16.5
Date Code 20171006 Instruction Manual SEL-400 Series Relays
DNP3 Communication
Introduction to DNP3
Figure 16.2 shows the DNP3 star network topology.
DNP3 multidrop networks that are used within substations often use an EIA-485
physical layer. The multidrop network is vulnerable to the failure of a single
transmitter. If any one transmitter fails in a state that disrupts signals on the net-
work, the network will fail. The DNP3 star network topology eliminates the net-
work transmitters and other single points of failure related to the physical
medium.
If you are planning either a DNP3 star or network topology, you should consider
the benefits of including an SEL communications processor such as the
SEL-2032 or SEL-3530 RTAC in your design. A network with a communications
processor is shown in Figure 16.3. A DNP3 network that includes a communica-
tions processor has a lower data latency and shorter scan time than comparable
networks through two primary mechanisms. First, the communications processor
collects data from all remotes in parallel rather than one-by-one. Second, the
master can collect all data with one message and response, drastically reducing
message overhead.
In the communications processor DNP3 network, you can also collect data from
devices that do not support the DNP3 protocol. The communications processor
can collect data and present it to the master as DNP3 data regardless of the proto-
col between the communications processor and the remote device.
Data Link Layer Operation
DNP3 employs a three-layer version of the seven-layer OSI (open systems inter-
connect) model called the enhanced performance architecture. The layer defini-
tion helps to categorize functions and duties of various software components that
make up the protocol. The middle layer, the data link layer, includes several func-
tions for error checking and media access control.
Figure 16.2 DNP3 Star Network Topology
Figure 16.3 DNP3 Network With Communications Processor
Master
Remote 2Remote 1 Remote n
Communications
Processor
Master
Remote 2Remote 1 Remote n
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