16.4
SEL-400 Series Relays Instruction Manual Date Code 20171006
DNP3 Communication
Introduction to DNP3
Binary Control Operations
DNP3 masters use Object 12 control relay output block to perform binary control
operations. The control relay output block has both a trip/close selection and a
code selection. The trip/close selection allows a single index to operate two
related control points, such as trip and close or raise and lower. Trip/close pair
operation is not recommended for new DNP3 devices, but is often included for
interoperability with older DNP3 master implementations.
The control relay output block code selection specifies either a latch or pulse
operation on the point. In many cases, DNP3 outstations have only a limited sub-
set of the possible combinations of the code field. Sometimes, DNP3 outstations
assign special operation characteristics to the latch and pulse selections.
Conformance Testing
In addition to the protocol specifications, the DNP User’s Group has approved
conformance testing requirements for all levels of outstation devices. Some
implementers perform their own conformance specification testing, while some
contract with independent companies to perform conformance testing.
Conformance testing does not always guarantee that a master and remote will be
fully interoperable (work together properly for all implemented features). Con-
formance testing does help to standardize the testing procedure and move the
DNP3 implementers toward a higher level of interoperability.
DNP3 Serial Network Issues
You can build a DNP3 network using either a multidrop or star topology. Each
DNP3 network has one or more DNP3 masters and DNP3 outstations.
Figure 16.1 shows the DNP3 multidrop network topology.
Table 16.3 DNP3 Access Methods
Access Method Description
Polled static Master polls for present value (Class 0) data only.
Polled report-by-
exception
Master polls frequently for event data and occasionally for Class 0
data.
Unsolicited report-by-
exception
Remote devices send unsolicited event data to the master, and the
master occasionally polls for Class 0 data.
Quiescent Master never polls and relies on unsolicited reports only.
Figure 16.1 DNP3 Multidrop Network Topology
Master
Remote 2Remote 1 Remote n
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