Application Scope - Siemens siprotec 7SD5 User Manual

1.2

Application Scope

The SIPROTEC
and distance protection. A multi-end fault locator allows to precisely locate faults in
two-ended lines, even with unfavourable operating or fault conditions.
The combined line protection is a selective short-circuit protection for overhead lines
and cables with single- and multi-ended infeeds in radial, ring or any type of meshed
systems of any transmission level. Measuring data are compared separately for each
phase. The network neutral can be earthed, compensated or isolated.
The device incorporates the functions which are normally required for the protection
of an overhead line feeder and is therefore capable of universal application. It may
also be applied as time graded back-up protection to all types of comparison protec-
tion schemes used on lines, transformers, generators, motors and busbars of all
voltage levels.
The inrush current restraint allows for the application of the 7SD5 even if a power
transformer is situated within the protected zone (ordering option) whose starpoint(s)
might also be isolated, earthed or provided with a Petersen coil.
A major advantage of the differential protection principle is the instantaneous tripping
in the event of a short-circuit at any point within the entire protected zone. The current
transformers limit the protected zone at the ends towards the remaining system. This
rigid limit is the reason why the differential protection scheme shows such an ideal se-
lectivity.
The line protection system requires a 7SD5 device as well as a set of current trans-
formers at either end of the protected zone.
If the 7SD5 line protection is to be operated with distance protection as the main or
backup protection function, voltage transformers are required. They are also needed
for the acquisition and display of measured values (voltages, power, power factor).
The devices located at the ends of the protected zone exchange measuring informa-
tion via protection data interfaces using dedicated communication links (usually fibre
optic cables) or a communication network, provided that they operate with differential
protection. The distance protection can exchange measuring information via telepro-
tection functions with conventional connections (contacts), or transmit it through fast
command channels provided on the protection data interfaces (can be configured with
DIGSI). Two type 7SD5 devices can be used for an object with two ends to be protect-
ed: cables, overhead line or both, with or without unit-connected power transformer
(option). Employing type 7SD5*3, objects having 3 (three-terminal lines) or more ends
can be protected, besides two-terminal lines, also with or without unit-connected
transformers (option). Up to 6 ends can be covered, which means that smaller busbar
arrangements can also be protected. For each end a 7SD5*3 is used. Building up a
communication chain between 3 or more devices the outermost ends of the chain can
be equipped with the 7SD5*2 model. For more information refer to Section 2.2.1.
With two and more devices (= ends of the protected object) the communication can be
built up as a ring. This enables a redundant operation in case one communication line
fails. The devices will automatically find the remaining healthy communication lines.
But even with two ends, communication lines can be doubled to create redundancies.
Since fault-free data transmission is the prerequisite for the proper operation of the dif-
ferential protection system, it is continuously monitored internally.
In the event of a communication failure, if there is no backup channel available, the
devices can automatically be switched to the second main protection function, i.e. dis-
7SD5 Manual
C53000-G1176-C169-1
®
line protection 7SD5 is a protection relay that combines differential
1.2 Application Scope
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