1.2 Application Scope
19
7ST6 Manual
E50417-G1176-C251-A3
1.2
Application Scope
The SIPROTEC
®
4 7ST6, Numerical Overhead Contact Line Protection for AC
Traction Power Supply, is a selective and fast protection device for overhead contact
lines with single- and multi-ended infeeds.
The device incorporates the functions which are normally required for the protection
of an overhead contact line section and is therefore capable of universal application.
Protective
Elements
The basic function of the device is the recognition of the distance to the fault with dis-
tance protection measurement. It is supplemented by a range of other protection func-
tions:
When switching to a faulted line section, an undelayed trip signal can be output.
In the event of a failure of the measured voltages due to a fault in the secondary cir-
cuits (e.g. trip of the voltage transformer mcb or a fuse) the device can automatically
revert to an emergency operation with an integrated time overcurrent protection
(emergency time overcurrent protection), until the measured voltage again becomes
available. There is an additional 3-stage definite/inverse time overcurrent protection
operating in parallel to, and independent of, the distance protection. This time overcur-
rent protection has three current-independent stages and one current-dependent
stage. For inverse time overcurrent protection, several curves of different standards
are provided. The stages can be combined in any way. Moreover, a high-speed over-
current protection function with a tripping time of less than 2 ms is integrated.
Most short-circuit functions work in conjunction with an integrated automatic reclose
function which is designed for 8 reclosing attempts. Before reclosure, the validity of
the reclosure can be checked by voltage and/or synchronism check by the device (this
can be ordered as an option).
Beside the short-circuit protection functions described above, the device offers addi-
tional protection functions such as multiple-stage overvoltage and undervoltage pro-
tection, circuit breaker failure protection, and thermal overload protection, which pro-
tects the overhead contact line from excessive heating due to overloads. The fault
locator supports fast location of the fault after a short-circuit. The inrush restraint
feature is used for a clear distinction between operating and fault conditions during
switching operations. The defrosting protection feature provides high-sensitivity de-
tection of short-circuits during defrosting of the overhead contact line.
Control Functions
Depending on the ordered variant the device provides control functions which can be
accomplished for activating and deactivating switchgear via the integrated operator
panel, the system interface, binary inputs and a personal computer with the operating
software DIGSI
®
. The status of the primary equipment can be transmitted to the device
via auxiliary contacts connected to binary inputs. The present status (or position) of
the primary equipment can be displayed on the device, and used for interlocking or
plausibility monitoring. The number of the primary equipment to be switched is limited
by the binary inputs and outputs available in the device or the binary inputs and
outputs allocated for the switch position indications. Depending on the primary equip-
ment being controlled, one binary input (single point indication) or two binary inputs
(double point indication) may be used for this process. The capability of switching
primary equipment can be restricted by a setting associated with switching authority
(Remote or Local), and by the operating mode (interlocked/non-interlocked, with or
without password request). Processing of interlocking conditions for switching (e.g.
switching error protection) can be established with the aid of integrated, user-config-
urable logic functions.
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