1MRS751802-MUM
REX 521
151
Protection Relay
Technical Reference Manual, Standard Configurations
instantaneous trip of the busbar system. On the other hand, it is difficult to find the
right setting value since a close-up fault in a feeder can cause the circuit breaker of
the in-feeder to trip instead of the feeder protection relay.
In a double busbar system where the busbar circuit breaker is closed and two main
transformers are connected in parallel, the breaking capacity of the circuit breakers
of the outgoing feeders may not be sufficient and so tripping should be carried out
by the circuit breaker of the in-feeder. Then the current setting of the outgoing
instantaneous stage 3I>>> is set to the same level as the breaking capacity of the
feeders. This means that if the fault current exceeds the breaking capacity of the
outgoing feeders, the tripping is performed by the protection of the in-feeder. An
external control signal can be used for shifting to the second settings when the
transformers are used in parallel operation. Then the stage 3I>>> is active in parallel
operation and inhibited or has other settings when the parallel operation is not used.
The settings for the overcurrent protections can be found in:
Main menu\Protection\3I>\ … \3I>>>\Setting group 1\
where
the parameters
Operation mode
,
Start current
and
Operate time
for
the function can be set. In
Main menu\Protection\3I>\Control
setting\
can for example the
Drop-off time
and the length of the trip signal
Trip pulse
be set. The data of the three last operations, start or trip, are recorded
and the values of the most recent operation can be found in
Main menu\Protection\3I>\Recorded data1\…3\
.
9.2.3.2.
Earth fault protection
The earth fault stages can be used in different ways depending on the used earthing
principle. In this example with a low-resistance earthed network, the two stages are
used as back-up earth fault protection and as earth fault protection of the busbar
system. The low-set Io> stage of the earth fault protection serves as back-up
protection of the outgoing feeders and the high-set stage Io>> as the primary earth
fault protection of the busbar system. The instantaneous stage Io>>> is configured
to trip the breaker on the HV side of the transformer.
The settings for the earth fault current protections can be found in
Main menu\Protection\Io>\ … \Io>>>\
.
9.2.3.3.
Protection signal routing
The trip signal (Trip 1) of the protection functions are routed to the high speed power
output HSPO1 (x4.2.1/2/3/4) as well as the control-open signal for the circuit
breaker. The trip signals from the protection functions are routed to the output relay
via the output switchgroups. These settings can be found in
Main menu\Configuration\Output SWGRP\
.
As the HSPO1 is always routed to the “Trip 1” output signal, the settings are made
directly in
Main menu\Configuration\Output SWGRP\Trip 1
where
the checksum of the settings is displayed (255 by default).
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