R.6.8
SEL-421 Relay Reference Manual Date Code 20111215
DNP3 Communications
DNP3 in the SEL-421
A DNP technical bulletin (Control Relay Output Block Minimum
Implementation 9701-002) recommends that you use one point per Object 12,
control block output relay. You can use this method to perform Pulse On,
Pulse Off, Latch On, and Latch Off operations on selected remote bits.
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 DNP message to specify operation of the points shown in Control
Point Operation on page R.6.24.
Time Synchronization
The accuracy of DNP time synchronization is insufficient for most protection
and oscillography needs. DNP time synchronization provides backup time
synchronization in the event the relay loses primary synchronization through
the IRIG-B TIME input or some other high accuracy source. Enable time
synchronization with the TIMERQ setting and use Object 50, Variation 1, and
Object 52, Variation 2, to set the time via a DNP master.
TIMERQ can be set in one of three ways:
➤ A numeric setting of 1–32767 minutes specifies the rate at
which the SEL-421 shall request a time synchronization.
➤ A setting of M disables the SEL-421 from requesting a time
synchronization, but still allows the SEL-421 to accept and
apply time synchronization messages from the master.
➤ A setting of I disables the SEL-421 from requesting a time
synchronization, and sets the SEL-421 to ignore time
synchronization messages from the master.
Modem Support
The SEL-421 DNP implementation includes modem support. Your DNP
master can dial-in to the SEL-421 and establish a DNP3 connection. The
SEL-421 can automatically dial out and deliver unsolicited DNP event data.
When the relay dials out, it waits for the
CONNECT message from the local
modem and for assertion of the relay CTS line before continuing the DNP
transaction. This requires a connection from the modem DCD to the relay
CTS line.
NOTE: Contact SEL for information
on serial cable configurations and
requirements for connecting your
SEL-421 to other devices.
Either connect the modem to a computer and configure it before connecting it
to the relay, or program the appropriate modem setup string in the modem
startup string setting MSTR. Use the PH_NUM setting to set the phone
number that you want the relay to dial. The relay will automatically send the
ATDT modem dial command and then the contents of the PH_NUM setting
when dialing the modem. PH_NUM is a text setting that must conform to the
AT modem command set dialing string standard. Use a comma (,) for a pause
of four seconds. You may need to include a nine to reach an outside line or a
one if the number requires long distance access. You can also insert other
special codes your telephone service provider designates for block call
waiting and other telephone line features.
DNP3 Settings
The DNP3 protocol settings that become available when you select DNP3 on a
serial port are shown in Ta ble 6. 6. The DNP3 protocol settings are in the port
settings for the port that you select for the DNP3 protocol. You can use DNP3
on any of the serial ports, PORT F and PORT 1 through PORT 3, but you can only
enable DNP3 on one port at a time.
NOTE: RTS/CTS hardware flow
control is not available for a DNP3
modem connection. You must set the
port data speed slower than the
effective data rate of the modem.
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