Siemens SIPROTEC 7SS60, Руководство пользователя, Страница: 16 / 134

Introduction
1-4
7SS60 Manual
E50417-G1176-C132-A2
Isolator replica
module/preferential
treatment module This module can be used to implement 2 different functions which will be presented in
the following.
Isolator replica The isolator replica function detects the status of 2 isolators.
It allows e.g. to recognize the status of both isolators in a double busbar system. The
isolator status determines the allocation of the feeder currents to the appropriate mea-
suring system. It also ensures the stability and greatest possible selectivity of the pro-
tection system during dynamic processes such as switching operations.
Preferential
treatment If, during a changeover of a feeder in a double busbar system, both isolators of a feed-
er are closed for a short time, no selective protection of the two busbars is possible.
The same is true for busbar sections that are connected by closing a sectionalizing
isolator. Whereas each of the two sections has so far been protected by its own mea-
suring system, the protection function is assumed by only one measuring system after
connecting the two sections. This is referred to as preferential treatment.
As several relays or modules may be involved in the switching action, there may be
an undefined allocation of the differential and restraint currents to the measuring sys-
tems during a few milliseconds caused by different relay switching times.
The blocking pulse required for system stability is generated automatically on the
module within the corresponding time.
Also an auxiliary relay is included with two changeover contacts.
Command output
module 7TS720 This module comprises 8 independent command relays with 2 NO contacts each for
multiplication of the TRIP command generated by the 7SS601 measuring system.
It is necessary to multiply the TRIP command if the two NO contacts of the 7TR710
modules are not sufficient for command output to the circuit breakers. The measuring
system initiates the TRIP command first through a NO contact. In the simplest case,
an auxiliary voltage is fed directly from this contact onto the 7TS720 module, where it
causes one or more relay coils to pick up.
Transformers The differential current input I
d
of the 7SS60 is designed for 1 x I
n
= 100 mA. There-
fore, a transformer must be provided between the 7SS60 and the main current trans-
former. In phase-selective protection systems, matching transformers are used; oth-
erwise there will be summation current transformers.
Figure 1-2 Principle diagram of transformers in the 7SS60 (one phase of a phase-selective protection system)