ABB Industrial IT enabled REX 521 Technical Reference Manual, General page 31

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Technical Reference Manual, General
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The REX 521 includes an unbalanced IEC 60870-5-103 slave communication
interface.
The interface provides a fixed cross-coupling between the REX 521 application
(indications, commands and protection equipment) and the IEC 60870-5-103
protocol application data. The adjustable parameters are Baud rate and Unit
address. User-selectable measurand sets Frame type are available for the
analogue measurement values.
Star coupler unit
Star-coupler unit
e.g. RER 125
e.g. RER 125
R E X 5 2x
REX 521 and other IEC_103 based protection relays
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The physical bus topology is star-based. A star-coupler unit, for example RER 125,
is needed for connecting the REX 521 unit to a control system.The line idle state of
the fibre-optic interface is configurable ("light on" and "light off") with a parameter
Tx mode.
For more information about the IEC 60870-5-103 bus, refer to "Appendix A: IEC
60870-5-103 bus" on page 55.
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The REX 521 has a slave communication interface for Modbus system. Both ASCII
and RTU mode are supported.
The communication technique used in Modbus protocol is a master-slave technique.
The master can be connected to the slaves either directly or via modems by using a
compatible serial interface. However, only the direct connection can be used with
REX 521.
Monitoring and
control equipment
e.g. MicroSCADA
RS232C
Fibre-optic
modem
R E X 5 2x R E X 5 2x
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IEC_103/SP
A gateway
SPACOM-relay
IECsysrex_a
31