Supply of auxiliary drives in a rail vehicle with
electrical power
Description
The invention relates to a system for supplying
auxiliary devices in a rail vehicle with electrical
power. The invention furthermore relates to a method
for protecting a system such as this in the event of
inadvertent contact with a reference potential, in
particular with vehicle ground.
Locomotives or other rail vehicles or parts of trains
which are used to operate the rail vehicle or train
have additional devices, which allow operation, in
addition to the devices which are directly required for
traction (for example high-voltage system, traction
inverter and drive motors). These auxiliary devices
likewise require electrical power and, in specific
cases, are connected via an auxiliary device inverter
to a traction intermediate circuit, from which the
power required for traction is also taken. Examples are
fans for the drive motors, coolers for the converters,
compressors for compression of gases (for example in
order to produce compressed air for a braking
installation) , a fire extinguishing device in the
locomotive, electronic devices for controlling the
operation of the locomotives, the battery chargers,
heaters, for example screen heating, air-conditioners,
plug sockets, lighting devices. A further group of
electrical devices which in some circumstances are
arranged on rail vehicle units coupled to the
locomotives can be connected to the traction
intermediate circuit via their own additional inverter.
However, the invention is not restricted to use in
locomotives and can also be used in electrical systems
which have a traction intermediate circuit. In fact,
the electrical power required to operate the auxiliary
device system can also be provided in a different
manner. In this description, the term "energy source"
is used in a general form, even if this does not
actually relate to that part of an electrical system
which generates the electrical power. In fact the
electrical power is generated, for example, by a diesel
engine or, for example, is transmitted to the rail
vehicle via a high-voltage power supply system (for
example with an overhead wire or live rail) . However,
in the terminology of this description, any traction
intermediate circuit or DC voltage intermediate circuit
to which drive motors are also connected via a
converter is an energy source for the auxiliary device
system.
Normally, all auxiliary device systems in rail vehicles
are designed such that they do not require a reference
potential. This means that they can operate at a
fluctuating electrical potential with respect to
vehicle ground or "earth". When a contact, in
particular a short circuit, occurs with the vehicle
ground, the freely fluctuating state is cancelled and
the contact point is at the vehicle ground. This in
itself does not intrinsically lead to problems such as
high short-circuit currents. However, if a further
contact with vehicle ground occurs, high short-circuit
currents can result, which can destroy system
components and can also cause reactions with other
parts of the overall electrical system, for example
with the traction intermediate circuit and the
converters connected to it.
It has therefore already been proposed for the
auxiliary device system to be connected to the
reference potential via a series circuit comprising a
resistance and a circuit breaker. If a contact with the
reference potential occurs at a further point, the
short-circuit current that flows is limited by the
resistance, and the circuit breaker opens in accordance
with its time response characteristic.
However, the costs for a solution such as this are
relatively high. Furthermore, locomotives and drive
units normally have a plurality of auxiliary device
systems, thus further increasing the costs.
One object of the present invention is to specify a
system and a method of the type mentioned initially,
which make it possible to ensure effective protection
of an auxiliary device system, reliably, at low cost.
One fundamental consideration of the present invention
is that there is no need for the current limiting
resistance arranged in series with the circuit breaker.
Admittedly, if a second short circuit to the vehicle
ground were to occur, it is in theory possible for very
high short-circuit currents to flow via the circuit
breaker when it is still closed. However, these short-
circuit currents can be limited in a different manner.
A system is therefore proposed for supplying auxiliary
devices in a rail vehicle with electrical power,
wherein
- the system is connected via an isolating
transformer to an energy source, for example a DC
voltage intermediate circuit,
- the system is connected via a circuit breaker to
an electrical reference potential, in particular to
vehicle ground, without the interposition of a
resistance limiting the current flow,
- the circuit breaker is designed to open when a
current flow occurs through the closed circuit breaker
caused by an additional contact of the system with the
reference potential.
The term system for supplying auxiliary devices means
an arrangement with electrical lines which are used to
supply the auxiliary devices. In particular, the system
may be a three-phase system, as a result of which
auxiliary devices can be connected to one or more
phases of an AC power supply. In particular, the
circuit breaker can connect a starpoint of the three
phases to the reference potential.
"Without the interposition of the resistance" means
that the circuit breaker directly connects an
electrical line on the auxiliary device system to the
reference potential. "Directly" means that no discrete
component is arranged in this connection to increase
the direct-current resistance. The connecting lines
have a slight resistance, however. However, this
resistance is so small that it would not significantly
limit a high short-circuit current.
Circuit breakers may be in the form of switches which
are known per se, which detect a high current flow in
the form of automatic fuses and open the switching
contact in accordance with the tripping characteristic
of the circuit breaker when a limit value is exceeded
or when the current monitoring of the switch responds.
In general, an automatic fuse such as this must be
switched on by hand once the cause of the high current
flow has been rectified again.
In one preferred embodiment, the transformer is
connected on its primary side via a converter to the
energy source. The converter is operated by switching
current valves on and off, wherein a control is
provided to control the switching on and off, and is
designed such that, when a predetermined phase current
limit value is exceeded in one phase and/or if a total
current limit value is exceeded by the sum of the
currents in the plurality of phases, the current in
that phase or in all the phases is limited to the
respective limit value by controlling the valves such
that they are switched on and off appropriately. For
example, the time for which a phase is switched on
during one half-cycle of the alternating current is
reduced, or the phase current is offset in time in
comparison to the fault-free case.
The described controller for the converter, which, in
the case of a DC voltage intermediate circuit, is an
inverter, allows the current on the secondary side to
also be effectively limited, since the current levels
on the primary side and the secondary side are coupled
to one another via the inductances of the isolating
transformer. One example of a converter controller is
the controller offered by Bombardier Transportation
GmbH, Berlin, Germany, with the designation MITRAC DCU2.
The description of the associated protection mechanism
is given in German Patent Application DE 199 62 615 A1
and European Patent Application EP 1 110 797 A2. In one
preferred refinement, a capacitance can be connected in
parallel with the circuit breaker, in such a way that
the system is connected to the reference potential via
the capacitance, in parallel with the circuit breaker.
This makes it possible to dissipate so-called "common
mode" currents. Common-mode currents are currents which
flow at the same time in the same direction in all
phases, in contrast to the normal situation for a
polyphase system.
It is furthermore preferable for the system to be
connected to the reference potential via a high-value
resistance (for example of more than 2 0 kOhms) which is
arranged in parallel with the circuit breaker. In
consequence, a small current always flows via this
resistance.
The scope of the invention also includes a method for
protecting a system for supplying auxiliary devices in
a rail vehicle with electrical power. Refinements and
preferred embodiments of the invention result from the
description of the system. In particular, the following
is proposed:
A method for protecting a system for supplying
auxiliary devices in a rail vehicle with electrical
power in the event of inadvertent contact with a
reference potential, in particular with vehicle ground,
wherein
- the system is connected via an isolating
transformer to an energy source, for example a DC
voltage intermediate circuit,
- the system is connected via a circuit breaker to
an electrical reference potential, in particular to
vehicle ground, without the interposition of a
resistance limiting the current flow,
- the circuit breaker is opened when a current flow
occurs through the closed circuit breaker caused by an
additional contact of the system with the reference
potential.
Exemplary embodiments of the invention will now be
described with reference to the attached drawing. In
the individual figures of the drawing:
Figure 1shows a DC voltage intermediate circuit with
auxiliary devices connected to it, and
Figure 2shows the auxiliary device converter, the
isolating transformer and the protector
device as shown in figure 1, in the form of
an enlarged illustration with further details.
Figure 1 shows a diesel engine 1 which drives a
generator 3. In this case, the diesel engine 1 is the
drive engine which drives the locomotive, that is to
say moves it on the railway. The generator 3 produces a
three-phase alternating current which is rectified via
a rectifier 5. The rectifier 5 is connected to a DC
voltage intermediate circuit 7. The potentials in the
DC voltage intermediate circuit 7 are denoted P-UD+
(upper side of the intermediate circuit 7 as
illustrated in figure 1) and P-UD- (lower side of the
intermediate circuit 7 illustrated in figure 1) . For
example, the potential P-UD- may be connected to
vehicle ground at the point annotated with the
reference symbol 19.
The intermediate circuit 7 is connected to a traction
inverter 9, which supplies four drive motors 17 in the
rail vehicle via a three-phase connection, a braking
chopper 11, to which a braking resistance 12 is
connected, an auxiliary device inverter 13 which
supplies auxiliary devices 18 via a three-phase AC line,
and a load inverter 15 which supplies electrical power
to the loads, for example via a single-phase train
busbar in a coupled train.
The auxiliary device inverter 13 illustrated in figure
1 is connected to the auxiliary devices 18 via an
isolating transformer 14, which provides galvanic
isolation. In the illustrated embodiment, the system
for supplying electrical power to the auxiliary devices
18 has the transformer 14, the three-phase line and the
protector device 21. The auxiliary device inverter 13
is operated by a controller 22, which controls the
valves being switched on and off (for example bipolar
transistors, preferably IGBTs, or GTOs, gate turn-off
thyristors).
In comparison to the arrangement illustrated in figure
1, a multiplicity of modifications can be implemented.
For example, a connection to a single-phase high-
voltage power supply system (in the case of an AC
voltage power supply system via a rectifier) can be
provided instead of the diesel engine and the generator
and three-phase rectifier 5. In addition to the DC
voltage intermediate circuit 7, a further or a
plurality of further intermediate circuits can be
provided, via which some of the driving motors or
additional driving motors can be supplied with power.
Further devices can be connected to the DC voltage
intermediate circuit and/or can be integrated in it, in
particular fuses and/or a series resonant circuit. A
plurality of auxiliary device rectifiers can be
connected to the same DC voltage intermediate circuit.
The auxiliary device supply may be designed with only a
single phase.
In particular, the auxiliary devices 18 may be one or
more of the auxiliary devices mentioned in the
introductory part of this description. For example, the
auxiliary devices 18 also include a cooling device for
cooling the converter 13, the transformer 14, and/or
for cooling one or more of the other converters 9, 11,
15 and/or of the driving motors 17. The control devices
for controlling the operation of the converters 9, 11,
13, 15 may also belong to the auxiliary devices 18.
However, in extraordinary operation, it is possible to
dispense with operation of the converter 15 for
supplying coupled rail-vehicle units.
Figure 2 shows a three-phase embodiment of the
auxiliary device system 20. The inverter 13 which is
connected to the DC voltage intermediate circuit 7 (not
illustrated in figure 2) is connected on its AC voltage
side to the three phases X, Y, Z of a three-phase
connecting line, which is connected to the primary side
of the isolating transformer 14 at the terminals U1, V1,
W1. The secondary side of the isolating transformer 14
is connected at the terminals U2, V2, W2 to the three
phases U, V, W of the auxiliary device system 20.
In order to attenuate and filter interference harmonics,
a filter device 30 is connected to the three phases U,
V, W and, for example, has a plurality of filter
capacitors.
The protector device 21 is connected to the starpoint
26 on the secondary side of the transformer 14. Parts
of the protector device 21 are a circuit breaker 25, a
capacitor 27 connected in parallel with it (it is also
possible to provide a plurality of capacitors connected
in series and/or in parallel with one another) and a
high-value resistance 28, which is once again connected
in parallel with the switch 25 and the capacitor 27 and,
for example, has a resistance of at least 20 kOhms,
preferably at least 50 kOhms. The capacitor 27 reduces
high current surges or voltage spikes in the system 20
resulting from common-mode currents. The high-value
resistance 28 is used to fix the potential of the
auxiliary device system 20 and as a discharge
resistance for the capacitor 27, if the circuit breaker
25 has opened.
In the normal, fault-free state, the secondary side of
the transformer 14 is connected to vehicle ground only
via the closed circuit breaker 25, as is indicated
below the protector device 21 via a lateral stroke on
the line which ends there. Integrated sensors 31 for
the circuit breaker 25 detect the occurrence of high
short-circuit currents in the event of a fault, when a
short-circuit to vehicle ground occurs elsewhere, and a
controller opens the switch 25. The controller can be
integrated in the switch component, or can be switched
off separately.
Since, in theory, a very high current can flow between
the starpoint 2 6 and vehicle ground when the circuit
breaker 25 is closed, as long as the circuit breaker 25
has not yet been opened, the controller 22 for the
auxiliary device converter 13 is preferably designed so
as to avoid such extremely high currents by suitable
control of the converter 13. By way of example, for
this purpose, the currents for the phases X, Y, Z are
measured, and the measurement results are supplied to
the controller 22. The controller 22 evaluates whether
limit values in the individual phases and/or a total
limit value for all the phases have/has been exceeded.
If this is the case, the individual phase or all three
phases X, Y, Z is or are operated such that the
currents are limited again to the respective limit
value. A concept such as this for appropriate operation
of the valves of the converter 13 is known per se. The
invention now applies this principle to the situation
relating to the auxiliary device system 20. In this way,
the currents on the secondary side are also limited via
the inductive coupling of the primary side and
secondary side of the transformer 14, and extremely
high currents through the closed circuit breaker 25
before it is opened cannot occur.
Components which are known per se can be used as
circuit breakers which (as mentioned) have an
appropriate sensor system, in order to open the circuit
breaker in the event of a high current corresponding to
the time tripping characteristic. Another term for the
circuit breaker is therefore automatic fuse.
We Claim
1. A system (20) for supplying auxiliary devices (18)
in a rail vehicle with electrical power, wherein
the system (20) is connected via an isolating
transformer (14) to an energy source, for example a DC
voltage intermediate circuit (7),
- the system (20) is connected via a circuit breaker
(25) to an electrical reference potential, in
particular to vehicle ground, without the interposition
of a resistance limiting the current flow,
- the circuit breaker (25) is designed to open when
a current flow occurs through the closed circuit
breaker (25) caused by an additional contact of the
system (20) with the reference potential.
2. The system as claimed in claim 1, wherein the
system (20) is a three-phase system, and, when closed,
the circuit breaker (25) connects a starpoint (26) of
the three phases (U, V, W) to the reference potential.
3. The system as claimed in claim 1 or 2, wherein the
system (20) is connected to the reference potential via
a capacitance (27) which is arranged in parallel with
the circuit breaker (25) .
4. The system as claimed in one of claims 1 to 3,
wherein the system (20) is connected to the reference
potential via a high-value resistance (28) which is
arranged in parallel with the circuit breaker (25).
5. The system as claimed in one of claims 1 to 4,
wherein the transformer (14) is connected on its
primary side via a converter (13) to the energy source
(7) wherein the converter (13) is operated by switching
current valves on and off, wherein a controller (22) is
provided to control the switching on and off, and is
designed such that, when a predetermined phase current
limit value is exceeded in one phase (X, Y, Z) and/or
if a total current limit value is exceeded by the sum
of the currents in the plurality of phases (X, Y, Z),
the current in that phase (X, Y, Z) or in all phases (X,
Y, Z) is limited to the respective limit value by
controlling the valves to be switched on and off
appropriately.
6. A method for protecting a system (2 0) for
supplying auxiliary devices (18) in a rail vehicle with
electrical power in the event of inadvertent contact
with a reference potential, in particular with vehicle
ground, wherein
- the system (20) is connected via an isolating
transformer (14) to an energy source (7), for example a
DC voltage intermediate circuit,
- the system (20) is connected via a circuit breaker
(25) to an electrical reference potential, in
particular to vehicle ground, without the interposition
of a resistance limiting the current flow,
the circuit breaker (25) is opened when a current
flow occurs through the closed circuit breaker (25)
caused by an additional contact of the system (20) with
the reference potential.
7. The method as claimed in claim 6, wherein the
system (20) is a three-phase system (U, V, W) , and,
when closed, the circuit breaker (25) connects a
starpoint (2 6) of the three phases to the reference
potential.
8. The method as claimed in claim 6 or 7, wherein the
system is connected to the reference potential via a
capacitance (27) which is arranged in parallel with the
circuit breaker (25) .
9. The method as claimed in one of claims 6 to 8,
wherein the system (20) is connected to the reference
potential via a high-value resistance (28) which is
arranged in parallel with the circuit breaker.
10. The method as claimed in one of claims 6 to 9,
wherein the transformer (14) is connected on its
primary side via a converter (13) to the energy source
(7) wherein the converter (13) is operated by switching
current valves on and off, wherein when a predetermined
phase current limit value is exceeded in one phase (X,
Y, Z) and/or if a total current limit value is exceeded
by the sum of the currents in the plurality of phases
(X, Y, Z), the current in that phase (X, Y, Z) or in
all phases (X, Y, Z) is limited to the respective limit
value by controlling the valves to be switched on and
off appropriately.

The invention relates to a system (20) for supplying auxiliary drives (18) in a rail vehicle with
electrical power, wherein said system (20) is connected via an isolating transformer (14) to a
power source, such as a DC voltage intermediate circuit (7), wherein said system (20) is
connected without a resistor, which limits the current flow, interposed via a protective switch
(25) to an electrical reference potential, in particular to vehicle ground, and wherein said
protective switch (25) is designed to open upon passage of a current flow through said closed
protective switch (25), which is caused by an additional contact of said system (20) to said
reference potential.