D.10
SEL-751A Relay
Instruction Manual
Date Code 20100129
DNP3 Communications
DNP3 in the SEL-751A
If your master does not support the single-point-per-index messages or single
operation database points, you can use the trip/close operation or use the code
field in the DNP3 message to specify operation of the points shown in
.
Time Synchronization
The accuracy of DNP3 time synchronization is insufficient for most protection
and oscillography needs. DNP3 time synchronization provides backup time
synchronization in the event the device loses primary synchronization through
the IRIG-B input. You can enable time synchronization with the TIMERQ
n
setting and then use Object 50, Variation 1, and Object 52, Variation 2, to set
the time via the Session
n
DNP3 master (Object 50, variation 3 for DNP3
LAN/WAN).
By default, the SEL-751A accepts and ignores time set requests
(TIMERQ
n
=I). (This mode allows the SEL-751A to use a high accuracy, IRIG
time source, but still interoperate with DNP3 masters that send time
synchronization messages.) It can be set to request time synchronization
periodically by setting the TIMERQ
n
setting to the desired period. It can also
be set to not request, but accept time synchronization (TIMERQ
n
=M).
Modem Support
The SEL-751A DNP implementation includes modem support for serial ports.
Your DNP3 master can dial-in to the SEL-751A and establish a DNP3
connection. The SEL-751A can automatically dial out and deliver unsolicited
DNP3 event data.
When the device dials out, it waits for the “CONNECT” message from the
local modem and for assertion of the device CTS line before continuing the
DNP transaction. This requires a connection from the modem DCD to the
device CTS line.
NOTE:
Contact SEL for information
on serial cable configurations and
requirements for connecting your
SEL-751A to other devices.
You can either connect the modem to a computer and configure it before
connecting it to the SEL-751A, or program the appropriate modem setup
string in the modem startup string setting MSTR. You should use the
PH_NUM1 and (optional) PH_NUM2 settings to set the phone numbers that
you want the SEL-751A to call. The SEL-751A will automatically send the
ATDT modem dial command and then the contents of the PH_NUM1 setting
when dialing the modem. If PH_NUM2 is set, the RETRY1 setting is used to
configure the number of times the SEL-751A tries to dial PH_NUM1 before
dialing PH_NUM2. Similarly, the RETRY2 setting is the number of attempts
the SEL-751A tries to dial PH_NUM2 before trying PH_NUM1. MDTIME
sets the length of time from initiating the call to declaring it failed because of
no connection, and MDRET sets the time between dial-out attempts.
NOTE:
RTS/CTS hardware flow
control is not available for a DNP3
modem connection. You must use
either X-ON/X-OFF software flow
control or set the port data speed
slower than the effective data rate of
the modem.
The settings PH_NUM1 and PH_NUM2 must conform to the AT modem
command set dialing string standard, including:
➤
A comma (,) inserts a four second pause
➤
If necessary, use a 9 to reach an outside line
➤
Include a 1 and the area code if the number requires long
distance access
➤
Add any special codes your telephone service provider
designates to block call waiting and other telephone line
features.
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