Schweitzer Engineering Laboratories SEL-700G Series Instruction Manual Download

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D.8

SEL-700G Relay

Instruction Manual

Date Code 20170814

DNP3 Communications

DNP3 in the SEL-700G

Figure D.2

Message Transmission Timing

Transmission Control

If you use a media transceiver (for example, EIA-232 to EIA-485) or a radio
system for your DNP3 network, you may need to adjust data transmission
properties. Use the PREDLY and POSTDLY settings to provide a delay
between RTS signal control and data transmission (see Figure D.2). For
example, an EIA-485 transceiver typically requires 10 to 20 ms to change
from receive to transmit. If you set the pre-delay to 30 ms, you avoid data loss
resulting from data transmission beginning at the same time as RTS signal
assertion.

Event Data

DNP3 event data objects contain change-of-state and time-stamp information
that the SEL-700G collects and stores in a buffer. Points assigned in the
Binary Input Map that are also assigned in the Sequential Events Recorder
(SER) settings carry the time stamp of actual occurrence. Binary input points
not assigned in the SER settings carry a time stamp based on the DNP map
scan time. This may be significantly delayed from when the original source
changed and should not be used for sequence-of-events determination. The
DNP map is scanned approximately once per second to generate events. You
can configure the SEL-700G to either report the data without a polling request
from the master (unsolicited data) or hold the data until the master requests
this information with an event poll message.

With the event class settings ECLASSBn, ECLASSCn, and ECLASSAn, you
can set the event class for binary, counter, and analog inputs for session n. You
can use the classes as a simple priority system for collecting event data. The
SEL-700G does not treat data of different classes differently with respect to
message scanning, but it does allow the master to perform independent class
polls.

NOTE:

Most RTUs that act as

substation DNP3 masters perform an
event poll that collects event data of
all classes simultaneously. You must
confirm that the polling configuration
of your master allows independent
polling for each class before
implementing separate classes in the
SEL-700G.

For event data collection you must also consider and enter appropriate settings
for dead band and scaling operation on analog points shown in Table D.7. You
can either:

➤

set and use default dead band and scaling according to data type,
or

➤

use a custom data map to select dead bands on a point-by-point
basis.

See DNP3 Documentation on page D.12 for a discussion of how to set scaling
and dead-band operation on a point-by-point basis. Dead bands for analog
inputs can be modified at run-time by writing to object 34.

The settings ANADBAn, ANADBVn, and ANADBMn control default dead-
band operation for each type of analog data. Because DNP3 Objects 30 and 32
use integer data, you must use scaling to send digits after the decimal point
and avoid rounding to a simple integer value.

Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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