Introduction; Application; Figure 1.1 Line Differential Protection 7Sd600 For Operation With Two Pilot Wires, Block Diagram - Siemens SIPROTEC 7SD600 System Manual

Numerical line differential protection SIPROTEC 7SD600 V3.0
1

Introduction

1.1

Application

The numerical line differential protection 7SD600 is a
fast and discriminative short-circuit protection for ca
bles and overhead lines of all voltage levels, irrespec
tive of the method of neutral-point connection.
For example, it is particularly suited for short lines
where the reach of a distance protection cannot be
set small enough, or for meshed industrial and reticu
lation networks. It can be implemented no matter
how short the line. A current transformer, but not a
voltage transformer, is required at each end of the
line.
A significant advantage of the differential protection is
that, in the event of a short circuit, it trips and imme
diately disconnects, no matter where the short circuit
occurs within the protected zone. The current trans
formers at both ends define the protected zone. It is
this strict zone definition which produces the ideal
discrimination typical of the differential protection
principle. It also means that it is not necessary to de
lay the trip command as is usually the case with
time-graded protection systems.
The complete setup requires a 7SD600 device and a
4AM4930 summation transformer at each end of the
protected line. In order for the devices to work toge
ther, a symmetrical pilot wire pair is required between
the two stations.
For the protection to function properly, the pilot wires
must be healthy. For this reason, we always recom
mend pilot wire monitoring. This can disable the diffe
rential
protection (optional) if a fault is detected on the trans
mission link and outputs a corresponding indication.
Siemens AG January 1999
Introduction
System manual Order no. E50417-G1176-C069-A1
4AM4930
4AM4930
Figure 1.1 Line differential protection 7SD600 for operation with
two pilot wires, block diagram
In cases where a transformer is connected directly to
a cable or overhead line, i.e. without a circuit-breaker,
current transformers should be installed at the trans
former terminal, and the 7SD600 connected solely as
a line protection. The integrated stabilization with the
second harmonic in the differential current implies
that, that a transformer may, in principle, be included
in the protected zone of the 7SD600, however, it
does not offer the level of sensitivity provided by a
transformer differential protection.
In addition, this arrangement causes a delay of the
tripping time for the 7SD600.
1
7SD600
Station 1
Pilot
wire pair
max. 12 km
7SD600
Station 2
1 - 1