Technical data
1MRS751108-MUM
REX 521
37
Protection Relay
Technical Reference Manual, General
5.1.12.2. Isolated RS-485 connection on the rear panel
The RS-485 port is used for connecting the unit to the communication bus by using
twisted pair cable. When the shielded twisted pair cable is used (recommended), the
shield can be connected to the earthing connector which is located on the rear panel
(see “Terminal connections” on page 57).
The communication port can be used with three different protocols: SPA, Modbus
and DNP 3.0. The user must set the selected protocol manually by using the HMI or
the Relay Setting Tool
(Main menu\Configuration\Communication\Rear port). For
options, see the table Table 5.1.12.2-1.
5.1.12.3. Front panel optical connection for a PC
The front connector is standardized for ABB relay products and requires an opto-
cable (ABB art. No 1MKC950001-2).
The connector supports only the SPA bus protocol, and is connected to the RS-232
port of a standard PC. By using an optical connector, the PC is isolated galvanically
from the protection relay and disturbances are minimized.
Parameters for the serial communication, SPA address, Baud rate and
Slave status, can be changed manually in the HMI.
To ensure fluent communication flow, it is recommended to use 9.6 kbps baud rate.
5.1.12.4. The service pin located on the rear panel
The service pin located above the connector X3.2 is used only in systems
communicating over the LON bus. The service pin is used during the installation
process or in fault detection. When the service pin is pressed, the neuron_id is sent
to the LON bus.
5.1.12.5. SPA bus
The SPA bus protocol uses an asynchronous serial communication protocol (1 start
bit, 7 data bits + even parity, 1 stop bit). Adjustable parameters are Baud rate
(default 9,6 kbps) and SPA address (slave number). The communication
parameters for the front and the rear communication ports can be set individually.
The SPA bus protocol is sending events using event mask 1 (“V101” parameter of
each function block). The SPA event buffer stores the first 50 events.
Table 5.1.12.2-1 Rear port options
Option Rear port
SPA optical
LON optical
IEC_103 optical
Modbus optical
SPA - RS485 RS-485
Modbus - RS485 RS-485
DNP 3.0 - RS485 RS-485
DNP 3.0 optical