Measurement Connections; Protection; Phase Overcurrent Protection - ABB REX 521 Technical Reference Manual, Standard Configurations

REX 521
9.1.2.
9.1.3.
9.1.3.1.
106
Protection Relay
Technical Reference Manual, Standard Configurations

Measurement connections

The three-phase current transformers are connected to the connector X1.1 on the rear
panel. The rated currents of the measuring input are 1 A and 5 A.
)LJ  &RQQHFWLRQ GLDJUDP RI WKH VWDQGDUG FRQILJXUDWLRQ % ZLWK WKUHH
&7V LQ D UHVLGXDO FRQQHFWLRQ
The technical data of the current transformers are set via the Relay Setting Tool or
the local HMI. The settings can be found in
Main menu\Configuration\Meas. devices\. Please refer to
Technical Reference Manual, General (1MRS 751108-MUM) for further
information about how to set the rated currents.

Protection

All the necessary settings for the protection functions can be set via the Relay
Setting Tool or the local HMI. The settings can be found in
Main menu\Protection\.

Phase overcurrent protection

The phase overcurrent protection includes three stages. By using all the three stages
and giving each overcurrent stage its own start value and operate time, good
selectivity with short operate times can be obtained.
Normally, a two-stage overcurrent protection is sufficient. However, when the short-
circuit protection is based on blocking between the successive protection relays, the
high-set stage 3I>> can be used for blocking purpose. As this stage (3I>>) is not
used for tripping purposes, the blocking level can be freely set. This means that
when the 3I>> overcurrent stage of the outgoing feeder starts, a blocking signal is
provided to the 3I>>> overcurrent stage of the incoming feeder. When no blocking
signal is received, the overcurrent protection of the incoming feeder perceives the
fault as being within its own protection zone and trips the circuit breaker.
1MRS 751802-MUM
REX 521