D.6
SEL-787 Relay Instruction Manual Date Code 20150130
DNP3 Communications
DNP3 in the SEL-787
TCP/UDP Selection
The Committee recommends the selection of TCP or UDP protocol as per the
guidelines in Table D.4.
DNP3 in the SEL-787
The SEL-787 is a DNP3 Level 2 remote (outstation) device.
Data Access
Table D.5 lists DNP3 data access methods along with corresponding SEL-787
settings. You must select a data access method and configure each DNP3
master for polling as specified.
In both the unsolicited report-by-exception and quiescent polling methods
shown in Table D.5, you must make a selection for the PUNSOLn setting.
This setting enables or disables unsolicited data reporting at power up. If your
DNP3 master can send a message to enable unsolicited reporting on the
SEL-787, you should set PUNSOLn to No.
While automatic unsolicited data transmission on power up is convenient, this
can cause problems if your DNP3 master is not prepared to start receiving data
immediately on power up. If the master does not acknowledge the unsolicited
data with an Application Confirm, the device will resend the data until it is
acknowledged. On a large system, or in systems where the processing power
Table D.4 TCP/UDP Selection Guidelines
Use in the case of… TCP UDP
Most situations X
Non-broadcast or multicast X
Mesh Topology WAN X
Broadcast X
Multicast X
High-reliability single-segment LAN X
Pay-per-byte, non-mesh WAN, for example, Cellular Digital Packet Data
(CDPD)
X
Low priority data, for example, data monitor or configuration information X
Table D.5 DNP3 Access Methods
Access Method Master Polling SEL-787 Settings
Polled static Class 0 Set ECLASSBn, ECLASSCn,
ECLASSAn to 0; UNSOLn to No
Polled report-by-
exception
Class 0 occasionally, Class 1,
2, 3 frequently
Set ECLASSBn, ECLASSCn,
ECLASSAn to the desired event
class; UNSOLn to No
Unsolicited report-
by-exception
Class 0 occasionally, optional
Class 1, 2, 3 less frequently;
mainly relies on unsolicited
messages
Set ECLASSBn, ECLASSCn,
ECLASSAn to the desired event
class; set UNSOLn to Yes and
PUNSOLn to Yes or No
Quiescent Class 0, 1, 2, 3 never; relies
completely on unsolicited
messages
Set ECLASSBn, ECLASSCn,
ECLASSAn to the desired event
class; set UNSOLn and PUNSOLn
to Yes.
NOTE: Because unsolicited
messaging is problematic in most
circumstances, SEL recommends
using the polled report-by-exception
access method to maximize
performance and minimize risk of
configuration problems.
NOTE: In the settings below, the
suffix n represents the DNP3 session
number from 1 to 3. All settings with
the same numerical suffix comprise
the complete DNP3 session
configuration.
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