander Books. pp. 254?255.
ISBN
0-86101-919-9
.
OCLC
60209873
.
- ^
Haydock, David (1991).
SNCF
. "Modern Railways" special. London: Ian Allan.
ISBN
978-0-7110-1980-5
- ^
Cuynet, Jean (2005).
La traction electrique en France 1900?2005
. Paris: La Vie du Rail.
ISBN
2-915034-38-9
- ^
SVCs for load balancing and trackside voltage control
, ABB Power Technologies.
[1]
Archived
2007-02-06 at the
Wayback Machine
- ^
TGV power
Archived
May 4, 2009, at the
Wayback Machine
- ^
British Standards Institution (January 2005).
BS EN 50163:2004+A1:2007 Railway Applications. Supply voltages of traction systems
.
doi
:
10.3403/30103554
.
- ^
IEC 60850
? "Railway Applications. Supply voltages of traction systems"
- ^
"Railroad Coordination Manual Of Instruction, Section 2.1.5 Deseret Power Railway"
(PDF)
. Utah Department of Transportation. May 2015. p. 102
. Retrieved
8 November
2016
.
- ^
"GF6C #6001 PRESERVED"
. West Coast Railway Association, BC. May 2004. Archived from
the original
on February 18, 2009
. Retrieved
2011-01-09
.
- ^
Courtois, C. (1993).
"Why the 2*25 kV alternative? (autotransformer traction supply)"
.
IEE Colloquium on 50kV Autotransformer Traction Supply Systems - the French Experience
: 1/1?1/4.
- ^
Tom McGavin (Autumn 1988). "North Island Main Trunk Electrified".
New Zealand Railway Observer
.
45
(1).
New Zealand Railway and Locomotive Society
: 49.
ISSN
0028-8624
.
- ^
"Ministry of Railways (Railway Board)"
.
indianrailways.gov.in
. Retrieved
2023-07-05
.
- ^
"Balfour Beatty gets £16m Crossrail substation contract"
.
www.theconstructionindex.co.uk
. Retrieved
2023-07-05
.
- ^
The remainder of the French lines use 1 × 25 kV booster-transformer system.
- ^
Comparative Study of the Electrification Systems 1×25 kV and 2×25 kV
(PDF)
(Report). Madrid:
Ineco
. June 2011
. Retrieved
2017-03-30
.
- ^
"The Test Tracks: an Overview"
.
- ^
"French Train Hits 357 MPH Breaking World Speed Record"
. 4 April 2007.
- ^
"Traxx locomotive family meets European needs"
.
Railway Gazette International
. 2008-01-07
. Retrieved
2019-09-27
.
Traxx MS (multi-system) for operation on both AC (15 and 25 kV) and DC (1·5 and 3 kV) networks
Further reading
[
edit
]
- Keenor, Garry. Overhead line electrification for railways.
- Boocock, Colin (1991).
East Coast Electrification
. Ian Allan.
ISBN
0-7110-1979-7
.
- Gillham, J.C. (1988).
The Age of the Electric Train ? Electric Trains in Britain since 1883
. Ian Allan.
ISBN
0-7110-1392-6
.
- Glover, John (2003).
Eastern Electric
. Ian Allan.
ISBN
0-7110-2934-2
.
- Machefert-Tassin, Yves; Nouvion, Fernand; Woimant, Jean (1980).
Histoire de la Traction Electrique, vol.1
. La Vie du Rail.
ISBN
2-902808-05-4
.
- Nock, O.S. (1965).
Britain's new railway: Electrification of the London-Midland main lines from Euston to Birmingham, Stoke-on-Trent, Crewe, Liverpool and Manchester
. London: Ian Allan.
OCLC
59003738
.
- Nock, O.S. (1974).
Electric Euston to Glasgow
. Ian Allan.
ISBN
0-7110-0530-3
.
- Proceedings of the British Railways Electrification Conference, London 1960 ? Railway Electrification at Industrial Frequency
. London: British Railways Board. 1960.
- Semmens, Peter (1991).
Electrifying the East Coast Route
. Patrick Stephens Ltd.
ISBN
0-85059-929-6
.
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