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

1MRS 751802-MUM
9.3.2.
9.3.3.
9.3.3.1.
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.
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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 overcurrent protection includes three stages. The relay measures the phase
currents on the HV side. The definite-time instantaneous overcurrent stage 3I>>> is
set to operate on short circuits occurring on the primary side of the transformer and
most of the transformer itself. The fault currents are limited by the impedance of the
transformer so it does not detect faults on the secondary side of the transformer. The
3I>>> is current selective and it is set to a minimum operate time or instantaneous.
REX 521
REX 521
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