Note: Descriptions are shown in the official language in which they were submitted.
PROTECTIVE DEVICE FOR PROTECTING AN ELECTRICAL TRACK-
FIELD INFRASTRUCTURE, TRACK-FIELD POWER SUPPLY APPARATUS
AND METHOD FOR LIMITING POTENTIAL SHIFTS IN AN ELECTRICAL
TRACK-FIELD INFRASTRUCTURE
BACKGROUND OF THE INVENTION
[0001] The invention relates to a protective device for protecting an
electrical
track-field infrastructure from AC interference voltages, a track-field power
supply apparatus and method for limiting potential shifts in an electrical
track-
field infrastructure comprising a feed, at least one DC supply line and at
least
one protective device and a method for limiting potential shifts in an
electrical
track-field infrastructure.
[0002] Track-field power supply apparatus for supplying field elements (loads
in the track-field) is known from EP 3 247 015 Al [1].
[0003] For driving operation by means of electrical traction, a contact wire
system consisting of a substation feed, switching points, masts and a contact
wire (overhead line) is set up along the path. This means that a galvanically
connected, low-impedance line is present along the route. In the case of
electric traction operation, in many European countries the overhead line for
the driving current is supplied with a single-phase AC voltage from a
substation
with 15 kV 16.7 Hz. In practice, the return current is approximately 1/3 via
the
rail, 1/3 via a return conductor (ground cable) and to 1/3 via the ground.
[0004] The feed sections for the contact wire can be 10 to 20 km long,
depending on the design. The interference is therefore carried over long
distances (feed sections). The linear current-bearing elements (contact wire,
rail and ground cable) form a single-wind transformer with respect to the
cables
of the rail safety technology, which are located in the cable channels (cable
trough) guided in parallel. Magnetic fields which induce voltages and currents
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Date Recue/Date Received 2023-06-28
in metallic contact parts are formed between the contact wire and the reverse
current-carrying conductors. One speaks of interference voltages and
currents. Particularly affected are longitudinally guided conductors along the
rail section, e.g., cables of the power supply and control for field elements
of
the conducting and safety technology.
[0005] By means of interference voltages, potential shifts occur, wherein
"potential shifts" are understood to include shifts of the absolute voltage
relative to ground potential caused by the superposition of induced AC voltage
components on a static DC feed.
[0006] A further critical case in which the highest interference voltages
arise is
the "driving line short circuit." A driving line short circuit is produced in
most
cases by a contact wire falling down on the rail, for example by fallen trees,
icing and structural damage to the masts. The duration of these short-circuit
currents is 1-2 periods of the 16.7 Hz power supply, i.e., 60-120
milliseconds,
depending on the switchgear assembly.
[0007] In directive 819.0804 of DB [2], 250 VAC are specified for long-term
interference (driving operation) and 1500 VAC for short-term interference
(drive line short circuit) as limit values for the system protection. Because
the
interference voltage is dependent on the interference length, a galvanic
separation of the power supply and control lines is provided in known track-
field installations at certain distances (control distances) in order to
ensure that
these values are not exceeded. The distances of the galvanic separations
(control distances), which are relevant in this context in the case of railway
systems, are typically approximately 2.5 km, in the maximum case up to 6.5
km. This galvanic isolation occurs with AC lines by means of transformers and
in DC lines by means of longitudinal voltage decouplers (LSE) [3], [4]. A
disadvantage of this is the high technical effort for the potential-free power
transmission with the associated monitoring apparatus in a switch cabinet on
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Date Recue/Date Received 2023-06-28
the route. The additional apparatus further reduces the availability of the
overall installation.
[0008] The power supply apparatus known from [1] comprises a 2-pole bus
line segmented by load bus coupling elements with a positive and a negative
line conductor. The loads are connected to the bus line via the load bus
coupling elements. The energy is supplied via at least one feed bus coupling
element. The two line conductors have a low impedance to one another (feed)
and are operated with DC voltage. The power supply apparatus known from
[1] is an Isolee Terre (IT) system. A limitation of the superimposed
interference
voltage takes place by limiting the galvanically connected cable length
(interference length) and/or by using expensive reduction cables, which reduce
the inductive coupling by a special cable sheath structure. An interference
voltage therefore effects a superimposition of the induced AC contact wire
voltage on the DC power supply voltage.
OBJECT OF THE INVENTION
[0009] The object of the invention is to propose a protection device, a track-
field power supply apparatus and a method which enable a limitation of
potential shifts in an electrical track-field infrastructure, in particular
also for
use in a DC energy bus.
DESCRIPTION OF THE INVENTION
[0010] This object is achieved according to the invention by a protective
device
according to claim 1, a track-field power supply apparatus according to claim
5 and a method according to claim 16.
[0011] The protective device according to the invention for protecting an
electrical track-field infrastructure from AC interference voltages comprises:
a
line conductor which is at positive potential (positive line conductor), a
line
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Date Recue/Date Received 2023-06-28
conductor which is at negative potential (negative line conductor), a voltage-
limiting device comprising a first voltage-direction-dependent electronic
switching device and a second voltage-direction-dependent electronic
switching device, wherein the voltage-direction-dependent electronic switching
devices have a diode function, wherein the first voltage-direction-dependent
electronic switching device is connected between the line conductor which is
at positive potential and ground, and without electromagnetic interference
blocks in the direction from the line conductor at positive potential to
ground
potential, wherein the second voltage-direction-dependent electronic switching
device is connected between the line conductor which is at negative potential
and ground and without interference blocks in the direction from ground
potential to the line conductor which is at negative potential.
[0012] The protective device according to the invention is installed with a
low-
impedance connection to the ground potential (ground rail or the like) and has
at least one connection to the positive line conductor and at least one
connection to the negative line conductor.
[0013] The connection according to the invention of the voltage-direction-
dependent switching devices ensures that the potential of the positive wire is
never shifted below the ground potential and that the potential of the
negative
wire is never shifted above the ground potential. As a result, a load
connected
to the line conductors can be effectively protected against high voltages
relative to the ground potential by interference voltages.
[0014] As soon as a line conductor reaches ground potential, the
corresponding voltage-direction-dependent switching device becomes
conductive and represents a low-impedance connection to ground potential.
The protective device according to the invention therefore effects a brief one-
sided ground fault (ground fault of one of the line conductors) of the IT
power
supply apparatus.
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Date Recue/Date Received 2023-06-28
[0015] The protective device is in particular an input and/or output
protection
apparatus, i.e., a protective device, which protects the input or the output
(depending on the feed direction) of a component of a track-field
infrastructure.
[0016] A voltage-direction-dependent electronic switching device with diode
function comprises at least one electronic element. which is high-impedance
or low-resistance depending on the voltage applied to it. This can be an
active
or a passive electronic component. Preferably, the voltage-direction-
dependent electronic switching devices are diodes or controllable switches, in
particular switched transistors. In the case of diodes, the cathode of the
first
diode is connected to the positive line conductor, while the anode of the
first
diode is connected to ground potential; the anode of the second diode is
connected to the negative line conductor, while the cathode of the second
diode is at ground potential. In normal operation (i.e., without interference
voltage), the switching devices are therefore connected in blocking direction
(i.e., high-impedance). A switching device can also comprise multiple voltage-
direction-dependent electronic elements connected in series.
[0017] In an advantageous embodiment of the protective device according to
the invention, at least one of the voltage-direction-dependent electronic
switching devices is connected in series with a resistor for current
limitation.
The resistor connected in series prevents the switching device from blowing
when, in addition to a ground fault, traction return currents also flow at the
same time via ground. Multiple resistors can also be connected in series to
the
voltage-direction-dependent electronic switching device.
[0018] A particularly preferred embodiment of the protective device according
to the invention comprises a first surge protection apparatus, wherein the
first
surge protection apparatus is electrically connected between the positive line
conductor of the supply line and ground potential, and a second surge
protection apparatus, wherein the second surge protection apparatus is
electrically connected between the negative line conductor of the supply line
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Date Recue/Date Received 2023-06-28
and ground potential. The first surge protection apparatus with the first
switching device and the second surge protection apparatus with the second
switching device each form a parallel circuit. In this way, overvoltages
caused
by lightning events can be reduced.
[0019] The protective device according to the invention can be present as a
separate unit or integrated in a sleeve for galvanic connection of pipe
sections.
[0020] The invention also relates to a track-field power supply apparatus
comprising a feed, at least one DC supply line and at least one previously
described protection device, wherein the line conductors are part of a DC
supply line, which is electrically connected to the feed and is supplied with
energy by the feed.
[0021] The track-field power supply apparatus is an installation with the
Isolee
Terre (IT) network configuration. By means of the protective device according
to the invention, when a superimposed voltage causes a voltage shift beyond
the ground potential (in the case of positive line conductor in the negative
direction, in the case of negative line conductor in the positive direction),
a
temporary one-sided voltage limitation is brought about by means of a ground
fault on one side, which leads to a temporary loss of the IT properties of the
power supply apparatus.
[0022] A particularly preferred embodiment of the track-field power supply
apparatus according to the invention provides that a balancing resistor
assembly is connected between positive and negative line conductors of the
DC supply line in series with the feed, wherein the balancing resistor
assembly
comprises two identical resistor units connected in series and the center tap
of
the balancing resistor assembly is at ground potential. This results in the DC
voltage, which is "floating" due to the IT property of the power supply
apparatus, being distributed uniformly with respect to the ground potential
with
intact insulation (i.e., without effect of the inductive interference). This
means
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Date Recue/Date Received 2023-06-28
that both the voltage of the positive line conductor relative to ground
potential
and the voltage of the negative line conductor relative to ground potential is
half the DC feed voltage. A resistor unit can comprise multiple resistant
components.
[0023] A shift of the voltage ratios provides information on the insulation
conditions in the installation. Therefore, measuring units for measuring the
voltages dropping across the resistor units are preferably provided. By means
of the measuring units, shifts of the potentials of the line conductor
relative to
the ground potential can be detected. As a result, insulation faults can be
detected and their extent can be estimated. In addition, an insulation monitor
for IT networks can be used for insulation monitoring.
[0024] In a particularly preferred embodiment, the DC supply line is a bus
line.
[0025] In this case, the bus line is divided into bus segments by bus coupling
elements, each bus coupling element comprising further switching devices
(segmentation switches) for electrical separation of the bus line.
[0026] The bus coupling elements preferably comprise at least one feed bus
coupling element for connecting the feed to the bus line and at least one load
bus coupling element for connecting a load to the bus line.
[0027] In a specific embodiment, the balancing resistor assembly is part of
the
feed bus coupling element. As a result, a compact design of the components
can be achieved.
[0028] In order to protect the load bus coupling elements even in the case of
feeding from both sides, it is preferable for a protective device to be
arranged
on each side of a load bus coupling element. Between two load bus coupling
elements, two protective devices are thus preferably electrically connected to
the bus segment delimited by the two load bus coupling elements.
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Date Recue/Date Received 2023-06-28
[0029] Furthermore, it is advantageous if a protective device is arranged on
the side of the feed bus coupling element facing away from the feed. In this
way, the feed can also be protected against interference voltages or
interference currents.
[0030] As an alternative to a bus lines divided into bus segments, the bus
line
can be a galvanically connected bus line.
[0031] Preferably, multiple protective devices are provided also in the case
of
a galvanically connected bus line. These are preferably spaced apart from one
another by a few kilometers.
[0032] The invention also relates to a method for limiting potential shifts,
i.e.,
the voltage relative to the ground potential caused by the superimposition of
the interference voltage in an electrical track-field infrastructure caused by
an
interference voltage by means of an above-described protection device.
[0033] In a particularly preferred method variant, an automatic voltage-
dependent potential limitation takes place, in particular depending on the
signs
of the voltages of the line conductors with respect to ground potential.
[0034] It is particularly preferred if the potentials of the line conductors
are set
symmetrically around the ground potential by means of a balancing resistor
assembly. An insulation fault disclosure is preferably carried out by
measuring
the voltages dropping across the resistor units.
[0035] Further advantages of the invention can be found in the description and
the drawings. Likewise, according to the invention, the aforementioned
features and those which are to be explained below can each be used
individually or together in any desired combinations. The embodiments shown
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Date Recue/Date Received 2023-06-28
and described are not to be understood as an exhaustive list, but, rather,
have
an exemplary character for the description of the invention.
DETAILED DESCRIPTION OF THE INVENTION AND DRAWINGS
[0036] Figure 1 shows a basic embodiment of a protective device according to
the invention.
[0037] Figure 2 shows a protective device according to the invention with
overvoltage protection.
[0038] Figure 3 shows a track-field power supply apparatus according to the
invention with a segmented bus line.
[0039] Figure 4 shows a feed and a feed bus coupling element with an
integrated balancing resistor assembly.
[0040] Figure 5 shows the profile of the voltage of the wires relative to
ground
potential of a track-field power supply apparatus according to the invention
with
a common-mode-interference voltage.
[0041] Figure 6 shows a protective device according to the invention with
current limitation at ground fault.
[0042] Figure 7 shows a track-field power supply apparatus according to the
invention with a galvanically connected bus line.
[0043] Figure 1 and Figure 2 show two embodiments of a protective device 1,
1' according to the invention. The protective devices 1, 1' comprise a line
conductor (positive line conductor) 2a) and a line conductor at a negative
potential (negative line conductor 2b) of a power supply apparatus (not shown
in Figure 1 and Figure 2). A branch line 3a, 3b, which is connected
galvanically
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Date Recue/Date Received 2023-06-28
to the respective line conductor 2a, 2b, extends from each line conductor 2a,
2b and ends at ground potential. The branch lines 3a, 3b each comprise a
voltage-direction-dependent electronic switching device (here: diodes 4a, 4b).
The first diode 4a is connected between the positive line conductor 2a and
ground in such a way that without electromagnetic interference it blocks in
the
direction from the positive line conductor 2a to the ground potential.
Similarly,
the second diode 4b is connected between the negative line conductor 2b and
ground in such a way that without electromagnetic interference it blocks in
the
direction of the ground potential to the negative line conductor 2b. If the
line
conductors 2a, 2b of the power supply apparatus are thus not exposed to any
interference voltage, the diodes 4a, 4b of the protective devices 1, 1' have a
blocking effect and no current flow takes place via the ground connection of
the branch lines 3a, 3b. If the voltage ratio between a line conductor 2a, 2b
and the ground potential is influenced by an interference voltage such that
the
sign of the potential of the corresponding line conductor 2a, 2b changes
relative to the ground potential, the blocking effect of the associated diode
4a,
4b is canceled. A ground fault occurs on one side. The protective devices 1,
1'
according to the invention thus generate a one-sided ground fault when the
interference voltage causes a sign change of the potential difference between
one of the line conductors 2a, 2b and the ground potential.
[0044] In the particularly preferred embodiment of the protective device 1
according to the invention shown in Figure 2, a surge protection apparatus is
connected in parallel to each voltage-direction-dependent switching device 4a,
4b 5a, 5b. The surge protection apparatuses 5a, 5b are thus likewise
connected between one of the line conductors 2a, 2b and ground. The surge
protection apparatuses 5a, 5b each comprise a parallel circuit of a varistor 6
and a surge arrester 7. The surge protection apparatuses 5a, 5b are intended
to prevent an energy input, for example due to lightning strike, from causing
damage to electronic components of the power supply apparatus.
Date Recue/Date Received 2023-06-28
[0045] Figure 3 shows a power supply apparatus according to the invention 8
in which the protective device 1 shown in Figure 2 is used. The line
conductors
2a, 2b of the power supply apparatus 8 shown in Figure 3 are part of a bus
line
2, which supplies the load 9 with power. The power supply apparatus 8
furthermore comprises a ground connection 21, which is installed with a low-
impedance connection to the system ground (ground rail or the like). In
addition
to the line conductors 2a, 2b, the bus line 2 can also comprise further line
conductors (not shown). For the sake of clarity, the sheathing of the bus line
2
is shown schematically in Figure 3 only for a distance along the power supply
apparatus 8.
[0046] The loads 9 are connected to the bus line 2 via load bus coupling
elements 10. Via segmentation switches S1, the bus line can be subdivided
into bus segments. The power supply apparatus 8 also comprises a DC feed
11 via which the loads 9 are supplied with power.
[0047] In principle, it would be sufficient to provide protection devices 1 at
predetermined distances in the bus line 2. The distances are preferably
selected in such a way that, the interference due to the expected
superpositions of the voltages does not lead to the exceeding of limit values
predetermined for the system protection. However, in order to protect the
components of the power supply apparatus 8 from interference voltage even
in the case of a galvanically isolated bus line (with an opened segmentation
switch S1 in the load bus coupling element 10), in the embodiment of the power
supply apparatus 8 according to the invention shown in Figure 3 a protective
device 1 is provided upstream of each load bus coupling element.
[0048] Furthermore, it can be provided that the power supply apparatus 8, in
addition to the DC feed 11 shown in Figure 3, can have one or more further
feed(s) in order to implement a two-sided feed of the loads 9 (bidirectionally
operated power supply apparatus). In this case, as shown in Figure 3, a
protective device 1 according to the invention should be connected to each
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Date Recue/Date Received 2023-06-28
side of the load bus coupling element 10 (i.e., as well on the side facing the
feed 11 as on the side facing away from the feed 11). In this way, the load
bus
coupling element 10 is effectively protected against impermissibly high
interference voltages, even when there is feeding on both sides. The
protective
devices 1 then form both an input protection and an output protection.
[0049] In the power supply apparatus 8 according to the invention, the
protective device 1 according to the invention is also used as an output
protection for the feed 11. For this purpose, a protective device 1 is
connected
downstream of the feed 11.
[0050] The connection of the feed 11 to the bus line 2 is preferably
implemented
via a feed bus coupling element 12 as shown in detail in Figure 4. The
protective
device 1 downstream of the feed is preferably connected to the side of the
feed
bus coupling element facing away from the feed 11 and, as shown in Figure 4,
can be part of the feed bus coupling element 12. A diode pair 13 in the line
conductors 2a, 2b, prevents return flows into the feed 11, for example in the
event
that higher voltage is applied from distributed, redundant feeds to the power
supply apparatus, when the power supply apparatus is operated bidirectionally.
[0051] In order to distribute the voltage provided by the feed 11 uniformly
relative
to the ground potential, a balancing resistor assembly 14 is provided
downstream
of the feed 11 and is preferably part of the feed bus coupling element 12, as
shown
in Figure 4. The balancing resistor assembly 14 is connected in parallel to
the
feed 11. It includes two resistor units 18 and a center tap 15, which is at
ground
potential, between the resistor units 18. This ensures that when the
insulation is
intact (i.e., without effects of the inductive interference) the voltage of
the positive
line conductor 2a and the voltage of the negative line conductor 2b are of a
similar
magnitude in terms of amount, but differ in sign.
[0052] Shown in Figure 5 is the profile of the potentials of the positive line
conductor 2a and the negative line conductor 2b of the power supply apparatus
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Date Recue/Date Received 2023-06-28
8 shown in Figure 3 during an interference with a sinusoidal interference
voltage in the example of a short-circuit short circuit is shown. The voltage
UDC
provided by the feed 11 and applied between the two line conductors 2a, 2b
(potential difference) in the example shown is 600 V.
[0053] The balancing resistor assembly 14 distributes the potentials UDC+, UDC-
of the line conductors 2a, 2b symmetrically around the ground potential.
[0054] At the beginning (I) there is no interference, so that the potential
UDc+-of
the positive line conductor 2a is +300 V and the potential UDC of the negative
line
conductor 2b is -300 V. If an interference occurs, this results in the
potentials
UDC+, UDC- of the line conductors 2a, 2b shifting relative to the ground
potential,
wherein the voltage UDc_between the line conductors 2a, 2b remains constant.
In
the example shown, the potentials UDC+, UDC- of the line conductors 2a, 2b
first
shifts to higher values (II). If the interference voltage is now so high that
the
potential UDC_ of the negative line conductor 2a threatens to exceed the
ground
potential, the diode 4b of the protective device 1 becomes conductive and
represents a low-impedance connection to the ground potential (III) until the
potential shift due to the interference voltage is again low enough that the
potential
of the negative line conductor 2b moves back again within the negative range
(IV). The potential UDC+ of the positive line conductor 2a therefore does not
exceed a maximum potential Umax=UDc. Similarly, the diode 4a of the protective
device 1 is conductive when the potential of the positive line conductor 2a
threatens to undershoot the ground potential (V). The potential UDC_ of the
negative line conductor 2b therefore does not fall below a minimum potential
Umin=-UDc. The protective device 1 according to the invention therefore
ensures
that the voltage shift is limited when the interference voltage becomes so
great
that it would cause a change of sign of the potential of one of the line
conductors
2a, 2b. The brief situations in which one of the voltage-direction-dependent
electronic switching devices 4a, 4b is conductive correspond to a brief, one-
sided
ground fault of the IT power supply apparatus 8.
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Date Recue/Date Received 2023-06-28
[0055] In addition to limiting the voltage shift in the event of an
electromagnetic
interference, it is also important to detect such a high interference, so that
these events are also logged in the power supply system. This is implemented
in the feed bus coupling element 12 shown in Figure 4 by the voltage across
the individual resistor units 18 of the balancing resistor assembly 14 being
measured. For this purpose, corresponding measuring units 19 are connected
in parallel with the resistor units 18. If the voltages across the resistor
units
differ more than a previously determined acceptable limit value, it can be
assumed that an electromagnetic interference is taking place. In addition, an
insulation monitor 20 can be connected between the line conductors 2a, 2b.
[0056] PN diodes are preferably used as voltage-direction-dependent
electronic switching devices 4a, 4b.
[0057] The interference always takes place on both line conductors 2a, 2b.
This
is therefore a "common mode interference." Therefore, the two diodes 4a, 4b
are
never simultaneously conductive (which would correspond to a short circuit).
[0058] In the event that an external (non-intended) ground fault 16 occurs,
the
protective device 1, 1' can serve to limit the current flowing through the
ground
fault 16 in the affected line conductors 2a, 2b. For this purpose, in a
special
embodiment shown in Figure 6 in the branch lines 3a, 3b, a current limiting
resistor 17 is connected in series to the voltage-direction-dependent
electronic
switching devices 4a, 4b.
[0059] In addition to the segmented bus line 2 shown in Fig. 3, the protective
device according to the invention can also be used in a power supply
apparatus 8' with a permanently galvanically connected bus line 2', as shown
in Fig. 7. In this case, the load bus coupling elements 10' do not have any
switching elements for separating the bus line. The distances of the
protective
devices 1, 1' can be selected more flexibly here.
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Date Recue/Date Received 2023-06-28
List of reference signs
1, 1' protective devices
2 DC supply line - segmented bus line
2' DC supply line - galvanically connected bus line
2a positive line conductor
2b negative line conductor
3a, 3b branch lines
4a, 4b voltage-direction-dependent electronic switching devices, in
particular diodes
5a, 5b surge protection apparatus
6 varistors
7 surge arrester
8 power supply apparatus with segmented bus line
8' power supply apparatus with permanently galvanically connected
bus line
9 load
10 load bus coupling element - segmented bus line
10' load bus coupling element - galvanically connected bus line
11 DC feed
12 feed bus coupling element
13 diode pair for avoiding return flows into the feed
14 balancing resistor assembly
15 center tap of the balancing resistor assembly
16 ground fault caused by external circumstances
17 current limiting resistor
18 resistance unit of balancing resistor assembly
19 measuring units, voltage measuring devices
20 insulation monitor
21 ground connection
S1 further switching devices (segmentation switches)
UDC voltage provided by DC feed
Date Recue/Date Received 2023-06-28
U DC+ potential of the positive line conductor
UDC- potential of the negative line conductor
U max maximum potential of the positive line conductor
U min minimum potential of the negative line conductor
Bibliography
[1] EP 3 247 015 A1
[2] Ril 819.0804
Blitz- und Oberspannungsschutz von LST-Anlagen [Flash and
Surge Protection of LST systems];
3/15/2018
[3] DB Netze TM 2-2020-10352
Betriebserprobung
A04: Grundschaltung Langsspannungsentkoppler [Operating Test
A04: Basic circuit of longitudinal voltage decouplers]
[4] DB Netze
ESTW-NeuPro ¨ Lastenheft fur die Stromversorgung ESTW-
NeuPro [Specifications for the ESTW-NeuPro Power Supply]
16
Date Recue/Date Received 2023-06-28
