Schweitzer Engineering SEL-387-0, Instruction Manual

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G.19
Date Code 20170601 Instruction Manual SEL-387-0, -5, -6 Relay
Distributed Network Protocol
Point Remapping
MDRETI seconds before trying again and try MDRETN times before giving
up. If it fails to connect in the first try, it will try again at a later time every six
hours.
If the relay initiates a connection, it shall disconnect once there have been no
transactions for TIMEOUT time, using the disconnect command
“+++ATH<CR>”. Also, if an outside caller connects to the modem in the
SEL-387, the SEL-387 will disconnect the modem if there have been no
transactions for the TIMEOUT time.
Virtual Terminal
The purpose of this Virtual Terminal (VT) Protocol is to allow ASCII data
transfers between a master and an SEL relay over a DNP port. DNP3 objects
112 and 113 are used for embedding the ASCII communications over the
DNP port. At the master, each slave channel is assigned a Virtual Port number.
Only one channel, with a Virtual Port number of “0” (for ASCII), is supported
in the relay.
Object 112 is used with the Function code Write (FC = 2) to send data from
the Master side to the Slave side (IED) of the link.
Object 113 is used to send data from the relay side to the Master side of the
link. Master devices can use only Function codes Read (FC = 1). The relay
uses only Function codes Response (FC = 129).
The procedure for accessing these objects is as follows. Master devices
transmit data to relay devices by writing one or more of object 112 to a relay
using the Virtual Port number as the DNP point number. Relays send
information to the Master using the Virtual Port number by responding to a
Master READ (FC = 1) request of object 113. Messages can flow in either
direction at any time, however the relay sends messages only at the request of
the Master. There are no explicit procedures for the initiation or conclusion of
a VT session (i.e., implicit connections exist by the mere presence of a VT-
compatible Slave IED).
Virtual terminal supports all ASCII commands listed in the SEL-387 Relay
Command Summary . You do not need a password to login to a virtual terminal
session through a DNP port, but you will need the appropriate access levels
for setting changes and breaker operations. A virtual terminal session times
out in the same way as an ASCII session.