IEEE Electrification Magazine - September 2016 - 8

U
V
W
U
V
W

Three-Phase, 400-kV Utility Grid
Three-Phase,
110-kV, 50-Hz
Railway Distribution

Power Grid

A
B

G

C
I AB

Single-Phase,
25-kV, 50-Hz
Catenary

I CB

T1

i Tα

Figure 2. The connection of the 25-kV, 50-Hz railway supply to the
public grid. The catenary is fed sequentially from each phase of the
three-phase distribution network. G: generator.

T2

i Fa

iF β iT β
Traction Network

T
L1

compensators (SVCs) use thyristor-controlled reactors
and thyristor-switched capacitors. The SVCs are well
established but require large filters for the additional harmonics introduced by the thyristor switching. Alternatively, static synchronous compensators (STATCOMs) use
switch-mode converters to compensate for the reactive
power of single-phase transformers and to actively filter
the harmonics produced by the railway loads, with passive filters relatively smaller than those required by SVCs.
The STATCOMs can be connected to the three-phase grid
or the single-phase overhead line, and the topologies are
based on conventional two- or threelevel H-bridges. In East Asia, STATCOMs are used in conjunction with
V-V and Scott-connected transformers as railway power conditioners, as
shown in Figure 4. The converters are
single phase and inject currents in
parallel to the feeder transformers to
balance the power drawn from the
grid. An additional benefit of this
system is that it can also have the
function of an active power filter.
Because the converter is connected
between two consecutive phases of
the main supply, the neutral sections of the overhead
lines are still necessary.

F
Neutral Section
Figure 3. The V-V transformer connection with autotransformers
used in Japan and China.

Europe and China, increasing the power demand and,
therefore, the effect of the railway imbalance on the
utility grid. This is also further emphasized by the
stricter regulations on the imbalance introduced by the
owners of the utility grid.
Feeder stations with full-power
converters draw a nearly sinusoidal
balanced current at a near-unity
power factor. Therefore, they are
seen by the grid as balanced threephase loads and can draw power
from a lower-voltage bus. This not
only significantly reduces the cost
of the connection of the feeder station to the utility grid in terms of
equipment (e.g., less-expensive
sw i tchg e ar and m e asure m e n t
transformers) but also significantly
simplifies the location of the feeder stations on the
railway line since, very often, this is strictly related to
the location of the high-voltage transmission lines. As
the converter has fully controlled currents on the
three-phase side and a regulated voltage on the singlephase side, the utility grid can be fully isolated from
nonlinear traction loads, such as legacy locomotives
that use diode or thyristor rectifiers. The control of the
voltage on the single-phase side also allows the synchronization of the output voltages of multiple converters, thus creating a continuous overhead line
without neutral sections.
Because the output voltage is regulated, the effect of
the transformer output impedance can be mitigated.

Feeder stations with
full-power converters
draw a nearly
sinusoidal balanced
current at a nearunity power factor.

Full-Power Converter Solution
If the electrified line is supplied only by static frequency converters, they need to operate in all four quadrants and have adequate power ratings to supply the
full power required by the trains. However, not much
work has been done on static converters for 50-Hz railways, as the cost of active compensators like SVCs and
STATCOMs is significantly lower than that of full-size
converters because they have to be rated only for a
fraction of the power of the feeder station. This view is
changing as new high-speed lines are being built in

8

I E E E E l e c t r i f i cati o n M agaz ine / SEPTEMBER 2016

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R



Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2016

IEEE Electrification Magazine - September 2016 - Cover1
IEEE Electrification Magazine - September 2016 - Cover2
IEEE Electrification Magazine - September 2016 - 1
IEEE Electrification Magazine - September 2016 - 2
IEEE Electrification Magazine - September 2016 - 3
IEEE Electrification Magazine - September 2016 - 4
IEEE Electrification Magazine - September 2016 - 5
IEEE Electrification Magazine - September 2016 - 6
IEEE Electrification Magazine - September 2016 - 7
IEEE Electrification Magazine - September 2016 - 8
IEEE Electrification Magazine - September 2016 - 9
IEEE Electrification Magazine - September 2016 - 10
IEEE Electrification Magazine - September 2016 - 11
IEEE Electrification Magazine - September 2016 - 12
IEEE Electrification Magazine - September 2016 - 13
IEEE Electrification Magazine - September 2016 - 14
IEEE Electrification Magazine - September 2016 - 15
IEEE Electrification Magazine - September 2016 - 16
IEEE Electrification Magazine - September 2016 - 17
IEEE Electrification Magazine - September 2016 - 18
IEEE Electrification Magazine - September 2016 - 19
IEEE Electrification Magazine - September 2016 - 20
IEEE Electrification Magazine - September 2016 - 21
IEEE Electrification Magazine - September 2016 - 22
IEEE Electrification Magazine - September 2016 - 23
IEEE Electrification Magazine - September 2016 - 24
IEEE Electrification Magazine - September 2016 - 25
IEEE Electrification Magazine - September 2016 - 26
IEEE Electrification Magazine - September 2016 - 27
IEEE Electrification Magazine - September 2016 - 28
IEEE Electrification Magazine - September 2016 - 29
IEEE Electrification Magazine - September 2016 - 30
IEEE Electrification Magazine - September 2016 - 31
IEEE Electrification Magazine - September 2016 - 32
IEEE Electrification Magazine - September 2016 - 33
IEEE Electrification Magazine - September 2016 - 34
IEEE Electrification Magazine - September 2016 - 35
IEEE Electrification Magazine - September 2016 - 36
IEEE Electrification Magazine - September 2016 - 37
IEEE Electrification Magazine - September 2016 - 38
IEEE Electrification Magazine - September 2016 - 39
IEEE Electrification Magazine - September 2016 - 40
IEEE Electrification Magazine - September 2016 - 41
IEEE Electrification Magazine - September 2016 - 42
IEEE Electrification Magazine - September 2016 - 43
IEEE Electrification Magazine - September 2016 - 44
IEEE Electrification Magazine - September 2016 - 45
IEEE Electrification Magazine - September 2016 - 46
IEEE Electrification Magazine - September 2016 - 47
IEEE Electrification Magazine - September 2016 - 48
IEEE Electrification Magazine - September 2016 - 49
IEEE Electrification Magazine - September 2016 - 50
IEEE Electrification Magazine - September 2016 - 51
IEEE Electrification Magazine - September 2016 - 52
IEEE Electrification Magazine - September 2016 - Cover3
IEEE Electrification Magazine - September 2016 - Cover4
https://www.nxtbook.com/nxtbooks/pes/electrification_december2022
https://www.nxtbook.com/nxtbooks/pes/electrification_september2022
https://www.nxtbook.com/nxtbooks/pes/electrification_june2022
https://www.nxtbook.com/nxtbooks/pes/electrification_march2022
https://www.nxtbook.com/nxtbooks/pes/electrification_december2021
https://www.nxtbook.com/nxtbooks/pes/electrification_september2021
https://www.nxtbook.com/nxtbooks/pes/electrification_june2021
https://www.nxtbook.com/nxtbooks/pes/electrification_march2021
https://www.nxtbook.com/nxtbooks/pes/electrification_december2020
https://www.nxtbook.com/nxtbooks/pes/electrification_september2020
https://www.nxtbook.com/nxtbooks/pes/electrification_june2020
https://www.nxtbook.com/nxtbooks/pes/electrification_march2020
https://www.nxtbook.com/nxtbooks/pes/electrification_december2019
https://www.nxtbook.com/nxtbooks/pes/electrification_september2019
https://www.nxtbook.com/nxtbooks/pes/electrification_june2019
https://www.nxtbook.com/nxtbooks/pes/electrification_march2019
https://www.nxtbook.com/nxtbooks/pes/electrification_december2018
https://www.nxtbook.com/nxtbooks/pes/electrification_september2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2018
https://www.nxtbook.com/nxtbooks/pes/electrification_december2017
https://www.nxtbook.com/nxtbooks/pes/electrification_september2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2018
https://www.nxtbook.com/nxtbooks/pes/electrification_june2017
https://www.nxtbook.com/nxtbooks/pes/electrification_march2017
https://www.nxtbook.com/nxtbooks/pes/electrification_june2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2016
https://www.nxtbook.com/nxtbooks/pes/electrification_september2016
https://www.nxtbook.com/nxtbooks/pes/electrification_december2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2016
https://www.nxtbook.com/nxtbooks/pes/electrification_march2015
https://www.nxtbook.com/nxtbooks/pes/electrification_june2015
https://www.nxtbook.com/nxtbooks/pes/electrification_september2015
https://www.nxtbook.com/nxtbooks/pes/electrification_march2014
https://www.nxtbook.com/nxtbooks/pes/electrification_june2014
https://www.nxtbook.com/nxtbooks/pes/electrification_september2014
https://www.nxtbook.com/nxtbooks/pes/electrification_december2014
https://www.nxtbook.com/nxtbooks/pes/electrification_december2013
https://www.nxtbook.com/nxtbooks/pes/electrification_september2013
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