In DC traction systems, impermissible
touch voltages may occur between the
return circuit and the structure earth due
to operational and short-circuit currents.
In this case, a voltage-limiting device must
be used between the return circuit and
the structure earth in accordance with
IEC 62128-1 / EN 50122-1.
The Sitras® SCD reduces excessively high
voltages by reliably short-circuiting the
return circuit and structure earth temporarily. Furthermore, the formation of
stray currents is minimized by automatic
opening of the short-circuiting device.
Features
Fulfills all the criteria according to
IEC 62128-1 / EN 50122-1; is also
type-tested according to IEC 61992-6 /
EN 50123-6
Maximum protection for personnel and
equipment due to rapid response time
Low maintenance requirement thanks
to the use of a hybrid switching element which eliminates the need for
maintenance-intensive voltage fuses
High functionality and ease of use due
to programmable controller with display and keypad
Earthquake tested versions available
Electrical data
Steel cabinet
Plastic
housing
Maximum system voltage
[V]
3,000
3,000
Rated current
[A]
800
400
Rated short-time withstand
current 1 s
[kA]
5
5
Rated short-time withstand
current 10 ms*
(peak value sinusoidal half-wave)
[kA]
36 / 50
36 / 50
[switching
operations]
1.5 x 106
1.5 x 106
[switching
operations/h]
120
120
Steel cabinet
Plastic
housing
Mechanical lifespan
Operating frequency
Mechanical data
Dimensions (H x W x D)*
[mm]
Color*
Degree of protection
Weight
[kg]
1,800x600x500 1,000x1,000x450
RAL 7047
RAL 7032
IP40
IP55
150...170
120...140
* other values on request
Sitras SCD – Short-circuiting device
Voltage-limiting device for DC traction power supply
Product Information / Version 2.1.2
www.siemens.com/mobility
Short-circuiting device Sitras SCD
U
t
Hybrid
switching
element
Return circuit,
rail
Equipotential bonding busbar
Earth, structure earth
Contact resistance between rail
and structure earth
Block diagram Sitras SCD
Application
Protection against personal injury:
Impermissible touch voltages are prevented
Monitoring of the potential of the
return circuit:
Earth faults in the contact line are
detected, thus enabling them to be
cleared by feeder substations
Protection of installation:
Overvoltages in the installation, e.g.
due to lightning, are prevented
Design/main components
Hybrid switching element, consisting
of DC contactor and thyristor instantaneous trip
Measuring circuits for voltage (redundant) and current
Programmable controller, optionally
with Profibus interface
Function
In its basic state, the main contact of the
DC contactor is open and the thyristor
instantaneous trip is not conductive. The
voltage between the return circuit and the
equipotential bonding busbar is measured
and displayed and the voltage over time
evaluated.
If one of the limits stored in the programmable controller is exceeded, the DC contactor closes. The limits are stored in the
form of voltage-time characteristic curves.
For AC and DC voltages, there are characteristic curves which can be parameterized
differently. For the workshop area, it is
possible to change over to an additional,
separate characteristic curve.
In the short-time range, voltage evaluation takes place in parallel as control by the
programmable controller in a hardware
circuit which directly triggers the thyristor instantaneous trip. The flow of current
is detected by a programmable controller
and the DC contactor is then switched.
The Sitras SCD opens automatically when
the set closing time expires, the current is
not critical and a blocking condition does
not exist.
Blocking
If the number of trips within a specific time
is unusually high, opening of the DC contact is blocked and the Sitras SCD remains
in a state that ensures the safety of persons. The same applies if there is a very
high current for a long time. All the values
can be parameterized.
Blocking can be acknowledged locally or
via a remote control link and thus cancelled.
Control voltage failure
The Sitras SCD operates on the closedcircuit principle. This ensures that even if
the control voltage fails, the return circuit
and the equipotential bonding busbar are
automatically short-circuited and that the
system is safe for persons.
After the control voltage has been connected, the Sitras SCD returns to the state
it was in before failure of the control voltage.
All the states of the Sitras SCD can be signaled remotely.
Siemens AG
Industry Sector
Mobility Division
Electrification
P.O. Box 32 40
91050 Erlangen
Germany
[email protected]
www.siemens.com/mobility/
electrification
www.siemens.com
Version 2.1.2 / No. A6Z08100028228
The information in this document contains general descriptions of the technical options available, which do not always have to be
present in individual cases. If not stated otherwise, we reserve the right to include modifications, especially regarding the stated values
and dimensions.
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