Date Code 20111215 Reference Manual SEL-421 Relay
Section 6
R.Reference Manual
DNP3 Communications
The SEL-421 Relay provides a DNP3 (Distributed Network Protocol 3) Level
2 Slave interface for direct network connections to the relay. This section
covers the following topics:
➤ Introduction to DNP3
➤ DNP3 in the SEL-421
➤ DNP3 Documentation
➤ Application Example
➤ DNP LAN/WAN
➤ DNP LAN/WAN in the SEL-421
➤ DNP LAN/WAN Documentation
➤ DNP LAN/WAN Application Example
➤ Application Example
Introduction to DNP3
A SCADA (Supervisory Control and Data Acquisition) manufacturer
developed DNP3 from the lower layers of IEC 60870-5. DNP3 was designed
for use in telecontrol applications. The protocol has become popular for both
local substation data collection and telecontrol. DNP is one of the protocols
included in the IEEE Recommended Practice for Data Communication
between Remote Terminal Units and Intelligent Electronic Devices in a
Substation.
Rather than individual input and output points wired from the station RTU
(remote terminal unit) to the station IEDs (intelligent electronic devices),
many stations use DNP to convey measurement and control data to and from
the RTU. The RTU then forwards data to the off-site master station. By using
data communications rather than hard wiring, designers have reduced
installation, commissioning, and maintenance costs while increasing remote
control and monitoring flexibility.
The DNP User’s Group maintains and publishes DNP standards. See the DNP
User’s Group web site (www.dnp.org) for more information on DNP
standards, implementers of DNP, and tools for working with DNP.
DNP3 Specifications
DNP3 is a protocol with many features and many ways to accomplish tasks.
DNP3 is defined in a series of specifications known as the Basic 4. A
companion specification called the Subset Definitions simplifies DNP3
implementation by providing three standard interoperable implementation
levels. The levels are listed in Table 6.1.
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